Power conversion device and inverter control device

Abstract

The power conversion device of the present application includes: an active power command correction section that corrects an active power command inputted from the outside; a current command generation section that generates a pre-constraint current command for an alternating current power; a current command constraint section that generates a current command to which a constraint based on a prescribed limit value is applied to the pre-constraint current command; a current control section that generates a voltage command for the alternating current power based on the current command; and a suppressed power calculation section that calculates a suppressed power suppressed in the alternating current power due to the constraint, the current command constraint section generates the current command based on a comparison result of a current value in which an active component and a reactive component of the pre-constraint current command are combined and the limit value, the suppressed power calculation section calculates a difference between a pre-constraint power corresponding to the pre-constraint current command and a post-constraint power corresponding to the current command to calculate the suppressed power, and the active power command correction section corrects the active power command based on the suppressed power calculated by the suppressed power calculation section.

Description

Technical Field

[0001] This invention relates to power conversion devices and inverter control devices. Background Technology

[0002] Previously, power conversion devices were known to connect DC power sources such as solar panels and batteries to the power system, converting DC power output from the DC power source into AC power that matches the frequency and phase of the power system before inputting it into the power system. In recent years, grid-forming inverters (GFM) have been under development for such power conversion devices. Grid-forming inverters do not track the voltage, frequency, and phase of the power system when outputting AC power; instead, they determine the output voltage, frequency, and phase themselves. Grid-forming inverters can simulate synchronous generators to virtually supply inertial forces.

[0003] For the aforementioned grid-connected inverter, for example, the technology described in Patent Document 1 has been proposed. Patent Document 1 describes a grid-connected power conversion device whose control limits the d-axis current command value and q-axis current specification value, which correspond to the d-axis and q-axis components of the armature current of a virtual generator obtained by generator model calculation, to a specified limit.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2014-168351 Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] A phenomenon in power systems where abrupt phase changes occur is called phase jump. When a phase jump occurs in a power system, the phase difference between the AC power being output by a grid-connected inverter and the power system changes drastically, causing significant fluctuations in both the active and reactive components of the output current. In this situation, if at least one of the active or reactive components of the current command used to control the inverter circuit exceeds a preset limit, although the inverter circuit can be controlled according to the limited current command to suppress overcurrent, the grid-connected inverter cannot output the intended active power. This poses a risk of loss of synchronism due to increased frequency and phase commands, similar to those used in synchronous generators. However, Patent Document 1 does not consider this issue and cannot adequately prevent loss of synchronism during a power system phase jump.

[0009] In view of the above-mentioned problems, the present invention aims to provide a technology that enables continued operation of a power conversion device used as a grid-connected inverter during power system phase jumps.

[0010] Technical solutions to the problem

[0011] The power conversion device of the present invention can be connected to a power system, converting DC power supplied from a DC power source into AC power with added inertia, and outputting the AC power to the power system. The power conversion device includes: a first voltage command generation unit that generates a first voltage command based on a predetermined rated voltage; an active power command correction unit that obtains a corrected active power command obtained by correcting an externally input active power command; an angular frequency command generation unit that generates an angular frequency command for the AC power based on the corrected active power command obtained by the active power command correction unit; a phase command generation unit that generates a phase command based on the angular frequency command; a current command generation unit that generates a constrained pre-current command for the AC power based on the phase command and the first voltage command; and a unit that generates a current command for the current command. The system comprises: a current command constraint unit that generates a current command based on a predetermined limit value and applies a constraint to the pre-constraint current command; a current control unit that generates a voltage command for the AC power based on the current command generated by the current command constraint unit; and a suppression power calculation unit that calculates the suppression power suppressed in the AC power due to the constraint. The current command constraint unit generates the current command based on a comparison between the current value combining the active and reactive components of the pre-constraint current command and the limit value. The suppression power calculation unit calculates the suppression power by calculating the difference between the pre-constraint power corresponding to the pre-constraint current command and the post-constraint power corresponding to the current command. The active power command correction unit corrects the active power command based on the suppression power calculated by the suppression power calculation unit.

[0012] The inverter control device of the present invention is a device for controlling an inverter, wherein the inverter is capable of being connected to a power system, converting DC power supplied from a DC power source into AC power with added inertia, and outputting the AC power to the power system. The inverter control device includes: a first voltage command generation unit that generates a first voltage command based on a predetermined rated voltage; an active power command correction unit that obtains a corrected active power command obtained by correcting an externally input active power command; an angular frequency command generation unit that generates an angular frequency command for the AC power based on the corrected active power command obtained by the active power command correction unit; a phase command generation unit that generates a phase command based on the angular frequency command; and a current command that generates a pre-constraint current command for the AC power based on the phase command and the first voltage command. The system comprises: a generation unit; a current command constraint unit that generates a current command that imposes a constraint based on a predetermined limit value on the pre-constraint current command generated by the current command generation unit; a current control unit that generates a voltage command for the AC power based on the current command generated by the current command constraint unit; and a suppression power calculation unit that calculates the suppression power suppressed in the AC power due to the constraint. The current command constraint unit generates the current command based on a comparison between the current value combining the active and reactive components of the pre-constraint current command and the limit value. The suppression power calculation unit calculates the suppression power by calculating the difference between the pre-constraint power corresponding to the pre-constraint current command and the post-constraint power corresponding to the current command. The active power command correction unit corrects the active power command based on the suppression power calculated by the suppression power calculation unit.

[0013] Invention Effects

[0014] According to the present invention, a technology is provided that enables continued operation of a power conversion device used as a grid-connected inverter during power system phase jumps. Attached Figure Description

[0015] Figure 1 This is a diagram illustrating a structural example of a power conversion device according to one embodiment of the present invention.

[0016] Figure 2 This is an explanatory diagram illustrating the difference between the current limitation of the comparative example and that of the present invention. Detailed Implementation

[0017] Figure 1This is a diagram illustrating a structural example of a power conversion device according to one embodiment of the present invention. The power conversion device 100 of this embodiment converts DC power supplied from DC power source 1 into AC power and outputs it to power system 2, thereby realizing the supply of power from DC power source 1 to power system 2. It includes an inverter 3, a filter 4, a current sensor 5, a voltage sensor 6, and an inverter control device 10.

[0018] DC power supply 1 is connected to inverter 3 and outputs a specified DC power to inverter 3. DC power supply 1 can be, for example, a secondary battery such as a lithium-ion battery, nickel-metal hydride battery, or lead-acid battery, or a renewable energy source such as solar power or wind power. Alternatively, these can be combined to form DC power supply 1.

[0019] Inverter 3, for example, is constructed using a three-phase full-bridge circuit and operates under the control of inverter control device 10. It converts the DC power input from DC power supply 1 into AC power corresponding to the frequency and phase of power system 2, and outputs it to power system 2 via filter 4. Filter 4 removes unwanted high-order harmonic components from the AC power output by inverter 3.

[0020] Current sensor 5 measures the current value of the AC power output from inverter 3. Voltage sensor 6 measures the voltage value of the AC power output from inverter 3 after passing through filter 4 (the AC voltage value of power system 2). The measurement results of current sensor 5 and voltage sensor 6 are used as the current measurement value Iout and voltage measurement value Vout of the AC power output from power conversion device 100, and are respectively input to inverter control device 10.

[0021] The inverter control unit 10 includes functional modules such as a power calculation unit 11, a reactive power command unit 12, a first voltage command generation unit 13, an active power command correction unit 14, an angular frequency command generation unit 15, a phase command generation unit 16, a current command generation unit 17, a current command constraint unit 18, a current control unit 19, a main circuit control unit 20, and a power suppression calculation unit 21. The inverter control unit 10 can be configured, for example, by a microcomputer, and these functional modules can be implemented by running a predetermined program in the microcomputer. Alternatively, some or all of these functional modules can be implemented using hardware circuits such as logic ICs and FPGAs.

[0022] The power calculation unit 11 calculates the active power P and reactive power Q, which represent the active and reactive components of the AC power actually output by the power conversion device 100, based on the current measurement value Iout and voltage measurement value Vout obtained from the current sensor 5 and voltage sensor 6, respectively.

[0023] The reactive power command unit 12 generates a command value for the reactive component of the AC power output from the power conversion device 100 based on the voltage measurement value Vout obtained from the voltage sensor 6, and outputs this command value as a reactive power command Q*. Specifically, the reactive power command unit 12 multiplies the deviation (V0-Vout) between the rated voltage V0 (e.g., V0=200V) and the voltage measurement value Vout by a predetermined proportional gain KQ, thereby generating the reactive power command Q*.

[0024] The first voltage command generation unit 13 uses the reactive power Q calculated by the power calculation unit 11 and the reactive power command Q* output from the reactive power command unit 12 to generate a voltage command value, namely the first voltage command E*, before applying a current constraint to the AC power output from the power conversion device 100. Specifically, the first voltage command generation unit 13 performs PI control on the deviation (Q*-Q) between the reactive power command Q* and the reactive power Q, thereby generating the first voltage command E* based on the rated voltage V0.

[0025] The active power command correction unit 14 uses the suppression power Psupp (described later) calculated by the suppression power calculation unit 21 to correct the active power command P0 input from the outside, and outputs the correction result as the corrected active power command P*. The detailed method for the active power command correction unit 14 to calculate the corrected active power command P* will be described later.

[0026] The angular frequency command generation unit 15 generates a command value for the angular frequency of the AC power output from the power conversion device 100 based on the active power P calculated by the power calculation unit 11 and the corrected active power command P* calculated by the active power command correction unit 14. This command value is then output as the angular frequency command ω*. Specifically, the angular frequency command generation unit 15 calculates the value obtained by multiplying the deviation (P*-P) between the corrected active power command P* and the active power P by the reciprocal of a predetermined proportional gain, 1 / KP. This value is then compensated for with first-order lag and first-order lead, thereby calculating the angular frequency deviation Δω with virtual inertia. Then, the angular frequency deviation Δω is added to the rated angular frequency ω0 (e.g., 2π×50Hz) to generate the angular frequency command ω*.

[0027] The phase command generation unit 16 generates a command value, namely the phase command θ*, for the phase of the AC power output from the power conversion device 100 based on the angular frequency command ω* output from the angular frequency command generation unit 15. Specifically, the phase command generation unit 16 generates the phase command θ* by integrating the angular frequency command ω*. Thus, the phase command θ* based on the angular frequency command ω* can be obtained. Alternatively, the phase command θ* can be obtained by dividing the value obtained by integrating the angular frequency command ω* by 2π.

[0028] The current command generation unit 17 generates a pre-constraint current command I for the AC power output from the power conversion device 100 based on the first voltage command E* based on the rated voltage V0 generated by the first voltage command generation unit 13, the phase command θ* based on the angular frequency command ω* obtained by the phase command generation unit 16, and the voltage measurement value Vout from the voltage sensor 6. Specifically, it calculates the deviation between the value of the voltage measurement value Vout after dq transformation based on the phase command θ* and the first voltage command E*, and calculates the pre-constraint current command I, which represents the current command before the current command constraint unit 18 applies the constraint. Thus, the current command generation unit 17 can generate a pre-constraint current command I for AC power based on the angular frequency command ω* generated by the angular frequency command generation unit 15 and the predetermined rated voltage V0.

[0029] The current command constraint unit 18 generates a current command I* after imposing a constraint according to a predetermined limit value on the pre-constraint current command I generated by the current command generation unit 17. Specifically, it compares the current value combining the active and reactive components of the pre-constraint current command I with the predetermined limit value. If the current value exceeds the limit value, it imposes a constraint on the pre-constraint current command I in a manner that makes the ratio of active to reactive components in the pre-constraint current command I consistent with the ratio of active to reactive components in the post-constraint current command I*, thereby generating the current command I*. Details of the constraints performed by the current command constraint unit 18 will be described later.

[0030] The current control unit 19 generates a voltage command V* for the AC power output from the power conversion device 100 based on the current command I* input from the current command constraint unit 18 and the current measurement value Iout from the current sensor 5. Specifically, the current control unit 19 calculates the deviation between the value of the current measurement value Iout after dq transformation according to the phase command θ* and the current command I*, and calculates the voltage command V* based on this deviation. Current control is performed using the constrained current command I* instead of the pre-constraint current command I, thereby suppressing overcurrent in the power conversion device 100.

[0031] The main circuit control unit 20 controls the operation of the inverter 3 based on the voltage command V* generated by the current control unit 19 and the phase command θ* obtained by the phase command generation unit 16. At this time, the main circuit control unit 20 performs PWM control based on the voltage command V* and the phase command θ*, thereby generating gate signals for each switching element of the inverter 3 and outputting these gate signals to the inverter 3. Thus, the inverter 3 can be driven to convert DC power to AC power in such a way that the voltage and phase of the AC power output from the inverter 3 to the power system 2 follow the changes in the voltage command V* and the phase command θ*.

[0032] The suppression power calculation unit 21 calculates the amount of power suppressed in the AC power output by the power conversion device 100 due to the constraint of the current command constraint unit 18, and outputs this value as the suppression power Psupp. Specifically, it calculates the difference between the power before constraint corresponding to the current command I before constraint calculated by the current command generation unit 17 and the power after constraint corresponding to the current command I* after constraint is applied by the current command constraint unit 18, and thereby calculates the suppression power Psupp.

[0033] The suppressed power Psupp calculated by the suppressed power calculation unit 21 is input to the active power command correction unit 14 for correcting the active power command P0 performed by the active power command correction unit 14. Specifically, the active power command correction unit 14 calculates and corrects the active power command P* based on the suppressed power Psupp according to the following formula (1), thereby correcting the active power command P0.

[0034]

[0035] Through the above description, the power conversion device 100 can operate in parallel with the power system 2 while maintaining virtual inertia. Furthermore, the suppression power Psupp generated by the constraint of the current command constraint unit 18 is calculated. After the active power command P0 is corrected based on this suppression power Psupp, the angular frequency command generation unit 15 calculates the angular frequency command ω*. Therefore, when the output power of the power conversion device 100 is suppressed due to the constraint of the current command constraint unit 18, the angular frequency command ω* and phase command θ* that reduce the output power can be calculated by subtracting the suppression portion from the active power command P0. As a result, even when a phase jump occurs in the power system 2, changes in the angular frequency command ω* and phase command θ* can be suppressed, and the power conversion device 100 can continue operating without losing synchronization.

[0036] Here, the current command constraint unit 18 can also set limit values ​​for the active and reactive components of the current command I before constraint, and apply constraints to the active and reactive components of the current command I before constraint using these limit values. However, such a current command constraint method cannot sufficiently constrain the current command I before constraint, and the power output from the power conversion device 100 may be too large during phase jumps. See below for reference. Figure 2 This illustrates the point.

[0037] Figure 2 This is an explanatory diagram illustrating the difference between the current limitation of the comparative example and that of the present invention. Figure 2 In the example, (a) is a comparative example, showing the current limitation situation when the current command constraint unit 18 sets limit values ​​for the active and reactive components of the current command I before constraint. On the other hand, (b) shows the situation as follows: Figure 1The current limitation situation described herein is when the current value combining the active and reactive components of the current command I before constraint is set as a limit value in the current command constraint unit 18.

[0038] In the comparative example of current limiting, limit values ​​Ilim are set for the active component (d-axis current Id) and reactive component (q-axis current Iq) of the pre-constraint current command I. When at least one of the d-axis current Id and the q-axis current Iq exceeds the limit value Ilim, the current value is limited to the limit value Ilim, thereby imposing a constraint on the pre-constraint current command I. Figure 2 In the comparative example shown in (a), the d-axis current Id exceeds the limit value Ilim and is therefore limited to the limit value Ilim. As a result, the current command constraint unit 18 applies a constraint to the pre-constraint current command I shown in vector 31, thereby generating the current command I* shown in vector 32.

[0039] On the other hand, in the current limiting of the present invention, the current value, i.e., the apparent current value, is the combination of the active component (d-axis current Id) and reactive component (q-axis current Iq) of the current command I before constraint. As shown by arc 30 in the figure, a limit value Ilim is set. When the apparent current value exceeds this limit value Ilim, the d-axis current Id and the q-axis current Iq are respectively limited to make the apparent current value consistent with the limit value Ilim, thereby constraining the current command I before constraint. Figure 2 In the example shown in (b), the current command constraint unit 18 applies a constraint to the pre-constraint current command I shown in vector 31, thereby generating the current command I* shown in vector 33. Furthermore, the suppression power Psupp calculated by the suppression power calculation unit 21 at this time can be expressed as the inner product of the difference between vector 31 and vector 33 (i.e., the current vector 34) and the measured voltage vector (not shown). The components of the measured voltage vector are the d-axis component and the q-axis component obtained by performing a dq transformation on the voltage measurement value Vout according to the phase command θ*.

[0040] like Figure 2 As shown in vector 32 of (a), the angles formed by the constrained current command I* of the comparative example with the d-axis (representing the magnitude of active current) and the q-axis (representing the magnitude of reactive current) have changed compared to the original vector 31. That is, it can be seen that the ratio of active to reactive components changes in the current constraint of the comparative example. On the other hand, as... Figure 2 As shown in vector 33 of (b), the angles formed by the constrained current command I* with the d-axis representing active current and the q-axis representing reactive current are unchanged compared to the original vector 31. That is, the current constraint of the present invention can constrain the current command I before constraint while maintaining the ratio of active and reactive components.

[0041] In the comparative example of current limiting, as explained above, the current command constraint unit 18 applies constraints independently to the active and reactive components using the limit value Ilim, thereby calculating the suppressed power Psupp. However, since the apparent current value of the current command I* is... Therefore, although both the active and reactive components of the current command I* are below the limit value Ilim, the apparent current exceeds the limit value Ilim. Thus, when a phase jump occurs in power system 2, although the active power command P0 can be corrected according to the suppression power Psupp, overcurrent may not be sufficiently suppressed. On the other hand, in the current limiting of the present invention, as explained above, the current command constraint unit 18 can maintain the original ratio of the active and reactive components of the current command I before constraint and apply a constraint to make the apparent current reach the limit value Ilim. Therefore, when a phase jump occurs in power system 2, the active power command P0 can be corrected according to the suppression power Psupp to suppress overcurrent.

[0042] According to the embodiments of the present invention described above, the following effects can be achieved.

[0043] (1) The power conversion device 100 can be connected to the power system 2 to convert DC power supplied from DC power source 1 into AC power with added inertia, and output the AC power to the power system 2. The power conversion device 100 has an inverter control device 10, which includes an active power command correction unit 14, an angular frequency command generation unit 15, a current command generation unit 17, a current command constraint unit 18, a current control unit 19, and a power suppression calculation unit 21. The active power command correction unit 14 obtains a corrected active power command P* obtained by correcting the active power command P0 input from the outside. The angular frequency command generation unit 15 generates an angular frequency command ω* for the AC power output by the power conversion device 100 based on the corrected active power command P* obtained by the active power command correction unit 14. The current command generation unit 17 generates a pre-constraint current command I for the AC power output of the power converter 100 based on the first voltage command E* generated by the first voltage command generation unit 13 (based on the rated voltage V0), the phase command θ* calculated by the phase command generation unit 16 based on the angular frequency command ω* generated by the angular frequency command generation unit 15, and the voltage measurement value Vout of the voltage sensor 6. The current command constraint unit 18 generates a current command I* that imposes a constraint based on a predetermined limit value Ilim on the pre-constraint current command I generated by the current command generation unit 17. The current control unit 19 generates a voltage command V* for the AC power output of the power converter 100 based on the current command I* generated by the current command constraint unit 18. The suppression power calculation unit 21 calculates the suppression power Psupp that is suppressed in the AC power output of the power converter 100 due to the constraint of the current command constraint unit 18. Here, the current command constraint unit 18 uses the apparent current value, which combines the active and reactive components of the pre-constraint current command I. The current command I* is generated by comparing the result with the limit value Ilim. The suppression power calculation unit 21 calculates the difference between the pre-constraint power corresponding to the pre-constraint current command I and the post-constraint power corresponding to the power command I*, thereby obtaining the suppression power Psupp. The active power command correction unit 14 corrects the active power command P0 based on the suppression power Psupp obtained by the suppression power calculation unit 21. In this way, in the power conversion device 100 used as a grid-type inverter, loss of synchronization can be avoided and operation can continue even when the power system 2 phase jumps.

[0044] (2) The current command constraint unit 18 applies a constraint to the current command I before constraint in such a way that the ratio of active to reactive components in the current command I before constraint is consistent with the ratio of active to reactive components in the current command I*. In this way, when a phase jump occurs in the power system 2, overcurrent can be effectively suppressed.

[0045] (3) Let the active power command be P0 and the suppression power be Psupp. The active power command correction unit 14 calculates the value P* of the corrected active power command according to the above formula (1). In this way, the suppression power Psupp that is suppressed in the AC power output by the power conversion device 100 due to the constraint of the current command constraint unit 18 can be accurately calculated, and the active power command P0 can be corrected.

[0046] Furthermore, the present invention is not limited to the above-described embodiments and modifications, and can be implemented using any constituent elements without departing from its spirit. Additionally, each embodiment and modification can be used individually or in combination. That is, the above-described effects can be achieved by arbitrarily combining the features of each embodiment in the present invention.

[0047] The above-described embodiments and modifications are merely examples, and the present invention is not limited to these contents as long as they do not impair the characteristics of the invention. Furthermore, while various embodiments and modifications have been described above, the present invention is not limited to these contents. Other methods conceivable within the scope of the technical concept of the present invention are also included within the scope of the present invention.

[0048] Explanation of reference numerals in the attached figures

[0049] 1…DC power supply

[0050] 2…Power System

[0051] 3…Inverter

[0052] 4…Filter

[0053] 5… Current sensor

[0054] 6…Voltage sensor

[0055] 10…Inverter control unit

[0056] 11…Power Calculation Department

[0057] 12…Reactive Power Command Section

[0058] 13…First Voltage Command Generation Unit

[0059] 14…Active Power Command Correction Unit

[0060] 15… Angular Frequency Command Generation Unit

[0061] 16…Phase Command Generation Unit

[0062] 17… Current Command Generation Unit

[0063] 18…Current Command Constraint Section

[0064] 19… Current Control Section

[0065] 20…Main Circuit Control Section

[0066] 21…Suppression Power Calculation Unit

[0067] 100… power conversion device.

Claims

1. A power conversion device capable of being connected to a power system, converting DC power supplied from a DC power source into AC power with added inertia, and outputting the AC power to the power system, the power conversion device being characterized in that it comprises: A first voltage command generation unit that generates a first voltage command based on a pre-defined rated voltage; An active power command correction unit that obtains a corrected active power command by correcting an externally input active power command; An angular frequency command generation unit generates an angular frequency command for the AC power based on the corrected active power command obtained by the active power command correction unit. A phase instruction generation unit that generates phase instructions based on the angular frequency instructions; A current command generation unit that generates a constraint-pre-current command for the AC power based on the phase command and the first voltage command; A current command constraint unit that generates a current command that applies a constraint based on a predetermined limit value to the current command generated by the current command generation unit before constraint; A current control unit that generates a voltage command for the AC power based on the current command generated by the current command constraint unit; and The suppression power calculation unit calculates the suppression power that is suppressed in the AC power due to the aforementioned constraint. The current command constraint unit generates the current command based on a comparison between the current value (combining the active and reactive components of the current command before constraint) and the limit value. The suppression power calculation unit calculates the difference between the pre-constraint power corresponding to the pre-constraint current command and the post-constraint power corresponding to the current command to obtain the suppression power. The active power command correction unit corrects the active power command based on the suppressed power calculated by the suppressed power calculation unit.

2. The power conversion device as described in claim 1, characterized in that: The current command constraint unit applies the constraint to the pre-constraint current command in such a way that the ratio of active to reactive components in the pre-constraint current command is consistent with the ratio of active to reactive components in the current command.

3. The power conversion device as described in claim 1, characterized in that: Let the active power command be P0 and the suppression power be Psupp. The active power command correction unit calculates the value P* of the corrected active power command according to the following formula (1): 。 4. An inverter control device for controlling an inverter, wherein the inverter is connectable to a power system, converts DC power supplied from a DC power source into AC power with added inertia, and outputs the AC power to the power system, the inverter control device being characterized in that it comprises: A first voltage command generation unit that generates a first voltage command based on a pre-defined rated voltage; An active power command correction unit is used to obtain a corrected active power command obtained by correcting an externally input active power command. An angular frequency command generation unit generates an angular frequency command for the AC power based on the corrected active power command obtained by the active power command correction unit. A phase instruction generation unit that generates phase instructions based on the angular frequency instructions; A current command generation unit that generates a constraint-pre-current command for the AC power based on the phase command and the first voltage command; A current command constraint unit that generates a current command that applies a constraint based on a predetermined limit value to the current command generated by the current command generation unit before constraint; A current control unit that generates a voltage command for the AC power based on the current command generated by the current command constraint unit; and The suppression power calculation unit calculates the suppression power that is suppressed in the AC power due to the aforementioned constraint. The current command constraint unit generates the current command based on a comparison between the current value (combining the active and reactive components of the current command before constraint) and the limit value. The suppression power calculation unit calculates the difference between the pre-constraint power corresponding to the pre-constraint current command and the post-constraint power corresponding to the current command to obtain the suppression power. The active power command correction unit corrects the active power command based on the suppressed power calculated by the suppressed power calculation unit.

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