JP7767908B2 - Inverter control device, program, and inverter control method - Google Patents

Description

The present invention relates to an inverter control device, a program, and an inverter control method.

In a conventional technology for converting DC power generated by solar power generation or the like into AC power and outputting it to a power grid, a technique is known in which an inverter is operated as a virtual synchronous generator to simulate the inertial force of a synchronous generator (see, for example, Patent Document 1).

JP 2014-168351 A

However, this technology had the problem that if the power grid experienced a short circuit or ground fault, an overcurrent or overvoltage would occur, damaging the power converter. Furthermore, because it had the characteristics of a synchronous generator, there were problems with the inability to use active islanding detection functions or perform constant power control.

The present invention aims to provide a system that can optimally control the current supplied to a power system even in the event of an accident such as a short circuit or ground fault in the power system, and that can use an active islanding detection function just before the system becomes isolated, enabling constant power control when necessary.

An inverter control device according to one aspect of the present invention is a voltage-type inverter control device that controls a power converter that converts DC power to AC power in accordance with a desired AC voltage signal, and includes a current reference generation unit that generates a current reference used when generating a control signal for controlling the power converter, the current reference being a value based on a current value flowing in an electric power system to which the AC power converted by the power converter is supplied; a fault detection unit that detects the occurrence of at least one of a short circuit and a ground fault in the electric power system to which the AC power converted by the power converter is supplied; and a fault detection unit that detects recovery from the system fault. The power supply device includes a recovery detection unit, a current reference switching unit that, when it is detected that the grid fault has occurred, switches the current reference to the current value supplied to the power grid a predetermined period before the grid fault occurred, and, when it is detected that the grid has recovered from the grid fault, switches the current reference to the current value flowing in the power grid , a constant power control unit that, when used for installation at a consumer facility, performs constant power control, which is control for supplying a constant amount of power to the power grid, and an APR usage permission unit that permits the constant power control unit to perform the constant power control, and the APR usage permission unit simulates the occurrence of the grid fault based on a predetermined control signal .

In addition, an inverter control device according to one aspect of the present invention further includes an islanding operation monitoring unit that monitors whether islanding is occurring, and an islanding operation determination unit that determines whether islanding is occurring. The islanding operation monitoring unit provides a second current reference having a specific frequency that is used when generating a control signal for detecting whether islanding is occurring, and the islanding operation determination unit determines whether islanding is occurring based on the magnitude of the harmonic voltage content of the specific frequency.

In addition, in an inverter control device according to one aspect of the present invention, the current reference creation unit creates the value of the current supplied to the power grid a predetermined period before the grid fault occurred by sampling and holding the current value immediately before the fault occurred.

In addition, in an inverter control device according to one aspect of the present invention, the fault detection unit compares the AC voltage waveform applied to the power grid with a predetermined reference waveform, and detects that the grid fault has occurred if the difference is equal to or greater than a predetermined value.

In an inverter control device according to one aspect of the present invention, the fault detection unit detects that a grid fault has occurred when the effective value of the AC voltage applied to the power grid is equal to or lower than a predetermined value.

In an inverter control device according to one aspect of the present invention, the fault detection unit detects that a grid fault has occurred when the amount of change in the absolute value of the AC current supplied to the power grid is equal to or greater than a predetermined value.

In addition, in an inverter control device according to one aspect of the present invention, the current reference creation unit creates the current reference at the time the grid fault occurs by adding a predetermined value to a sampled and held value of the current value immediately before the fault.

In an inverter control device according to one aspect of the present invention, the fault detection unit detects that the grid fault has occurred when zero-phase sequence voltage in the power grid is detected continuously for a predetermined period of time or longer.

In addition, in an inverter control device according to one aspect of the present invention, the recovery detection unit detects recovery from the grid fault when voltage fluctuations in the AC voltage applied to the power grid fall within a predetermined value.

In addition, in an inverter control device according to one aspect of the present invention, the recovery detection unit detects a pseudo recovery from the grid fault when the frequency of the AC voltage supplied to the power grid deviates from a predetermined range.

In addition, when the inverter control device according to one aspect of the present invention is used for installation at a consumer's facility, it further includes an active islanding detection function enablement unit that detects recovery from the grid fault when the fault detection unit detects the grid fault.

In addition, the inverter control device according to one aspect of the present invention further includes a voltage correction unit that corrects a voltage reference used when generating a control signal for controlling the power converter when recovery from the grid fault is detected, the voltage reference being a value based on the voltage value applied to the power grid to which the AC power converted by the power converter is supplied.

A program according to one aspect of the present invention provides a computer-controlled voltage-type inverter control device that controls a power converter that converts DC power to AC power in accordance with a desired AC voltage signal, the computer controlling the voltage-type inverter control device including: a current reference creation step of creating a current reference used when generating a control signal for controlling the power converter, the current reference being a value based on a current value flowing in a power grid to which the AC power converted by the power converter is supplied; a fault detection step of detecting that at least one of a short circuit and a ground fault has occurred in the power grid to which the AC power converted by the power converter is supplied; and a recovery detection step of detecting recovery from the grid fault. a current reference switching step for, when it is detected that the grid fault has occurred, switching the current reference to the current value supplied to the power grid a predetermined period before the grid fault occurred, and, when it is detected that the grid has recovered from the grid fault, switching the current reference to the current value flowing in the power grid; a constant power control step for performing constant power control, which is control for supplying constant power to the power grid, when used for installation at a consumer's facility; and an APR use permission step for permitting the constant power control to be performed by the constant power control step, wherein the APR use permission step simulates the occurrence of the grid fault based on a predetermined control signal .

An inverter control method according to one aspect of the present invention is an inverter control method for controlling a voltage-type inverter control device that controls a power converter that converts DC power to AC power in accordance with a desired AC voltage signal, the method including: a current reference creation step of creating a current reference used when generating a control signal for controlling the power converter, the current reference being a value based on a current value flowing in a power grid to which the AC power converted by the power converter is supplied; a fault detection step of detecting that at least one of a short circuit and a ground fault has occurred in the power grid to which the AC power converted by the power converter is supplied; and a fault detection step of detecting that a system fault has occurred in the power grid to which the AC power converted by the power converter is supplied. a current reference switching process for, when it is detected that the grid fault has occurred, switching the current reference to a current value supplied to the power grid a predetermined period before the grid fault occurred, and, when it is detected that the grid has recovered from the grid fault, switching the current reference to a current value flowing in the power grid ; a constant power control process for performing constant power control, which is control for supplying constant power to the power grid, when used for installation at a consumer facility; and an APR use permission process for permitting the constant power control to be performed by the constant power control process, wherein the APR use permission process simulates the occurrence of the grid fault based on a predetermined control signal .

According to the present invention, even if an accident such as a short circuit or ground fault occurs in the power system, the current supplied to the power system can be appropriately controlled, and an active islanding detection function is used to prevent islanding and enable constant power operation.

1 is a diagram for explaining an overview of a power control system according to an embodiment of the present invention; FIG. 2 is a functional configuration diagram showing an example of a functional configuration of the inverter control device according to the present embodiment. 1 is a block diagram showing an example of a functional configuration of a power control system according to an embodiment of the present invention. FIG. 4 is a diagram for explaining the function of an isolated-operation determination unit according to the present embodiment. 2 is a block diagram showing an example of a current reference creating unit, a fault detecting unit, a restoration detecting unit, and a current reference switching unit according to the present embodiment. FIG. FIG. 1 is a diagram showing an equivalent circuit of a power conversion system according to the prior art. FIG. 1 is a diagram showing an example of a virtual synchronous generator according to the prior art.

[Prior Art]
First, the prior art will be described with reference to FIGS.
Conventionally, synchronous generators using rotating machinery such as thermal power plants and hydroelectric power plants have been known. The frequency of the voltage generated by these synchronous generators is not expected to change suddenly, so even if the amount of power usage in the power grid to which the synchronous generator supplies power suddenly increases or an accident such as a ground fault or short circuit occurs, the synchronous generator can respond to such a sudden change by inertia force.

On the other hand, renewable energy power sources that convert renewable energy such as solar power into DC power have been introduced as power sources that do not use synchronous generators. In the case of renewable energy power sources, an inverter is used to convert the DC power into AC power before it is supplied to the power grid. Such renewable energy power sources have difficulty responding to sudden changes in power usage in the power grid, such as when a sudden increase in power usage occurs or when an accident such as a ground fault or short circuit occurs.

A typical power grid is supplied with a mixture of electricity generated by synchronous generators and electricity converted to AC power using renewable energy. In power grids where the proportion of electricity generated by synchronous generators is high, inertia can be used to respond to sudden changes in power usage, such as sudden increases in power consumption or accidents such as ground faults or short circuits.

However, with the increasing introduction of renewable energy in recent years, as the proportion of renewable energy connected to the power grid increases, it may become difficult to respond to sudden changes in the power grid, such as a sudden increase in usage or the occurrence of an accident such as a ground fault or short circuit.

Research and development is therefore being conducted on a virtual synchronous generator (VSG), a technology that simulates the inertial force of a synchronous generator in an inverter attached to a renewable energy power source. A virtual synchronous generator simulates a synchronous generator by controlling a power converter that converts direct current to alternating current based on the power supplied to the power grid.

6 is a diagram showing an equivalent circuit of a power conversion system according to the prior art. As a premise for explaining the virtual synchronous generator according to the prior art, the equivalent circuit of the power conversion system 9 according to the prior art will be explained with reference to the same figure.
The power conversion system 9 includes an internal induced voltage 91 , an impedance 92 , and a grid 93 .

In a typical synchronous generator, a magnetic flux is generated by passing a current through a field circuit, and a voltage is generated in the armature winding as the rotor rotates. The internal induced voltage 91 represents the voltage generated by the rotation.
Impedance 92 represents the impedance of the generator.
The grid 93 represents a power grid to which power is supplied. The grid 93 is connected to a plurality of consumers.

A voltage drop occurs in the internal induced voltage 91 according to the current Iref flowing in the grid 93 and the generator's impedance 92. In other words, the voltage obtained by subtracting the voltage drop due to the impedance 92 from the internal induced voltage 91 is supplied to the grid 93 as the terminal voltage VS.

7 is a diagram showing an example of a virtual synchronous generator according to the prior art. With reference to this figure, an example of a virtual synchronous generator according to the prior art will be described.
The power conversion system 9A includes a storage battery 94, a power converter 95, a grid 93, and a voltage-type virtual synchronous generator control device 90A. The storage battery 94 is an example of a DC voltage source. The power converter 95 is an example of a voltage-type power converter (VSC: Voltage Source Converter) that operates in accordance with an AC voltage signal that should be generated (or is desired to be generated). The power conversion system 9A simulates an energy balance disruption when the amount of power used in the grid 93 suddenly increases or when an accident such as a ground fault or short circuit occurs, i.e., when the energy balance of the grid 93 is disrupted.

The power conversion system 9A converts DC power stored in a storage battery 94 into AC power using a power converter 95 and supplies the AC power to a grid 93. The power converter 95 is controlled by a voltage-type virtual synchronous generator control device 90A.
The power converter 95 includes a semiconductor, and converts DC power into AC power by switching the semiconductor. A control signal for the semiconductor is generated by a voltage-type virtual synchronous generator control device 90A.

The voltage-type virtual synchronous generator control device 90A generates a gate pulse, which is a control signal for controlling the switching of the power converter 95, based on the system voltage, which is the terminal voltage of the system 93, and the AC current supplied by the power converter 95.
The gate pulse is generated by a gate voltage generator 911 based on a voltage equivalent to the terminal voltage generated by the voltage type virtual synchronous generator control device 90A. The voltage equivalent to the terminal voltage is generated by subtracting a voltage equivalent to the voltage drop from a voltage equivalent to the internal induced voltage, as indicated by reference numeral 912.

The voltage equivalent to the voltage drop is generated by multiplying the AC current (actual output current) by the generator-equivalent impedance.

The voltage type virtual synchronous generator control device 90A generates a voltage peak value Vm and an angular velocity ωt to generate a voltage equivalent to the internal induced voltage.
Here, a synchronous generator using a normal rotating machine also monitors the terminal voltage, controls the field current so that the terminal voltage is constant, and controls the internal induced voltage. The voltage type virtual synchronous generator control device 90A controls the deviation between the system voltage VS and the system voltage reference, thereby controlling the voltage peak value Vm.

Next, the generation of the angular velocity ωt will be described. First, the output reference is a simulation of the turbine output. Furthermore, the active power sense indicates the power supplied to the grid 93. At reference numeral 915, the active power sense is subtracted from the output reference.
At reference numeral 916, the actual angular velocity is obtained by adding the value (i.e., Δω) obtained by dividing the value generated at reference numeral 915 by the inertia constant M and integrating the result with respect to s to the reference angular velocity ω0. The voltage-type virtual synchronous generator control device 90A further integrates the obtained actual angular velocity with respect to s to generate the angular velocity ωt.
In a synchronous generator using a normal rotating machine, the difference between the energy output from the turbine and the energy going from the generator to the grid becomes the speed deviation. The generation of the angular velocity ωt simulates this operation.

Here, when considering using a virtual synchronous generator as a power source in an island area, there may be cases where the virtual synchronous generator is connected in parallel with a diesel generator or the like, or the diesel generator or the like is disconnected and only the renewable energy power source is connected to the power grid, so the voltage-type virtual synchronous generator control device 90A is easier to handle.
The embodiment described below is based on the above-described voltage type virtual synchronous generator control device 90A.

However, the voltage-type virtual synchronous generator control device 90A has the disadvantage of generating an overcurrent when power usage in the power system suddenly increases or when an accident such as a ground fault or short circuit occurs (hereinafter simply referred to as an accident). This embodiment aims to solve the problem of preventing the generation of an overcurrent when an accident occurs, enabling the activation of an islanding operation detection function when installed at a consumer's facility, and enabling constant power control.

[Embodiment]
1 is a diagram for explaining an overview of a power control system according to this embodiment. The overview of the power control system 1 will be explained with reference to the diagram.
The power control system 1 includes a storage battery 20 , a power converter 30 , a power system 40 , and an inverter control device 10 .

The storage battery 20 is an example of a DC power source. The storage battery 20 stores DC power DCP generated by a renewable energy power generation device, such as a solar power generation device (not shown). The storage battery 20 discharges the stored DC power DCP to the power grid 40.

The power converter 30 converts the direct current power DCP stored in the storage battery 20 into alternating current power ACP. The power converter 30 includes, for example, a semiconductor, and converts the direct current power DCP into alternating current power ACP by switching the semiconductor based on the control of the inverter control device 10. The power converter 30 supplies the converted alternating current power ACP to the power grid 40.

The power grid 40 is supplied with AC power ACP converted by the power converter 30. Multiple consumers are connected to the power grid 40. Furthermore, a power source other than the storage battery 20, such as a diesel generator, may also be connected to the power grid 40.

The inverter control device 10 detects system abnormalities such as overcurrents caused by a sudden increase in power usage in the power system 40, and short circuits and ground faults in the power system 40. The inverter control device 10 also detects when the power system 40 has recovered from a system abnormality after the system abnormality has occurred in the power system 40. An electrical signal containing information about a system abnormality such as an overcurrent, short circuit, or ground fault in the power system 40, and information indicating recovery from the system abnormality, is referred to as a detection signal DS. The inverter control device 10 controls the power converter 30 based on the detection signal DS. A signal used by the inverter control device 10 to control the power converter 30 is referred to as a control signal CS. The control signal CS may include a pulse signal that switches semiconductors provided in the power converter 30.

2 is a functional configuration diagram showing an example of the functional configuration of the inverter control device according to this embodiment. An example of the functional configuration of the inverter control device 10 will be described with reference to the diagram. The inverter control device 10 includes a fault detection unit 110, a recovery detection unit 140, a switching control unit 150, a current reference creation unit 120, and a current reference switching unit 130.
The inverter control device 10 is a voltage-type inverter control device that controls a power converter 30 that converts direct current power DCP into alternating current power ACP in accordance with a desired alternating current voltage signal to be applied to a power system 40 .

At least some of the functions of the inverter control device 10 may be realized by hardware executing a software program. The hardware referred to here may be, for example, a CPU (Central Processing Unit), LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), GPU (Graphics Processing Unit), etc. The above-mentioned program is stored in a storage device equipped with a storage medium. The storage medium referred to here may be, for example, an HDD (Hard Disk Drive), flash memory, ROM (Read Only Memory), DVD (Digital Versatile Disc), etc. Furthermore, the above-mentioned program may be a differential program that realizes some of the functions of the inverter control device 10.

The fault detection unit 110 detects that at least one of a short circuit and a ground fault has occurred in the power grid 40 to which the AC power ACP converted by the power converter 30 is supplied. The fault detection unit 110 may, for example, generate a reference voltage waveform and detect the occurrence of a grid fault based on the result of comparing the grid voltage waveform applied to the power grid 40 with the reference voltage waveform. The fault detection unit 110 outputs information including whether or not a grid fault has occurred to the switching control unit 150 as fault detection information ADI.

The recovery detection unit 140 detects that the power grid 40 has recovered from the grid fault. The fault detection unit 110 may detect that the power grid 40 has recovered from the grid fault, for example, based on voltage fluctuations in the grid voltage waveform applied to the power grid 40. The recovery detection unit 140 outputs information including whether or not the power grid 40 has recovered from the grid fault as recovery detection information RDI to the switching control unit 150.

The switching control unit 150 acquires accident detection information ADI from the accident detection unit 110 and acquires recovery detection information RDI from the recovery detection unit 140. The switching control unit 150 controls the current reference switching unit 130 based on at least one of the acquired accident detection information ADI or recovery detection information RDI. The control signal that controls the current reference switching unit 130 is referred to as switching information SWI. The switching control unit 150 outputs the switching information SWI to the current reference switching unit 130.

The current reference creating unit 120 creates a current reference Iref used when generating a control signal CS for controlling the power converter 30. The current reference Iref is a value based on the value of a current flowing in the power grid 40 to which the AC power ACP converted by the power converter 30 is supplied.
Specifically, the current reference creation unit 120 outputs to the current reference switching unit 130 the d-axis current Id (d-axis current reference Idref11), the q-axis current Iq (q-axis current reference Iqref11), which are information indicating the current value flowing in the power grid 40, and the d-axis current reference Idref12 and the q-axis current reference Idref12, which are information indicating the current value supplied to the power grid 40 a predetermined period before the system fault occurred in the power grid 40.

For example, the current reference creation unit 120 samples and holds the value of the current flowing through the power grid 40 immediately before the fault, thereby creating a d-axis current reference Idref12 and a q-axis current reference Iqref12, which are the current values supplied to the power grid 40 immediately before the fault. "Immediately before the fault" may be a predetermined period before the grid fault occurs.

The current reference switching unit 130 switches the d-axis current reference Idref1 to either the d-axis current reference Idref11 or the q-axis current reference Iqref12 in accordance with the switching information SWI. The current reference switching unit 130 also switches the q-axis current reference Iqref1 to either the q-axis current reference Iqref11 or the q-axis current reference Iqref12 in accordance with the switching information SWI.
Specifically, when the occurrence of a grid fault is detected, the current reference switching unit 130 switches the current reference Iref (d-axis current reference Idref1, q-axis current reference Iqref1) to the current value supplied to the power grid 40 a predetermined period before the occurrence of the grid fault. Furthermore, when the current reference switching unit 130 detects recovery from the grid fault, it switches the current reference Iref (d-axis current reference Idref1, q-axis current reference Iqref1) to the current value flowing in the power grid 40.

3 is a block diagram showing an example of the functional configuration of the power control system according to this embodiment. The details of the power control system 1 will be described with reference to the diagram. The power control system 1 includes an inverter control device 10, a DC power supply 51, a power converter 52, a current transformer 53, a transformer 54, and a system voltage acquisition unit 55.
The DC power supply 51 is an example of the storage battery 20 described with reference to Fig. 1. The power converter 52 is an example of the power converter 30 described with reference to Fig. 1. The power converter 52 supplies power to the power grid 40 via a transformer 54.

The inverter control device 10 includes a current reference creation/switching unit 62, a grid fault detection unit 64, an active islanding detection function enabling unit 68, an islanding operation monitoring unit 69, and a voltage correction unit 71.

The current reference creation/switching unit 62 creates current references Idref1 and Iqref1 based on the currents Ia, Ib, and Ic obtained from the current transformer 53. The current reference creation/switching unit 62 switches the d-axis current reference Idref1 to either current reference Idref11 or current reference Idref12, and the q-axis current Iqref1 to either current reference Iqref11 or current reference Iqref12, depending on the switching information SWI. In other words, the current reference creation/switching unit 62 has the functions of the current reference creation unit 120 and current reference switching unit 130 described with reference to FIG. 2.

The system fault detection unit 64 uses a predetermined method to detect that at least one of a short circuit and a ground fault has occurred in the power system 40. In other words, the system fault detection unit 64 is a specific example of the fault detection unit 110 described with reference to Figure 2.

When the inverter control device 10 is used at a consumer's facility and the fault detection unit 110 detects a grid fault, the active islanding detection function enable unit 68 is a function that detects recovery from the grid fault. The active islanding detection function enable unit 68 is turned on when the inverter control device 10 is used at a consumer's facility, etc. By turning on the active islanding detection function enable unit 68, the active islanding detection function becomes available when a fault is detected.

The islanding operation monitoring unit 69 monitors whether or not islanding operation is occurring. The islanding operation monitoring unit 69 is a function that constantly monitors when islanding operation detection is required at the customer's installation. Both the islanding operation detection function and the constant monitoring function may be used, or only one may be used. The islanding operation monitoring unit 69 provides a current reference value for a specific frequency and controls the current. By providing a current reference value for a specific frequency and controlling the current, a voltage of a specific frequency is superimposed on the commercial frequency. Here, the voltage that appears when the system is connected to the grid is different from that when the system is operating in islanding mode. The islanding operation monitoring unit 69 detects islanding operation by utilizing the characteristic that the voltage that appears when the system is connected to the grid is different from that when the system is operating in islanding mode.

The islanding operation monitoring unit 69 is supplied with, for example, frequencies f1, f2, ..., fn (n is a natural number equal to or greater than 1). More specifically, 0.01 × sin(2πf1·t) is supplied as a current reference signal having frequency f1, 0.01 × sin(2πf2·t) is supplied as a current reference signal having frequency f2, ..., 0.01 × sin(2πfn·t) is supplied as a current reference signal having frequency fn. These signals supply currents of frequencies (f1±f0), (f2±f0), and (fn±f0) to the power grid 40, and voltages i(f1±f0)Z, i(f2±f0)Z, and i(fn±f0)Z appear due to the grid impedance Z (f0 is a commercial frequency, e.g., 50 Hz or 60 Hz). Since the system impedance Z when the system is interconnected and the system impedance Z when the system is an isolated system are different from each other, the inverter control device 10 can detect the isolated operation from a change in iZ.
The current reference signal having the frequency fn is also referred to as a second current reference. The second current reference is used when generating a control signal for detecting whether or not an islanding operation is occurring.

In addition, when the inverter control device 10 is used by a consumer or the like, the active islanding detection function enable unit 68 may be turned on and a current reference signal having frequencies f1, f2, ..., fn may be input at all times.
The number of input current reference signals may be one or more.
Furthermore, the coefficient 0.01 shown in FIG. 3 is just an example, and a different value may be used.
The frequencies f1, f2, ..., fn may be, for example, 80 [Hz], 130 [Hz], 180 [Hz], etc.

Here, the inverter control device 10 further includes an isolated operation determination unit 691. The isolated operation determination unit 691 determines whether or not an isolated operation is occurring. The isolated operation determination unit 691 will be described with reference to the drawings.
FIG. 4 is a diagram for explaining the function of the isolated-operation determination unit according to this embodiment.
The islanding operation determination unit 691 detects the content rate (ratio of specific harmonic components to commercial frequency components) of harmonic voltages of frequencies (f1±f0), (f2±f0), and (fn±f0) contained in the AC voltage using FFT (Fast Fourier Transform) or a band-pass filter. The islanding operation determination unit 691 has a function of determining that islanding is occurring if the detected value is equal to or greater than a predetermined value. The predetermined value or greater may preferably be equal to or greater than 0.05.
If the detected value continues for a certain period of time or more, the isolated-operation determination unit 691 determines that the power converter 52 is in isolated operation and stops the power converter 52 .
4 shows an example of detecting the frequencies (f1-f0), (f2-f0), and (fn-f0), but a method of detecting the frequencies (f1+f0), (f2+f0), and (fn+f0) may also be used. Alternatively, a method of detecting both frequencies may also be used. (f1-f0), (f2-f0), (fn-f0), (f1+f0), (f2+f0), and (fn+f0) are also referred to as specific frequencies.

The voltage correction unit 71 corrects the voltage reference Vref when the recovery detection unit 140 detects that the grid has recovered from the fault. The voltage reference Vref is a reference value used when generating a control signal CS for controlling the power converter 30, and is a value based on the voltages Va, Vb, and Vc applied to the power grid 40 to which the AC power ACP converted by the power converter 30 is supplied.

Figure 5 is a block diagram showing an example of the current reference creation unit, fault detection unit, recovery detection unit, and current reference switching unit according to this embodiment. Specific examples of the current reference creation/switching unit 62 (current reference creation unit 120 and current reference switching unit 130), the grid fault detection unit 64 (fault detection unit 110), and the voltage correction unit 71 are described below.

First, a specific example of the accident detection unit 110 will be described. The accident detection unit 110 includes at least one of the first accident detection unit 111, the second accident detection unit 112, the third accident detection unit 113, the fourth accident detection unit 114, and the fifth accident detection unit 115. If the accident detection unit 110 includes multiple of the first accident detection unit 111 to the fifth accident detection unit 115, the outputs of the respective accident detection units may be connected by an OR circuit.

The first fault detection unit 111 compares voltages Va, Vb, and Vc, which are AC voltages applied to the power grid 40, with a reference waveform. Voltages Va, Vb, and Vc are acquired by the grid voltage acquisition unit 55. The reference waveform may be, for example, the waveform shown in equation (1) below.

The first fault detection unit 111 detects that a grid fault has occurred when the result of comparing the grid voltage with a reference waveform is equal to or greater than a predetermined value. That is, the first fault detection unit 111 compares the AC voltage waveform applied to the power grid 40 with a predetermined reference waveform, and detects that a grid fault has occurred when the difference is equal to or greater than a predetermined value. The predetermined value or greater may be, for example, 0.5 PU or greater.

The second fault detection unit 112 detects the zero-phase-sequence voltage of the power grid 40. The second fault detection unit 112 detects that a grid fault has occurred based on the detected zero-phase-sequence voltage of the power grid 40. The second fault detection unit 112 detects that a grid fault has occurred, for example, when it detects the zero-phase-sequence voltage of the power grid 40 continuously for a predetermined period of time or more. The predetermined period of time or more may be, for example, 100 ms (milliseconds) or more.

The third fault detection unit 113 detects the occurrence of a grid fault based on the amount of change in the absolute values of current Ia, current Ib, and current Ic, which are currents supplied to the power grid 40. The third fault detection unit 113 detects the occurrence of a grid fault, for example, when any of the amounts of change in the absolute values of current Ia, current Ib, and current Ic is equal to or greater than a predetermined value. "Above the predetermined value" may be, for example, equal to or greater than 1 [A/μs (ampere/microsecond)].

The fourth fault detection unit 114 detects the occurrence of a grid fault based on the effective values Vrms of voltages Va, Vb, and Vc, which are AC voltages applied to the power grid 40. The fourth fault detection unit 114 detects the occurrence of a grid fault, for example, when the effective values Vrms of voltages Va, Vb, and Vc are equal to or less than a predetermined value. Specifically, the fourth fault detection unit 114 performs three-phase to two-phase conversion based on voltages Va, Vb, and Vc, and detects the occurrence of a grid fault when the effective values Vrms of voltages Vd and Vq are equal to or less than a predetermined value. The predetermined value or less may be, for example, 0.5 PU or less.

The fifth fault detection unit 115 simulates a grid fault based on a predetermined control signal. In this case, the fifth fault detection unit 115 simulates a grid fault based on a signal from a control device (not shown) or a setting signal. When operating at a constant power level, such as when installed at a consumer's facility, constant power control is possible by simulating a grid fault.
The fifth fault detection unit 115 is also referred to as an APR use permission unit. The APR use permission unit permits a constant power control unit (or an APR control unit) (not shown) to perform constant power control. The constant power control is a control for supplying a constant amount of power to the power grid 40 when the inverter control device 10 is used for a consumer installation.

Next, a specific example of the recovery detection unit 140 will be described. The recovery detection unit 140 includes at least one of a first recovery detection unit 141 and a second recovery detection unit 142. If the recovery detection unit 140 includes both the first recovery detection unit 141 and the second recovery detection unit 142, the outputs of the respective recovery detection units may be connected by an OR circuit.

The first recovery detection unit 141 detects recovery from a grid fault based on the effective values Vrms of voltages Va, Vb, and Vc, which are AC voltages applied to the power grid 40. The first recovery detection unit 141 detects recovery from a grid fault, for example, when the voltage fluctuations of the effective values Vrms of voltages Va, Vb, and Vc fall within a predetermined value. "Within the predetermined value" may be within 2% or within 1.15 PU.

The second recovery detection unit 142 detects an abnormality in the system state during current control based on the frequency f of the AC voltage supplied to the power system 40. Specifically, if the result of time-differentiating the frequency f of the AC voltage falls outside a predetermined range, it detects a pseudo-recovery from a system fault. The predetermined range may be +10 or greater or -10 or less.

Next, we will explain a specific example of the current reference creation/switching unit 62. The current reference creation/switching unit 62 includes a current reference creation unit 120 and a current reference switching unit 130.

The current reference creating unit 120 samples and holds the current value from a predetermined period of time before the present. The predetermined period of time may be, for example, 5 ms before the present. The current reference creating unit 120 samples and holds the current value from 5 ms before the present, for example, to set the current value immediately before the accident as the current reference Iref.
The current reference generator 120 may generate the current reference Iref at the time when the grid fault occurs by multiplying the sampled and held current value immediately before the fault by Nx or by adding a predetermined value to it. The predetermined value may be 0.5 PU.

The current reference switching unit 130 switches the current reference Iref to either the current current value or the current value immediately before the accident based on the switching information SWI.

In addition, three-phase to two-phase conversion may be performed based on the currents Ia, Ib, and Ic flowing through the power grid 40, and a current reference creation unit 120 and a current reference switching unit 130 may be provided for each of the currents Id and Iq.

[Summary of the embodiment]
As described above, the inverter control device 10 according to this embodiment includes the current reference creating unit 120 to create the current reference Iref, the fault detecting unit 110 to detect the occurrence of at least one of a short circuit and a ground fault in the power grid 40, the recovery detecting unit 140 to detect recovery from the grid fault, and the current reference switching unit 130 to switch the current reference Iref depending on whether or not there is a grid fault. Specifically, the inverter control device 10 includes the current reference switching unit 130, so that when it detects that a grid fault has occurred, it switches the current reference Iref to a current value that existed a predetermined period before the grid fault occurred, and when it detects that the grid has recovered from the grid fault, it returns the current reference Iref to the original reference.
Therefore, according to this embodiment, even if a system fault occurs in the power system 40, it is possible to suppress overcurrent and stably operate the power control system 1. Furthermore, according to this embodiment, when a system fault occurs in the power system 40, in addition to suppressing overcurrent, it is also possible to control the current supplied to the power system 40 until the system is restored from the system fault.

Furthermore, according to this embodiment, the current reference creation unit 120 creates the current value for a predetermined period before the grid fault occurs by sampling and holding the current value immediately before the fault. Therefore, according to this embodiment, even if a grid fault occurs in the power grid 40, it is possible to easily control the current supplied to the power grid 40 until the grid is restored from the fault.

Here, when the power control system 1 is applied to a consumer or the like connected to a distribution line, etc., if the distribution line is disconnected due to an accident or the like and becomes an isolated system, it is preferable that the inverter control device 10 of the power control system 1 has a function to detect isolated operation and quickly stop it.
According to this embodiment, the fault detection unit 110 compares the AC voltage waveform applied to the power grid 40 with a predetermined reference waveform, and detects the occurrence of a grid fault when the difference is equal to or greater than a predetermined value. That is, the fault detection unit 110 detects the occurrence of a grid fault based on a slight disturbance that would result in an isolated grid. Therefore, according to this embodiment, the active islanding detection function can be used before a fault is detected on a distribution line and the system transitions to islanding operation. Therefore, according to this embodiment, the active islanding detection function can be used before the system enters an islanding state while taking advantage of the characteristics of the virtual synchronous generator. Furthermore, if an islanding state occurs, the islanding state can be detected by detecting an abnormal voltage or an abnormal frequency, and rapid parallel-off can be achieved.
According to this embodiment, the current reference Iref after the detection of a grid fault is the value immediately before switching. Therefore, even if a false detection occurs when the grid is not an isolated grid, the grid voltage value does not decrease. Therefore, according to this embodiment, the grid can be restored to the state before the detection of the grid fault in a short time, and substantial influence can be suppressed.

Furthermore, according to this embodiment, the fault detection unit 110 detects that a grid fault has occurred when the effective value of the AC voltage applied to the power grid 40 is equal to or lower than a predetermined value. In other words, the fault detection unit 110 detects that a grid fault has occurred based on a slight disturbance that results in an isolated grid.

Here, if a load with a large inrush current, such as a transformer, is connected in parallel to an isolated system, there is a risk of an overcurrent occurring. In the case of an overcurrent caused by an inrush current, the drop in AC voltage may be small, unlike in the case of a short-circuit fault.

According to this embodiment, the fault detection unit 110 detects that a grid fault has occurred when the amount of change in the absolute value of the AC current supplied to the power grid 40 is equal to or greater than a predetermined value. In other words, the fault detection unit 110 detects that a grid fault has occurred based on a slight disturbance that results in an isolated grid.

Here, the active power output of the power control system 1 changes in response to frequency fluctuations in the power grid 40. Because the voltage phase generated by the power converter 30 is determined by the equation of motion, a synchronizing force acts in response to changes in the grid voltage phase, and an increase in the inertial force of the power grid is expected. Therefore, in island areas and the like, there are cases where the introduction of renewable energy is increased and the operation of diesel generators is suppressed. In such cases, the frequency fluctuation suppression function of the storage battery 20 is expected to be effective.
It is best to charge a storage battery at a constant power level near the end of its charge. If the charging power fluctuates, it is possible that the end-of-charge voltage will be detected and charging will be stopped before the ideal end of charge is reached. If this situation occurs repeatedly, the storage battery capacity will not be fully utilized and will also decrease.
Therefore, when multiple inverter control devices 10 are operating in parallel, it is desirable to enable constant power operation near the end of charging and discharging for the number of inverter control devices 10 that does not affect the expected frequency control.

According to this embodiment, the occurrence of a pseudo-system fault is assumed by providing islanding operation information (APR use permission signal) in parallel with the detection of a system fault.
According to this embodiment, since the power reference value changes in a stepwise manner, the change may be made gentler through a power change rate limiter in order to minimize the influence on the power grid 40 .

Furthermore, according to this embodiment, the current reference creation unit 120 creates the current reference Iref at the time when the grid fault occurs by multiplying the sampled and held current value immediately before the grid fault by Nx or adding a predetermined value to it. Therefore, according to this embodiment, when switching the current reference Iref, the current value can be switched gradually, thereby preventing sudden current changes.

Furthermore, according to this embodiment, the fault detection unit 110 detects that a grid fault has occurred when it detects zero-phase voltage in the power grid 40 continuously for a predetermined period of time or more. Therefore, according to this embodiment, it is possible to easily detect that a grid fault has occurred.

Furthermore, according to this embodiment, the recovery detection unit 140 detects that recovery from the grid fault has occurred when the voltage fluctuation of the AC voltage applied to the power grid 40 falls within a predetermined value. In other words, according to this embodiment, when recovery from the grid fault has occurred, the current value currently flowing through the power grid 40 can be set as the reference Iref, and the power grid 40 can be operated as a virtual synchronous generator.

Furthermore, according to this embodiment, the recovery detection unit 140 detects that a pseudo recovery from a grid fault has occurred if the frequency of the AC voltage supplied to the power grid 40 deviates from a predetermined range. Therefore, according to this embodiment, recovery from a grid fault can be easily detected.

If a diesel generator is generating electricity and a virtual synchronous generator connected to the same bus is operating in parallel, and a short circuit occurs in the power grid, the diesel generator that is generating electricity will accelerate (in other words, its rotor angular speed will increase), and the virtual synchronous generator that is charging will decelerate. In other words, after the fault is cleared, the phases of the two voltage sources will be separated, causing a large cross current to flow and potentially impairing stable operation.

According to this embodiment, the voltage correction unit 71 is provided, which corrects the voltage reference Vref when recovery from a grid fault is detected. Therefore, this embodiment allows for a smooth transition of the voltage reference value.

In addition, all or part of the functions of each unit provided in the inverter control device 10 in the above-described embodiment may be realized by recording a program for realizing these functions on a computer-readable recording medium, and then loading and executing the program recorded on this recording medium into a computer system. Note that the term "computer system" here includes hardware such as the OS and peripheral devices.

In addition, "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage units such as hard disks built into computer systems. Furthermore, "computer-readable recording medium" may also include devices that dynamically store programs for a short period of time, such as communication lines when transmitting programs over networks like the Internet or communication lines like telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within computer systems that serve as servers or clients in such cases. Furthermore, the above-mentioned programs may be those that implement some of the functions described above, or may be those that can implement the functions described above in combination with programs already stored in the computer system.

The above describes an embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

1...power control system, 10...inverter control device, 20...storage battery, 30...power converter, 40...power system, 110...fault detection unit, 111...first fault detection unit, 112...second fault detection unit, 113...third fault detection unit, 114...fourth fault detection unit, 115...fifth fault detection unit, 120...current reference creation unit, 130...current reference switching unit, 140...recovery detection unit, 141...first recovery detection unit, 142...second recovery detection unit, 15 0...Switching control unit, 51...DC power supply, 52...Power converter, 53...Current transformer, 54...Transformer, 55...Grid voltage acquisition unit, 62...Current reference creation and switching unit, 64...Grid fault detection unit, 68...Active islanding detection function enable unit, 69...Islanding monitoring unit, 71...Voltage correction unit, DCP...DC power, ACP...AC power, CS...Control signal, DS...Detection signal, ADI...Fault detection information, RDI...Recovery detection information, SWI...Switching information

Claims (14)

A voltage-type inverter control device that controls a power converter that converts DC power to AC power in accordance with a desired AC voltage signal,
a current reference generation unit that generates a current reference used when generating a control signal for controlling the power converter, the current reference being a value based on a current value flowing in an electric power grid to which AC power converted by the power converter is supplied; and
a fault detection unit that detects the occurrence of at least one of a short circuit and a ground fault in an electric power system to which the AC power converted by the power converter is supplied;
a recovery detection unit that detects recovery from the grid fault;
a current reference switching unit that switches the current reference to a current value supplied to the power grid a predetermined period before the occurrence of the power grid fault when it is detected that the power grid fault has occurred, and that switches the current reference to a current value flowing in the power grid when it is detected that the power grid has recovered from the power grid fault ;
When used for installation at a consumer, a constant power control unit performs constant power control, which is control for supplying constant power to the power grid;
an APR use permission unit that permits the constant power control unit to perform the constant power control;
Equipped with
The APR use permission unit simulates the occurrence of the system fault based on a predetermined control signal.
Inverter control device. an islanding operation monitoring unit that monitors whether or not the system is in islanding operation;
an isolated operation determination unit that determines whether or not the power plant is in isolated operation,
the islanding operation monitoring unit provides a second current reference used when generating a control signal for detecting whether or not an islanding operation is occurring, the second current reference having a specific frequency;
The inverter control device according to claim 1 , wherein the islanding operation determination unit determines whether or not the inverter is in islanding operation based on the magnitude of a content rate of harmonic voltage at a specific frequency. 3. The inverter control device according to claim 1, wherein the current reference creation unit creates a value of a current supplied to the power grid a predetermined period before the occurrence of the grid fault by sampling and holding a current value immediately before the fault. 4. The inverter control device according to claim 1, wherein the fault detection unit compares an AC voltage waveform applied to the power grid with a predetermined reference waveform, and detects that the grid fault has occurred when a difference between the AC voltage waveform and a predetermined value is equal to or greater than a predetermined value. The inverter control device according to claim 1 , wherein the fault detection unit detects that the grid fault has occurred when an effective value of the AC voltage applied to the power grid is equal to or lower than a predetermined value. The inverter control device according to claim 1 , wherein the fault detection unit detects that the grid fault has occurred when a change in an absolute value of the AC current supplied to the power grid is equal to or greater than a predetermined value. 4. The inverter control device according to claim 1, wherein the current reference creation unit creates the current reference at the time when the grid fault occurs by adding a predetermined value to a sampled and held value of a current value immediately before the fault. The inverter control device according to claim 1 , wherein the fault detection unit detects that the grid fault has occurred when a zero-phase sequence voltage of the power grid is detected continuously for a predetermined period of time or more. The inverter control device according to claim 1 , wherein the recovery detection unit detects recovery from the grid fault when voltage fluctuation of the AC voltage applied to the power grid falls within a predetermined value. The inverter control device according to claim 1 , wherein the recovery detection unit detects a pseudo recovery from the grid fault when a frequency of the AC voltage supplied to the power grid deviates from a predetermined range. The inverter control device according to claim 10, further comprising an active islanding operation detection function enabling unit that detects recovery from the grid fault when the fault detection unit detects the grid fault , when the inverter control device is used for installation at a consumer facility. 12. The inverter control device according to claim 1, further comprising: a voltage correction unit that corrects a voltage reference used in generating a control signal for controlling the power converter when recovery from the grid fault is detected, the voltage reference being a value based on a voltage value applied to the power grid to which AC power converted by the power converter is supplied. A computer controls a voltage-type inverter control device that controls a power converter that converts DC power into AC power in accordance with a desired AC voltage signal.
a current reference creation step of creating a current reference used when generating a control signal for controlling the power converter, the current reference being a value based on a current value flowing in an electric power grid to which AC power converted by the power converter is supplied;
a fault detection step of detecting that at least one of a short circuit and a ground fault has occurred in an electric power system to which the AC power converted by the power converter is supplied;
a recovery detection step of detecting recovery from the grid fault;
a current reference switching step of switching the current reference to a current value supplied to the power grid a predetermined period before the occurrence of the power grid fault when it is detected that the power grid fault has occurred, and switching the current reference to a current value flowing in the power grid when it is detected that the power grid has recovered from the power grid fault ;
When used for installation at a consumer, a constant power control step of performing constant power control, which is control for supplying constant power to the power grid;
an APR use permission step of permitting the constant power control to be performed by the constant power control step;
Execute
The APR use permission step includes: simulating the occurrence of the system fault based on a predetermined control signal;
program. An inverter control method for controlling a voltage-type inverter control device that controls a power converter that converts DC power to AC power in accordance with a desired AC voltage signal, comprising:
a current reference creation step of creating a current reference used when generating a control signal for controlling the power converter, the current reference being a value based on a current value flowing in an electric power grid to which AC power converted by the power converter is supplied;
a fault detection step of detecting that at least one of a short circuit and a ground fault has occurred in an electric power system to which the AC power converted by the power converter is supplied;
a recovery detection step of detecting recovery from the grid fault;
a current reference switching step of switching the current reference to a current value supplied to the power grid a predetermined period before the occurrence of the power grid fault when it is detected that the power grid fault has occurred, and switching the current reference to a current value flowing in the power grid when it is detected that the power grid has recovered from the power grid fault ;
When used for installation at a consumer, a constant power control step of performing constant power control, which is control for supplying constant power to the power grid;
an APR use permission step of permitting the constant power control to be performed by the constant power control step;
and
The APR use permission step includes: simulating the occurrence of the system fault based on a predetermined control signal;
Inverter control method.