JP5523395B2 - Power converter - Google Patents

Description

  The present invention relates to a power converter that converts DC power into AC power, for example, a power converter that converts DC power of a distributed power source such as a solar battery into AC power and outputs the AC power to an AC system.

As a conventional power conditioner device as a power conversion device, there is a device that converts DC power from a power generation system such as a solar cell into AC power and outputs the AC power to a system.
That is, a power conditioner device that converts DC power generated in the power generation system into AC power, and outputs the AC power as a system output to a system outside the power generation system via a system auxiliary machine inside the power generation system The system output current detecting means for detecting the system output current of the system output, and the current control means for controlling the output current of the AC power based on the system output current detected by the system output current detecting means. And the current control means includes a harmonic current extraction means for extracting a harmonic current from the system output current detected by the system output current detection means, and a harmonic extracted by the harmonic current extraction means. Based on the current, the output current of the AC power is set to cancel the harmonic current included in the system output. Gosuru there is a power conditioner device having a harmonic current cancellation means (e.g., see Patent Document 1).

Japanese Patent Application Laid-Open No. 2004-274813

In the conventional power conversion device as described above, depending on the output impedance of the system, the oscillation of the current control system is induced, and when the oscillation continues, a large harmonic current continues to flow out of the inverter and adversely affects the system. There was a case to give.
The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a power conversion device that can suppress harmonic current flowing out from an inverter.

In the power conversion device according to the present invention, a power conversion device including an inverter and an output current control device,
The inverter converts DC to AC and outputs an output current to the AC system.
The output current control device includes harmonic current detection means, control means, current control command means, and gain change means,
The harmonic current detection means detects a harmonic current included in the output current,
The control means amplifies the difference between the output current and the target current and outputs it as a current deviation,
The current control command means transmits a current control command signal for controlling the output current to the inverter based on the current deviation,
The gain changing means changes the gain of the control means based on the magnitude of the harmonic current.

The present invention is a power conversion device including an inverter and an output current control device,
The inverter converts DC to AC and outputs an output current to the AC system.
The output current control device includes harmonic current detection means, control means, current control command means, and gain change means,
The harmonic current detection means detects a harmonic current included in the output current,
The control means amplifies the difference between the output current and the target current and outputs it as a current deviation,
The current control command means transmits a current control command signal for controlling the output current to the inverter based on the current deviation,
The gain changing means changes the gain of the control means based on the magnitude of the harmonic current.
Harmonic current flowing out from the inverter can be suppressed.

1 shows a configuration of a power conversion apparatus according to Embodiment 1 of the present invention, in which FIG. 1 (a) is a configuration diagram showing an overall configuration, and FIG. 1 (b) is a configuration showing a detailed configuration of output current control means. FIG. It is a block diagram which shows the detailed structure of the 1st controller of FIG. It is a wave form diagram for demonstrating operation | movement of the harmonic current detection means of FIG. It is a block diagram which shows the detailed structure of the output filter of FIG. It is a characteristic view which shows the frequency characteristic of a current control system. It is a characteristic diagram for demonstrating the influence which the gain of a controller has on the frequency characteristic of a current control system. It is a figure which shows the requirements for the responsiveness and stability of an output electric power control part by the magnitude of the impedance of a system | strain. FIG. 6 is a configuration diagram illustrating a configuration of a control signal wave generating unit according to a second embodiment.

Embodiment 1 FIG.
FIGS. 1-7 shows Embodiment 1 for implementing this invention, FIG. 1 shows the structure of a power converter device, and FIG. 1 (a) is a block diagram which shows the whole structure. FIG. 1B is a configuration diagram showing a detailed configuration of the output current control unit. 2 is a block diagram showing the detailed configuration of the first controller, FIG. 3 is a waveform diagram for explaining the operation of the harmonic current detecting means, and FIG. 4 is a block diagram showing the detailed configuration of the output filter. FIG. 5 is a characteristic diagram showing the frequency characteristics of the current control system, and FIG. 6 is a characteristic chart for explaining the influence of the gain of the controller on the frequency characteristics of the current control system. FIG. 7 is a diagram showing requirements for the responsiveness and stability of the output current control unit according to the impedance of the system.

  In FIG. 1, the power converter converts DC power from a DC power source 1 into three-phase AC power and outputs it to an AC system (load) 9. Note that the DC power source 1 is constituted by, for example, a solar cell or a fuel cell. The power converter includes an input circuit 2 for connecting to the DC power source 1, a converter 3 that steps up and down the voltage of the DC power source 1 to an optimum voltage for operating the inverter 4, and a DC voltage that is the output of the converter 3. An inverter 4 for converting to AC voltage, an output filter 5 as a filter device for reducing harmonics in the output voltage of the inverter 4 and smoothing the output voltage waveform, an output circuit 6 for connection to the system 9, and a DC Input voltage sensor 11 and input current sensor 12 for detecting voltage Vd and current Jd of power supply 1, system voltage sensor 21 for detecting system voltage Va and output current Ja, output current sensor 22, and detection of each sensor, respectively. A total controller 7 that controls the output power Pa to the system 9 by controlling the converter 3 and the inverter 4 according to the values is provided.

  The comprehensive control device 7 has an output current control unit 8 as an output current control device. The detailed configuration of the output current control unit 8 is shown in FIG. 1B. The subtractor 81, the control signal wave generating unit 82, the PWM signal output unit 83 as the current control command unit, and the harmonic current detection Means 85, comparator 86, external input means 87, and OR circuit 88 are provided. The control signal wave generating means 82 includes a controller switching means 821 as a gain changing means, first and second controllers 822 and 823 as control means, and an integrator content equalizing means 825.

The operation of the power conversion device configured as described above will be described below.
The integrated control device 7 of the power conversion device detects the DC voltage Vd, the DC current Jd, and the AC system voltage Va input from the DC power source 1, and according to the state of the DC power source 1 or the system voltage Va, The target current Jas (FIG. 1 (b)) is determined. The subtractor 81 obtains a difference ΔJa between the target current Jas and the current output current Ja of the inverter 4 that is the output of the current sensor, and the first controller 822 or the second controller 823 receives the input difference ΔJa. And a signal wave Vc as a current deviation for adjusting the duty factor of the switching element of the inverter 4 is output by PI calculation and amplification. The PWM signal output means 83 is a current control command signal that controls the opening / closing operation of a switching element (not shown) as the opening / closing means of the inverter 4 from the signal wave Vc output from the first controller 822 or the second controller 823. PWM signal Sg is generated, and the output current Ja of the inverter 4 is controlled.

  On the other hand, the harmonic current detection means 85 detects the harmonic current Jah in the output current Ja (detailed operation will be described later). The comparator 86 is a comparator with a time limit function, and compares the output of the harmonic current detection means 85 with a preset upper limit value JHL of the outflow harmonic current, and the output of the harmonic current detection means 85 is predetermined. A signal is issued when a state exceeding the upper limit value JHL as a value continues for a predetermined time (details will be described later). The OR circuit 88 outputs a signal S1 with the logical sum of the signal from the comparator 86 and the input from the external input means 87 as a truth value. The controller switching unit 821 switches between the controller 822 and the controller 823 when the truth value “1” is input. When switching between the controller 822 and the controller 823, the integrator content identifying unit 825 performs switching. The values of integrators (not shown) included in the controller 822 and the controller 823 are aligned between the first and second controllers 822 and 823.

  FIG. 4 schematically shows an example of the operation of the harmonic current detection means 85 that detects the harmonic current Jah in the output current Ja. In this example, the harmonic current detection means 85 subtracts the extracted value (fundamental wave component) Jaf filtered so as to extract only the fundamental wave component Jaf from the detected output current Ja from the output current Ja. The wave current Jah is obtained. The harmonic current Jah in the output current thus obtained is subjected to absolute value processing to obtain an absolute value | Jah |, and further averaged to obtain an average value Jahm, thereby obtaining the harmonic current content in the output current Ja. Is normalized and output. The average value Jahm which is a normalized value of the harmonic current content in the output current Ja and the upper limit value (reference value of the normalized value) JHL of the outflow harmonic current are compared by the comparator 86, and the harmonic current When the state where the content exceeds the upper limit value JHL continues for a predetermined time, a signal is output to the OR circuit 88. The OR circuit 88 that has received the signal outputs a switching signal that is a signal of truth value “1” to the controller switching means 821, and switches between the first controller 822 and the second controller 823. The second controller 823 performs arithmetic processing and amplification.

  The output current control unit 8 in the present embodiment has two controllers that perform feedback control of the output current Ja, that is, first and second controllers 822 and 823. FIG. 2 shows the configuration of the first and second controllers 822. The first controller 822 includes a proportional gain 822a, an adder 822b, a controller output limiter 822c, and an integration circuit 822d. The integration circuit 822d has an integration gain 822e, an integration limiter 822f, and a primary delay 822f. The second controller 823 has the same configuration as that of the first controller 822. Although not shown, the second controller 823 includes a proportional gain, an adder, a controller output limiter, and an integration circuit. The integration circuit includes an integration gain and an integration circuit. It has a limiter and first-order lag. Each of the controllers 822 and 823 performs PI calculation and amplification based on the input signal. The controllers 822 and 823 have different gains between the two controllers according to the impedance condition of the system 9 that can be assumed. In this embodiment, the gain of the controller 823 is the controller 822. It is set smaller than the gain. When the harmonic current content exceeds a certain value as described above, a signal transmitted from the comparator 86 or an external switching signal input from the external input means 87 is input. The truth value “1” output from 88 is output to the controller switching means 821, and the controller switching means 821 receiving this changes the gain of the control means by switching between the controller 822 and the controller 823. At the time of switching between the controller 822 and the controller 823, if the contents of the integrators included in the controllers 822 and 823 are different between the controllers 822 and 823, the outputs of the controllers 822 and 823 at the time of switching will Since there is a possibility of switching continuously, the contents of the integrators of the controllers 822 and 823 are made identical by the integrator contents equalizing means 825.

Here, the detail of the effect by switching the controller 822,823 of the output current control part 8 is demonstrated.
In general, the factors that determine the gain of the controller include its responsiveness and stability. Immediate response is the speed at which the output current converges to the target output current, and stability is stable current control without causing hunting of the output current due to the influence of the controller under all possible conditions. To operate the device.

First, the requirement for responsiveness will be described.
In a power converter for linking a DC power source and a system as shown in the present embodiment, there may be a demand to continue to operate as much as possible with respect to a transient fluctuation of the system 9. . Therefore, for example, in order to continue the operation when an instantaneous drop occurs in the system voltage, the controller is configured to suppress the increase in the output current Ja so that the output current as the device does not exceed the upper limit value. Need to work. The increase rate dJa / dt of the output current at this time is expressed by the following equation, assuming that the impedance of the system 9 is only an inductance component, for example.
dJa / dt = dVs / Ls
Here, dVs: system voltage fluctuation amount, Ls: system impedance.
That is, the increase rate of the output current Ja decreases as the system impedance increases. From this, it can be said that the responsiveness of the current control system is required as the system impedance is small, and the responsiveness of the current control system may be low as the system impedance is large. Accordingly, the responsiveness is determined by the degree of system disturbance to be dealt with and the magnitude of the system impedance.

Next, the requirement for stability will be described.
When the output filter 5 constituting the power converter is, for example, a T-type LCL filter as shown in FIG. 4, the circuit transfer characteristics (frequency characteristics) of the current control system of the power converter including the controller are 5 and includes an unstable point frequency. The greater the value of the gain (vertical axis in FIG. 5) at this unstable point frequency, the greater the possibility that the stability of the current control system will be impaired. In FIG. 4, the output filter 5 is an LCL filter in which reactors 51 and 52 and a capacitor 53 are connected in a T shape.

  FIG. 5A shows a circuit transfer characteristic A of the current control system when the system impedance is small, and has an unstable point A1 (4 kHz, gain 2). FIG. 5B shows a circuit B of the current control system when the system impedance is large, and has an unstable point B1 (18 kHz, gain 23). The gain at the unstable point B1 of the current control system increases as the system impedance increases (FIG. 5B). That is, the stability of the current control system changes depending on the magnitude of the system impedance. When the gain at the unstable point frequency of the current control system increases, the controller hunts and the probability that the output current of the inverter 4 includes an extra harmonic current increases. It shows the gain and stability of the current control system and corresponds to the gain of the current control system.

  In order to suppress the hunting of the controller as described above, it is effective to reduce the amplification gain of the controller. For example, FIG. 6A is the same as the loop transfer characteristic B of the current control system shown in FIG. 5B, but FIG. 6B shows the gain of the controller in FIG. This is the loop transfer characteristic C of the current control system in the case of 10 and the gain at the unstable point C1 is smaller than that in FIG. From the above, it can be seen that responsiveness and stability are affected by the magnitude of the system impedance. FIG. 7 shows a table showing the relationship between the responsiveness required during system disturbance and the stability of the current control system with respect to the system impedance condition.

  From FIG. 7, in order to maintain the stability of the controller, it is necessary to design the gain with the maximum possible system impedance. On the other hand, assuming that the system impedance is low, the current control system is responsive. It is understood that it is necessary to increase the value. As described above, to increase the responsiveness of the current control system, it is necessary to increase the gain of the controller, but in order to maintain stability, it is necessary to reduce the gain of the controller. In many cases, it is difficult to set the gain of the controller to satisfy both of these requirements. As an effective measure in the case where such gain setting is difficult, there is a measure to use a reactor having a large inductance value for the reactors 51 and 52 constituting the output filter 5 of the power converter. However, with such measures, depending on the system disturbance to be expected, the reactors 51 and 52 of the output filter 5 may become large, and the power converter may be increased in size and cost.

In the power conversion device according to the present embodiment, the output current control unit 8 has two controllers 822 and 823 having different gain settings, detects the harmonic current Jah in the output current Ja, and the harmonic current Jah is constant. It has the controller switching means 821 which switches the controllers 822 and 823 when it becomes above. As a result, it is possible to prevent the oscillation (hunting) of the current control system from continuing and a large harmonic current from flowing out to the output filter 5 and the system 9 continuously and adversely affecting the output filter 5 and the system 9. That is, it is possible to suppress the harmonic current flowing out from the inverter 4 to the output filter 5 and the system 9 and prevent the output filter 5 and the system 9 from being adversely affected. Further, when the power converter is installed in a place having different system impedances, the reactor of the output filter 5 is switched by switching the controllers 822 and 823 depending on the magnitude of the harmonic current Jah in the detected output current Ja. Since it is possible to cope with changes in system impedance and system disturbances that occur depending on the installation location without increasing the inductance values of 51 and 52, it is possible to reduce the size, cost, and weight of the device. It is.
Further, when the system impedance is known in advance or when it is known that the system impedance is changed due to construction or the like, a switching signal is input to the OR circuit 88 using the external input means 87, and the manual operation is performed manually. It is also possible to change the current control gain by switching the controllers 822 and 823.

In addition, in the power converter device by this Embodiment, in the output current control part 8, although it has two controllers, it has three or more and switches each controller according to the level of a harmonic current. You may comprise as follows.
Further, in the output current control unit 8, the controller is composed of two first and second controllers 822 and 823, and the controller used according to the level of the harmonic current Jah is the controller 822 and 823. When the harmonic current is generated, the harmonic current Jah of the output filter 5, the output circuit 6, or the inverter 4, that is, the conductive part through which the output current Ja flows is heated according to the magnitude of the harmonic current Jah. In order to increase the temperature, a temperature detector may be provided to monitor the temperatures, detect the harmonic current via the temperature, and switch the controller according to the magnitude. In this case, the time limit function in the comparator 86 can be replaced by a time constant of temperature rise.

Embodiment 2. FIG.
FIG. 8 is a configuration diagram showing the configuration of the control signal wave generating means according to the second embodiment. In FIG. 8, the control signal wave generating means 182 has a PI calculator 182a as a control means and a gain adjuster 182b as a gain changing means. The control signal wave generating means 182 is provided in place of the control signal wave generating means 82 in FIG. 1, and other configurations of the output current control unit are not shown but are the same as those of the first embodiment shown in FIG. It is the same thing.

In such a control signal wave generator 182, the difference ΔJa from the subtractor 81 is input to the PI calculator 182 a, the PI calculation and the amplified signal are input to the gain adjuster 182 b, the gain is adjusted, and the signal wave Vc is output to the PWM signal output means 83 (hereinafter also see FIG. 1B). Upon receiving the signal wave Vc, the PWM signal output means 83 generates a PWM signal Sg for controlling the switching operation of a switching element (not shown) of the inverter 4 from the signal wave Vc, and outputs the output current Ja output from the inverter 4 to the system 9. The harmonic current Jah is reduced by controlling. At this time, when the harmonic current content in the output current Ja detected by the harmonic current detection means 85 exceeds the upper limit value JHL for a predetermined time, a signal is sent from the comparator 86 to the OR circuit 88. The OR circuit 88 that receives the output signal issues a signal of truth value “1” to the gain adjuster 182b, and the gain adjuster 182b changes the gain to a predetermined value.
Instead of issuing truth values “0” and “1” signals from the OR circuit 88, the analog value of the harmonic current Jah detected from the harmonic current detecting means 85 is directly output to the gain adjuster 182b. You may make it adjust a gain according to the magnitude | size of an analog value.

1 DC power supply, 4 inverter, 7 total control device, 8 output current control unit, 9 systems,
5 output filters, 22 output current sensors, 51 reactors, 53 capacitors,
81 subtractor, 82 control signal wave generating means, 821 controller switching means,
822, 823 controller, 825 integrator content equalization means, 83 PWM signal output means,
85 harmonic current detection means, 86 comparator, 87 external input means, 88 OR circuit,
182 Control signal wave generating means, 182a PI calculator, 182b Gain adjuster.

Claims (8)

A power conversion device including an inverter and an output current control device,
The inverter converts DC to AC and outputs an output current to the AC system.
The output current control device includes harmonic current detection means, control means, current control command means, and gain change means,
The harmonic current detection means detects a harmonic current included in the output current,
The control means amplifies the difference between the output current and the target current and outputs it as a current deviation,
The current control command means transmits a current control command signal for controlling the output current to the inverter based on the current deviation,
The power conversion device, wherein the gain changing means changes the gain of the control means based on the magnitude of the harmonic current. Having a filter device,
The power converter according to claim 1, wherein the filter device is interposed between the inverter and the AC system to smooth the output voltage of the inverter. The control means has first and second controllers having different gains, and a difference between the output current and the target current is amplified by the first controller or the second controller. And
The power conversion device according to claim 1 or 2, wherein the gain changing means changes the gain of the control means by switching between the first controller and the second controller. The first and second controllers each have integration means, and the integration means integrates the difference between the output current and the target current,
The gain changing means has integrating means content identifying means, and the integrating means content identifying means controls the contents of the integrating means when switching between the first controller and the second controller. The power converter according to claim 3, wherein the power converters are the same. The power conversion device according to any one of claims 1 to 4, wherein the gain changing means changes the gain of the control means when the magnitude of the harmonic current exceeds a predetermined value. 4. The harmonic current detection means includes a temperature detection device that detects a temperature of a conductive portion through which the output current flows, and detects the harmonic current via the temperature. The power converter of any one of Claims. The power conversion device according to claim 6, wherein the gain changing means changes the gain of the control means when the temperature exceeds a certain value. The power conversion device according to any one of claims 1 to 7, wherein the gain changing means is configured to change the gain of the control means by an external gain change signal.

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