JP7168240B2 - Power converters, power generation systems, power transfer systems, load systems, and power transmission and distribution systems - Google Patents

Description

The present invention relates to a power conversion system, a power converter, a power conversion method, a power generation system, an active power transfer system, a power grid, a power transfer system, a load system, and a power transmission and distribution system.

Wind power, solar power, and the like are attracting attention as renewable energy. A power generator that generates power using wind power or sunlight converts DC power generated by a power conversion system called a power conditioner into AC power and outputs the AC power to a power system. For example, a power conversion system for photovoltaic power generation is provided with a boost chopper and a converter. The converted DC voltage is shaped into a predetermined AC waveform by a converter. At this time, the converter outputs an AC voltage that is substantially the same voltage as the system voltage but has a different phase, so that the electric power generated by the power generator can be supplied to the power system.

JP 2016-152634 A

However, in the conventional power conversion system, in addition to the system voltage and the phase of the system voltage, the DC voltage of the converter and the like are controlled. Therefore, control of the AC voltage in the converter is complicated, and when the system voltage changes, it takes time for the AC voltage output from the converter to follow the changed system voltage. Therefore, for example, if an accident occurs in the power system and the system voltage drops suddenly, the potential difference between the output voltage of the power conversion system and the system voltage increases, causing an overcurrent to flow through the power conversion system. , the power conversion system may stop or fail. As described above, conventional power conversion systems have the problem of low resistance to disturbances such as system failures and instantaneous power drops, and low robustness.

Further, in the conventional power converter, in addition to the system voltage and the phase of the system voltage, the DC voltage of the converter and the like are controlled. Therefore, control of the AC voltage in the converter is complicated, and it takes time to control the output of the converter. In particular, phase detection processing using PLL (Phase Locked Loop) and DFT (Discrete Fourier transform) is performed to detect the phase of the system voltage. Takes time to control. Therefore, for example, when the phase of the system voltage changes abruptly, the output of the converter cannot follow the change in the system voltage, and the difference voltage between the output voltage of the power converter and the system voltage increases, An overcurrent may flow through the converter, causing the power converter to stop or malfunction. As described above, the conventional power converter has a problem of low resistance to disturbance such as a phase jump of the system voltage and low robustness.

Accordingly, the present invention has been made in view of the problems as described above, and includes a highly robust power conversion system, a power conversion device, a power conversion method, a power generation system, an active power transfer system, a power system, and a power transfer system. , load systems and power transmission and distribution systems.

A power conversion device according to the present invention is a power conversion device connected to an AC voltage source via a grid impedance, comprising: a converter for outputting a predetermined AC voltage; and a power supply voltage detector for detecting the voltage of the AC voltage source. and a controller for controlling the converter, wherein the controller controls the converter based on a voltage component based on the detected voltage and a voltage out of phase with the detected voltage. do.

In the power converter according to the present invention, the control unit controls a voltage component based on the detected voltage, a reactive component voltage obtained by multiplying the detected voltage by q (q is a real number), and a phase from the detected voltage ( 2n−1)·90 degrees (n is a positive integer equal to or greater than 1), and the sum of the voltage shifted by d times (d is a real number) and the active component voltage is output from the converter.

In the power converter according to the present invention, the value of d is a negative real number.

In the power converter according to the present invention, the power supply voltage detector detects the voltage of the interconnection impedance on the AC voltage source side, and the control unit detects a voltage component based on the detected voltage and the detected voltage and an output voltage command generator for calculating a voltage command for controlling the converter based on the voltage delayed by 1/4 period of the voltage.

The output voltage command generation unit of the power conversion device according to the present invention integrates the voltage delayed by 1/4 period by a negative real number.

In the power conversion device according to the present invention, the predetermined AC voltage output by the converter is obtained by multiplying the detected voltage by a value obtained by adding 1 to the impedance (unit system display) of the interconnection impedance voltage value or less.

In the power converter according to the present invention, the limiter values of q and d are determined based on the relationship that the square root of the sum of the squares of q and d is equal to the interconnection impedance (expressed in units).

The control unit of the power converter according to the present invention calculates a compensation voltage that compensates for a phase shift between the voltage detected by the power supply voltage detector and the actual voltage of the AC voltage source.

The control unit of the power converter according to the present invention calculates a compensation voltage for compensating for the voltage for the voltage drop in the interconnection impedance.

The control unit of the power conversion device according to the present invention generates a sum voltage of a voltage component based on the detected voltage and a delayed voltage obtained by multiplying a voltage phase-shifted from the detected voltage by d (d is a real number), as described above. A converter is caused to output, and reactive power and active power to be output are controlled based on the detected phase shift between the voltage and the lag voltage.

In the power converter according to the present invention, the voltage out of phase with the detected voltage is calculated by differentiating the detected voltage and multiplying the result by a real number.

The power converter according to the present invention differentiates the detected voltage, and adds the product of the differentiated voltage and the inductance value of the interconnection impedance and the product of the detected voltage and the resistance value of the interconnection impedance. A calculation means is provided.

According to the present invention, since the voltage based on the detected voltage of the AC voltage source is output to the converter, the output voltage of the power conversion system can follow the fluctuations of the AC voltage source, and an overcurrent flows in the power conversion system. Since destruction of the conversion system can be suppressed, it is possible to provide a power conversion system and a power conversion method that are resistant to disturbances and have high robustness.

According to the present invention, the first converter outputs a first predetermined voltage based on the voltage of the AC voltage source, and outputs an AC voltage based on the first predetermined voltage and the second predetermined voltage to the AC voltage source. and the first control device outputs the first predetermined voltage. Therefore, even if the voltage of the AC voltage source suddenly drops, the first predetermined voltage follows the sudden change in the voltage and the power conversion system Output voltage can be lowered. As a result, it is possible to prevent overcurrent from flowing through the power conversion system and destroying the power conversion system, so that it is possible to provide a power conversion system and a power conversion method that are resistant to external disturbances and have high robustness.

Furthermore, according to the present invention, even if the phase of the AC voltage source changes significantly, the voltage component based on the detected voltage can follow the voltage of the AC voltage source, and the output voltage of the converter containing the voltage component is also the AC voltage. Since it is possible to follow changes in the phase of the voltage of the voltage source, it is possible to suppress an increase in the voltage difference between the voltage of the AC voltage source and the output voltage of the power converter. As a result, it is possible to prevent an overcurrent from flowing through the power conversion device and cause the power conversion device to fail, so that a power conversion device that is resistant to external disturbances and has high robustness can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows the power conversion system of 1st Embodiment of this invention. FIG. 2A is a schematic diagram showing the configuration of the R-phase first conversion section of the present invention, and FIG. 2B is a schematic diagram showing the configuration of the R-phase second conversion section. 1 is a phasor diagram representing a power conversion system; FIG. It is a schematic diagram showing the power conversion system of other embodiments of the present invention. It is a schematic diagram showing the power conversion system of other embodiments of the present invention. It is a schematic diagram showing the power conversion system of other embodiments of the present invention. 4 is a graph showing simulation results of the output current of the power conversion system; It is the schematic which shows the power converter device of 2nd Embodiment of this invention. FIG. 3 is a schematic diagram showing the configuration of an R-phase conversion section of the present invention; FIG. 10A is a phasor diagram showing the power converter of the present invention, and FIG. 10B is a phasor diagram in which a part of the phasor diagram of FIG. 10A is enlarged. FIG. 11A is a phasor diagram explaining an increase in reactive power, and FIG. 11B is a phasor diagram explaining an increase in active power. It is a schematic diagram showing a control part of a 3rd embodiment. It is the schematic which expands and shows a part of control part of the modification of 3rd Embodiment. It is a schematic diagram showing a voltage compensation value calculation block provided in a control unit of a modification of the third embodiment.

1. First Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 7. FIG.

(1) Overall configuration of the power conversion system of the first embodiment of the present invention As shown in FIG. 1, the power conversion system 1 includes a first converter 2, a second converter 3, and A first control device 4 that controls the operation, a second control device 5 that controls the operation of the second converter 3, and a capacitor that detects the capacitor voltage (DC capacitor voltage) of the capacitor 20 of the first converter 2, which will be described later. It is provided with a voltage detector 10 and a power supply voltage detector 11 that measures the voltage of a power system as an AC voltage source. In the power conversion system 1, for example, an active power source 7 such as a wind power generator or a solar power generator is connected to the positive side input terminal P and the negative side input terminal N of the first converter 2, and the DC voltage is effective. Power is supplied between the positive input terminal P and the negative input terminal N from the power source 7 .

The power conversion system 1 converts input DC power into AC power and supplies it to the power system. At this time, the power conversion system 1 causes a potential difference between the power conversion system 1 and the power system. As a result, a current corresponding to the potential difference flows from the power conversion system 1 to the power grid, and active power is output from the power conversion system 1 to the power grid, that is, from the active power source 7 to the power grid. A capacitor voltage detector 10 is connected to a positive input terminal P and a negative input terminal N, detects a voltage between the positive input terminal P and the negative input terminal N as a capacitor voltage, and outputs the detected voltage to a second It is sent to the control device 5. The power supply voltage detector 11 is provided at a connection point between the power conversion system 1 and the power system. The power supply voltage detector 11 detects the connection point voltages of the R-phase, S-phase, and T-phase of the power system as the system voltage, and sends the detected voltage of each phase to the first control device 4 . The power supply voltage detector 11 is also connected to the second control device 5 by wiring (not shown), and sends the detected interconnection point voltage to the second control device 5 .

The first converter 2 includes a positive input terminal P, a negative input terminal N, a first conversion section 21, and a capacitor 20, and has a three-phase full bridge circuit configuration. Capacitor 20 is directly connected to positive input terminal P and negative input terminal N and is charged with DC power supplied from active power source 7 . The first converter 21 converts the capacitor voltage (for example, V1) of the capacitor 20 into a first predetermined voltage approximately equal to the AC voltage of the power system, and outputs an AC phase voltage approximately equal to the AC voltage of the power system. In the case of the present embodiment, the first converter 21 includes an R-phase first converter 21R, an S-phase first converter 21S, and a T-phase first converter 21T. It can be converted into voltages corresponding to phases, S phases, and T phases. As the capacitor 20, a capacitor with a rated voltage higher than the peak value of the voltage of the electric power system is used.

Since the R-phase first conversion section 21R, the S-phase first conversion section 21S, and the T-phase first conversion section 21T have the same configuration, the R-phase first conversion section 21R will be described as a representative. The R-phase first converter 21R includes a high-side switch 22H, a low-side switch 22L, and an output terminal 23R. In the R-phase first conversion section 21R, a high side switch 22H and a low side switch 22L are connected in series, and an output terminal 23R is provided at a connection point between the high side switch 22H and the low side switch 22L. The high-side switch 22H side of the R-phase first conversion section 21R is connected to the positive input terminal P, and the low-side switch 22L side of the R-phase first conversion section 21R is connected to the negative input terminal N.

Therefore, when the high-side switch 22H is on and the low-side switch 22L is off, the R-phase first converter 21R outputs the positive capacitor voltage +V1 from the output terminal 23R, and the high-side switch 22H is off and the low-side switch 22L is When turned on, it outputs a negative capacitor voltage -V1 from the output terminal 23R. Thus, the R-phase first converter 21R converts the DC voltage into the AC voltage by switching the high-side switch 22H and the low-side switch 22L on and off.

As shown in FIG. 2A, the high-side switch 22H and the low-side switch 22L are composed of a switching element 24 such as an IGBT and a freewheeling diode 25, for example. In the high-side switch 22H and the low-side switch 22L, the positive side of the switching element 24 (IGBT collector) and the negative side of the freewheeling diode 25 are connected, and the negative side of the switching element 24 (IGBT emitter) and the positive side of the freewheeling diode 25 are connected. A switching element 24 and a freewheeling diode 25 are connected in anti-parallel.

In this manner, the high-side switch 22H and the low-side switch 22L connect the switching element 24 and the freewheeling diode 25 in anti-parallel, so that a voltage is applied from the negative side to the positive side of the high-side switch 22H and the low-side switch 22L. At this time, current flows through the freewheeling diode 25 to prevent current from flowing from the emitter to the collector of the IGBT, which is the switching element 24, thereby protecting the IGBT.

Returning to FIG. 1 again, the first control device 4 controls the high-side switch 22H and the low-side switch 22L of the R-phase first converter 21R, the S-phase first converter 21S, and the T-phase first converter 21T (not shown). It is connected by wiring and controls on/off of the high side switch 22H and the low side switch 22L. In the present embodiment, the first control device 4 switches the high-side switch 22H and the low-side switch 22L on and off by Pulse Width Modulation (PWM) control to switch between the R-phase first converter 21R and the S-phase. Capacitor voltages output from the output terminals 23R, 23S, and 23T of the first conversion section 21S and the T-phase first conversion section 21T are converted into voltages corresponding to the ON times of the high-side switch 22H and the low-side switch 22L. . The first control device 4 converts the capacitor voltage by PWM control to output a first predetermined voltage, and causes the output voltage of the first converter 2 to follow the interconnection point voltage.

In the present embodiment, when the first controller 4 receives the R-phase, S-phase, and T-phase voltages from the power supply voltage detector 11, the first controller 4 uses them as voltage command values, the R-phase first conversion unit 21R, the S-phase PWM control is performed to control the output voltages of the 1 converter 21S and the T-phase first converter 21T. The voltage from the power supply voltage detector 11 may be converted into the output voltage commands R-phase V _ref1 , S-phase V _ref1 , and T-phase V _ref1 by proportional multiplication or computation for compensating for first-order lag. In this case, assuming that the first-order lag due to voltage detection by the power supply voltage detector 11 is expressed as 1/(T1s+1), the first-order lag is obtained by multiplying 1/(T1s+1) by the correction term (T1s+1)/(T2s+1). The effect can be mitigated (where s is the Laplacian operator, T1>>T2). In this case, a compensating element having a transfer function of (T1s+1)/(T2s+1) is inserted between the power supply voltage detector 11 and the first controller 4 .

After that, the first control device 4 controls the R-phase first converter 21R, the S-phase first converter 21S, and the T-phase converter _21S according to the output voltage commands R-phase _Vref1 , S-phase _Vref1 , and T-phase Vref1. A gate pulse for ON/OFF-controlling the high-side switch 22H and the low-side switch 22L (more specifically, the IGBT gate) of the 1 conversion unit 21T is generated for each switch, and the corresponding R-phase first conversion unit 21R, A gate pulse is output to the high-side switch 22H and the low-side switch 22L of the S-phase first conversion section 21S and the T-phase first conversion section 21T. The gate pulses R-phase g _conv1 , S-phase g _conv1 , and T-phase g _conv1 are generated by known pulse width modulation (PWM) using the output voltage commands R-phase V _ref1 , S-phase V _ref1 , and T-phase V _ref1 as modulation waves. be done.

The first controller 4 controls on/off of the high-side switch 22H and the low-side switch 22L of the R-phase first conversion section 21R, the S-phase first conversion section 21S, and the T-phase first conversion section 21T by the gate pulse. be done. The first control device 4 switches on/off the high-side switch 22H and the low-side switch 22L in the R-phase first conversion section 21R, the S-phase first conversion section 21S, and the T-phase first conversion section 21T. The capacitor voltage of capacitor 20 is converted to a first predetermined voltage based on the voltage of the power system. In this manner, the first control device 4 controls the power system from the output terminals 23R, 23S, and 23T of the R-phase first converter 21R, the S-phase first converter 21S, and the T-phase first converter 21T. AC voltages approximately equal to those of the R-phase, S-phase, and T-phase are output.

The second converter 3 is connected to the R-phase second converter 31R, the capacitor 30R connected to the R-phase second converter 31R, the S-phase second converter 31S, and the S-phase second converter 31S. a capacitor 30S, a T-phase second converter 31T, and a capacitor 30T connected to the T-phase second converter 31T; The second phase converter 31T has an electrically independent configuration. The second converter 3 is the difference voltage (second predetermined voltage) between the output voltage of the power conversion system 1 required for the power conversion system 1 to output any current or power to the power system and the interconnection point voltage to output Capacitors 30R, 30S, and 30T may be selected from capacitors having a rated voltage higher than the second predetermined voltage, and can be appropriately selected based on a target output voltage, which will be described later. In this embodiment, it is assumed that the capacitors 30R, 30S, and 30T are the same capacitor. In this embodiment, the first predetermined voltage is a voltage with the average potential of the positive input terminal P and the negative input terminal N of the first converter 2 as a reference potential. The second predetermined voltage is a voltage based on the terminals 32RI, 32SI, 32TI of the second converter 3 connected to the output terminals 23R, 23S, 23T of the first converter 2 .

The R-phase second converter 31R will be described with reference to FIG. 2B. The R-phase second converter 31R includes high-side switches 33IH and 33OH and low-side switches 33IL and 33OL. The R-phase second conversion section 31R has a configuration in which a high side switch 33IH and a low side switch 33IL are connected in series, a high side switch 33OH and a low side switch 33OL are connected in series, and these are connected in parallel. there is The R-phase second converter 31R has a terminal 32RI at the connection point between the high-side switch 33IH and the low-side switch 33IL, and the terminal 32RI serves as an input-side terminal to connect the R-phase first converter 31R of the first converter 2. 21R to the output terminal 23R. The R-phase second converter 31R has an output terminal 32RO at the connection point between the high-side switch 33OH and the low-side switch 33OL.

In this embodiment, the high-side switches 33IH and 33OH and the low-side switches 33IL and 33OL may have a lower voltage rating than the switches of the first converter 2. A low-voltage low-loss switching element with small switching loss can be used. By doing so, the switching frequency of the high side switches 33IH and 33OH and the low side switches 33IL and 33OL can be increased, and the response of the output voltage of the second converter 3 to the output voltage command described later can be improved. can be done. Furthermore, in the R-phase second converter, since synchronous rectification is performed, a freewheeling diode is omitted. The high-side switches 33IH and 33OH and the low-side switches 33IL and 33OL may be configured by connecting switching elements and freewheeling diodes in anti-parallel as described above.

The R-phase second converter 31R is a converter with a two-level full-bridge circuit configuration. 32RO, and −V2 can be output between the terminal 32RI and the output terminal 32RO when the high side switch 33IH and the low side switch 33OL are on, and in other cases, the terminal 32RI and the output terminal 32RO. The output between and becomes zero. Thus, the R-phase second converter 31R can output voltages between ±V2 and zero. The S-phase second conversion section 31S and the T-phase second conversion section 31T also have the same configuration as the R-phase second conversion section 31R. The R-phase second conversion unit 31R, the S-phase second conversion unit 31S, and the T-phase second conversion unit 31T are two-way choppers in which two switches connected in series and a capacitor are connected in parallel. It can also be a converter of circuitry.

Returning to FIG. 1 again, in the second converter 3, the terminals 32RI, 32SI, and 32TI of the R-phase second converter 31R, the S-phase second converter 31S, and the T-phase second converter 31T are connected to the R-phase converter. 1 converter 21R, S-phase first converter 21S, and T-phase first converter 21T are connected to output terminals 23R, 23S, and 23T, respectively, and are electrically connected in series with the first converter 2. there is Therefore, the potentials of the output terminals 32RO, 32SO, 32TO of the second converter 3 when the average potential of the positive input terminal P and the negative input terminal N is used as the reference potential are the R-phase potentials of the first converter 2. 1 converter 21R, S-phase first converter 21S, and T-phase first converter 21T, and the R-phase second converter 31R, S-phase second converter 31S, and T-phase second converter 31T. , and the power conversion system 1 outputs the total voltage. In the second converter 3, the output terminals 32RO, 32SO, and 32TO of the R-phase second converter 31R, the S-phase second converter 31S, and the T-phase second converter 31T are connected to reactors (also called interconnected impedance). It is connected to the R-phase, S-phase, and T-phase of the electric power system via 12R, 12S, and 12T, respectively, and is connected to the electric power system.

The second control device 5 is connected to each high-side switch and each low-side switch of the R-phase second conversion section 31R, the S-phase second conversion section 31S, and the T-phase second conversion section 31T by wiring (not shown). , controls the second converter 3 . The second control device 5 controls on/off of each high-side switch and each low-side switch of the R-phase second conversion section 31R, the S-phase second conversion section 31S, and the T-phase second conversion section 31T. In the present embodiment, the second control device 5 switches between the terminals 32RI, 32SI, and 32TI and the output terminals 32RO, 32SO, and 32TO by turning on/off each high-side switch and each low-side switch by PWM control. Capacitor voltages of the capacitors 30R, 30S, and 30T to be converted into voltages corresponding to the ON times of the high-side switch 22H and the low-side switch 22L. The second control device 5 converts the capacitor voltages of the capacitors 30R, 30S, 30T by PWM control to output a second predetermined voltage between the terminals 32RI, 32SI, 32TI and the output terminals 32RO, 32SO, 32TO.

The second control device 5 performs, for example, AC current control, active power control, reactive power control, and the like, which are performed by control devices for conventional grid-connected converters. In addition, the second control device 5 performs DC capacitor voltage control of other converters, that is, control of the capacitor voltage of the capacitor 20 of the first converter 2 . Since AC current control, active power control, and reactive power control are the same as those of the conventional control method, description thereof will be omitted, and the operation of the second control device 5 will be described with a focus on DC capacitor voltage control.

A control device for a conventional grid-connected converter performs DC capacitor control of a converter whose output voltage is controlled by the control device, but does not perform DC capacitor voltage control of other converters. In contrast, according to the invention, the second control device 5 also controls the capacitor voltage of the capacitor 20 of the other converter, namely the first converter 2 . The capacitor voltage of capacitor 20 will be high if the active power flowing into power conversion system 1 from active power source 7 is greater than the active power flowing out of power conversion system 1 to the power grid. On the other hand, the capacitor voltage of the capacitor 20 becomes low if the active power flowing into the power conversion system 1 from the active power source 7 is smaller than the active power flowing out of the power conversion system 1 to the power grid. That is, by increasing or decreasing the active power output from the power conversion system 1 to the power system, the balance between the active power flowing into the power conversion system 1 and the active power flowing out of the power conversion system 1 is changed, and the capacitor voltage of the capacitor 20 is changed. can be increased or decreased. Specifically, by reducing the active power flowing out of the power conversion system 1 to the power system, the capacitor voltage of the capacitor 20 can be increased, and the active power flowing out of the power conversion system 1 into the power system is increased. As a result, the capacitor voltage of capacitor 20 can be reduced. Therefore, the DC capacitor voltage can be controlled by controlling the active power exchanged between the electric power system and the power conversion system 1 .

More specifically, in the power conversion system 1, the first predetermined voltage, which is the output voltage of the first converter 2, is made equal to the interconnection point voltage, so the output voltage of the second converter 3 is Control the magnitude of the second predetermined voltage. The active power output by the power conversion system 1 is greatly affected by the voltage phasor output by the second converter 3 . Therefore, a description will be given using the arbitrary phase phasor shown in FIG. Since the first converter 2, the second converter 3, and the interconnection impedance are connected in series, the interconnection point voltage is the sum of the first predetermined voltage, the second predetermined voltage, and the interconnection X voltage ( See Figure 1). The grid X voltage is the voltage applied to the grid impedance. In this example, the second predetermined voltage is a vector obtained by multiplying a vector delayed in phase by 90 degrees from the first predetermined voltage by an arbitrary real number. In order for the power conversion system 1 to output active power, the second predetermined voltage needs to lead the interconnection point voltage and the first predetermined voltage by 90 degrees in phase, but the future voltage value cannot be known. Therefore, in the present embodiment, a voltage whose phase is delayed by 90 degrees with respect to the interconnection point voltage is obtained, and the voltage whose phase is delayed by 90 degrees is multiplied by a negative real number to obtain a voltage whose phase is advanced by 90 degrees. . That is, the voltage obtained by multiplying the interconnection point voltage detected 1/4 period before by a negative real number may be used as the second predetermined voltage. In the example of FIG. 3 as well, a vector obtained by multiplying a voltage delayed by 90 degrees with a negative value is described as the second predetermined voltage. The amount of active power that the power conversion system 1 exchanges with the power system can be adjusted by changing the amplitude of the second predetermined voltage with respect to the interconnection point voltage. That is, by changing the amplitude of the second predetermined voltage, the phase difference between the output voltage vector of the power conversion system 1 and the interconnection point voltage is changed, and the active power can be adjusted.

Here, since the first predetermined voltage is controlled to be the same voltage as the detected value of the interconnection point voltage (system voltage) detected by the power supply voltage detector 11, ideally, the interconnection point voltage is with Therefore, the voltage applied to the interconnection impedance becomes a voltage obtained by inverting the phase of the second predetermined voltage. In the present embodiment, since the grid impedance is ideally an inductance, the current flowing through the grid impedance (the current flowing from the power conversion system 1 to the power grid) has a phase that is 90 degrees behind the grid X voltage. .

In this case, the current phasor and the tie-point voltage phasor are in opposite directions, and the current is in phase with the tie-point voltage, so the product of the current and the tie-point voltage is delivered to the grid from the tie-point voltage. becomes active power. Therefore, by increasing or decreasing the current, the active power that flows out from the power conversion system 1 to the power system can be increased or decreased. When viewed from the output voltage of the second converter 3, the phase of the current is advanced by 90 degrees, and the magnitude of the current is a value obtained by dividing the second predetermined voltage by the impedance of the interconnection impedance. Therefore, by increasing or decreasing the second predetermined voltage, the current can be increased or decreased, and the active power exchanged between the power conversion system 1 and the power system can be controlled. Therefore, by increasing or decreasing the second predetermined voltage, the second control device 5 increases or decreases the active power exchanged between the power conversion system 1 and the power system, and the active power flowing into the power conversion system 1 and the power conversion system The capacitor voltage of the capacitor 20 of the first converter 2 can be controlled by adjusting the balance with the active power flowing out of the first converter 2 . The second control device 5 determines a second predetermined voltage based on the capacitor voltage of the capacitor 20 detected by the capacitor voltage detector 10, and causes the second converter 3 to output the second predetermined voltage. Thus, the second control device 5 controls the capacitor voltage of the capacitor 20 of the first converter 2 by adjusting the second predetermined voltage to balance the capacitor voltage of the capacitor 20 .

For example, when the capacitor voltage detected by the capacitor voltage detector 10 is higher than a predetermined value, the second control device 5 increases the second predetermined voltage, which is 90 degrees ahead of the interconnection point voltage, thereby increasing the current. increase the active power flowing out of the power conversion system 1 to the power system, make the active power flowing out of the power conversion system 1 larger than the active power flowing into the power conversion system 1, and increase the capacitor voltage of the capacitor 20. Lower. When the capacitor voltage detected by the capacitor voltage detector 10 is lower than a predetermined value, the second control device 5 lowers the second predetermined voltage whose phase is 90 degrees ahead of the interconnection point voltage, thereby reducing the current. , the active power flowing out from the power conversion system 1 to the power system is reduced, the active power flowing into the power conversion system 1 is made larger than the active power flowing out from the power conversion system 1, and the capacitor voltage of the capacitor 20 is increased. .

Also, when the capacitor voltage is lower than the predetermined value, the power conversion system 1 receives active power from the power system to charge the capacitor 20 and balance the capacitor voltage of the capacitor 20 of the first converter 2 . In this case, the second control device 5 obtains a voltage whose phase is delayed by 90 degrees with respect to the interconnection point voltage, and causes the second converter 3 to output a voltage obtained by multiplying the voltage by a positive real number. That is, the voltage obtained by multiplying the interconnection point voltage detected 1/4 period before by a positive real number may be used as the second predetermined voltage.

In addition, the power conversion system 1 can transfer reactive power to and from the electric power system, and can also transfer reactive power to and from the electric power system while performing capacitor voltage control (giving and receiving of active power) as described above. can. In this case, the reactive power is transferred to the voltage component for transferring active power (the voltage component whose phase is delayed by 90 degrees or the voltage component whose phase is advanced by 90 degrees from the phase of the detected interconnection point voltage). The second converter 3 outputs a second predetermined voltage obtained by adding the voltage components of . A voltage component for transmitting and receiving reactive power is a voltage in phase with the detected interconnection point voltage or a voltage 180 degrees out of phase, and is calculated by multiplying the detected interconnection point voltage by a real number.

In this way, the second control device 5 adjusts the magnitude of the voltage component for transmitting and receiving active power and the voltage component for transmitting and receiving reactive power, which are included in the second predetermined voltage, so that the power conversion system 1 can adjust the amount of active and reactive power that is transferred to and from the power system. Therefore, the second control device 5 controls the voltage component for transmitting and receiving the active power, that is, the voltage component whose phase is delayed by 90 degrees from the phase of the detected interconnection point voltage, or the voltage component whose phase is advanced by 90 degrees. controls the capacitor voltage of the capacitor 20 of the first converter 2 according to the magnitude of . The second control device 5 can adjust the active power output from the second converter 3 by conventional vector control, balance the capacitor voltage, and adjust the amount of reactive power.

On the other hand, it is necessary to limit the output voltage of the second converter 3 in order to suppress the overcurrent from flowing through the power conversion system 1 when a system disturbance such as a system accident or an instantaneous power drop occurs. Preferably, the output voltage of the second converter 3 is limited to 1/4 or less of the output voltage of the first converter 2 . In particular, by limiting the capacitor voltages of the capacitors 30R, 30S, and 30T of the second converter 3, the output voltage can be reliably suppressed. The capacitor voltages of the capacitors 30R, 30S, and 30T of the second converter 3 are preferably set to approximately 1/4 to 1/20 times the capacitor voltage of the capacitor 20 of the first converter 2.

More specifically, the ratio X of the capacitor voltage of the second converter 3 to the capacitor voltage of the first converter 2 is preferably set from the interconnection impedance and the allowable overcurrent level. Here, X is set so as to satisfy X<impedance of interconnection impedance (in units)/overcurrent limit magnification. The overcurrent limit magnification is a value that can be arbitrarily set depending on how much overcurrent is allowed to flow through the power conversion system 1 . The impedance of the interconnection impedance is the value of the inductance of the reactors 12R, 12S, and 12T in this embodiment. As will be described later, when the interconnected impedance is a converter, its leakage inductance is the impedance, which is often about 0.05 p.u. to 0.2 p.u. in units. In the unit system, the impedance value of the interconnection impedance is represented by the voltage drop when the reference current flows through the interconnection impedance. For example, if the grid impedance value is 0.1 p.u., the voltage drop when the reference current flows is 0.1 p.u. means. For example, if the interconnection impedance is 10% and the overcurrent limiting factor is 1.25 times, X=0.1 p.u.×1.25 times=approximately 1/8.

In practice, the second controller 5 provides output voltage commands R-phase V _ref2 , S-phase V _ref2 , and T-phase V for the second converter 3 to output a second predetermined voltage based on the capacitor voltage of the capacitor 20 and the like. Calculate _ref2 . Specifically, when the power conversion system 1 wants to output an arbitrary active power, the value obtained by integrating the interconnection point voltage detection value with a negative real number is multiplied by a negative real number after 1/4 cycle (from the time of detection to the interconnection point voltage ), the voltage command values (output voltage command R-phase V _ref2 , S-phase V _ref2 , T-phase V _ref2 ) are set. When it is desired to receive active power, the value obtained by multiplying the detected voltage value by a positive real number is used as the voltage command value after 1/4 cycle. On the other hand, when it is desired to transfer reactive power, the voltage command value is obtained by multiplying the system voltage detection value by a real number. When it is desired to transfer both active power and reactive power, the sum of the voltage command value for active voltage input/output and the voltage command value for reactive power input/output is used as the voltage command value. Further, the real value to be integrated with the interconnection point voltage can be appropriately adjusted based on the capacitor voltage of the capacitor 20 or the like. The second control device 5 controls the R-phase second converter 31R, the S-phase second converter 31S, and the T-phase second converter _31S according to the output voltage commands R-phase _Vref2 , S-phase _Vref2 , and T-phase Vref2. A gate pulse for turning on/off each high-side switch and each low-side switch of the section 31T is generated for each switch and sent to each corresponding high-side switch and each low-side switch. The gate pulses R-phase g _conv2 , S-phase g _conv2 , and T-phase g _conv2 are generated by known PWM using the output voltage commands R-phase V _ref2 , S-phase V _ref2 , and T-phase V _ref2 as modulation waves.

In addition, the voltage phase of the second converter 3 is ideally opposite to the interconnection impedance (reactors 12R, 12S, 12T) as described later, so the second converter 3 alone outputs The power applied is reactive power, and ideally the voltages of the capacitors 30R, 30S, and 30T do not change except for intra-cycle fluctuations. Therefore, the power required for voltage control of the capacitors 30R, 30S, and 30T of the second converter 3 is very small, can be easily supplied from an external circuit, and can be easily controlled.

Each high side switch and each low side switch are on/off controlled by the gate pulse. The second controller 5 switches on/off each high-side switch and each low-side switch in the R-phase second conversion section 31R, the S-phase second conversion section 31S, and the T-phase second conversion section 31T. To maintain the capacitor voltage at an appropriate voltage by increasing or decreasing the second predetermined voltage, more specifically, the voltage component 90 degrees out of phase with the interconnection point voltage according to the capacitor voltage of the capacitor 20 of the first converter 2 to output a second predetermined voltage. Therefore, in the second converter 3, the output terminals 23R, 23S and 23T are connected, the output terminals 32RO, 32SO and 32TO of the R-phase second converter 31R, S-phase second converter 31S and T-phase second converter 31T are applied to the first predetermined voltage and the second predetermined voltage. Outputs the AC voltage to which the voltage is added.

In this embodiment, the same first predetermined voltage as the interconnection point voltage of the electric power system is output from the first converter 2, and the second predetermined voltage generated by the second converter 3 is added to the first predetermined voltage to total A voltage is output from the second converter 3 and is output to the power system via reactors 12R, 12S, and 12T. Therefore, since the interconnection point voltage and the first predetermined voltage are equal, the voltage (interconnection X voltage) applied to both ends of the reactors 12R, 12S, and 12T has the opposite phase of the second predetermined voltage, and the interconnection X voltage causes the reactor 12R , 12S, 12T. When alternating current flows through the reactors 12R, 12S, and 12T, the phase of the alternating current lags behind the alternating voltage by 90 degrees, so the phase of the current flowing through the reactors 12R, 12S, and 12T lags the grid X voltage by 90 degrees. . The currents flowing through the reactors 12R, 12S, and 12T become the currents flowing through the second converter 3, and the second predetermined voltage is in the opposite phase of the interconnection X voltage, so the currents flowing through the second converter 3 are as described above. The phase leads the second predetermined voltage by 90 degrees. Therefore, the power output from the second converter 3 ideally becomes reactive power, and voltage fluctuations in the capacitors 30R, 30S, and 30T of the second converter 3 do not occur (except for intra-cycle fluctuations). Therefore, ideally, it is not necessary to control the capacitor voltages of the capacitors 30R, 30S, and 30T, and the control of the second converter 3 by the second controller 5 can be simplified. Capacitor voltage compensation is possible with a very simple external circuit even if the capacitor voltage fluctuates slightly due to the effects of measurement delays.

Note that the power conversion system 1 of the present invention operates even if the active power source 7 is removed from the first converter 2 . Moreover, the power conversion system 1 of the present invention is not limited to the operation in the three-phase balanced state, but also operates in the three-phase unbalanced state.

(2) Actions and effects of the first embodiment In the above configuration, the power conversion system 1 is connected to the power system (AC voltage source) via the reactors 12R, 12S, and 12T (interconnection impedance). A power supply voltage detector 11 that detects an interconnection point voltage (voltage), a first converter 2 that outputs a first predetermined voltage that is an AC voltage based on the detected interconnection point voltage, and a first converter 2. provided with a second converter 3 for outputting a second predetermined voltage and a first controller 4 for causing the first converter 2 to output a first predetermined voltage, based on the first predetermined voltage and the second predetermined voltage It is configured to output an alternating voltage to the power system.

Therefore, in the power conversion system 1, the first converter 2 outputs the first predetermined voltage based on the interconnection point voltage, and outputs the AC voltage based on the first predetermined voltage and the second predetermined voltage to the power system. and the first control device 4 outputs the first predetermined voltage. Therefore, even if the voltage of the AC voltage source suddenly drops, the first predetermined voltage follows the sudden change in the voltage and the power conversion system 1 output voltage can be reduced. As a result, it is possible to prevent an overcurrent from flowing through the power conversion system 1 and cause the power conversion system to fail, so that a power conversion system that is resistant to disturbances and has high robustness can be provided.

Furthermore, the power conversion system 1 sets the capacitor voltages of the capacitors 30R, 30S, and 30T of the second converter 3 to about 1/4 to 1/20 of the capacitor voltage of the capacitor 20 of the first converter 2, Even if the voltage of the AC voltage source suddenly drops, the output voltage of the second converter 3, which is the difference voltage from the interconnection point voltage, does not become excessively large with respect to the interconnection point voltage, and overcurrent is prevented. It can suppress the occurrence.

(3) Other Embodiments of the First Embodiment The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention. For example, the first converter 2 and the second converter 46 are connected in series by the transformer 50, as in the power conversion system 40 shown in FIG. You may do so. The power conversion system 40 includes a first converter 2, a second converter 46, a first controller 4 that controls the operation of the first converter 2, and a second controller that controls the operation of the second converter. 5 , a capacitor voltage detector 10 , a power supply voltage detector 11 , and a transformer 50 as a grid impedance, and are linked to the power system via the transformer 50 .

Below, it demonstrates centering around the structure different from the power conversion system 1. FIG. In the power conversion system 40, the output terminals 23R, 23S, and 23T of the first converter 2 are connected to a first R-phase secondary winding 53R and a first S-phase secondary winding (not shown in FIG. 4) of the transformer 50, which will be described later. ) and the first T-phase secondary winding (not shown in FIG. 4), respectively. Other configurations of the first converter 2 are the same. In the second converter 46, an R-phase second converter 41R, an S-phase second converter 41S, a T-phase second converter 41T, and a capacitor 44 are connected in parallel. It has a similar three-phase full bridge circuit configuration. The R-phase second converter 41R, the S-phase second converter 41S, and the T-phase second converter 41T are composed of a high-side switch 42H and a low-side switch 42L connected in series. Output terminals 43R, 43S, and 43T are provided at connection points between.

When the high-side switch 42H is on and the low-side switch 42L is off, the second converter 46 can output a positive voltage approximately equal to the capacitor voltage of the capacitor 44 from the output terminals 43R, 43S, and 43T. is off and the low-side switch 42L is on, a negative voltage approximately equal to the capacitor voltage of the capacitor 44 can be output from the output terminals 43R, 43S, and 43T. Capacitor 44 is selected to have a rated voltage greater than the output target voltage described above. The second converter 46, like the second converter 3, is controlled by the second controller 5 and outputs a second predetermined voltage from the output terminals 43R, 43S, 43T. The output terminals 23R, 23S, and 23T of the second converter 46 are connected to the second R-phase secondary winding 57R, the second S-phase secondary winding (not shown in FIG. 4), and the second T-phase secondary winding of the transformer 50. Each is connected to a winding (not shown in FIG. 4).

The transformer 50 has a primary side connected to each phase of the electric power system, and a secondary side connected to each phase of the first converter 2 and each phase of the second converter 46 . The number of turns of the primary side coil (for example, the 1st R-phase primary winding 51R described later) and the secondary side coil (for example, the 1st R-phase secondary winding 53R) is added to the first predetermined voltage output by The voltage obtained by multiplying the ratio and the second predetermined voltage output from the second converter 46 are applied to the primary side coil (eg, the 2nd R-phase primary winding 55R) and the secondary side coil (eg, the 2nd R-phase primary winding 55R). The total voltage obtained by adding the voltage multiplied by the turns ratio of the phase secondary winding 57R) is output to the power system (hereinafter, the turns ratio of the primary side coil and the secondary side coil is simply referred to as the turns ratio called). Since the transformer 50 has the same configuration for each of the R-phase, S-phase, and T-phase, the description will focus on the R-phase here. The power conversion system 40 includes a first R-phase primary winding 51R, a first R-phase secondary winding 53R, a first R-phase core 52R, a second R-phase primary winding 55R, and a second R-phase secondary winding. 57R and a first R phase core 56R. The 1st R-phase primary winding 51R and the 1st R-phase secondary winding 53R are magnetically coupled to the 2nd R-phase primary winding 55R and the 2nd R-phase secondary winding 57R with the same polarity. The first R-phase primary winding 51R and the second R-phase primary winding 55R are also magnetically coupled with the same polarity. Therefore, the first R-phase secondary winding 53R and the second R-phase secondary winding 57R generate magnetic fields in the same direction.

The first R-phase primary winding 51R and the first R-phase secondary winding 53R are wound around the first R-phase core 52R. In the present embodiment, since the first predetermined voltage is made equal to the interconnection point voltage, the number of turns of the first R-phase primary winding 51R and the first R-phase secondary winding 53R are the same (the number of turns ratio is 1). )I have to. Therefore, a voltage equal to the first predetermined voltage applied to the first R-phase secondary winding 53R is generated in the first R-phase primary winding 51R. Similarly, the second R-phase primary winding 55R and the second R-phase secondary winding 57R are wound around the second R-phase core 56R. In this embodiment, since the number of turns of the second R-phase primary winding 55R and the second R-phase secondary winding 57R are the same (turn ratio 1), the voltage applied to the second R-phase secondary winding 57R is A voltage equal to the second predetermined voltage is developed across the second R-phase primary winding 55R.

The first R-phase primary winding 51R and the second R-phase primary winding 55R are connected in series. Therefore, the voltage obtained by multiplying the first predetermined voltage generated in the first R-phase primary winding 51R by the turns ratio (1 in this embodiment) and the second predetermined voltage generated in the second R-phase primary winding 55R are The voltage multiplied by the turns ratio (1 in this embodiment) can be added together and output to the R phase of the power system. Although the turns ratio can be adjusted as appropriate, it is set so that the voltage generated in the first R-phase primary winding 51R is approximately equal to the R-phase connection point voltage of the electric power system. If the turns ratio is other than 1, the first predetermined voltage is determined based on the tie point voltage and the turns ratio.

In the power conversion system 40 connected to the active power source 7 that supplies active power to the system, such as wind power generation and solar power generation, the second predetermined voltage, which is the output voltage of the second converter 46, is usually set to the system voltage or the first voltage. Active power is output by setting the phase ahead of the predetermined voltage by 90 degrees. If the active power flowing out of the power conversion system 40 to the power system is larger than the active power flowing into the power conversion system 40 from the active power source 7, the capacitor voltage of the capacitor 20 of the first converter 2 will drop. In this case, by reducing the second predetermined voltage, which is the output voltage of the second converter 46, the active power output to the system is reduced and the voltage of the capacitor 20 is restored to the predetermined voltage. In other words, the power conversion system 40 thereby reduces the phase difference between the voltage generated in the coil on the primary side of the transformer 50 and the power system, thereby reducing the active power output from the power conversion system 40 to the power system. In this way, the power conversion system 40 makes the active power flowing out of the power conversion system 40 to the power grid smaller than the active power flowing into the power conversion system 40 to raise the capacitor voltage. The power conversion system 40 outputs a second predetermined voltage based on the capacitor voltage from the second converter 46 to control the capacitor voltage of the capacitor 20 . When the turns ratio is other than 1, the second predetermined voltage is set according to the turns ratio.

Further, like the power conversion system 60 shown in FIG. 5, in which the same components as those in FIGS. 64S and 64T may be connected in series. The power conversion system 60 includes a first converter 2, a second converter 46, a first controller 4 that controls the operation of the first converter 2, and a second controller that controls the operation of the second converter. 5, capacitor voltage detector 10, power supply voltage detector 11, iron cores 67R, 67S, 67T, primary windings 68R, 68S, 68T wound around iron cores 67R, 67S, 67T, and secondary windings 64R, 64S, and 64T.

In this embodiment, the number of turns of the primary winding 68R and the number of turns of the secondary winding 64R are made equal, the number of turns of the primary winding 68S and the number of turns of the secondary winding 64S are made equal, and the number of turns of the primary winding 68R is equal to that of the secondary winding 64S. The number of turns of the wire 68T and the number of turns of the secondary winding 64T are equal. Actually, a power supply voltage detector that measures the connection point voltage as the system voltage of the S-phase power system and a power supply voltage detector that measures the connection point voltage as the system voltage of the T-phase power system are also provided. 5 shows only the power supply voltage detector 11 that measures the interconnection point voltage as the system voltage of the R-phase power system. The first predetermined voltage is controlled to be equal to the AC phase voltage at the interconnection point.

Transformer 70 has cores 67R, 67S, 67T, primary windings 68R, 68S, 68T, and secondary windings 64R, 64S, 64T. The primary windings 68R, 68S, 68T are connected to an R-phase power system 65R, an S-phase power system 65S, and a T-phase power system 65T. The secondary windings 64R, 64S, 64T have one ends connected to the output terminals 23R, 23S, 23T of the first converter 2 and the other ends connected to the output terminals 43R, 43S, 43T of the second converter 46. there is The leakage impedance of transformer 70 functions as the interconnection impedance of power conversion system 60 .

Based on the concept of the unit method, the differential voltage between the output voltage of the power conversion system 60 and the system voltage is applied to the leakage impedance. That is, the leakage impedance of the primary winding and the secondary winding functions as interconnection impedance. Thus, current flows between primary windings 68R, 68S, 68T and R-phase power system 65R, S-phase power system 65S, and T-phase power system 65T.

As in the other embodiments, by shifting the phase of the output of the second converter 46, that is, the second predetermined voltage by 90 degrees from the first predetermined voltage, the active power can be input and output.

In the power conversion system 60, by shifting the phase of the second predetermined voltage from the first predetermined voltage by 90 degrees and increasing or decreasing the second predetermined voltage, the active power flowing out from the power conversion system 60 to the power system can be increased or decreased. . That is, the voltage of capacitor 20 can be adjusted.

Moreover, in this embodiment, the output power of the second converter 46 can be made reactive power by setting the second predetermined voltage to the same phase as the interconnection point voltage.

In the above embodiment, the case where the power conversion system 1 includes the first converter 2 having a three-phase full-bridge circuit configuration has been described, but the present invention is not limited to this, and the same configuration as in FIG. You may make it provide the 1st converter 102 which is a 3-phase NPC (Neutral-Point-Clamped) 3 level converter like the power conversion system 100 shown in FIG. 6 with the code|symbol. The first converter 102 includes a positive input terminal P, a negative input terminal N, a first conversion section 210, and a capacitor. The first converter 102 will be described below, focusing on the difference in configuration from the first converter 2 . The first conversion section 210 of the first converter 102 includes an R-phase first conversion section 210R, an S-phase first conversion section 210S, and a T-phase first conversion section 210T.

Since the R-phase first conversion section 210R, the S-phase first conversion section 210S, and the T-phase first conversion section 210T have the same configuration, the R-phase first conversion section 210R will be described as a representative. The R-phase first conversion unit 210R includes a switch series body in which four switches, a high-high side switch SA, a high-low side switch SB, a low-high side switch SC, and a low-low side switch SD are connected in series, and two diodes D connected in series. It is composed of a connected diode series body. The diode series body has a negative side connected to a connection point between the high-high side switch SA and the high-low side switch SB, and a positive side connected to a connection point between the low-high side switch SC and the low-low side switch SD.

In the R-phase first conversion section 210R, the high-high side switch SA side of the switch series body is connected to the positive side input terminal P, and the low/low side switch SD side is connected to the negative side input terminal N. The R-phase first conversion section 210R is provided with an output terminal 230R at the connection point between the high-low side switch SB and the low-high side switch SC, and the output terminal 230R is connected to the terminal 32RI of the R-phase second conversion section 31R of the second converter 3. It is connected. In this embodiment, the high-high side switch SA, the high-low side switch SB, the low-high side switch SC, and the low-low side switch SD have a structure in which a switching element such as an IGBT and a freewheeling diode are connected in anti-parallel. Not limited.

The first converter 102 includes, as a capacitor, a capacitor series body in which a high side capacitor 200H and a low side capacitor 200L are connected in series. Although the same capacitor is used for the high side capacitor 200H and the low side capacitor 200L in this embodiment, capacitors having different rated voltages may be used. The rated voltages of the high-side capacitor 200H and the low-side capacitor 200L are selected so that the total value of the rated voltages is higher than the peak value of the voltage of the power system. A capacitor voltage detector 10 is connected to the positive side of the high side capacitor 200H and the negative side of the low side capacitor 200L. The total value with the capacitor voltage of 200 L is detected and sent to the second controller 5 . In order to balance the voltages of the high-side capacitor 200H and the low-side capacitor 200L, the capacitor voltages of the high-side capacitor 200H and the low-side capacitor 200L may be measured and sent to the second control device 5 .

In the first converter 102, the R-phase first converter 210R, the S-phase first converter 210S, the T-phase first converter 210T, and the capacitor series are connected in parallel. Furthermore, a connection point between the two diodes D of the R-phase first conversion section 210R and a connection point of the two diodes D of the S-phase first conversion section 210S are connected by a wiring 240 . A connection point between the two diodes D of the S-phase first converter 210S and a connection point of the two diodes D of the T-phase first converter 210T are connected by a wiring 241 .

Furthermore, a connection point between the two diodes D of the T-phase first conversion section 210T and a connection point between the high side capacitor 200H and the low side capacitor 200L of the capacitor series are connected by a wiring 242 . Therefore, the R-phase first conversion unit 210R, the S-phase first conversion unit 210S, and the T-phase first conversion unit 210T are controlled by switches to output zero and the high-side capacitor 200H from the output terminals 230R, 230S, and 230T. Three voltages can be output: a voltage and a voltage obtained by subtracting the capacitor voltage of the low-side capacitor 200L from the zero voltage. Note that the output voltage (first predetermined voltage) of the first converter 102 is a potential based on the connection point between the high-side capacitor 200H and the low-side capacitor 200L.

The function and control of the first converter 102 are the same as those of the first converter 2 . The first converter 102 repeats turning on and off of each switch by a gate pulse from the first controller 4, and outputs AC voltages approximately equal to the detected interconnection point voltage from the output terminals 230R, 230S, and 230T. Thus, by using the NPC 3-level converter for outputting three voltages as the first converter, a voltage closer to a sine wave can be output.

The capacitor voltages of the capacitors 30R, 30S, and 30T of the second converter 3 are reduced to 1/6 of the capacitor voltage of the first converter 102, that is, the total voltage of the high-side capacitor 200H and the low-side capacitor 200L. Then, the power conversion system 1 can output 9-level voltages quantized by the capacitor voltages of the capacitors 30R, 30S, and 30T of the second converter 3 from the output terminals 32RO, 32SO, and 32TO, respectively. Further, if the capacitor voltages of the capacitors 30R, 30S, and 30T of the second converter 3 are set to 1/4 of the total voltage of the capacitor voltage of the high side capacitor 200H and the capacitor voltage of the low side capacitor 200L of the first converter 2, the power The conversion system 1 can output 7-level voltages quantized by the capacitor voltages of the capacitors 30R, 30S, and 30T of the second converter 3. FIG. The first predetermined voltage output from the first converter 102 is a voltage using the average potential of the positive input terminal P and the negative input terminal N of the first converter 102 as a reference potential.

In the above embodiment, the case where the power conversion system supplies power to a three-phase AC AC voltage source has been described. can also be In this case, the power conversion system 1 may be used, the reactor 12R may be connected to a single-phase AC voltage source, and power may be supplied from the power conversion system 1 to the AC voltage source. Further, the S-phase first converter 21S and the T-phase first converter 21T are removed from the first converter 2 of the power conversion system 1, and the S-phase second converter 31S and the T-phase second converter 3 are removed from the second converter 3. The conversion unit 31T may be removed, and the power conversion system 1 may be used as a single-phase AC power conversion system to supply power to a single-phase AC voltage source. Also, the first converter 2 may be configured as a single-phase NPC 3-level converter.

In the above embodiment, the case of supplying power to an electric power system as an AC voltage source has been described. can also be supplied.

Further, in the above embodiment, the first converter 2 is controlled to output the first predetermined voltage equal to the interconnection point voltage. However, in practice, there is a case where the phasor of the interconnection point voltage and the first predetermined voltage deviates (out of phase) due to a detection delay of the interconnection point voltage and a control delay of the output voltage control of the first converter 2. be. Therefore, the power conversion system 1 performs control so that the second control device 5 compensates for the phase shift between the first predetermined voltage, which is the output voltage of the first converter 2, and the interconnection point voltage with the second predetermined voltage. is preferred. By doing so, the power conversion system 1 can output more appropriate active power to the power system.

Specifically, the second control device 5 calculates a phasor due to the phase shift, calculates a phase shift compensation voltage as a compensation voltage for compensating for the phase shift based on the phasor, and calculates a voltage obtained by adding the phase shift compensation voltage. The second converter 3 outputs the second predetermined voltage. Since the phase shift between the first predetermined voltage and the interconnection point voltage results in a phasor approximately perpendicular to the interconnection point voltage, the output voltage of the second converter 3 follows the second predetermined voltage with this perpendicular phasor (phase deviation compensation voltage) are added together.

Furthermore, the interconnection impedance (reactors 12R, 12S, 12T) actually has a resistance component. That is, the product of the resistance component of the interconnection impedance and the current is the voltage difference between the interconnection point voltage and the first predetermined voltage. The second control device 5 calculates a voltage drop compensation voltage as a compensation voltage for compensating for this differential voltage, and controls the second converter 3 to output a voltage to which the voltage drop compensation voltage is added as a second predetermined voltage. is preferred.

(4) Use of the power conversion system of the first embodiment The power conversion systems 1, 40, 60, and 100 generate power with an active power source 7 such as a wind power generator or a solar power generator, as described above. It is used to supply the converted power to the power grid or AC voltage source. Such a power generation system including the power conversion system 1 (40, 60, 100) is provided with a frequency detector that detects the frequency of the power system, sends the detected frequency to the second control device 5, It is also possible to control the second predetermined voltage, which is the output voltage of the second converter, based on the frequency of the power system. For example, if the grid frequency is below the reference range, the grid is overdemanded. In this case, the second control device 5 raises the second predetermined voltage to increase the amount of active power supplied to the power system. On the other hand, if the grid frequency is higher than the reference range, the grid is over-supplied. In this case, the second control device 5 reduces the second predetermined voltage to reduce the amount of active power supplied to the power system.

Also, instead of the active power source 7, the power conversion system 1 (40, 60, 100) is connected to the supply side power system, and the supply side power system to the power system (hereinafter referred to as the demand side power system). The power conversion system 1 (40, 60, 100) may be used as an active power transfer system that transfers power. In this case as well, the second control device 5 determines the second predetermined voltage based on the frequency of the demand side power system and the capacitor voltage of the capacitor 20 of the first converter 2, and the power conversion system 1 (40, 60, 100) may be controlled to control the amount of active power transferred from the power system on the supply side to the power system on the demand side. In addition, the second control device 5 determines the second predetermined voltage based on commands from the command center of the demand side power system and the command center of the supply side power system, and the power conversion system 1 (40, 60, 100) You may make it control the active power which outputs.

Also, as another application, it may be used as a load system that receives supply of active power.

(5) Verification test of the first embodiment Using the configuration of the power conversion system 1 shown in FIG. 1, the time change of the output current of each phase of the power conversion system 1 was calculated by electric circuit simulation. At this time, 0.5 seconds after the start of the simulation, the voltage of the R phase was reduced to 1/10 to simulate the operation when an accident occurred in the electric power system and the system voltage dropped rapidly. The graph in FIG. 7 shows the results. In FIG. 7, the horizontal axis is time and the vertical axis is current. When the R-phase voltage drops to 1/10, in a conventional power conversion system, an overcurrent flows through the power conversion system and the R-phase output current rises sharply. However, as can be seen from FIG. 7, in the power conversion system 1, when the R-phase voltage drops to 1/10, the R-phase output current drops and no overcurrent occurs. Even after that, the value of the output current is smaller than before the voltage drop of the R phase, but it can be seen that the operation is stable. Although not shown in FIG. 7, the R-phase output current then recovers to the level before the drop in the R-phase voltage. In this way, the power conversion system of the present invention is robust because it suppresses the occurrence of overcurrent and prevents damage due to overcurrent even in an emergency when the R-phase voltage drops to 1/10. It can be seen that it is highly

[Explanation of symbols in the first embodiment]
Reference Signs List 1, 40, 60 power conversion system 2 first converter 3, 46 second converter 4 first controller 5 second controller 7 active power source 12R, 12S, 12T reactor

2. Second Embodiment A second embodiment of the present invention will be described with reference to FIGS. 8 to 11B. In addition, in describing the second embodiment, all the numbers of the components are renumbered in FIGS. 8 to 11B.

(1) Overall configuration of the power converter according to the second embodiment of the present invention In this embodiment, as shown in FIG. A power conversion device 1 as a power conversion system of the present invention will be described by taking as an example a case where it is used in a power generation system 100 that supplies power to a power system as a power source. The power generation system 100 includes an active power source 7, a power converter 1, and a grid impedance. The interconnection impedance is an impedance inserted between the converter 2 and the power system in order to link the converter 2 to the power system, and is inductors 12R, 12S, and 12T in this embodiment. The power generation system 100 converts the DC voltage obtained by the active power source 7 into a predetermined three-phase AC voltage by the power conversion device 1, and connects it to each phase of the power system via the inductors 12R, 12S, and 12T. do. Note that the present embodiment will be described assuming a power system in which the frequency of the AC voltage is 50 Hz.

The power conversion device 1 includes a converter 2, a control unit 4 as a control device that controls the operation of the converter 2, a power supply voltage detector 11 that detects an interconnection point voltage described later as the voltage of the power system, It comprises a frequency detector 103 that detects the frequency of the power system, a gain controller 104, and a capacitor voltage detector 105 that detects a capacitor voltage (DC capacitor voltage) of the capacitor 20 of the converter 2, which will be described later. The power conversion device 1 has, for example, an active power source 7 connected to a positive input terminal P and a negative input terminal N of the converter 2, and a positive input terminal P and a negative input terminal N from the active power source 7. supplied via

The converter 2 has a positive input terminal P, a negative input terminal N, a converter, and a capacitor 20 . Capacitor 20 is directly connected to positive input terminal P and negative input terminal N and is charged with DC power supplied from active power source 7 . The converter converts the capacitor voltage (for example, V1) of the capacitor 20 into a predetermined AC voltage approximately equal to the interconnection point voltage. In the case of this embodiment, the conversion unit is composed of an R-phase conversion unit 21R, an S-phase conversion unit 21S, and a T-phase conversion unit 21T. It can be converted to the corresponding interconnection point voltage. As the capacitor 20, a capacitor having a rated voltage higher than the peak value of the interconnection point voltage is used.

Since the R-phase conversion section 21R, the S-phase conversion section 21S, and the T-phase conversion section 21T have the same configuration, the R-phase conversion section 21R will be described as a representative. The R-phase converter 21R includes a high-side switch 22H, a low-side switch 22L, and an output terminal 23R. In the R phase conversion section 21R, a high side switch 22H and a low side switch 22L are connected in series, and an output terminal 23R is provided at a connection point between the high side switch 22H and the low side switch 22L. The high side switch 22H side of the R phase conversion section 21R is connected to the positive side input terminal P, and the low side switch 22L side of the R phase conversion section 21R is connected to the negative side input terminal N.

Therefore, when the high-side switch 22H is on and the low-side switch 22L is off, the R-phase conversion unit 21R outputs a positive capacitor voltage +V1 from the output terminal 23R, and when the high-side switch 22H is off and the low-side switch 22L is on. At this time, a negative capacitor voltage -V1 is output from the output terminal 23R. Thus, the R-phase converter 21R converts the DC voltage into the AC voltage by switching the high-side switch 22H and the low-side switch 22L on and off. The converter 2 includes an R-phase conversion section 21R, an S-phase conversion section 21S, a T-phase conversion section 21T, and a capacitor 20, which are configured by connecting the high-side switch 22H and the low-side switch 22L in series, and the capacitor 20 is connected in parallel. and has a three-phase full-bridge circuit configuration.

As shown in FIG. 9, the high-side switch 22H and the low-side switch 22L are composed of a switching element 24 such as an IGBT and a freewheeling diode 25, for example. In the high-side switch 22H and the low-side switch 22L, the positive side of the switching element 24 (IGBT collector) and the negative side of the freewheeling diode 25 are connected, and the negative side of the switching element 24 (IGBT emitter) and the positive side of the freewheeling diode 25 are connected. A switching element 24 and a freewheeling diode 25 are connected in anti-parallel.

In this manner, the high-side switch 22H and the low-side switch 22L connect the switching element 24 and the freewheeling diode 25 in anti-parallel, so that a voltage is applied from the negative side to the positive side of the high-side switch 22H and the low-side switch 22L. At this time, current flows through the freewheeling diode 25 to prevent current from flowing from the emitter to the collector of the IGBT, which is the switching element 24, thereby protecting the IGBT.

Returning to FIG. 8 again, the output terminals 23R, 23S, and 23T are connected to the R-phase, S-phase, and T-phase of the power system via inductors 12R, 12S, and 12T, respectively. In this specification, connection points between the inductors 12R, 12S, and 12T and the R-phase, S-phase, and T-phase of the electric power system are called interconnection points. The power supply voltage detector 11 is provided at this interconnection point, and measures the voltage on the power system side (AC voltage source side) of the inductors 12R, 12S, and 12T. The power supply voltage detector 11 detects the connection point voltages of the R phase, S phase, and T phase of the power system as the voltage of the power system, and sends the detected connection point voltages of each phase to the control unit 4 .

The control unit 4 includes a multiplication unit 33, a reactive component voltage generation unit 34, an active component voltage generation unit 35, a phase delay unit 31, an output voltage command generation unit 36, and a gate pulse generation unit 37. ing. The multiplication unit 33 , the reactive component voltage generation unit 34 , and the phase delay unit 31 are connected to the power supply voltage detector 11 and receive the interconnection point voltage of each phase from the power supply voltage detector 11 . When the multiplication unit 33 receives the interconnection point voltage of each phase, it multiplies the interconnection point voltage of each phase by 1 and sends it to the output voltage command generation unit 36 as an interconnection point voltage component. In this embodiment, the multiplier 33 is a multiplier with a gain of one.

In this way, the interconnection point voltage component is simply the detected voltage of the interconnection point voltage multiplied by one, that is, the detected system voltage is output as it is, and is not subjected to complicated control. Even if the phase of the point voltage is abruptly shifted, the connection point voltage can be followed. Therefore, since the output voltage of the power conversion device 1 can follow the change in the interconnection point voltage, an increase in the difference voltage between the interconnection point voltage and the output voltage of the power conversion device 1 is suppressed, and the power conversion It is possible to suppress overcurrent from flowing through the device 1 . Note that the interconnection point voltage of each phase may be directly input to the output voltage command generation part 36 as an interconnection point voltage component without providing the multiplication part 33 .

Reactive component voltage generation unit 34, upon receiving the interconnection point voltage of each phase, multiplies the interconnection point voltage of each phase by q to cause reactive power to flow in and out between power converter 1 and the power system. , the reactive component voltage is calculated and sent to the output voltage command generation unit 36 . In the present embodiment, the reactive component voltage generator 34 is a multiplier with a gain of q, multiplies the interconnection point voltage by q, and outputs the result to the output voltage command generator 36 . q is a real number, and is appropriately set depending on the reactive power that the power converter 1 wants to input/output, as described later.

When the phase delay unit 31 receives the interconnection point voltage of each phase, the phase delay unit 31 delays the phase of the interconnection point voltage of each phase by 90 degrees (π/2, that is, 1/4 period), and the active component voltage generation unit 35 Send out. In this embodiment, the phase delay unit 31 is a delay circuit, and since the power system is a system with a frequency of 50 Hz, it delays the detection signal of the interconnection point voltage of each phase by 5 ms. When the power system frequency is 50 Hz, one cycle of the system voltage is 20 ms, so a signal delay of 5 ms corresponds to a phase delay of 90 degrees. Therefore, by delaying the detection signal of the interconnection point voltage by 5 ms, the output of the phase delay unit 31 is delayed by 90 degrees with respect to the phase of the interconnection point voltage at the time of output. When the frequency of the electric power system is 60 Hz, one period is approximately 16.7 ms, so the detection signal is delayed approximately 4.2 seconds. Thus, the delay time of the signal in the phase delay unit 31 is set according to the frequency of the electric power system.

When the active component voltage generator 35 receives the interconnection point voltage of each phase with a phase delay of 90 degrees, it multiplies the received interconnection point voltage of each phase by d to increase the voltage between the power converter 1 and the power system. In order to allow active power to flow in and out, the active component voltage is calculated and sent to the output voltage command generation unit 36 . In the present embodiment, the active component voltage generator 35 is a multiplier with a gain of d, multiplies the interconnection point voltage by d, and sends it to the output voltage command generator 36 . d is a real number, and is appropriately set according to the active power that the power converter 1 wants to input/output, as will be described later.

Here, in order to output active power from the power converter 1 to the power system, the phase of the active voltage component must lead the phase of the interconnection point voltage. In particular, in order to output effective power efficiently, it is desirable that the phase is advanced by 90 degrees. However, the future phase cannot be known in practice. Therefore, in the present embodiment, the phase delay unit 31 delays the phase of the connection point voltage by 90 degrees, the gain of the active component voltage generation unit 35 is set to a negative real number, and the phase-delayed voltage by 90 degrees is set to a negative value. By accumulating the real numbers, the effective voltage component is set to a voltage whose phase is advanced by 90 degrees with respect to the interconnection point voltage.

When receiving the interconnection point voltage component of each phase, the reactive component voltage of each phase, and the active component voltage of each phase, the output voltage command generation unit 36 generates the interconnection point voltage and the reactive component voltage. , and the active component voltage are added for each phase to calculate the sum voltage.

The output voltage command generation unit 36 uses Pulse Width Modulation (PWM) for outputting the sum voltage calculated for each phase from the R-phase conversion unit 21R, the S-phase conversion unit 21S, and the T-phase conversion unit 21T. modulation) output voltage commands R-phase V _ref , S-phase V _ref , and T-phase V _ref are generated and sent to the gate pulse generator 37 . The output voltage command generator 36 normalizes the calculated sum voltage to generate the output voltage commands R-phase V _ref , S-phase V _ref , and T-phase V _ref . The gate pulse generation unit 37 switches the high-side switches of the R-phase conversion unit 21R, the S-phase conversion unit 21S, and the T-phase conversion unit 21T according to the output voltage commands R-phase _Vref , S-phase _Vref , and T-phase _Vref . 22H and the low-side switch 22L (more specifically, the gate of the IGBT) is generated for each switch. The gate pulses are generated by known pulse width modulation (PWM) using the output voltage commands R-phase V _ref , S-phase V _ref , and T-phase V _ref as modulation waves.

Note that the normalization for PWM may be performed in the output voltage command generation unit 36 or may be performed in a preceding stage thereof.

The gate pulse generator 37 is connected to the R-phase converter 21R, the S-phase converter 21S, and the high-side switch 22H and the low-side switch 22L of the T-phase converter 21T by wiring (not shown), and generates the generated gate pulse. A gate pulse is output to each switch, and to the corresponding R-phase conversion section 21R, S-phase conversion section 21S, and high-side switch 22H and low-side switch 22L of the T-phase conversion section 21T. The R-phase conversion section 21R, the S-phase conversion section 21S, and the T-phase conversion section 21T control the ON times of the high-side switch 22H and the low-side switch 22L by gate pulses, and change the capacitor voltage of the capacitor 20 to the output voltage command. and output the predetermined AC voltage to the electric power system. The controller 4 thus controls the converter 2 . Then, the control unit 4 controls the converter 2 based on the voltage component based on the detected interconnection point voltage and the voltage obtained by delaying the phase of the detected interconnection point voltage by 90 degrees (1/4 period delay). By including the output voltage command generation unit 36 that calculates the voltage command for the conversion, the converter 2 can be caused to output the active power more efficiently.

Next, the operation of the power converter 1 will be described using phasor diagrams shown in FIGS. 10A and 10B. Even if each phase is unbalanced, it can be controlled without problems, but for simplicity, it is assumed that each phase is in a balanced state and there is no phase voltage unbalance. In the power conversion device 1, the converter 2 generates an interconnection point voltage component that is approximately equal to the interconnection point voltage, a reactive component voltage that has the same phase as the interconnection point voltage component, and a phase that is 90 degrees from the interconnection point voltage component. Since the sum voltage with the leading active component voltage is output, the output voltage of the converter 2 is a voltage leading the interconnection point voltage in phase, as shown in FIG. 10A. As described above, the voltage component whose phase is advanced by 90 degrees is created by multiplying the voltage whose phase is delayed by 90 degrees from the interconnection point voltage by a negative real number. Since the converter 2 is connected to the power system through the inductors 12R, 12S, 12T, the interconnection X voltage, which is the difference voltage between the output voltage of the converter 2 and the interconnection point voltage, is applied to the inductors 12R, 12S, 12T. (See FIG. 8). Due to this grid X voltage, currents whose phases are delayed by 90 degrees from the grid X voltage flow through the inductors 12R, 12S, and 12T, and power is supplied from the power converter 1 to the power system.

As shown in FIG. 10B, which is an enlarged part of the phasor diagram of FIG. 10A, this current consists of a current phasor Ih opposite to the interconnection point voltage and a current phasor 90 degrees out of phase with the interconnection point voltage. Iv. Therefore, the current flowing through the inductors 12R, 12S, and 12T contains a current component in phase with the interconnection point voltage, and the active power represented by the product of the current component and the interconnection point voltage is the power from the power converter 1. output to the system. In addition, the current flowing through the inductors 12R, 12S, and 12T includes a current component that is 90 degrees out of phase with the interconnection point voltage, and the reactive power represented by the product of the current component and the interconnection point voltage is the power converter 1. supplied to the power system from Thus, the power converter 1 can supply active power and reactive power.

In addition, the power conversion device 1 can change the reactive power to be output by changing the gain q of the reactive component voltage generation unit 34, and can change the gain d of the active component voltage generation unit 35 to output Active power can be changed. FIG. 11A is a phasor diagram when the value of the gain q, which was originally a positive real number, is increased from the state of the phasor diagram of FIG. 10B to increase the reactive component voltage. Due to the increase in the reactive component voltage, the current flowing through the power converter 1 also increases. As a result, the magnitude of the current phasor Ih increases, the current component 90 degrees out of phase with the interconnection point voltage also increases, and the lagging reactive power supplied to the power system also increases. By reducing the value of q, the reactive power to be supplied can be reduced, and by setting the value of q to a negative real number, reactive power can flow into the power converter 1 from the power system.

Similarly, FIG. 11B shows the phasor when the value of the gain d, which was initially a negative real number, is made smaller and the magnitude on the vector of the effective component voltage is increased from the state of the phasor diagram of FIG. 10B. It is a diagram. Due to the increase in the magnitude of the active component voltage, the current flowing through the power converter 1 also increases. As a result, the magnitude of the current phasor Ih increases, the current component in phase with the interconnection point voltage also increases, and the active power supplied to the power system also increases. By reducing the value of d, the supplied active power can be reduced, and by setting the value of d to a positive real number, active power can flow into the power conversion device 1 from the power system.

Here, the values of the gain q of the reactive component voltage generator 34 and the gain d of the active component voltage generator 35 are approximately −0.2≦q and d≦+0.2 (or the absolute values of q and d is 0.2 or less). This is because if the values of q and d are out of this range, the current flowing through the power conversion device 1 will increase and the power conversion device 1 may break down.

Further, the values of the gain q of the reactive component voltage generator 34 and the gain d of the active component voltage generator 35 are such that the AC voltage of each phase output by the converter 2 is the impedance of the interconnection impedance, that is, the inductor 12R , 12S, and 12T by adding 1 to the value of the inductance L (expressed in unit system), and setting them so as to be equal to or less than the voltage value obtained by multiplying the system voltage of each phase. By doing so, it is possible to further suppress overcurrent from flowing through the power conversion device 1 . It should be noted that the inductance in the unit system is the inductance of an inductor expressed as a voltage drop when a reference current flows through the inductor. For example, if the inductance L is 0.1 (p.u.), the voltage drop (corresponding to voltage loss) when the reference current flows is 0.1 (p.u.), that is, the inductor means that there is a voltage drop of 10% at .

Further, the limiter values of the gain q of the reactive component voltage generator 34 and the gain d of the active component voltage generator 35 are set so as to satisfy the expression (1), that is, the square root of the sum of the squares of q and d is the inductor 12R. , 12S and 12T, respectively, to be equal to the inductance L (in units). By doing so, it is possible to further suppress the overcurrent flowing through the power conversion device 1 and continue the operation even in the event of a system failure. However, if overcurrent is allowed, L is multiplied by the overcurrent limit magnification. The overcurrent limit magnification is a value that can be arbitrarily set depending on how much overcurrent is allowed to flow through the power converter 1 .

The gain control unit 104 is based on the interconnection point voltage detected by the power supply voltage detector 11, the power system frequency detected by the frequency detector 103, and the capacitor voltage of the converter 2 detected by the capacitor voltage detector 105. The values of the gain q of the reactive component voltage generator 34 and the gain d of the active component voltage generator 35 are determined, and the reactive power and active power output by the power converter 1 are controlled.

For example, when the capacitor voltage is higher than a predetermined range, the active power flowing out of the power conversion device 1 to the power system is made larger than the active power flowing into the power conversion device 1 from the active power source 7, thereby reducing the capacitor voltage. can. That is, the gain control unit 104 increases the value of the gain d of the active component voltage generation unit 35 and increases the active power output by the power conversion device 1, so that The active power flowing out from the power conversion device 1 to the power system is balanced with the active power flowing out from the power converter 1 . On the other hand, when the capacitor voltage is lower than the predetermined range, the active power flowing out of the power conversion device 1 to the power system is made smaller than the active power flowing into the power conversion device 1 from the active power source 7, thereby reducing the capacitor voltage. can rise. That is, the gain control unit 104 reduces the value of the gain d of the active component voltage generation unit 35 and reduces the active power output by the power conversion device 1, so that the power flowing into the power conversion device 1 from the active power source 7 The active power flowing out from the power conversion device 1 to the power system is balanced with the active power flowing out from the power converter 1 .

Further, for example, when the interconnection point voltage is lower than the reference range, the gain control section 104 increases the value of the gain q of the reactive component voltage generating section 34 to increase the interconnection point voltage, that is, the system voltage. On the other hand, when the interconnection point voltage is higher than the reference range, the gain control section 104 reduces the value of the gain q of the reactive component voltage generation section 34 to reduce the system voltage. Further, if the grid frequency is lower than the reference range, the grid is overdemanded. In this case, the gain control unit 104 reduces the value of the gain d of the active component voltage generation unit 35 set to a negative real number (increases the absolute value of d) to reduce the amount of active power supplied to the electric power system. increase. On the other hand, when the frequency of the power system is higher than the reference range, the gain control unit 104 increases the value of the gain d of the active component voltage generation unit 35 set to a negative real number (reduces the absolute value of d). ), reducing the supply of active power to the power system and reducing the frequency. Alternatively, the gain control unit 104 sets the value of the gain d to a positive real number, and causes active power to flow into the power converter 1 from the power system.

(2) Actions and effects of the second embodiment In the above configuration, the power conversion device (power conversion system) 1 is connected to the power system (AC voltage source) via the inductors 12R, 12S, and 12T (interconnection impedance). A converter 2 that outputs a predetermined AC voltage, a power supply voltage detector 11 that detects the connection point voltage of the power system (the voltage of the AC voltage source), and a control unit (control device) 4 that controls the converter 2 The control unit 4 is configured to control the converter 2 based on an interconnection point voltage component based on the detected interconnection point voltage and a voltage out of phase with the detected interconnection point voltage. did.

Therefore, in the power converter 1, even when the phase of the power system changes significantly, the interconnection point voltage component based on the detected interconnection point voltage can follow the interconnection point voltage, and the converter including the interconnection point voltage component Since the output voltage of 2 can also follow the change in the phase of the interconnection point voltage, it is possible to suppress an increase in the difference voltage between the interconnection point voltage and the output voltage of the power converter 1 . As a result, it is possible to prevent an overcurrent from flowing through the power conversion device 1 and cause the power conversion device to fail.

Further, in the power conversion device 1, the control unit 4 detects an interconnection point voltage component based on the detected interconnection point voltage, a reactive component voltage obtained by q times the detected interconnection point voltage (q is a real number), and a detected d times (d is a real number) the voltage shifted by (2n-1) 90 degrees (n is a positive integer of 1 or more) from the grid connection point voltage 2, the amount of active power and reactive power can be controlled, and a highly robust power converter can be provided.

Furthermore, the power converter 1 limits the gain q of the reactive component voltage generator 34 and the gain d of the active component voltage generator 35 within the above-described ranges, so that the current flowing through the power converter 1 is excessive. It is possible to prevent it from becoming a current, and it is possible to further suppress the overcurrent from flowing through the power conversion device 1 .

(3) Other Embodiments of Second Embodiment The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. For example, in the above embodiment, the case where the converter 2 of the power converter 1 is connected to the power system via the inductors 12R, 12S, and 12T has been described, but the present invention is not limited to this. You may make it connect the converter 2 to a power system via.

In the above embodiment, the case where the control unit 4 causes the converter 2 to output the sum voltage including the active component voltage obtained by multiplying the voltage delayed by 90 degrees from the interconnection point voltage by d has been described. The invention is not limited to this, and the control unit 4 generates an active component voltage delayed by 450 degrees, 810 degrees, . . . You may make it output the sum voltage containing. Alternatively, a voltage delayed in phase from the connection point voltage by 270 degrees, 630 degrees, . That is, the control unit 4 converts the sum voltage including the active component voltage obtained by multiplying the voltage (2n−1) 90 degrees (n is a positive integer of 1 or more) by d from the interconnection point voltage. output to device 2. In addition, when using a voltage whose phase is delayed by 270 degrees + 360n degrees (n is a positive integer of 1 or more) from the interconnection point voltage and the active power is to flow from the power converter 1 to the power system, d is a negative value. set to It should be noted that the phase shift need not strictly match (2n−1)·90 degrees (where n is a positive integer equal to or greater than 1).

Further, in the above embodiment, by changing the values of the gain q of the reactive component voltage generator 34 and the gain d of the active component voltage generator 35, the reactive power and the active power output from the power converter 1 are However, the present invention is not limited to this, and the control unit 4 can arbitrarily set the phase shift of the active component voltage (hereinafter referred to as the lag voltage) from the interconnection point voltage. , it is also possible to control the reactive power and the active power output by the power converter 1 . In the following description, it is assumed that the gain q=0. In this case, the phase delay of the delayed voltage from the interconnection point voltage is (2n−1) 90 degrees (n is a positive integer of 1 or more), and the current flowing through the power conversion device 1 is the interconnection point voltage. Since the phases are the same or opposite, active power can flow in and out between the power conversion device 1 and the power system.

On the other hand, when the phase delay of the lag voltage from the interconnection point voltage is (n−1) 180 degrees (n is a positive integer equal to or greater than 1), the current flowing through the power converter 1 is less than the interconnection point voltage. Since the current is a current whose phase is delayed by 90 degrees or advanced by 90 degrees, reactive power can flow in and out between the power converter 1 and the power system. If the phase delay of the delayed voltage from the interconnection point voltage is set to a value other than the above, the current flowing through the power conversion device 1 will have a current component that is in phase with or opposite to the interconnection point voltage, and a phase that is out of phase with the interconnection point voltage. Since the current component includes a current component delayed by 90 degrees or advanced in phase by 90 degrees, reactive power and active power corresponding to the phase shift can flow in and out between the power converter 1 and the power system. In this way, the control unit 4 calculates the sum voltage of the voltage component based on the detected interconnection point voltage and the delay voltage obtained by multiplying the voltage phase-shifted from the detected interconnection point voltage by d (where d is a real number). By causing the converter 2 to output and controlling the reactive power and the active power to be output based on the detected phase shift between the interconnection point voltage and the lag voltage, the power conversion device 1 and the power system It is possible to control the reactive power and active power flowing in and out. The phase shift between the interconnection point voltage and the active component voltage can be adjusted by adjusting the delay time of the interconnection point voltage detection signal in the phase delay unit 31 . In this way, when the controller 4 controls the reactive power and the active power based on the connection point voltage and the lag voltage, the reactive component voltage generator 34 may be removed from the controller 4 .

In the above embodiment, the case where the power conversion device 1 supplies power to a three-phase AC AC voltage source has been described, but the present invention is not limited to this, and power is supplied to a single-phase AC AC voltage source. You can also make In this case, the power conversion device 1 may be used, the inductor 12R may be connected to a single-phase AC voltage source, and power may be supplied from the power conversion device 1 to the AC voltage source. Further, the S-phase conversion unit 21S and the T-phase conversion unit 21T are removed from the converter 2 of the power conversion device 1, and the power conversion device 1 is used as a single-phase AC power conversion device, and power is supplied to the single-phase AC voltage source. may be supplied.

In the above embodiment, the case of supplying power to an electric power system as an AC voltage source has been described. can also be supplied.

Further, in the above-described embodiment, due to a delay in detection of the interconnection point voltage, there is a phasor shift (phase difference) between the interconnection point voltage used for calculation of the sum voltage in the control unit 4 and the actual interconnection point voltage. deviation) may occur. Therefore, in the power conversion device 1, the control unit 4 may also control the above phase shift. By doing so, the power conversion device 1 can more stably output active power to the power system. Specifically, it is preferable to shorten the delay time of the active power component by the detection delay.

Further, the control unit 4 calculates a phase shift compensation voltage as a compensation voltage, and adds the voltage obtained by adding the phase shift compensation voltage to the sum voltage to compensate for the phase shift. For example, the phase shift compensation voltage may be calculated based on an average amount of phase shift caused by detection delay, which has been measured in advance.

Furthermore, although the inductors 12R, 12S, and 12T ideally have only inductance components, they actually have resistance components. Therefore, when voltage is applied to the inductors 12R, 12S, and 12T, voltage drops occur. A differential voltage is generated between the actual output voltage of the power conversion device 1 and the ideal output voltage of the power conversion device 1 by this voltage drop. That is, the voltage phasor of the product of the resistance components of the inductors 12R, 12S, and 12T and the current is the difference voltage. The control unit 4 may calculate a voltage drop compensation voltage as the compensation voltage and add the voltage drop compensation voltage to the sum voltage to compensate for this difference voltage.

In the above embodiment, the case where the power converter 1 is used in the power generation system 100 has been described, but the present invention is not limited to this. The power conversion device 1 may be used in a power transfer system that connects and transfers power from a supply-side power system to a power system (hereinafter referred to as a demand-side power system). In this case, similarly to the power generation system 100, the gain control unit 104 adjusts the values of the gains q and d based on the system voltage of the demand-side power system, the frequency, and the voltage of the capacitor of the converter 2 of the power converter 1. It is also possible to control the reactive power and active power output by the power conversion device 1 and control the amount of power transferred from the supply-side power system to the demand-side power system. In addition, the gain control unit 104 determines the values of the gains q and d based on commands from the command center of the demand-side power system and the command center of the supply-side power system. Active power may be controlled.

In the above-described embodiment, the power converter 1 is used in the power generation system 100, but the present invention is not limited to this, and can be used in a load system, for example. In the load system, for example, the power conversion device 1 may be connected to a power storage system such as a load that consumes active power instead of the active power source or a storage battery that takes in and out the active power. By setting the gain d to a positive real number by the gain control unit 104, active power can be supplied to the secondary battery and the active power load.

Further, the power converter 1, the power generation system 100, the power transmission/reception system, the load system, and the like described above are connected via electric wires to construct a power transmission/distribution system that supplies the generated power to various consumers. can also

In the above embodiment, the case of using an IGBT as the switching element 24 has been described, but the present invention is not limited to this. An FET or the like can be used. The freewheeling diode 25 can be omitted by using a bidirectionally conductive FET or MOS-FET for so-called synchronous rectification.

In the above embodiment, the case where the voltage value detected by the power supply voltage detector 11 is used as the value of the detected interconnection point voltage has been described, but the present invention is not limited to this. For example, the connection point voltage (the voltage of the AC voltage source) is calculated by calculating the moving average of the voltage detection value detected by the power supply voltage detector 11 for the period of one cycle of the carrier wave used for pulse width modulation control. can be The pulse width modulation control is for the output control of the converter 2, ie for generating the gate pulse for each switch of the converter 2. FIG. By doing so, it is possible to suppress the occurrence of ripples in the calculated (detected) interconnection point voltage, and it is possible to output a voltage component closer to the actual interconnection point voltage. Furthermore, since calculation of the moving average has a light calculation load, the detection delay can be reduced, and the output voltage of the power converter can follow the fluctuation of the interconnection point voltage.

In this case, for example, the control unit 4 is provided with a moving average calculation unit that includes a memory and a calculation unit. Specifically, the memory stores the detected voltage value detected by the power supply voltage detector 11 for a period of one cycle of the carrier wave. Then, the calculation unit calculates the average value of the detected voltage values stored in the memory. By calculating the average of the detected voltage values stored in the memory, the average of the voltages detected during the predetermined period is calculated, and the moving average of the detected voltage values is calculated. The calculated average of the detected voltage values is used as the interconnection point voltage.

The memory can be composed of known storage devices such as DRAM, SRAM, flash memory and hard disk drives, for example. The arithmetic unit can be realized by dedicated hardware for calculating the average value of detected voltages, a general-purpose processor and built-in software, a program executed by a PC, or the like. A power conversion device that calculates an interconnection point voltage using a moving average in this way may be used in the above power generation system, power transfer system, load system, and power transmission/distribution system. A moving average filter may be provided separately from the control unit 4 to calculate the moving average of the interconnection point voltage V as described above.

In the above embodiment, the voltage phase delay unit 31 delays the phase of the interconnection point voltage of each phase by 1/4 cycle, thereby generating a voltage out of phase with the detected interconnection point voltage. However, the present invention is not limited to this. For example, by calculating a time differential of the detected interconnection point voltage, a voltage that is out of phase with the interconnection point voltage (approximately 1/4 cycle) may be calculated. This utilizes the theorem that when a sine wave is differentiated, the phase advances by 90 degrees.

For example, a time differentiation calculation section is provided in the control section 4, the detected interconnection point voltage is input to the time differentiation calculation section, and the interconnection point voltage is time-differentiated. The time partial operation unit may be realized by hardware such as a differential operation circuit, or may be a processor that executes a time differential operation program. Further, for example, differential operation may be performed discretely using the difference between the current and the interconnection point voltage a predetermined time (for example, one control cycle) ago. Further, the interconnection point voltage calculated by moving average of the detected voltage values may be time-differentiated to calculate a voltage out of phase with the interconnection point voltage. Furthermore, a power conversion device that calculates by time-differentiating the connection point voltage detected in this way may be used in the above power generation system, power transfer system, load system, and power transmission/distribution system. Although the phase deviation may deviate from the 1/4 period for convenience of calculation, an error of about ±5% is permissible.

[Description of Codes in Second Embodiment]
1 Power conversion device (power conversion system)
2 converter 4 control unit (control device)
7 active power source 12R, 12S, 12T inductor

3. Third Embodiment A power conversion device (power conversion system) according to a third embodiment has a moving average filter, does not have a gain control section, and has a configuration and operation of a control section. It differs from the power converter 1 of the embodiment. Below, the power conversion device of the third embodiment will be described with reference to FIGS. 12 to 14, focusing on the configuration different from the power conversion device 1 of the second embodiment.

In the power conversion apparatus of the third embodiment, the connection point voltage (hereinafter simply referred to as the detected voltage) as the voltage of the AC voltage source detected by the power supply voltage detector is treated as the current command value. More precisely, since the active current and the detected voltage have the same phase, the active current command value is calculated as a real multiple of the detected voltage, and the active voltage command value (active component voltage) is calculated from the active current command value. . In the third embodiment, the active current command value is determined by setting the detected voltage to the current command value of 1 pu. For example, when the active current command value (pu value) is 0.2 pu, the active current command value is obtained by multiplying the detected voltage by 0.2. On the other hand, regarding the reactive current command value, the current command value 1 pu is obtained by shifting the phase of the detected voltage by 90 degrees. Similar to the active current command value, the reactive current command value is determined by multiplying the detected voltage phase-shifted by 90 degrees by a real number.

FIG. 12 is a diagram showing part of the power converter of the third embodiment. The power conversion apparatus of the third embodiment includes a moving average filter 4600, and the detected interconnection point voltage V is smoothed by performing a moving average within a predetermined time range in the moving average filter 4600, and is input to the control unit 4000. be. The configuration and operation of the moving average filter 4600 are the same as the method of calculating the moving average of the interconnection point voltage V described in the other embodiment of the second embodiment, so description thereof will be omitted.

A control unit (control device) 4000 includes a phase compensation block 4100, a 90-degree phase advance calculation block 4200, a reactive component calculation block (calculation means) 4300, an effective component calculation block (calculation means) 4400, and a voltage command generation block. 4001 and PWM block 4500 . The operation of the controller 4000 will be described below.

The detected interconnection point voltage (detected voltage) V is smoothed through a moving average filter 4600 and then taken into the control section 4000 . A signal of the detected voltage V taken into the control section 4000 is inputted to the phase compensation block 4100 . The output of phase compensation block 4100 is input to effective component calculation block 4400 , 90-degree phase advance calculation block 4200 , and voltage command generation block 4001 .

In the effective component calculation block 4400, after the detected voltage V and the effective current command value (pu value) input from the phase compensation block 4100 are multiplied by the multiplier 4401, the multiplication result of the multiplier 4401 is It is converted into an active current command effective value Iref_dr. Then, in the effective component calculation block 4400, the effective current command effective value Iref_dr is input to the voltage estimation unit 4403, and from the effective current command effective value Iref_dr, it is necessary to apply the current to the interconnection impedance (reactor) in order to pass the current. A certain voltage value (effective component voltage estimated value Vi_d) is estimated, and the estimation result is output to the voltage command generation block 4001 as an effective voltage command value. Specifically, the effective component calculation block 4400 time-differentiates the effective current command effective value Iref_dr calculated from the detected voltage V, the product of the differentiated effective current command effective value Iref_dr and the inductance value of the interconnection impedance, and the effective current command effective value Iref_dr. By adding the current command effective value Iref_dr and the product of the resistance value of the interconnection impedance, the effective component voltage estimated value Vi_d is estimated.

As described above, when the current value is time-differentiated, a voltage whose phase is advanced by 90 degrees is calculated. Therefore, if the product of the calculation result and -1 is taken, it is equivalent to a voltage whose phase is delayed by 90 degrees. Since the positive and negative signs are interchanged depending on the directions of the current and voltage, this can be said to be a modified example of calculating the voltage delayed by 90 degrees. Since the detected interconnection point voltage V is regarded as a current value, the voltage whose phase is shifted by 90 degrees (1/4 period) from the detected interconnection point voltage V is obtained by differentiating the detected interconnection point voltage V. It can be calculated by multiplying by a real number (here, multiplied by the inductance value L of the interconnection impedance). This technique can also be applied to the second embodiment described above. When considering the resistance value of the interconnection impedance, the product of the interconnection point voltage and the resistance value of the interconnection impedance is added. When calculating a voltage whose phase is delayed by 90 degrees, it is further multiplied by -1.

In the 90-degree phase advance calculation block 4200, the phase of the detected voltage V input from the phase compensation block 4100 is rotated by 90 degrees using the rotation matrix, thereby advancing the phase by 90 degrees and generating the invalid component calculation block 4300. is entered in In the reactive component calculation block 4300, after the output of the 90-degree lead calculation block (phase lead voltage value) and the reactive power command value (pu value) are multiplied by the multiplier 4301, the output of the multiplier 4301 is converted to the current converter 4302. to the reactive current command effective value Iref_qr. Then, in the reactive component calculation block 4300, the reactive current command effective value Iref_qr is input to the voltage estimator 4303, and the reactive current command effective value Iref_qr is time-differentiated. A voltage value (estimated reactive component voltage value Vi_q) that needs to be applied to the interconnection impedance (reactor) is estimated, and the estimated result is output to the voltage command generation block 4001 as a reactive voltage command value (reactive component voltage) be done. Specifically, the voltage estimator 4303 differentiates the reactive current command effective value Iref_qr calculated from the phase lead voltage value, the product of the differentiated reactive current command effective value Iref_qr and the inductance value of the interconnection impedance, and the reactive current The reactive component voltage estimated value Vi_q is estimated by adding the command effective value Iref_qr and the product of the resistance value of the interconnection impedance.

The output of the 90-degree phase advance calculation block 4200 is a voltage whose phase is advanced by 90 degrees (1/4 period) from the input interconnection point voltage V. FIG. Therefore, the product of the output of the 90-degree phase lead calculation block 4200 and -1 is equivalent to a voltage whose phase is delayed by 90 degrees. Since whether or not the product with -1 is necessary depends on whether the reactive power is positive or negative, the 90-degree phase advance calculation block 4200 can also be said to be a modified example of calculating a voltage delayed by 90 degrees. Therefore, the voltage that is out of phase with the detected grid-connection point voltage is obtained by converting the detected grid-connection point voltage V to three-phase to two-phase, then rotating the phase by 90 degrees using the rotation matrix, and further to It can be calculated by converting. This technique can also be applied to the second embodiment described above.

In voltage command generation block (output voltage command generation unit) 4001 , detected voltage V input from phase compensation block 4100 , effective voltage command value input from effective component calculation block 4400 , and reactive component calculation block 4300 are input. and the reactive voltage command value are added to generate a voltage command for the power converter. The voltage command is input to the PWM block 4500 and normalized within the PWM block 4500 . In PWM block 4500, the normalized voltage command is modulated by PWM to generate a gate pulse for each switch of the converter, and the gate pulse is output to each switch to drive each switch.

Next, the operation of each block that constitutes the control unit 4000 will be described. First, the operation of phase compensation block 4100 will be described. A phase compensation block 4100 compensates for the phase of the detected voltage V delayed by the smoothing by the moving average filter 4600 . Specifically, the phase of the input detection voltage V is advanced by the phase delayed by the moving average filter 4600 . More specifically, it is preferable to advance the phase corresponding to half the moving average calculation time. As means for advancing the phase, like a 90-degree phase advance calculation block 4200 described later, after three-phase to two-phase conversion, the phase is advanced by the phase by the rotation matrix to perform two-to-three phase conversion.

Next, the operation of the 90-degree phase advance calculation block 4200 will be described. The 90-degree phase advance calculation block 4200 converts the detected voltage V of each phase input from the phase compensation block 4100 into a three-phase to two-phase conversion unit 4201, and converts the detected voltage V after the three-phase to two-phase conversion. Phase rotation section 4202 advances the phase by 90 degrees in the rotation matrix. The 90-degree phase advance calculation block 4200 performs two-to-three-phase conversion on the detected continuous pressure V whose phase is advanced by 90 degrees in a two-to-three-phase converter 4203, and invalidates the detected voltage V of each phase whose phase is advanced by 90 degrees. Output to operation block 4300 . Note that the 90-degree phase advance calculation block 4200 may delay the phase by 90 degrees. However, in this case, the sign of the reactive current command value is opposite.

Next, the invalid portion calculation block 4300 and the valid portion calculation block 4400 will be described. These two blocks are described together because their operations are substantially the same. Current converter 4302 and current converter 4402 divide the voltage value (multiplier 4301 or the output of multiplier 4401) by the phase voltage rated voltage, convert it to the current rated value ampere value, and obtain the active current command effective value Iref_dr, invalid A current command effective value Iref_qr is calculated.

Voltage estimating section 4303 and voltage estimating section 4403 calculate active component voltage estimated value Vi_d from active current command effective value Iref_dr, and compute reactive current command effective value Iref_qr and reactive component voltage estimated value Vi_q. This calculation is performed by the following equations (2) and (3).
Vi_d=(Ls+R)·Iref_dr (2)
Vi_q=(Ls+R)·Iref_qr (3)
Here, L is the inductance value of each phase, R is the resistance value of the reactor of each phase, and s is the Laplace operator. The active current command effective value Iref_dr (reactive current command effective value Iref_qr) is differentiated and multiplied by the inductance value L, and the product of the active current command effective value Iref_dr (reactive current command effective value Iref_qr) and the resistance value is added to the multiplication result. , an effective component voltage estimated value Vi_d (reactive component voltage estimated value Vi_q) is calculated. The reactive component calculation block 4300 outputs the calculated reactive component voltage estimated value Vi_q as the reactive voltage command value to the voltage command generation block 4001, and the effective component calculation block 4400 outputs the calculated effective component voltage estimated value Vi_d as the active voltage command value. , to the voltage command generation block 4001 .

Since the power conversion device of the third embodiment has the control unit 4000, it has high robustness against phase jumps. Furthermore, the power conversion device of the third embodiment can remove ripples in the detected interconnection point voltage V by including the moving average filter 4600 .

(Modification 1 of the third embodiment)
When noise enters the detected interconnection point voltage V, Vi_d and Vi_q calculated by the voltage estimating section 4303 and the voltage estimating section 4403 fluctuate greatly. In such a case, the voltage estimating unit 4303 and the voltage estimating unit 4403 convert the equations (2) and (3) to the equations (4) and (5) in which the differentiation operation is an incomplete differentiation, and the effective component voltage It is preferable to calculate the estimated value Vi_d and the reactive component voltage estimated value Vi_q. T in equations (4) and (5) is a time constant and can be set arbitrarily.
Vi_d=(Ls/(Ts−1)+R)·Iref_dr (4)
Vi_q=(Ls/(Ts−1)+R)·Iref_qr (5)

(Modification 2 of the third embodiment)
Furthermore, considering the case where the influence of noise cannot be avoided even with incomplete differentiation, it is preferable to provide a limiter to the outputs of the invalid component calculation block 4300 and the effective component calculation block 4400 . The limiter value is the same as the voltage (both positive and negative) applied to the interconnection impedance when the rated current flows through the interconnection impedance, or has a slight margin, for example, 1 of the voltage. It is preferable to set it to around 0.5 times.

(Modification 3 of the third embodiment)
When the detected value of the interconnection point voltage V is treated as the current command value as in the third embodiment, if the harmonic voltage is superimposed on the system, the harmonics are also superimposed on the interconnection point voltage V. Furthermore, when the system voltage (interconnection point voltage V) fluctuates, the current command value also fluctuates. Therefore, it is preferable to take measures against these. Note that the fluctuation of the system voltage (interconnection point voltage V) here means that there is a difference between the rated value of the system voltage and the value of the interconnection point voltage.

First, measures against harmonics will be described. For low-order harmonics, for example, the detected interconnection point voltage V is passed through a notch filter, and for high-order harmonics, for example, the detected interconnection point voltage V is passed through a low-pass filter. Then, it is preferable to attenuate the harmonics superimposed on the interconnection point voltage V and to attenuate the harmonics superimposed on the current command value. Harmonics may be attenuated by filtering the active current command effective value, the reactive current command effective value, or the like.

If the above low-pass filter is used as a countermeasure against incomplete differential calculation by the above equations (4) and (5) and harmonics, a phase delay occurs in the effective voltage command value and the ineffective voltage command value. In order to compensate for this phase lag, it is preferable to slightly increase the active current command value and add the active current to the reactive current when passing the reactive current. Similarly, when passing an active current, it is preferable to slightly increase the reactive current command value and add the reactive current to the active current.

(Modification 4 of the third embodiment)
Next, in Modification 4, countermeasures against various errors in the interconnection point voltage V will be described. First, when converting the effective current command effective value Iref_dr and the reactive current command effective value Iref_qr into the voltage to be applied to the interconnection impedance, the phase is delayed if the incomplete differentiation is used instead of the differentiation. A method of compensating for the phase lag will be described. The control unit of Modification 4 differs in the configuration of the invalid component calculation block 4300 and the effective component calculation block 4400 of the control unit 4000 of the third embodiment shown in FIG. FIG. 13 is an enlarged view showing a part of the control unit of Modification 4, which corresponds to the area surrounded by the dashed line in the control unit 4000 shown in FIG. The configuration of the control unit other than the area shown in FIG. 13 is the same as that of the third embodiment, so the description is omitted.

Like the invalid component calculation block 4300a and the effective component calculation block 4400a shown in FIG. 13, when performing phase lag compensation, both blocks cannot be completely separated and interfere with each other.

First, the operation of the invalid component calculation block 4300a will be described. As in the third embodiment, the reactive current command effective value Iref_qr of each phase converted from the reactive current command value by the current converter 4302 is calculated by the multiplier 4309 in the voltage compensation value calculation block described later. The same phases are multiplied with the voltage compensation value of , respectively, to compensate for voltage fluctuations. The reactive current command effective value Iref_qr with the voltage fluctuation compensated is output to filter block 4305 to attenuate harmonics. Filter block 4305 is composed of, for example, a low-pass filter.

Reactive current command effective value Iref_qr with harmonics attenuated is calculated by multiplying active current command effective value Iref_dr by real number β in multiplier 4406 in multiplier 4307, and the current for phase lag compensation in filter block 4305 is added. and input to voltage estimation section 4303 . Then, in the voltage estimator 4303, the reactive component voltage estimated value Vi_q, which is the voltage of the interconnection impedance required for the added current to flow, is calculated by the above equation (3) or (5), and the reactive voltage command Output to limiter block 4308 as a value.

In the limiter block 4038, when the invalid voltage command value is within the predetermined range, the invalid voltage command value is output to the voltage command generation block 4001 as it is. is output to the voltage command generation block 4001 as the output of the reactive component calculation block 4300a, that is, the reactive voltage command value. Further, in the reactive component calculation block 4300a, the reactive current command effective value Iref_qr whose harmonics have been attenuated in the filter block 4305 is multiplied by a real number β in the multiplier 4306, and is used as the current for compensating the phase lag in the filter block 4405. It is output to minute calculation block 4400a.

Next, the operation of effective amount calculation block 4400a will be described. As in the third embodiment, the active current command effective value Iref_dr of each phase converted from the active current command value by the current converter 4402 is The same phases are multiplied with the voltage compensation value of , respectively, to compensate for voltage fluctuations. The effective current command effective value Iref_dr compensated for voltage fluctuation is output to filter block 4405 to attenuate harmonics.

Active current command effective value Iref_dr with harmonics attenuated is obtained by multiplying reactive current command effective value Iref_qr by real number β in multiplier 4306 and adding current for phase lag compensation in filter block 4305 in multiplier 4407. , is input to the voltage estimator 4403 . Then, in the voltage estimating unit 4403, the effective component voltage estimated value Vi_d, which is the voltage of the interconnection impedance required to flow the added current, is calculated by the above equation (2) or (4), and the effective voltage command Output to limiter block 4408 as a value.

In the limiter block 4408, when the effective voltage command value is within the predetermined range, the effective voltage command value is output as it is to the voltage command generation block 4001, and when the effective voltage command value deviates from the predetermined range, the preset limiter value is output to the voltage command generation block 4001 as the output of the effective amount calculation block 4400a, that is, the effective voltage command value. Further, in effective component calculation block 4400a, active current command effective value Iref_dr whose harmonics have been attenuated in filter block 4405 is multiplied by real number β in multiplier 4306, and is used as current for compensating for phase lag in filter block 4305. It is output to minute calculation block 4300a.

In voltage command generation block (output voltage command generation unit) 4001 , detected voltage V input from phase compensation block 4100 , effective voltage command value input from effective component calculation block 4400 , and reactive component calculation block 4300 are input. and the reactive voltage command value are added to generate a voltage command for the power converter. In addition, it is preferable to provide a limiter to the effective voltage command value and the ineffective voltage command value so as to prevent an excessive current from flowing. It is preferable that the limiter has a value that provides a necessary margin for the minimum and maximum voltages applied to the interconnection impedance when the rated current flows.

Finally, a voltage compensation value calculation block for calculating a voltage compensation value for compensating voltage fluctuations will be described. A voltage compensation value calculation block is provided in the control unit 4000 and calculates a voltage compensation value for each phase from the input detection voltage V of each phase. FIG. 14 shows a voltage compensation value calculation block 4700 for calculating a voltage compensation value for compensating a current command value (reactive current command effective value, active current command effective value) when voltage fluctuates in steady state. A voltage compensation value calculation block 4700 calculates a voltage compensation value for each phase (R phase, S phase, and T phase). Since the calculation operation of the voltage compensation value is the same for each phase, the R phase will be described below as a representative.

In the voltage compensation value calculation block 4700 , the detected value of the R-phase interconnection point voltage V smoothed by the moving average filter 4600 is input, and the multiplier 4701 calculates the square value of the detected voltage. The squared value of the detected voltage is output to quarter period delay section 4702 and adder 4703 . The 1/4 period delay unit 4702 is composed of, for example, a memory. The 1/4 cycle delay unit 4702 holds the squared value of the detected voltage in memory for a period of 1/4 cycle. , to the adder 4703 . The adder 4703 adds the squared value (current value) of the detected voltage input from the multiplier 4701 and the past value of the squared value of the detected voltage input from the 1/4 period delay unit 4702, and obtains the root Output to the calculation unit 4704 .

Root calculation section 4704 performs root calculation on the output of adder 4703 and inputs the result to divider 4705 . A divider 4705 divides the output of the root calculator 4704 by √2. The division result is a value corresponding to the effective value of the R-phase interconnection point voltage V. FIG. Divider 4705 outputs the division result to R-phase voltage compensation value calculation section 4706 as the effective value of interconnection point voltage V. FIG. The value of the R-phase rated phase voltage is also input to the R-phase voltage compensation value calculation unit 4706 . The R-phase voltage compensation value calculation unit 4706 divides the R-phase rated voltage by the effective value of the R-phase interconnection point voltage V to calculate the R-phase voltage compensation value.

In general electric power systems, voltage fluctuations during steady state are small, so voltage fluctuations can often be tolerated in PCS (Power Conditioning Subsystem) applications. For example, the voltage fluctuation of the power distribution system in Japan is only ±10% during normal operation.

In addition, if voltage compensation for voltage fluctuations is performed at the time of a system fault, an unnecessary current will flow. Therefore, when the interconnection point voltage value exceeds the steady-state range, it is preferable not to perform voltage fluctuation compensation. It is preferable to set a limiter for each phase voltage compensation value based on the normal voltage tolerance value or a voltage value to which a certain amount of margin is added to the normal voltage tolerance value for performing or not performing voltage compensation. Note that if the voltage compensation calculation (calculations in the multipliers 4309 and 4409) is placed before the differential calculation (calculations in the voltage estimating units 4303 and 4403) as in Modification 4, switching between with and without voltage fluctuation compensation can be performed. There is a possibility that a large voltage command value will be output in the differentiation calculation immediately after. Therefore, it is preferable to put the voltage compensation calculation after the differential calculation. In addition, when inserting in the preceding stage, between the voltage compensation value calculation block 4700 and the multipliers 4309 and 4409, a multiplication means such as a multiplier capable of multiplying by a real number is inserted, and the voltage compensation is gradually stopped so as not to suddenly stop the voltage compensation. It is necessary to take measures to reduce the gain of the multiplying means.

You may use the power converter of 3rd Embodiment and its modification for said electric power generation system, an electric power transfer system, a load system, and an electric power transmission/distribution system.

Claims (20)

A power conversion device connected to an AC voltage source via a grid impedance,
a converter that outputs a predetermined AC voltage;
a power supply voltage detector that detects the voltage of the AC voltage source;
A control unit that controls the converter,
The power conversion device, wherein the control unit controls the converter based on a voltage component based on the detected voltage and a voltage out of phase with the detected voltage. The control unit provides a voltage component based on the detected voltage, a reactive component voltage obtained by multiplying the detected voltage by q (q is a real number), and a phase of (2n−1) 90 degrees ( 2. The power converter according to claim 1, wherein n is a positive integer equal to or greater than 1) and a voltage obtained by multiplying the deviated voltage by d (where d is a real number) is output to the converter. The power converter according to claim 2, wherein the value of d is a negative real number. The power supply voltage detector detects the voltage of the interconnection impedance on the AC voltage source side,
The control unit is an output voltage command generation unit that calculates a voltage command for controlling the converter based on a voltage component based on the detected voltage and a voltage delayed by 1/4 period of the detected voltage. The power converter according to claim 1, comprising: The power conversion device according to claim 4, wherein the output voltage command generation unit integrates the quarter-cycle delayed voltage by a negative real number. 2. The predetermined AC voltage output by the converter is equal to or less than a voltage value obtained by multiplying the detected voltage by a value obtained by adding 1 to the impedance (unit system display) of the interconnection impedance. 6. The power converter according to any one of 1 to 5. The power according to claim 2 or 3, wherein the limiter values of the q and the d are determined based on the relationship that the square root of the sum of the squares of the q and the d is equal to the impedance (unit system display) of the interconnection impedance. conversion device. The control unit according to any one of claims 1 to 7, wherein the control unit calculates a compensation voltage that compensates for a phase shift between the voltage detected by the power supply voltage detector and the actual voltage of the AC voltage source. A power converter as described. The power conversion device according to any one of claims 1 to 7, wherein the control unit calculates a compensation voltage for compensating for a voltage drop in the interconnection impedance. The control unit causes the converter to output a sum voltage of a voltage component based on the detected voltage and a delayed voltage obtained by multiplying a voltage phase-shifted from the detected voltage by d (d is a real number),
The power converter according to claim 1, wherein reactive power and active power to be output are controlled based on a phase shift between the detected voltage and the lag voltage. A power generation system comprising the power converter according to any one of claims 1 to 10. A power exchange system comprising the power converter according to any one of claims 1 to 10. A load system comprising the power converter according to any one of claims 1 to 10. A power transmission and distribution system comprising the power converter according to any one of claims 1 to 10, the power generation system according to claim 11, the power transfer system according to claim 12, or the load system according to claim 13. 2. The power converter according to claim 1, wherein the voltage out of phase with the detected voltage is calculated by differentiating the detected voltage and multiplying the result by a real number. 2. Computing means for differentiating the detected voltage and adding the product of the differentiated voltage and the inductance value of the interconnection impedance and the product of the detected voltage and the resistance value of the interconnection impedance. 16. The power converter according to 15 . A voltage that is out of phase with the detected voltage is calculated by converting the detected voltage into three-phase to two-phase, rotating the phase by 90 degrees using a rotation matrix, and then performing two-to-three-phase conversion. The power converter according to claim 1. After converting the detected voltage to three-phase to two-phase, the phase is rotated by 90 degrees using a rotation matrix, and the phase lead voltage value calculated by further performing two-to-three-phase conversion is differentiated, and the differentiated phase The power conversion apparatus according to claim 1 or 17 , further comprising a calculation means for adding a product of a lead voltage value and an inductance value of said interconnection impedance and a product of said phase lead voltage value and a resistance value of said interconnection impedance. pulse width modulated control controlling said converter;
2. The voltage of the AC voltage source according to claim 1, wherein the voltage of the AC voltage source is calculated by calculating a moving average of the voltage detection value detected by the power supply voltage detector for a period corresponding to one cycle of the carrier wave used for the pulse width modulation control. Power converter. The power converter according to claim 1 or 19 , wherein the control section calculates a voltage out of phase with the detected voltage by calculating time differentiation of the voltage of the AC voltage source.

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