Power converter and inverter control device

Abstract

In the present invention, a power converter comprises an active power command correction unit for obtaining a corrected active power command obtained by correcting an active power command inputted from outside the power converter, a current command generation unit for generating a pre-restriction current command for AC power, a current command restriction unit for generating a current command in which a restriction based on a prescribed limit value is imposed on the pre-restriction current command, a current control unit for generating a voltage command for the AC power on the basis of the current command, and a suppressed power calculation unit for determining the suppressed power suppressed by the AC power due to the restriction, wherein the current command restriction unit generates the current command on the basis of the result from comparing the limit value and a current value obtained by combining active and reactive components of the pre-restriction current command, the suppression power calculation unit calculates the difference between pre-restriction power corresponding to the pre-restriction current command and post-restriction power corresponding to the current command to determine the suppression power, and the active power command correction unit corrects the active power command on the basis of the suppressed power obtained by the suppression power calculation unit.

Description

Power conversion devices, inverter control devices

[0001] The present invention relates to a power conversion device and an inverter control device.

[0002] Conventionally, power conversion devices have been known that are connected between a DC power source, such as a solar panel or a storage battery, and a power grid, converting DC power output from the DC power source into AC power that matches the frequency and phase of the power grid and inputting the converted AC power into the power grid. Among such power conversion devices, grid-forming (GFM) inverters have been developed in recent years. A grid-forming inverter does not output AC power in accordance with the voltage, frequency, and phase of the power grid, but instead determines its own output voltage, frequency, and phase. A grid-forming inverter can simulate a synchronous generator and supply a simulated inertial force.

[0003] Regarding the above-mentioned grid-forming inverter, for example, a technology described in Patent Document 1 has been proposed. Patent Document 1 describes a grid-connected power conversion device that controls a d-axis current command value and a q-axis current command value corresponding to the d-axis component and the q-axis component of the armature current of a virtual generator calculated by a generator model so as to be limited within predetermined limits.

[0004] Japanese Patent Application Publication No. 2014-168351

[0005] In power systems, a phenomenon called a phase jump, in which the phase changes suddenly, can occur. When a phase jump occurs in a power system, the phase difference between the AC power being output and the power system changes suddenly in a grid-connected inverter during grid-connected operation, which can cause large fluctuations in the active and reactive components of the output current. If at least one of the active and reactive components of the current command used to control the inverter circuit exceeds a preset limit, the inverter circuit is controlled by the limited current command, suppressing overcurrent. However, the grid-connected inverter cannot output the active power it should output, and the frequency and phase commands used to simulate a synchronous generator increase, potentially resulting in a loss of synchronization. However, Patent Document 1 does not take this issue into consideration and is therefore unable to adequately avoid loss of synchronization and continue operation when a phase jump occurs in the power system.

[0006] In view of the above-mentioned problems, an object of the present invention is to provide a technology that enables a power conversion device used as a grid-forming inverter to continue operation even when a phase jump occurs in the power grid.

[0007] A power conversion device according to the present invention is connectable to an electric power system, converts DC power supplied from a DC power source into AC power with inertia added, and outputs the AC power to the electric power system, and 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 by correcting an active power command input from outside; 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 pre-constraint current command for the AC power based on the phase command and the first voltage command; The power converter includes a current command constraint unit that generates a current command that imposes a constraint on the pre-constraint current command based on a predetermined limit value, 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 a suppression power that is suppressed by the AC power based on the constraint, wherein the current command constraint unit generates the current command based on a comparison result between a current value that is a combination of an active component and a reactive component of the pre-constraint current command and the limit value, the suppression power calculation unit calculates the suppression power by calculating a difference between a pre-constraint power corresponding to the pre-constraint current command and a post-constraint power corresponding to the current command, and the active power command correction unit corrects the active power command based on the suppression power calculated by the suppression power calculation unit.An inverter control device according to the present invention is a device that can be connected to an electric power system, controls an inverter that converts DC power supplied from a DC power source into AC power with inertia added thereto, and outputs the AC power to the electric power system, and 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 by correcting an active power command input from outside; 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 pre-constraint 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 by imposing a constraint based on a predetermined limit value on the pre-constraint current command generated by the current command constraint 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 a suppression power that is suppressed by the AC power based on the constraint, wherein the current command constraint unit generates the current command based on a comparison result between a current value that is a combination of an active component and a reactive component of the pre-constraint current command and the limit value, the suppression power calculation unit calculates the suppression power by calculating a difference between a pre-constraint power corresponding to the pre-constraint current command and a post-constraint power corresponding to the current command, and the active power command correction unit corrects the active power command based on the suppression power calculated by the suppression power calculation unit.

[0008] According to the present invention, it is possible to provide a technology that enables a power conversion device used as a grid-forming inverter to continue operation even when a phase jump occurs in the power grid.

[0009] 1 is a diagram illustrating an example of the configuration of a power conversion device according to an embodiment of the present invention;

[0010] 1 is a diagram showing an example of the configuration 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 a DC power source 1 into AC power and outputs the AC power to a power grid 2, thereby realizing power supply from the DC power source 1 to the power grid 2, and includes an inverter 3, a filter 4, a current sensor 5, a voltage sensor 6, and an inverter control device 10.

[0011] The DC power supply 1 is connected to the inverter 3 and outputs a predetermined DC power to the inverter 3. The DC power supply 1 may be, for example, a secondary battery such as a lithium ion battery, a nickel-metal hydride battery, or a lead-acid battery, or may be a renewable energy power supply such as a solar power generation or a wind power generation. The DC power supply 1 may also be configured by a combination of these.

[0012] The inverter 3 is configured using, for example, a three-phase full-bridge circuit, and operates under the control of the inverter control device 10 to convert DC power input from the DC power source 1 into AC power according to the frequency and phase of the power grid 2, and outputs it to the power grid 2 via the filter 4. The filter 4 removes unnecessary high-frequency components from the AC power output from the inverter 3.

[0013] The current sensor 5 measures the current value of the AC power output from the inverter 3. The voltage sensor 6 measures the voltage value (AC voltage value of the power grid 2) of the AC power output from the inverter 3 after it has passed through the filter 4. The measurement results from the current sensor 5 and the voltage sensor 6 are input to the inverter control device 10 as a measured current value Iout and a measured voltage value Vout of the AC power output from the power conversion device 100, respectively.

[0014] The inverter control device 10 has functional blocks including 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 suppression power calculation unit 21. The inverter control device 10 is configured, for example, by a microcomputer, and these functional blocks can be realized by executing a predetermined program on the microcomputer. Alternatively, some or all of these functional blocks may be realized using hardware circuits such as logic ICs or FPGAs.

[0015] The power calculation unit 11 calculates active power P and reactive power Q, which respectively represent the active component and reactive component of the AC power actually output by the power conversion device 100, from the current measurement value Iout and voltage measurement value Vout obtained from the current sensor 5 and voltage sensor 6, respectively.

[0016] 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 measured voltage value Vout acquired from the voltage sensor 6, and outputs the command value as a reactive power command Q*. Specifically, the reactive power command unit 12 generates the reactive power command Q* by multiplying the deviation (V0-Vout) between the rated voltage V0 (for example, V0=200 V) and the measured voltage value Vout by a predetermined proportional gain KQ.

[0017] The first voltage command generating unit 13 uses the reactive power Q calculated by the power calculating unit 11 and the reactive power command Q* output from the reactive power commanding unit 12 to generate a first voltage command E*, which is a voltage command value before current constraints are imposed on the AC power output from the power conversion device 100. Specifically, the first voltage command generating unit 13 generates the first voltage command E* based on the rated voltage V0 by PI control of the deviation (Q*-Q) between the reactive power command Q* and the reactive power Q.

[0018] The active power command corrector 14 corrects the active power command P0 input from outside based on a suppression power Psupp (described later) calculated by the suppression power calculator 21, and outputs the correction result as a corrected active power command P*. The method of calculating the corrected active power command P* by the active power command corrector 14 will be described in detail later.

[0019] 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, and outputs the command value as the angular frequency command ω*. Specifically, the angular frequency command generation unit 15 calculates a value 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, and performs first-order lag and first-order lead compensation on this value to calculate an angular frequency deviation Δω to which pseudo-inertia has been applied. The angular frequency command ω* is then generated by adding the angular frequency deviation Δω to the rated angular frequency ω0 (e.g., 2π×50 Hz).

[0020] The phase command generating unit 16 generates a phase command θ*, which is a command value 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 generating unit 15. Specifically, the phase command generating unit 16 generates the phase command θ* by integrating the angular frequency command ω*. This makes it possible to obtain the phase command θ* based on the angular frequency command ω*. Note that the phase command θ* may be the remainder obtained when the value obtained by integrating the angular frequency command ω* is divided by 2π.

[0021] The current command generating 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* generated by the first voltage command generating unit 13 and based on the rated voltage V0, the phase command θ* based on the angular frequency command ω* obtained by the phase command generating unit 16, and the measured voltage Vout by the voltage sensor 6. Specifically, the current command generating unit 17 obtains a deviation between the first voltage command E* and a value obtained by dq transforming the measured voltage Vout based on the phase command θ*, and calculates a pre-constraint current command I that represents the current command before constraint is imposed by the current command constraint unit 18, based on this deviation. In this way, the current command generating unit 17 can generate the pre-constraint current command I for the AC power, based on the angular frequency command ω* generated by the angular frequency command generating unit 15 and the predetermined rated voltage V0.

[0022] The current command constraint unit 18 generates a current command I* by imposing a constraint based on a predetermined limit value on the pre-constraint current command I generated by the current command generation unit 17. Specifically, the current value obtained by combining the active and reactive components of the pre-constraint current command I is compared with a predetermined limit value, and if the current value exceeds the limit value, the current command I* is generated by imposing a constraint on the pre-constraint current command I so that the ratio of the active and reactive components in the pre-constraint current command I matches the ratio of the active and reactive components in the post-constraint current command I*. Details of the constraint imposed by the current command constraint unit 18 will be described later.

[0023] 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 by the current sensor 5. Specifically, the current control unit 19 obtains the deviation between the current command I* and a value obtained by dq transforming the current measurement value Iout based on the phase command θ*, and calculates the voltage command V* based on this deviation. Overcurrent in the power conversion device 100 is suppressed by controlling the current using the post-constraint current command I* instead of the pre-constraint current command I.

[0024] 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* determined 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* to generate gate signals for each switching element of the inverter 3 and output these gate signals to the inverter 3. This allows the inverter 3 to be driven to convert DC power to AC power so that the voltage and phase of the AC power output from the inverter 3 to the power grid 2 change in accordance with the voltage command V* and the phase command θ*.

[0025] The suppression power calculation unit 21 calculates the magnitude of the 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 the value as the suppression power Psupp. Specifically, the suppression power Psupp is calculated by calculating the difference between the pre-constraint power according to the pre-constraint current command I calculated by the current command generation unit 17 and the post-constraint power according to the current command I* constrained by the current command constraint unit 18.

[0026] The suppression power Psupp calculated by the suppression power calculation unit 21 is input to the active power command correction unit 14 and is used for correcting the active power command P0 performed by the active power command correction unit 14. Specifically, the active power command correction unit 14 corrects the active power command P0 by calculating a corrected active power command P* based on the suppression power Psupp using the following equation (1): P*=P0-Psup (1)

[0027] As described above, the power conversion device 100 can be operated in a grid-connected manner with the power grid 2 while virtually having inertia. Furthermore, the suppression power Psupp due to the constraint of the current command constraint unit 18 is calculated, and the active power command P0 is corrected based on this suppression power Psupp, after which the angular frequency command generation unit 15 calculates the angular frequency command ω*. As a result, even if the output power of the power conversion device 100 is suppressed due to the constraint of the current command constraint unit 18, the suppression amount can be subtracted from the active power command P0, thereby calculating the angular frequency command ω* and the phase command θ* so as to reduce the output power. As a result, even if a phase jump occurs in the power grid 2, changes in the angular frequency command ω* and the phase command θ* are suppressed, and the power conversion device 100 can continue operating while avoiding loss of synchronism.

[0028] Here, the current command constraint unit 18 can set limit values ​​for each of the active and reactive components of the pre-constraint current command I, and can use these limit values ​​to impose constraints on each of the active and reactive components of the pre-constraint current command I. However, with such a current command constraint method, it is not possible to impose a sufficient constraint on the pre-constraint current command I, and the power output from the power conversion device 100 may become excessive during a phase jump. This point will be described below with reference to FIG. 2.

[0029] 2 is an explanatory diagram of the difference between the current limiting according to the comparative example and the present invention. In Fig. 2, (a) shows, as a comparative example, the state of current limiting when the current command constraining unit 18 sets limit values ​​for each of the active and reactive components of the pre-constraint current command I. On the other hand, (b) shows the state of current limiting when the current command constraining unit 18 sets limit values ​​for the combined current value of the active and reactive components of the pre-constraint current command I, as explained in Fig. 1.

[0030] In the current limiting according to the comparative example, a limit value Ilim is set for each of 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 this limit value Ilim, the current value is limited to the limit value Ilim, thereby imposing a constraint on the pre-constraint current command I. In the comparative example shown in FIG. 2A , the d-axis current Id exceeds the limit value Ilim, and therefore is limited to the limit value Ilim. As a result, the current command constraint unit 18 imposes a constraint on the pre-constraint current command I indicated by the vector 31, thereby generating a current command I* indicated by the vector 32.

[0031] On the other hand, in the current limiting according to the present invention, a limit value Ilim is set for the apparent current value √(Id^2 + Iq^2), which is the sum of the active component (d-axis current Id) and reactive component (q-axis current Iq) of the pre-constraint current command I, as shown by an arc 30 in the figure. If the apparent current value exceeds this limit value Ilim, the d-axis current Id and the q-axis current Iq are each limited so that the apparent current value coincides with the limit value Ilim, thereby imposing a constraint on the pre-constraint current command I. In the example shown in FIG. 2( b), the current command constraint unit 18 imposes a constraint on the pre-constraint current command I represented by vector 31, thereby generating a current command I* represented by vector 33. At this time, the suppression power Psupp calculated by the suppression power calculation unit 21 is represented by the dot product of a current vector 34, which is the difference between vectors 31 and 33, and a measured voltage vector (not shown). The components of the measured voltage vector are a d-axis component and a q-axis component obtained by dq transforming the measured voltage Vout based on the phase command θ*.

[0032] As shown by vector 32 in FIG. 2A, the angle between the d-axis, which indicates the magnitude of the active current, and the angle between the q-axis, which indicates the magnitude of the reactive current, of the post-constraint current command I* of the comparative example are changed from the original vector 31. In other words, it can be seen that the ratio of the active component to the reactive component changes in the current limiting of the comparative example. On the other hand, as shown by vector 33 in FIG. 2B, the angle between the d-axis, which indicates the active current, and the angle between the q-axis, which indicates the reactive current, of the post-constraint current command I* of the present invention are unchanged from the original vector 31. In other words, the current limiting of the present invention can impose a constraint on the pre-constraint current command I while maintaining the ratio of the active component to the reactive component.

[0033] In the current limiting according to the comparative example, as described above, the current command constraint unit 18 applies constraints using the limit value Ilim independently to the active and reactive components to calculate the suppression power Psupp. However, since the apparent current value of the current command I* is √(Ilim^2 + Iq^2), the active and reactive components of the current command I* are each equal to or less than the limit value Ilim, but the apparent current exceeds the limit value Ilim. Therefore, when a phase jump occurs in the power system 2, the active power command P0 can be corrected using the suppression power Psupp, but overcurrent suppression may be insufficient. On the other hand, in the current limiting according to the present invention, as described above, the current command constraint unit 18 can apply constraints so that the apparent current becomes the limit value Ilim while maintaining the ratio of the active and reactive components of the original pre-constraint current command I. Therefore, when a phase jump occurs in the power system 2, the overcurrent can be suppressed and the active power command P0 can be corrected using the suppression power Psupp.

[0034] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0035] (1) The power conversion device 100 is connectable to the power grid 2, converts DC power supplied from a DC power source 1 into AC power with inertia, and outputs the AC power to the power grid 2. The power conversion device 100 includes an inverter control device 10, which includes an active power command corrector 14, an angular frequency command generator 15, a current command generator 17, a current command constraint unit 18, a current controller 19, and a suppression power calculator 21. The active power command corrector 14 calculates a corrected active power command P* by correcting an active power command P0 input from outside. The angular frequency command generator 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* calculated by the active power command corrector 14. The current command generating 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* generated by the first voltage command generating unit 13 and based on the rated voltage V0, the phase command θ* calculated by the phase command generating unit 16 based on the angular frequency command ω* generated by the angular frequency command generating unit 15, and the voltage measurement value Vout by the voltage sensor 6. The current command constraining unit 18 generates a current command I* by imposing a constraint on the pre-constraint current command I generated by the current command generating unit 17 based on a predetermined limit value Ilim. 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* generated by the current command constraining unit 18. The suppression power calculation unit 21 calculates a suppression power Psupp that is suppressed in the AC power output from the power conversion device 100 due to the constraint of the current command constraining unit 18. Here, the current command constraint unit 18 generates the current command I* based on the comparison result between the apparent current value √(Id^2 + Iq^2), which is the sum of the active and reactive components of the pre-constraint current command I, and the limit value Ilim, and the suppression power calculation unit 21 calculates the difference between the pre-constraint power according to the pre-constraint current command I and the post-constraint power according to the current command I*, to obtain 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. As a result, in the power conversion device 100 used as a grid-forming inverter, it is possible to avoid step-out and continue operation even when a phase jump occurs in the power grid 2.

[0036] (2) The current command constraint unit 18 imposes constraints on the pre-constraint current command I so that the ratio of the active component to the reactive component in the pre-constraint current command I matches the ratio of the active component to the reactive component in the current command I*. This makes it possible to sufficiently suppress overcurrent even when a phase jump occurs in the power system 2.

[0037] (3) The active power command corrector 14 calculates the corrected active power command value P* using the above-mentioned formula (1) with the active power command as P0 and the suppressed power as Psupp. In this way, it is possible to accurately calculate the suppressed power Psupp, which is the AC power output by the power conversion device 100 due to the constraint imposed by the current command constraintor 18, and correct the active power command P0.

[0038] The present invention is not limited to the above-described embodiments and modifications, and can be implemented using any components within the scope of the present invention. Each embodiment and modification may be employed alone, or multiple embodiments and modifications may be employed in any combination. In other words, the present invention can achieve the above-described effects by combining the features of each embodiment in any combination.

[0039] The above-described embodiments and modifications are merely examples, and the present invention is not limited to these details as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these details. Other aspects that can be considered within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention.

[0040] DESCRIPTION OF SYMBOLS 1... DC power supply 2... Power system 3... Inverter 4... Filter 5... Current sensor 6... Voltage sensor 10... Inverter control device 11... Power calculation unit 12... Reactive power command unit 13... First voltage command generation unit 14... Active power command correction unit 15... Angular frequency command generation unit 16... Phase command generation unit 17... Current command generation unit 18... Current command constraint unit 19... Current control unit 20... Main circuit control unit 21... Suppression power calculation unit 100... Power conversion device

Claims

1. A power conversion device connectable to an electric power system, converting DC power supplied from a DC power source into AC power with inertia and outputting the AC power to the electric power system, comprising: 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 by correcting an active power command input from outside; 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 pre-constraint 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 by imposing 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 obtains suppression power suppressed in the AC power by the constraint, the current command constraint unit generates the current command based on a comparison result between a current value obtained by combining an active component and a reactive component of the pre-constraint current command and the limit value; the suppression power calculation unit calculates the suppression power by calculating a difference between a pre-constraint power according to the pre-constraint current command and a post-constraint power according to the current command; and the active power command correction unit corrects the active power command based on the suppression power calculated by the suppression power calculation unit.

2. A power conversion device according to claim 1, wherein the current command constraint unit imposes the constraint on the pre-constraint current command so that the ratio of active components to reactive components in the pre-constraint current command matches the ratio of active components to reactive components in the current command.

3. The power conversion device according to claim 1, wherein the active power command correction unit determines the corrected active power command value P* by the following equation (1), where P0 is the active power command and Psupp is the suppressed power: P*=P0−Psupp (1) 4. A device connectable to an electric power system, for controlling an inverter that converts DC power supplied from a DC power source into AC power with inertia and outputs the AC power to the electric power system, comprising: 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 by correcting an active power command input from outside; 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 pre-constraint 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 by imposing 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 obtains suppression power suppressed in the AC power by the constraint, the current command constraint unit generates the current command based on a comparison result between a current value obtained by combining an active component and a reactive component of the pre-constraint current command and the limit value; the suppression power calculation unit calculates the suppression power by calculating a difference between a pre-constraint power according to the pre-constraint current command and a post-constraint power according to the current command; and the active power command correction unit corrects the active power command based on the suppression power calculated by the suppression power calculation unit.

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