Power converter control device, power converter control method, and power converter control program

Abstract

This power converter control device for controlling a voltage output by a power converter connected to a power line for supplying power from a power system to a load includes: an opposing voltage calculation unit for calculating an opposing voltage that is a voltage having the same phase and the same amplitude as the voltage of the power system; a voltage change amount calculation unit for acquiring an output current command value that is a current output to the power converter, and calculating a voltage change amount when the power converter outputs the output current command value by open control from the output current command value; and a voltage command value output unit for outputting a voltage command value, which is a voltage obtained by combining the opposing voltage and the voltage change amount, to the power converter.

Description

Power converter control device, power converter control method, and power converter control program

[0001] The present invention relates to a power converter control device, a control method for a power converter, and a control program for a power converter.

[0002] The voltage and frequency of a power system fluctuate due to power fluctuations of loads connected to the power lines of the power system, distributed power sources, etc. A power converter that converts DC power from a DC power source such as a solar cell or a storage battery into AC power is connected to the power lines of the power system, and a power converter control device is used that controls the output voltage to suppress the voltage and frequency fluctuations of the power system.

[0003] As shown in Non-Patent Document 1, for example, this type of power converter control device includes a phase control unit that calculates the phase of the voltage output by the power converter from the deviation between an active power command value and an active power output value, and an amplitude control unit that calculates the amplitude of the voltage output by the power converter from the deviation between a reactive power command value and a reactive power output value. The above power converter control device determines the control amount of the voltage output by the power converter based on the output values ​​of the phase control unit and the amplitude control unit.

[0004] "Efforts to commercialize measures to reduce inertia in response to the shift to renewable energy as the main power source," Journal of the Institute of Electrical Engineers of Japan, Vol. 143, No. 4, April 1, 2023

[0005] However, if the voltage of a power line drops due to a power line short circuit or other accident in a power system, the active power output value and reactive power output value of a conventional power converter control device will decrease, which will increase the control amount of the voltage output by the power converter, and there is a risk that a current greater than the command value will flow.

[0006] Furthermore, with the recent trend toward renewable energy as the primary power source, it is expected that multiple distributed power sources will be connected to the same bus via power converters. In this case, when feedback control of the voltage output from one power converter is performed as in the above-mentioned power converter control device, the feedback control amount may fluctuate depending on the control amount of the other power converter, which may result in unstable phenomena such as flicker.

[0007] The present invention has been made in view of the above problems, and has as its main object to make a power converter output a current according to a command value regardless of fluctuations in the voltage of the power system.

[0008] That is, the power converter control device according to the present invention is a power converter control device that controls a voltage output by a power converter connected to a power line, and is characterized by comprising: a counter voltage calculation unit that calculates a counter voltage which is a voltage of the same phase and amplitude as the voltage of the power system; a voltage change amount calculation unit that acquires an output current command value and calculates, by open control from the output current command value, an amount of voltage change when the power converter outputs the output current command value; and a voltage command value output unit that outputs a voltage command value that is a combination of the counter voltage and the amount of voltage change to the power converter.

[0009] With this configuration, the counter voltage is a voltage of the same phase and amplitude as the voltage of the power grid, and the voltage command value output unit outputs a voltage command value that combines the counter voltage and the voltage change amount to the power converter. Therefore, the voltage of the power grid is canceled by the counter voltage, and only the voltage change amount is applied to the interconnection transformer and interconnection reactor of the power converter. Therefore, regardless of fluctuations in the voltage of the power grid, the power converter can output a current according to the output current command value. Furthermore, because the voltage change amount calculation unit calculates the voltage change amount using open control, even if multiple distributed power sources are connected to the same bus, the voltage change amount does not fluctuate depending on the control amount of the other distributed power sources. Therefore, even if multiple distributed power sources are connected to the same bus, instability phenomena such as flicker can be prevented.

[0010] The output current command value is preferably at least one of a fundamental wave positive-sequence active current, a fundamental wave positive-sequence reactive current, a fundamental wave negative-sequence current, and a non-fundamental frequency current.

[0011] With this configuration, when the voltage change amount calculation unit acquires the fundamental wave positive-sequence active current and the fundamental wave positive-sequence reactive current, it is possible to suppress voltage fluctuations or frequency fluctuations in the power system. Also, when the voltage change amount calculation unit acquires the fundamental wave negative-sequence current, it is possible to suppress imbalance of the fundamental wave voltage or fundamental wave current. Furthermore, when the voltage change amount calculation unit acquires the non-fundamental frequency current, it is possible to suppress harmonic voltage distortion.

[0012] A voltage-controlled inverter (hereinafter also referred to as a GFM inverter) that supplies inertial force to a power line is particularly susceptible to overcurrent caused by fluctuations in the voltage of the power grid compared to other power converters. Therefore, it is preferable that the power converter controlled by the power converter control device is a voltage-controlled inverter that supplies inertial force to the power line.

[0013] With this configuration, regardless of fluctuations in the voltage of the power grid, the current output from the power converter is the output current command value, so that overcurrent in the GFM inverter can be suppressed.

[0014] The voltage change amount calculation unit further includes a positive-sequence voltage calculation unit that calculates a positive-sequence voltage as the voltage change amount, and the positive-sequence voltage calculation unit acquires the output current command value and the phase of the power grid, and calculates the positive-sequence voltage from the output current command value by open control so as to be synchronized with the phase of the power grid.

[0015] With this configuration, the power converter outputs a voltage that is a combination of the counter voltage and the positive-phase voltage, so that the voltage of the power grid is canceled out by the counter voltage, and the power converter can output only the positive-phase voltage that corresponds to the output current command value.

[0016] It is preferable that the positive-sequence voltage calculation unit calculates an instantaneous voltage value of active power and an instantaneous voltage value of reactive power from the active current command value and the reactive current command value by open control, respectively, and calculates the positive-sequence voltage by combining the instantaneous voltage value of active power and the instantaneous voltage value of reactive power.

[0017] With this configuration, the positive-sequence voltage calculation unit calculates the instantaneous voltage value of active power and the instantaneous voltage value of reactive power, thereby enabling both frequency fluctuation and voltage fluctuation to be suppressed. Specifically, since the positive-sequence voltage calculation unit calculates the instantaneous voltage value of active power, active power is supplied to the power grid when the frequency of the power grid drops, and active power is supplied to the power converter when the frequency of the power grid rises. This allows frequency fluctuation to be suppressed. Furthermore, since the positive-sequence voltage calculation unit calculates the instantaneous voltage value of reactive power, reactive power is supplied to the power grid when the node voltage, which is the voltage at the point where the power grid and the power converter voltage are connected, drops, and reactive power is supplied to the power converter when the node voltage rises. This allows voltage fluctuation to be suppressed.

[0018] For example, when a large number of non-rotating generators without inertia, such as current-controlled solar generators, are connected to a power grid to serve as the main power source, the inertia of the rotating generators may become insufficient to adjust supply and demand, potentially causing the power system to become unstable. Therefore, the output current command value acquired by the positive-sequence voltage calculation unit is preferably an active current command value including inertia and a reactive current command value including inertia.

[0019] With this configuration, when the power converter converts DC power from a non-rotating generator into AC power, it can supply sufficient inertia to the load, thereby stabilizing the power system. Note that "including inertial force" means that the generator supplying power to the load has the ability to autonomously reduce frequency changes in the power system.

[0020] The voltage change amount calculation unit further includes a negative-phase-sequence voltage calculation unit that calculates a negative-phase-sequence voltage as the voltage change amount, and the negative-phase-sequence voltage calculation unit acquires a phase command value of the negative-phase-sequence voltage and the output current command value, and calculates the negative-phase-sequence voltage from the phase command value of the negative-phase-sequence voltage and the output current command value by open control.

[0021] In addition, the voltage change amount calculation unit may further include a non-fundamental wave component calculation unit that calculates a non-fundamental wave component, which is a frequency different from the fundamental frequency of the power system, as the voltage change amount, and the non-fundamental wave component calculation unit may acquire a phase command value of the non-fundamental wave component and the output current command value, and calculate the non-fundamental wave component from the phase command value of the non-fundamental wave component and the output current command value by open control.

[0022] With this configuration, the power converter can output a current to compensate for voltage imbalance or non-fundamental component, thereby suppressing the equivalent negative-phase current of the generator, preventing winding overheating and burnout, and improving the utilization rate of the generator. In addition, since the negative-phase voltage or non-fundamental component can be output as desired, harmonic voltage distortion or voltage imbalance due to a single-phase load or a rectifier load can be suppressed, thereby improving power quality. Furthermore, since the power converter outputs a voltage that combines the negative-phase voltage or non-fundamental component with a counter voltage, the voltage of the power grid is canceled by the counter voltage, and only the negative-phase voltage or non-fundamental component is output to the power grid. Therefore, the power converter can reliably output only the negative-phase voltage or non-fundamental component, regardless of fluctuations in the power grid voltage.

[0023] A control method for a power converter, which controls a voltage output by a power converter connected to a power line for supplying power from a power grid to a load, includes: calculating a counter voltage, which is a voltage having the same phase and amplitude as a voltage of the power grid; obtaining an output current command value, which is a current to be output by the power converter; calculating a voltage change amount, which is a voltage when the power converter outputs the output current command value, by open control from the output current command value; and causing the power converter to output a voltage obtained by combining the counter voltage and the voltage change amount. Also, a control program for a power converter, which controls a voltage output by a power converter connected to a power line for supplying power from a power grid to a load, includes causing a computer to function as a counter voltage calculation unit that calculates a counter voltage, which is a voltage having the same phase and amplitude as a voltage of the power grid;

[0024] With this configuration, it is possible to obtain the same effects as those of the above-described power converter control device.

[0025] According to the present invention configured as described above, it is possible to cause the power converter to output a current according to a command value, regardless of fluctuations in the voltage of the power grid.

[0026] Fig. 1 is a schematic diagram showing the configuration of a power system in the present embodiment; Fig. 2 is a diagram showing functional blocks of a power converter control device in the same embodiment; Fig. 3 is a simulation result showing the output waveform of a power converter in the same embodiment; Fig. 4 is a simulation result showing the output waveform of a power converter in the same embodiment when a short circuit occurs; Fig. 5 is a simulation result showing the voltage waveform output by a power converter and the voltage waveform of a power system in the same embodiment when a short circuit occurs; Fig. 6 is a diagram showing functional blocks of a power converter control device in another embodiment;

[0027] An embodiment of a power system according to the present invention will be described below with reference to the drawings. Note that, for ease of understanding, some parts may be omitted or exaggerated in schematic form in all of the drawings shown below. Identical components will be assigned the same reference numerals and descriptions thereof will be omitted.

[0028] <System Configuration> The power system 100 in this embodiment is connected to a power line B for supplying power from the power grid 10 to a load 20, and supplies AC power to the load 20. Specifically, the power system 100 includes a DC power supply 30 that supplies DC power, a power converter 40 that converts the DC power to AC power and supplies the AC power to the power line B, a measurement unit 50 that measures the current flowing through the power line B or the voltage of the power line B, and a power converter control device 60 that controls the voltage output by the power converter 40. In this embodiment, a distributed power source 70 is connected to the power line B in parallel with the power system 100. Each unit will be described.

[0029] The DC power supply 30 is, for example, a non-rotating power generator such as a solar power generator or a wind power generator, or a power storage device such as a storage battery or a secondary battery.

[0030] Power converter 40 converts DC power supplied from DC power supply 30 into AC power and supplies it to power line B. Specifically, power converter 40 is a GFM inverter (Grid Forming Inverter), which is a voltage-controlled inverter, and is capable of supplying inertial force to power line B. As shown in FIG. 1 , power converter 40 is connected to power line B from the high-voltage side as viewed from the power line B via a circuit breaker S, an interconnection transformer T, and an interconnection reactor L.

[0031] The measurement unit 50 has a function as a voltage measurement unit that measures the voltage of the power line B using, for example, a known voltage transformer, and a function as a current measurement unit that measures the current flowing through the power line B using, for example, a known current transformer. Specifically, as shown in Fig. 1 , the measurement unit 50 measures the current and voltage between the circuit breaker S and the interconnection transformer T. Here, the voltage measured by the measurement unit 50 corresponds to the voltage of the power system 10.

[0032] The power converter control device 60 is a dedicated or general-purpose computer equipped with a CPU, internal memory, an input / output interface, an A / D converter, etc., and controls the voltage output by the power converter 40 based on a predetermined command value. Specifically, the power converter control device 60 includes a counter voltage calculation unit 61 that calculates a counter voltage Vabc, which is a voltage having the same phase and amplitude as the voltage of the power grid 10, a voltage change amount calculation unit 62 that calculates a voltage change amount when the power converter 40 outputs an output current command value, which is a current to be output by the power converter 40, and a voltage command value output unit 63 that outputs a voltage command value Vref, which is a command value for the voltage to be output by the power converter 40. The power converter control device 60 may be integrated with the power converter 40, or may be a separate device separate from the power converter 40.

[0033] The counter voltage calculation unit 61 acquires the voltage measured by the measurement unit 50, calculates a voltage having the same phase and amplitude as the voltage measured by the measurement unit 50, and sets the calculated voltage as the counter voltage Vabc. The phase used by the counter voltage calculation unit 61 to calculate the counter voltage Vabc may be acquired from the voltage measured by the measurement unit 50, or may be acquired from phase information input via external input means (not shown).

[0034] The voltage change amount calculation unit 62 acquires an output current command value, which is a current to be output by the power converter 40, and calculates the voltage change amount when the power converter 40 outputs the output current command value by open control from the output current command value. The open control here refers to calculating the voltage change amount from the output current command value by a known calculation method without feeding back the voltage output by the power converter 40.

[0035] In this embodiment, the output current command value is an active current command value i ｐ ref and reactive current command value i ｑ ref, a negative-phase current command value I, which is a current command value for suppressing the imbalance between the fundamental wave voltage and the fundamental wave current; ２ ref, and a non-fundamental current command value I, which is a current command value for suppressing harmonic voltage distortion. ｎIt includes at least one of ref.

[0036] In this embodiment, the voltage change amount is the amount of change in the voltage when the power converter 40 outputs the active current command value i ｐ ref and reactive current command value i ｑ The positive-phase voltage change amount ΔV, which is the voltage change amount when ref is output １ abc, the power converter 40 outputs the negative-phase current command value I ２ The negative phase voltage change amount ΔV, which is the voltage change amount when outputting ref ２ abc, and the power converter 40 is a non-fundamental wave current command value I ｎ The non-fundamental wave component change amount ΔV, which is the voltage change amount when outputting ref ｎ It contains at least one of abc.

[0037] Specifically, the voltage change amount calculation unit 62 calculates the positive-phase voltage change amount ΔV １ a positive-phase voltage calculation unit 621 that calculates a, b, c, and a negative-phase voltage change amount ΔV ２ a, b, c, and a negative-phase-sequence voltage calculation unit 622 for calculating the non-fundamental wave component change amount ΔV ｎ and a non-fundamental wave component calculation unit 623 that calculates abc.

[0038] The positive-sequence voltage calculation unit 621 acquires the output current command value and the phase of the power grid 10, and calculates the positive-sequence voltage change amount ΔV from the output current command value by open control so as to synchronize with the phase of the power grid 10. １ Specifically, the positive-sequence voltage calculation unit 621 calculates the active current command value i ｐ ref and reactive current command value i ｑ By open control from ref, the instantaneous voltage value ΔV of the active power ｐ abc and reactive power instantaneous voltage value ΔV ｑ Calculate abc and calculate the instantaneous voltage value ΔV of the active power ｐ abc and reactive power instantaneous voltage value ΔV ｑ By combining a, b, and c, the positive sequence voltage change amount ΔV １ abc is calculated. Then, the positive-sequence voltage calculation unit 621 calculates the positive-sequence voltage change amount ΔV １ A method for calculating abc will be described.

[0039] The positive-sequence voltage calculation unit 621 receives the active current command value i ｐ ref and reactive current command value i ｑ ref is obtained. Here, the active current command value i ｐ ref and reactive current command value i ｑ ref includes the inertial force. Note that "including the inertial force" means that the power converter 40 has the ability to autonomously reduce the frequency change of the power system 100.

[0040] Then, the positive-sequence voltage calculation unit 621 calculates the active current gain Kp corresponding to the active current and the reactive current gain Kq corresponding to the reactive current as the active current command value i ｐ ref and reactive current command value i ｑ ref to calculate an active power voltage amplitude command value ΔEp and a reactive power voltage amplitude command value ΔEq. In this embodiment, the active power voltage amplitude command value ΔEp and the reactive power voltage amplitude command value ΔEq are effective values. Here, the active current gain Kp and the reactive current gain Kq are determined by an interconnection impedance, which is the impedance of the device that interconnects the power converter 40 to the power line B. The interconnection impedance is determined to be approximately 10% to 15% of the device capacity of the interconnected device. The device capacity of the interconnected device here refers to, for example, the device capacity of the interconnection transformer T and the device capacity of the harmonic filter reactor inside the power converter 40.

[0041] Furthermore, the positive-sequence voltage calculation unit 621 acquires the phase of the power grid 10 from the voltage measured by the measurement unit 50. Then, the positive-sequence voltage calculation unit 621 calculates a first phase θp that is the same phase as the phase of the power grid 10 and a second phase θq that is a phase that is delayed by 90 degrees from the phase of the power grid 10. Note that the positive-sequence voltage calculation unit 621 may acquire the phase of the power grid 10 from phase information input via an external input means (not shown).

[0042] Then, the positive-phase voltage calculation unit 621 calculates the instantaneous voltage value ΔV in the active power by positive-phase instantaneous voltage control, which is a control for converting the effective value of the voltage into an instantaneous value of the voltage, from the voltage amplitude command value ΔEp of the active power and the first phase θp. ｐFurthermore, the positive-phase voltage calculation unit 621 calculates the instantaneous voltage value ΔV of the reactive power from the voltage amplitude command value ΔEq of the reactive power and the second phase θq by positive-phase instantaneous voltage control. ｑ Then, the positive-sequence voltage calculation unit 621 calculates the instantaneous voltage value ΔV of the active power. ｐ abc and reactive power instantaneous voltage value ΔV ｑ By combining a, b, and c, the positive sequence voltage change amount ΔV １ Calculate abc.

[0043] The negative-phase-sequence voltage calculation unit 622 calculates a phase command value θ of the negative-phase-sequence voltage. ２ ref and negative-phase current command value I ２ ref is acquired, and the phase command value θ of the negative-phase voltage is ２ ref and negative-phase current command value I ２ By open control from ref, the negative phase voltage change amount ΔV ２ The negative-phase-sequence voltage calculation unit 622 calculates the negative-phase-sequence voltage change amount ΔV ２ A method for calculating abc will be described.

[0044] The negative-phase-sequence voltage calculation unit 622 receives a phase command value θ of the negative-phase-sequence voltage via an external input means (not shown). ２ ref and negative-phase current command value I ２ Get ref.

[0045] Next, the negative-phase-sequence voltage calculation unit 622 calculates the negative-phase-sequence current command value I ２ The voltage amplitude command value ΔE2 of the negative-phase-sequence voltage is calculated by multiplying ref by a predetermined gain K2. Note that the gain K2 is determined by the interconnection impedance, similar to the active current gain Kp and the reactive current gain Kq.

[0046] Then, the negative-phase-sequence voltage calculation unit 622 calculates the voltage amplitude command value ΔE2 of the negative-phase-sequence voltage and the phase command value θ of the negative-phase-sequence voltage. ２ By controlling the negative-phase instantaneous voltage from ref, the negative-phase voltage change amount ΔV ２ Calculate abc.

[0047] The non-fundamental wave component calculation unit 623 calculates the phase command value θn of the non-fundamental wave component and the non-fundamental wave current command value I ｎ ref is acquired, and the phase command value θn of the non-fundamental wave component and the non-fundamental wave current command value Iｎ By open control from ref, the non-fundamental wave component change amount ΔV ｎ In this embodiment, the non-fundamental wave component is, for example, a harmonic component or an interharmonic. ｎ A method for calculating abc will be described.

[0048] The non-fundamental wave component calculation unit 623 receives the phase command value θn of the non-fundamental wave component and the non-fundamental wave current command value I ｎ Here, the phase command value θn of the non-fundamental wave component and the non-fundamental wave current command value I ｎ ref is a value determined by the order of the non-fundamental wave component.

[0049] Next, the non-fundamental wave component calculation unit 623 calculates the non-fundamental wave current command value I ｎ The voltage amplitude command value ΔEn of the non-fundamental wave component is calculated by multiplying ref by a predetermined gain Kn. Note that when the inductance component of the interconnection impedance is dominant (i.e., when the resistance component is sufficiently negligible compared to the inductance component), the gain Kn is determined by multiplying the interconnection impedance by the order of the non-fundamental wave component.

[0050] The non-fundamental wave component calculation unit 623 calculates the voltage amplitude command value ΔEn of the non-fundamental wave component and the phase command value θ ｎ By controlling the instantaneous voltage from ref, the non-fundamental wave component change amount ΔV ｎ Calculate abc.

[0051] The voltage command value output unit 63 calculates a voltage command value Vref by combining the counter voltage Vabc and the voltage change amount, and outputs the voltage command value Vref to the power converter 40. Specifically, the voltage command value output unit 63 calculates a positive-phase voltage change amount ΔV １ abc, negative sequence voltage change amount ΔV ２ abc and non-fundamental wave component change amount ΔV ｎThe counter voltage Vabc and the voltage change amount are combined to calculate a voltage command value Vref. When the voltage command value Vref is output from the voltage command value output unit 63, the power converter 40 outputs a voltage to the load 20 by, for example, PWM control in accordance with the voltage command value Vref.

[0052] <Simulation Results> The output waveform of the power converter 40 when the voltage of the power converter 40 is controlled using the power converter control device 60 of this embodiment is shown below by simulation.

[0053] 3 shows the voltage waveform, current waveform, active power waveform, and reactive power waveform output by the power converter 40 under the control of the power converter control device 60 when there is no abnormality in the power system 10, such as a short-circuit fault. In FIG. 3, the power converter 40 applies a voltage change 1.5 seconds after the start of the simulation. As can be seen from FIG. 3, it was confirmed that the current output from the power converter 40 was zero before the power converter 40 applied the voltage change. It was also confirmed that when the power converter 40 applied the voltage change, the active power and reactive power increased in accordance with the magnitude of the amplitude of the applied voltage change.

[0054] FIG. 4 shows the voltage and current waveforms output by the power converter 40 when the power converter 40 applies a voltage change under the control of the power converter control device 60 and an abnormality in the power grid 10, such as a short-circuit fault, occurs. In FIG. 4 , the power converter 40 applies a voltage change 1.5 seconds after the start of the simulation, and a two-phase short-circuit fault occurs between 2.0 and 2.2 seconds after the start of the simulation. As can be seen from FIG. 4 , the phase and amplitude of the current output from the power converter 40 do not fluctuate before and after the two-phase short-circuit fault. Therefore, it was confirmed that overcurrent is prevented from flowing from the power converter 40 regardless of fluctuations in the voltage of the power grid 10. Furthermore, as shown in FIG. 5 , it was confirmed that the phase and amplitude of the voltage output by the power converter 40 matched the phase and amplitude of the voltage of the power grid 10 both before and after the short-circuit fault occurred.

[0055] <Effects of the Present Embodiment> According to the power converter control device 60 of the present embodiment, the counter voltage Vabc has the same phase and amplitude as the voltage of the power grid 10, and the power converter 40 outputs a voltage command value Vref that is a combination of the counter voltage Vabc and the voltage change amount. As a result, the voltage of the power grid 10 is canceled out by the counter voltage Vabc, and only the voltage change amount is applied to the interconnection transformer T and the interconnection reactor L of the power converter 40. Therefore, regardless of fluctuations in the voltage of the power grid 10, the power converter 40 can output a current according to the output current command value. Furthermore, because the voltage change amount calculation unit 62 calculates the voltage change amount using open control, the voltage change amount does not vary depending on the control amount of the distributed power source 70, even if the distributed power source 70 is connected to the same power line B. Therefore, even if the DC power source 30 and the distributed power source 70 are connected to the same power line B, instability phenomena such as flicker can be prevented.

[0056] Other Embodiments The present invention is not limited to the above-described embodiments.

[0057] 6, the non-fundamental component calculation unit 623 may calculate non-fundamental components of different orders. Specifically, the non-fundamental component calculation unit 623 calculates a first non-fundamental component change amount ΔV ｎ１ a first non-fundamental wave component calculation unit 623a that calculates abc and a second non-fundamental wave component change amount ΔV corresponding to the second order n2 ｎ２ The first non-fundamental wave component change amount ΔV may be calculated by a second non-fundamental wave component calculation unit 623b. Here, the order n1 of the first non-fundamental wave component and the order n2 of the second non-fundamental wave component are different orders. ｎ１ abc and the second non-fundamental wave component change amount ΔV ｎ２ The calculation method of abc is the non-fundamental wave component change amount ΔV ｎ The calculation method is the same as that for abc.

[0058] In this case, as shown in FIG. 6, the voltage command value output unit 63 outputs the positive-phase voltage change amount ΔV １ abc, negative sequence voltage change amount ΔV ２abc, first non-fundamental wave component change amount ΔV ｎ１ abc and the second non-fundamental wave component change amount ΔV ｎ２ The voltage command value output unit 623 then combines the counter voltages Vabc and the voltage change amount to calculate the voltage command value Vref. Note that the non-fundamental wave component calculation unit 623 may calculate three or more different orders of non-fundamental wave components.

[0059] In the above embodiment, the positive-sequence voltage calculation unit 621, the negative-sequence voltage calculation unit 622, and the non-fundamental wave component calculation unit 623 acquire the voltage change amount phase command value and the output current command value via an external input means (not shown), but this is not limiting. For example, the voltage change amount phase command value and the output current command value may be stored in an internal memory of the power converter control device 60, and the positive-sequence voltage calculation unit 621, the negative-sequence voltage calculation unit 622, and the non-fundamental wave component calculation unit 623 may acquire each command value from the internal memory.

[0060] In the above embodiment, the voltage change amount calculation unit 62 includes a positive-phase voltage calculation unit 621, a negative-phase voltage calculation unit 622, and a non-fundamental wave component calculation unit 623, but the voltage change amount calculation unit 62 may include at least one of these three calculation units.

[0061] In the above embodiment, the active current command value and the reactive current command value include the inertial force, but if a sufficient inertial force is supplied to the load 20, the active current command value and the reactive current command value do not need to include the inertial force.

[0062] Furthermore, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. For example, it will be understood by those skilled in the art that the above-described exemplary embodiments are specific examples of the following aspects.

[0063] (Aspect 1) A power converter control device that controls a voltage output by a power converter connected to a power line for supplying power from a power grid to a load, the power converter control device comprising: a counter voltage calculation unit that calculates a counter voltage, which is a voltage of the same phase and amplitude as a voltage of the power grid; a voltage change amount calculation unit that acquires an output current command value, which is a current to be output by the power converter, and calculates, by open control from the output current command value, an amount of voltage change when the power converter outputs the output current command value; and a voltage command value output unit that outputs a voltage command value, which is a voltage obtained by combining the counter voltage and the amount of voltage change, to the power converter.

[0064] (Aspect 2) The power converter control device according to aspect 1, wherein the output current command value is at least one of a fundamental wave positive-sequence active current, a fundamental wave positive-sequence reactive current, a fundamental wave negative-sequence current, and a non-fundamental frequency current.

[0065] (Aspect 3) The power converter control device according to aspect 1 or 2, wherein the power converter is a voltage-controlled inverter that supplies inertial force to the power line.

[0066] (Aspect 4) A power converter control device according to any one of Aspects 1 to 3, wherein the voltage change amount calculation unit further includes a positive sequence voltage calculation unit that calculates a positive sequence voltage, which is a voltage change amount that compensates for the active power of the load, and the positive sequence voltage calculation unit acquires the output current command value and the phase of the power grid, and calculates the positive sequence voltage from the output current command value by open control so as to be synchronized with the phase of the power grid.

[0067] (Aspect 5) The power converter control device according to Aspect 4, wherein the output current command value acquired by the positive-sequence voltage calculation unit is an active current command value including an inertial force and a reactive current command value including an inertial force.

[0068] (Aspect 6) A power converter control device according to aspect 4 or 5, wherein the positive-phase voltage calculation unit calculates an instantaneous voltage value of active power and an instantaneous voltage value of reactive power from an active current command value and a reactive current command value by open control, respectively, and calculates the positive-phase voltage by combining the instantaneous voltage value of active power and the instantaneous voltage value of reactive power.

[0069] (Aspect 7) A power converter control device according to any one of Aspects 1 to 6, wherein the voltage change amount calculation unit further includes a negative-phase voltage calculation unit that calculates a negative-phase voltage, which is a voltage change amount that compensates for a voltage imbalance in the load, and the negative-phase voltage calculation unit acquires a phase command value of the negative-phase voltage and the output current command value, and calculates the negative-phase voltage from the phase command value of the negative-phase voltage and the output current command value by open control.

[0070] (Aspect 8) A power converter control device according to any one of Aspects 1 to 7, wherein the voltage change amount calculation unit further includes a non-fundamental wave component calculation unit that calculates a non-fundamental wave component, which is a frequency different from a fundamental frequency of the power system, as the voltage change amount, and the non-fundamental wave component calculation unit acquires a phase command value of the non-fundamental wave component and the output current command value, and calculates the non-fundamental wave component from the phase command value of the non-fundamental wave component and the output current command value by open control.

[0071] (Aspect 9) A control method for a power converter that controls a voltage output by a power converter connected to a power line for supplying power from a power system to a load, the control method for a power converter comprising: calculating a counter voltage, which is a voltage having the same phase and amplitude as the voltage of the power system; obtaining an output current command value, which is a current to be output by the power converter; calculating, from the output current command value, by open control, a voltage change amount when the power converter outputs the output current command value; and causing the power converter to output a voltage that is a combination of the counter voltage and the voltage change amount.

[0072] (Aspect 10) A control program for a power converter that controls a voltage output by a power converter connected to a power line for supplying power from a power system to a load, the control program for a power converter causing a computer to perform the following functions: a counter voltage calculation unit that calculates a counter voltage, which is a voltage of the same phase and amplitude as the voltage of the power system; a voltage change amount calculation unit that acquires an output current command value, which is a current to be output by the power converter, and calculates a voltage change amount when the power converter outputs the output current command value by open control from the output current command value; and a voltage command unit that causes the power converter to output a voltage that is a combination of the counter voltage and the voltage change amount.

[0073] According to the present invention, it is possible to cause a power converter to output a current according to a command value, regardless of fluctuations in the voltage of the power grid.

[0074] REFERENCE SIGNS LIST 100 Power system 10 Power grid 20 Load 30 DC power supply 40 Power converter 50 Measurement unit 60 Power converter control device 61 Counter voltage calculation unit 62 Voltage change amount calculation unit 621 Positive sequence voltage calculation unit 622 Negative sequence voltage calculation unit 623 Non-fundamental wave component calculation unit 70 Distributed power source B Power line S Circuit breaker T Injection transformer L Interconnection reactor

Claims

1. A power converter control device for controlling the voltage output by a power converter connected to a power line for supplying power from a power system to a load, the power converter control device comprising: a counter-voltage calculation unit that calculates a counter-voltage that is a voltage having the same phase and the same amplitude as the voltage of the power system; a voltage change amount calculation unit that acquires an output current command value that is a current to be output to the power converter and calculates, by open-loop control from the output current command value, a voltage change amount when the power converter outputs the output current command value; and a voltage command value output unit that outputs, to the power converter, a voltage command value that is a voltage obtained by synthesizing the counter-voltage and the voltage change amount.

2. The power converter control device according to claim 1, wherein the output current command value is at least one of a fundamental wave positive-phase active current, a fundamental wave positive-phase reactive current, a fundamental wave negative-phase current, and a non-fundamental wave frequency current.

3. The power converter control device according to claim 1, wherein the power converter is a voltage-controlled inverter that supplies inertial force to the power line.

4. The voltage change amount calculation unit further includes a positive-phase voltage calculation unit that calculates a positive-phase voltage as the voltage change amount, and the positive-phase voltage calculation unit acquires the output current command value and the phase of the power system and calculates the positive-phase voltage so as to be synchronized with the phase of the power system by open-loop control from the output current command value. The power converter control device according to claim 1.

5. The output current command value acquired by the positive-phase voltage calculation unit is an active current command value including inertial force and a reactive current command value including inertial force. The power converter control device according to claim 4.

6. The positive-phase voltage calculation unit calculates, by open-loop control from the active current command value and the reactive current command value, an instantaneous voltage value of active power and an instantaneous voltage value of reactive power, respectively, and calculates the positive-phase voltage by synthesizing the instantaneous voltage value of active power and the instantaneous voltage value of reactive power. The power converter control device according to claim 4.

7. The voltage change amount calculation unit further includes a negative-phase voltage calculation unit that calculates a negative-phase voltage as the voltage change amount, and the negative-phase voltage calculation unit acquires a phase command value of the negative-phase voltage and the output current command value and calculates the negative-phase voltage by open-loop control from the phase command value of the negative-phase voltage and the output current command value. The power converter control device according to claim 1.

8. The voltage change amount calculation unit further includes a non-fundamental wave component calculation unit that calculates the voltage change amount using a non-fundamental wave component, which is a frequency different from the fundamental frequency of the power system, as the voltage change amount. The non-fundamental wave component calculation unit acquires the phase command value of the non-fundamental wave component and the output current command value, and calculates the non-fundamental wave component by open-loop control from the phase command value of the non-fundamental wave component and the output current command value. The power converter control device according to any one of claims 1 to 7.

9. A control method for a power converter that controls the voltage output by a power converter connected to a power line for supplying power from a power system to a load, the method including calculating a counter voltage that is in phase and has the same amplitude as the voltage of the power system, acquiring an output current command value that is the current to be output to the power converter, calculating, by open-loop control from the output current command value, the voltage change amount when the power converter outputs the output current command value, and outputting to the power converter a voltage obtained by synthesizing the counter voltage and the voltage change amount.

10. A control program for a power converter that controls the voltage output by a power converter connected to a power line for supplying power from a power system to a load, the program causing a computer to function as a counter voltage calculation unit that calculates a counter voltage that is in phase and has the same amplitude as the voltage of the power system, a voltage change amount calculation unit that acquires an output current command value that is the current to be output to the power converter and calculates, by open-loop control from the output current command value, the voltage change amount when the power converter outputs the output current command value, and a voltage command unit that outputs to the power converter a voltage obtained by synthesizing the counter voltage and the voltage change amount.

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