Controller and control method for power converter

Abstract

To provide a power converter controller and a control method that can switch between the isolated operation and the grid-connected operation without changing a control method, continues the grid-connected operation even when a momentary voltage drop occurs during the grid-connected operation, and can quickly recover from the voltage drop state at the time of voltage recovery.SOLUTION: A controller of a power converter calculates a frequency target value on the basis of the calculation of multiplying a value based on the deviation of the active power from an active power command value by a coefficient indicating the first drooping characteristic, calculates an internal phase difference angle from the frequency target value, calculates a current target value by using the internal phase difference angle, generates a current command value by limiting the current target value within a predetermined first range, calculates a power correction value on the basis of the deviation of the current command value from the current target value, corrects the frequency target value by the power correction value, generates a limit voltage obtained by limiting the voltage in the AC wiring within a predetermined limit range, and generates a drive signal for the power converter by using the deviation of the current output to the AC wiring with respect to the current command value, and the limit voltage.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a controller and a control method for a power converter. [Background technology]

[0002] In a power supply system in which an AC power supply system and a power storage facility are interconnected, such as a microgrid, a power converter is connected between the AC power supply system and the power storage facility to convert AC power from the AC power supply system into DC power and convert DC power from the power storage facility into AC power.

[0003] If a malfunction occurs in a part of such a power system, a momentary voltage drop may occur in the AC wiring between the AC power system and the energy storage facility. Even if such a momentary voltage drop occurs, it is required to continue grid-connected operation and, when the voltage in the AC power system recovers, to quickly restore the power output from the power converter to the AC wiring from the voltage drop state. For example, the Grid Interconnection Regulations (JEAC9701-2019), an approved standard by the Japan Electrotechnical Standards Committee, stipulates as one of the Fault Ride Through (FRT) requirements that, if the residual voltage is 20% or more, operation must continue for a voltage drop lasting 0.3 seconds without a phase change, and that output must be restored to 80% or more of the level before the voltage drop within 0.1 seconds after voltage recovery in the AC power system.

[0004] On the other hand, Patent Document 1 listed below proposes a power converter used in such a power supply system, which can switch to independent operation by disconnecting a power storage facility from the AC power supply system without changing the control method, and can also switch from independent operation to grid-connected operation by reconnecting the power storage facility to the AC power supply system.

[0005] Specifically, the power converter in Patent Document 1 is controlled by virtual generator model control, which, assuming that a virtual prime mover generator is connected instead of the power converter, estimates the current that the virtual prime mover generator should output, and determines the estimated current as the target current value to be output by the power converter. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2013 / 008413 Summary of the Invention [Problem to be solved by the invention]

[0007] In the control mode of a power converter that simulates a virtual prime mover generator as in Patent Document 1, there is room for improvement in order to continue grid-connected operation when an instantaneous voltage drop occurs in the AC wiring and to quickly recover from the voltage drop state when the voltage in the AC power supply system recovers.

[0008] The present disclosure is intended to solve the above-mentioned problems, and aims to provide a controller and control method for a power converter that can switch between independent operation and grid-connected operation without changing the control method, that can continue grid-connected operation even if a momentary voltage drop occurs during grid-connected operation, and that can quickly recover from a voltage drop state when the voltage in the AC power system recovers. [Means for solving the problem]

[0009] A controller of a power converter according to one aspect of the present disclosure is a controller of a power converter that performs power conversion between an energy storage facility and an AC power supply system, and the controller acquires a voltage and a frequency in AC wiring that connects the AC power supply system and the power converter, and a current output from the power converter to the AC wiring, calculates a frequency target value by a frequency target value calculation process that includes an operation of multiplying a value based on a first deviation that is a deviation of the power converter active power from a predetermined active power command value by a coefficient that indicates the first drooping characteristic, so that a relationship of frequency with respect to power converter active power output by the power converter to the AC wiring has a predetermined first drooping characteristic, calculates an internal phase difference angle by integrating a second deviation that is a deviation of the frequency in the AC wiring from the frequency target value, and ... with respect to a predetermined reactive power command value. calculates an internal electromotive voltage target value by adding a predetermined reference voltage to a value based on a third deviation that is a deviation of the power converter reactive power output by the power converter; calculates a current target value from the internal phase difference angle, the internal electromotive voltage target value, and a voltage in the AC wiring, and generates a current command value by limiting the current target value to within a predetermined first range; calculates a power correction value from a fourth deviation that is a deviation of the current command value from the current target value and the voltage in the AC wiring, and corrects the frequency target value by correcting the first deviation using the power correction value; generates a limit voltage that limits the voltage in the AC wiring to within a predetermined limit range; and generates a voltage command value by adding the limit voltage to a value based on a fifth deviation that is a deviation of the current output to the AC wiring from the current command value.

[0010] A control method for a power converter according to another aspect of the present disclosure is a control method for a power converter that performs power conversion between an electricity storage facility and an AC power supply system, the control method comprising: acquiring a voltage and a frequency in AC wiring that connects the AC power supply system and the power converter, and a current output from the power converter to the AC wiring; calculating a frequency target value by a frequency target value calculation process including an operation of multiplying a value based on a first deviation, which is a deviation of the power converter active power from a predetermined active power command value, by a coefficient indicating the first drooping characteristic so that a relationship of frequency with respect to the power converter active power output by the power converter to the AC wiring has a predetermined first drooping characteristic; calculating an internal phase difference angle by integrating a second deviation, which is a deviation of the frequency in the AC wiring from the frequency target value; a power correction value is calculated from a fourth deviation, which is the deviation of the current command value from the current target value, and the voltage on the AC wiring, and the frequency target value is corrected by correcting the first deviation using the power correction value; a limit voltage is generated by limiting the voltage on the AC wiring to a predetermined second range; and a drive signal for the power converter is generated by adding the limit voltage to a value based on a fifth deviation, which is the deviation of the current output to the AC wiring from the current command value, to generate a voltage command value. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to switch between independent operation and grid-connected operation without changing the control method, and even if a momentary voltage drop occurs during grid-connected operation, it is possible to continue grid-connected operation and quickly recover from the voltage drop state when the voltage in the AC power system recovers. [Brief explanation of the drawings]

[0012] [Figure 1]FIG. 1 is a block diagram showing a schematic configuration of a power supply system including a controller for a power converter according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a block diagram showing the configuration of a frequency target value calculation unit in the controller shown in FIG. [Figure 3] FIG. 3 is a block diagram showing the configuration of an internal phase difference angle calculation unit in the controller shown in FIG. [Figure 4] FIG. 4 is a block diagram showing the configuration of an internal electromotive voltage target value calculation unit in the controller shown in FIG. [Figure 5] FIG. 5 is a block diagram showing the configuration of a current command value calculation unit in the controller shown in FIG. [Figure 6] FIG. 6 is a block diagram showing the configuration of a drive signal generating unit in the controller shown in FIG. [Figure 7] FIG. 7 is a graph showing the change in output power over time in the first simulation. [Figure 8] FIG. 8 is a graph showing the change in frequency over time in the first simulation. [Figure 9] FIG. 9 is a graph showing the change in the internal phase difference angle over time in the first simulation. [Figure 10] FIG. 10 is a graph showing the time variation of the d-axis current command value and the d-axis current in the example in the first simulation. [Figure 11] FIG. 11 is a graph showing the time variation of the d-axis current command value and the d-axis current of the comparative example in the first simulation. [Figure 12] FIG. 12 is a graph showing the change over time in the output current from the power converter in the first simulation. [Figure 13] FIG. 13 is a graph showing the time variation of AC voltage and frequency in the AC wiring based on the results of the second simulation for the example. [Figure 14] FIG. 14 is a graph showing the time changes of AC voltage and frequency in the AC wiring, based on the results of the second simulation for Comparative Example 1. [Figure 15]FIG. 15 is a graph showing the time changes of AC voltage and frequency in the AC wiring, based on the results of the second simulation for Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following, elements having the same or the same functions are denoted by the same reference numerals throughout the drawings, and redundant description thereof will be omitted.

[0014] [System Configuration] Fig. 1 is a block diagram showing a schematic configuration of a power supply system including a controller for a power converter according to an embodiment of the present disclosure. As shown in Fig. 1, the power supply system 1 according to the present embodiment includes an AC power supply system 2 such as a commercial power supply system, a power storage facility 3, and a power converter 4. The AC power supply system 2 and the power converter 4 are connected by AC wiring 5. The power storage facility 3 and the power converter 4 are connected by DC wiring 6. In the present embodiment, a case is illustrated in which the AC power supply system 2 is a three-phase AC system.

[0015] The power storage facility 3 includes a secondary battery, an electric double layer capacitor, a fuel cell, etc. The power converter 4 includes a plurality of power semiconductor elements, and by switching the power semiconductor elements on / off at high speed, converts DC power from the power storage facility 3 into AC power and outputs it to the AC wiring 5, or converts AC power from the AC power supply system 2 into DC power and stores it in the power storage facility 3. A controller 10 is connected to the power converter 4 for controlling the on / off of the power semiconductor elements.

[0016] The power supply system 1 includes a voltage detector 7 and a current detector 8. The voltage detector 7 detects the voltage in the AC wiring 5. The current detector 8 detects the current output from the power converter 4 to the AC wiring 5. For example, the voltage detector 7 is a transformer known as a PT (Potential Transformer), and the current detector 8 is a current transformer known as a CT (Current Transformer). The detected voltage and current are input to a controller 10.

[0017] A state detector 9 is connected to the power storage equipment 3 to detect the state of the power storage equipment 3, such as voltage, current, temperature, and pressure. The output of the state detector 9 is input to a state monitor 11. The state monitor 11 monitors the state of the power storage equipment 3 and also calculates the SOC (State Of Charge) that indicates the charging rate of the power storage equipment 3. The state monitor 11 is connected to the controller 10, and when it detects an abnormal state of the power storage equipment 3, it transmits an abnormality signal to the controller 10. When the controller 10 receives the abnormality signal from the state monitor 11, it stops the operation of the power converter 4.

[0018] The controller 10 includes a computer such as a microcontroller, a personal computer, etc. For example, the controller 10 includes a CPU, a main memory such as a RAM, a communication interface, etc.

[0019] It should be noted that the functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuitry. In this specification, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where hardware is a processor, which is considered a type of circuit, the circuit, unit, means, or section is a combination of hardware and software, and software is used to configure the hardware or processor.

[0020] The controller 10 includes control blocks, namely, a voltage calculation unit 71, a current calculation unit 72, a power calculation unit 73, a frequency target value calculation unit 80, an internal phase difference angle calculation unit 82, an internal electromotive voltage target value calculation unit 83, a current command value calculation unit 84, and a drive signal generation unit 85. As described above, each of these control blocks is considered to be a processing circuit or a circuit. By executing processing in each control block, the controller 10 performs virtual generator model control, which simulates the power that a virtual generator would output to the AC wiring 5 if the virtual generator were connected to the AC wiring 5 instead of the power converter 4, and controls the power that the power converter 4 outputs to the AC wiring 5. Each control block will be described in detail below.

[0021] [Voltage calculation section] The voltage calculation unit 71 calculates the instantaneous voltage v of each phase detected by the voltage detector 7. a ,v b ,v c The AC voltage Vac is calculated using the following formula:

[0022]

number

[0023] Furthermore, the voltage calculation unit 71 calculates the frequency fac and phase φ in the AC wiring 5 by a known PLL (Phase Lock Loop) calculation. ac In addition, the voltage calculation unit 71 calculates the instantaneous voltage v of each phase. a ,v b ,v c and phase φ ac From the above, the d-axis voltage Vd and the q-axis voltage Vq, which are voltages on each coordinate axis of the rotating coordinate system of the AC voltage, i.e., the dq coordinate system, are calculated by the following equations. a ,v b ,v c The voltages Vd, Vq and frequency fac in the AC wiring 5 are obtained from the

[0024]

number

[0025] [Current calculation section] The current calculation unit 72 calculates the instantaneous current i of each phase detected by the current detector 8. a ,i b ,i c Then, the AC current Iac output from the power converter 4 to the AC wiring 5 is calculated using the following equation.

[0026]

number

[0027] The current calculation unit 72 calculates the instantaneous current i of each phase detected by the current detector 8. a ,i b ,i cand the phase φac calculated by the voltage calculation unit 71, the d-axis current Id and the q-axis current Iq, which are currents on each coordinate axis of the rotating coordinate system of the AC current, are calculated by the following equation. a ,i b ,i c The currents Id and Iq in the AC wiring 5 are obtained from the

[0028]

number

[0029] [Power calculation section] The power calculation unit 73 calculates the corresponding power converter active power Pac and power converter reactive power Qac using the following equations from the voltages Vd, Vq calculated by the voltage calculation unit 71 and the currents Id, Iq calculated by the current calculation unit 72. Note that hereinafter, the power converter active power Pac and power converter reactive power Qac may also be simply referred to as active power Pac and reactive power Qac.

[0030]

number

[0031] In the present embodiment, as described above, an example has been described in which the active power Pac and the reactive power Qac are calculated from the voltages Vd, Vq and the currents Id, Iq obtained from the voltage detector 7 and the current detector 8, respectively. However, this is not limiting. For example, instead of this, the power supply system 1 may include a power detector that detects the active power Pac and the reactive power Qac in the AC wiring 5. That is, the controller 10 may obtain the active power Pac and the reactive power Qac from an external source. For example, the power detector may be configured with a known wattmeter. Note that, hereinafter, the voltages Vd, Vq in the AC wiring 5 obtained by the voltage calculation unit 71 may be referred to as system voltages, and the currents Id, Iq output from the power converter 4 to the AC wiring 5 obtained by the current calculation unit 72 may be referred to as system currents.

[0032] [Frequency target value calculation section] Fig. 2 is a block diagram showing the configuration of a frequency target value calculation unit in the controller shown in Fig. 1. As shown in Fig. 2, a frequency target value calculation unit 80 performs a frequency target value calculation process. In the frequency target value calculation process, the frequency target value calculation unit 80 calculates a frequency target value fac_ref so that the relationship between the active power Pac and the frequency fac has a predetermined first drooping characteristic. Note that the first drooping characteristic means a characteristic in which the frequency fac decreases as the active power Pac increases, and the frequency fac increases as the active power Pac decreases.

[0033] Specifically, the frequency target value calculation unit 80 subtracts the power correction value Pac_cmp described later from the first deviation D1 = Pac_cmd - Pac, which is the deviation of the active power Pac from a predetermined active power command value Pac_cmd, and multiplies the result by a droop coefficient Dr_p, which indicates the first drooping characteristic, to calculate a value.

[0034] In this embodiment, the frequency target value calculation unit 80 inputs the calculated value to a first-order lag calculation unit 86, which performs first-order lag calculation. As a result, the moment of inertia generated in the actual generator is simulated in the virtual generator model. Note that the moment of inertia generated in the generator may be simulated by calculation processing other than first-order lag calculation.

[0035] Furthermore, the value output from the first-order lag calculation unit 86 is input to an upper and lower limiter 87. The upper and lower limiter 87 limits the value output from the first-order lag calculation unit 86 to a value between a predetermined upper limit and a predetermined lower limit, and outputs the frequency reference value Δfac_ref. Note that the frequency reference value Δfac_ref may be calculated without providing the first-order lag calculation unit 86, the upper and lower limiter 87, or both, in the frequency target value calculation unit 80.

[0036] The frequency target value calculation unit 80 adds a predetermined frequency command value fac_cmd to the frequency reference value Δfac_ref output from the upper / lower limiter 87 to calculate the frequency target value fac_ref.

[0037] When the power consumption of the load connected to the AC wiring 5 increases and the frequency fac in the AC wiring 5 decreases, the phase lead of the AC voltage in the AC wiring 5 increases relative to the AC voltage output by the power converter 4. In response to this, the controller 10 decreases the frequency target value fac_ref to offset the phase lead. As a result, the active power Pac output by the power converter 4 increases.

[0038] Conversely, when the power consumption of the load connected to the AC wiring 5 decreases and the frequency fac in the AC wiring 5 increases, the lag phase of the AC voltage in the AC wiring 5 increases relative to the AC voltage output by the power converter 4. In response to this, the controller 10 increases the frequency target value fac_ref to offset this lag phase. As a result, the active power Pac output by the power converter 4 decreases.

[0039] [Internal phase difference angle calculation section] Fig. 3 is a block diagram showing the configuration of an internal phase difference angle calculation unit in the controller shown in Fig. 1. As shown in Fig. 3, an internal phase difference angle calculation unit 82 calculates a second deviation D2=fac_ref-fac, which is the deviation of the frequency fac in the AC wiring 5 from the frequency target value fac_ref calculated by the frequency target value calculation unit 80, and inputs this to an integrator 88 for integration. The integrator 88 calculates an internal phase difference angle θ in the virtual generator by integrating the rotational speed of the virtual generator obtained by multiplying the second deviation D2 by a coefficient Kw for unit conversion.

[0040] [Internal electromotive force target value calculation section] Fig. 4 is a block diagram showing the configuration of an internal electromotive voltage target value calculation unit in the controller shown in Fig. 1. As shown in Fig. 4, an internal electromotive voltage target value calculation unit 83 calculates an AC voltage target value Vac_ref based on the reactive power Qac calculated by the power calculation unit 73. Here, the internal electromotive voltage target value calculation unit 83 calculates the AC voltage target value Vac_ref so that the relationship between the reactive power Qac and the AC voltage Vac has a predetermined second drooping characteristic. Note that the second drooping characteristic means a characteristic such that as the reactive power Qac increases, the AC voltage Vac decreases, and as the reactive power Qac decreases, the AC voltage Vac increases.

[0041] Specifically, the internal electromotive force target value calculation unit 83 multiplies the third deviation D3=Qac_cmd-Qac, which is the deviation of the reactive power Qac from a predetermined reactive power command value Qac_cmd, by a droop coefficient Dr_q according to the second drooping characteristic, and adds the AC voltage command value Vac_cmd, which is a predetermined reference voltage, to the multiplied value to calculate the AC voltage target value Vac_ref.

[0042] The internal electromotive force target value calculation unit 83 generates the internal electromotive force target value Ef_ref by performing a proportional-integral calculation on the deviation of the AC voltage Vac from the AC voltage target value Vac_ref. The transfer function in the proportional-integral calculation is expressed as Kp+Ki / s, for example, where Kp is the proportional gain and Ki is the integral gain. In this way, by providing the second drooping characteristic to the third deviation D3, which is the deviation of the reactive power Qac from the reactive power command value Qac_cmd, it is possible to easily realize a control mode simulating automatic voltage regulation (AVR) control using the reactive power Qac in the virtual generator.

[0043] The internal electromotive force target value calculation unit 83 may perform a first-order lag calculation on the result of the proportional-plus-integral calculation of the deviation of the AC voltage Vac from the AC voltage target value Vac_ref, similarly to the frequency target value calculation unit 80. The internal electromotive force target value calculation unit 83 may also apply upper and lower limiters to the result of the proportional-plus-integral calculation of the deviation of the AC voltage Vac from the AC voltage target value Vac_ref or the result of the first-order lag calculation.

[0044] [Current command value calculation section] Fig. 5 is a block diagram showing the configuration of a current command value calculation unit in the controller shown in Fig. 1. As shown in Fig. 5, in a current command value calculation unit 84, the internal phase difference angle θ calculated by an internal phase difference angle calculation unit 82, the internal electromotive voltage target value Ef_ref calculated by an internal electromotive voltage target value calculation unit 83, and the d-axis voltage Vd and q-axis voltage Vq calculated by the voltage calculation unit 71 are input to a function calculation unit 89. The function calculation unit 89 performs the calculation shown in the following equation to calculate current target values ​​Id_ref and Iq_ref.

[0045]

number

[0046] The current target values ​​Id_ref and Iq_ref calculated by the above formula are the current values ​​that flow through the overall impedance r+jx when it is assumed that the overall impedance r+jx is connected between a power supply that outputs the same voltage as the AC voltage Vac in the AC wiring 5 and a power supply that outputs the same voltage as the internal electromotive force target value Ef_ref.

[0047] By the way, the total impedance r+jx is the internal impedance r of the storage facility 3. s +jx s and the external impedance r between the storage facility 3 and the AC power supply system 2. l +jx l However, the internal impedance r s +jx s is almost equal to zero, and the total impedance r+jx is the external impedance r between the storage facility 3 and the AC wiring 5 l +jx l However, as described above, in this embodiment, when calculating the current target values ​​Id_ref and Iq_ref, the internal impedance r s +jx s and the external impedance r between the storage facility 3 and the AC power supply system 2. l +jx lThe total impedance r+jx, which is the sum of

[0048] In particular, the internal impedance r of the storage facility 3 s +jx s By virtually increasing the internal impedance of the energy storage facility 3, the impedance of the power converter 4 increases, the total impedance r+jx is found, and the current target values ​​Id_ref and Iq_ref are calculated using this virtual impedance, thereby enabling stable operation. This is because when multiple power converters 4 are operated in parallel, even a slight voltage difference between the power converters 4 can cause a large imbalance in the output balance, since the impedance of the power converters 4 is low. By virtually increasing the internal impedance of the energy storage facility 3, the impedance of the power converter 4 increases, and it is possible to prevent the output balance from becoming unstable due to the voltage difference. For example, if the internal impedance r s +jx s In reality, this is almost zero, but if the resistance component of the total impedance is set to 0.1 PU and the reactance component to 0.4 PU, considerable stabilization can be achieved.

[0049] That is, the current command value calculation unit 84 assumes that a virtual generator is connected to the AC wiring 5 instead of the power converter 4, and estimates a current value to be output to the AC wiring 5 when the virtual generator generates the internal electromotive voltage calculated by the internal electromotive voltage target value calculation unit 83 and the internal phase difference angle calculation unit 82. This prevents the apparent impedance of the power converter 4 from increasing and the system from becoming unstable during interconnected operation with the AC power supply system 2 or during parallel operation of power converters 4.

[0050] Furthermore, the current command value calculation unit 84 generates the current command values ​​Id_cmd, Iq_cmd by limiting the current target values ​​Id_ref, Iq_ref to within a predetermined first range. That is, the current target values ​​Id_ref, Iq_ref, which are outputs of the function calculation unit 89, are input to limiters 90, 91, respectively.

[0051] When the d-axis current target value Id_ref is equal to or greater than the upper limit value of the first range, the limiter 90 outputs the upper limit value as the d-axis current command value Id_cmd. When the d-axis current target value Id_ref is equal to or less than the lower limit value of the first range, the limiter 90 outputs the lower limit value as the d-axis current command value Id_cmd. When the d-axis current target value Id_ref is within the first range, the limiter 90 outputs the d-axis current target value Id_ref as the d-axis current command value Id_cmd. The limiter 91 performs the same limiting process as the limiter 90 on the q-axis current target value Iq_ref. Note that the upper and lower limit values ​​set by the limiters 90 and 91 may be different values ​​or may be the same value. The current command values ​​Id_cmd and Iq_cmd output by the limiters 90 and 91 are input to the drive signal generating unit 85.

[0052] Furthermore, the current command value calculation unit 84 calculates a power correction value Pac_cmp from the system voltages Vd and Vq and the current deviations Id_cmp and Iq_cmp obtained as fourth deviations D4d and D4q, which are the deviations of the current command values ​​Id_cmd and I_cmd from the current target values ​​Id_ref and Iq_ref.

[0053] More specifically, the current command value calculation unit 84 generates a d-axis current deviation Id_cmp=D4d=Id_ref−Id_cmd by subtracting the d-axis current command value Id_cmd, which is the output of limiter 90, from the d-axis current target value Id_ref, which is the input to limiter 90. Similarly, the current command value calculation unit 84 generates a q-axis current deviation Iq_cmp=D4q=Iq_ref−Iq_cmd by subtracting the q-axis current command value Iq_cmd, which is the output of limiter 91, from the q-axis current target value Iq_ref, which is the input to limiter 91. The current deviations Id_cmp, Iq_cmp and system voltages Vd, Vq are input to a power correction value calculation unit 92.

[0054] The power correction value calculation unit 92 calculates a power correction value Pac_cmp by adding the value obtained by multiplying the d-axis voltage Vd by the d-axis current deviation Id_cmp and the value obtained by multiplying the q-axis voltage Vq by the q-axis current deviation Iq_cmp. That is, the power correction value Pac_cmp is expressed as Pac_cmp=Vd*Id_cmp+Vq*Iq_cmp.

[0055] The current command value calculation unit 84 limits the current command values ​​Id_cmd, Iq_cmd to within a first range relative to the current target values ​​Id_ref, Iq_ref, which are theoretical current outputs calculated from the virtual generator model, so as not to trip the power converter 4. The power correction value Pac_cmp corresponds to the power that could not be output due to the above-mentioned constraints of the power converter 4, relative to the theoretical current output calculated from the virtual generator model.

[0056] As described above, the power correction value Pac_cmp is input to the frequency target value calculation unit 80. As shown in Fig. 2, the frequency target value calculation unit 80 subtracts the power correction value Pac_cmp from the first deviation D1, which is the deviation of the active power Pac from a predetermined active power command value Pac_cmd. As a result, the frequency target value calculation unit 80 corrects the first deviation D1 = Pac_cmd - Pac using the power correction value Pac_cmp, thereby correcting the frequency target value fac_ref.

[0057] In this way, by limiting the current command values ​​Id_cmd, Iq_cmd to the theoretical current output calculated from the virtual generator model, even if the power converter 4 does not output power according to the virtual generator model, the frequency target value calculation unit 80 calculates the frequency target value fac_ref on the assumption that the power converter 4 outputs power according to the virtual generator model. Therefore, it is possible to prevent the frequency target value fac_ref from becoming excessive due to the current command values ​​Id_cmd, Iq_cmd being limited.

[0058] [Drive signal generation section] Fig. 6 is a block diagram showing the configuration of a drive signal generation unit in the controller shown in Fig. 1. As shown in Fig. 6, the currents Id and Iq, the phase φac, and the current command values ​​Id_cmd and Iq_cmd in the AC wiring 5 are input to the drive signal generation unit 85. The drive signal generation unit 85 generates a drive signal So that causes the grid currents Id and Iq to become the current command values ​​Id_cmd and Iq_cmd, and outputs the drive signal So to the power converter 4.

[0059] Specifically, the drive signal generator 85 performs proportional-plus-integral operations on fifth deviations D5d=Id_cmd-Id and D5q=Iq_cmd-Iq, which are deviations of the grid currents Id and Iq from the current command values ​​Id_cmd and Iq_cmd. Furthermore, the drive signal generator 85 generates a limit voltage that limits the grid voltage within a predetermined limit range. The limit voltage is a voltage that allows at least the d-axis voltage Vd or the q-axis voltage Vq to vary within the predetermined limit range.

[0060] In this embodiment, a d-axis voltage Vd is input to the drive signal generation unit 85. The d-axis voltage Vd input to the drive signal generation unit 85 is then input to a limiter 93. The limiter 93 outputs a d-axis limit voltage Vdl that limits the d-axis voltage Vd to a predetermined second range. In this embodiment, the magnitude of the d-axis limit voltage Vdl is between 0 and 1, where 1 is the rated voltage of the d-axis voltage Vd. The drive signal generation unit 85 adds the d-axis limit voltage Vdl to the result of the proportional-plus-integral calculation for the fifth deviation D5d regarding the d-axis current Id. In other words, when the magnitude of the d-axis voltage Vd is equal to or less than the rated voltage, the d-axis limit voltage Vdl added to the result of the proportional-plus-integral calculation for the fifth deviation D5d regarding the d-axis current Id can change depending on the d-axis voltage Vd at that time.

[0061] In this embodiment, the q-axis limit voltage is not added to the result of the proportional-plus-integral calculation of the fifth deviation D5q related to the q-axis current Iq, which is equivalent to adding a fixed value of 0 as a conventional q-axis voltage addition term.

[0062] Furthermore, the drive signal generation unit 85 subtracts an interference component from the result of a proportional-plus-integral calculation on the fifth deviations D5d, D5q related to the current in the AC wiring 5. Interference occurs between the d-axis current Id and the q-axis current Iq in the virtual generator in that a change in the d-axis current Id causes a change in the q-axis current Iq, and a change in the q-axis current Iq causes a change in the d-axis current Id. The drive signal generation unit 85 performs a deinterference process to remove such interference components from the voltage command values ​​Vd_cmd, Vq_cmd that are based on the current command values ​​Id_cmd, Iq_cmd.

[0063] Specifically, the drive signal generator 85 subtracts the q-axis interference component XqIq obtained by multiplying the q-axis current Iq by a predetermined gain Xq from the result of the proportional-plus-integral calculation of the fifth deviation D5d related to the d-axis current Id. Similarly, the drive signal generator 85 adds the d-axis interference component XdId obtained by multiplying the d-axis current Id by a predetermined gain Xd to the result of the proportional-plus-integral calculation of the fifth deviation D5q related to the q-axis current Iq.

[0064] From the above, the drive signal generation unit 85 calculates the voltage command values ​​Vd_cmd and Vq_cmd from the current command values ​​Id_cmd and Iq_cmd using the following equations: where Kd, Kq, Xd, and Xq represent predetermined gains, and Tid and Tiq represent predetermined time constants.

[0065]

number

[0066] The drive signal generating unit 85 calculates the instantaneous voltage v of each phase of the AC wiring 5, which is a three-phase AC, from the voltage command values ​​Vd_cmd and Vq_cmd. a ,v b ,v c The target value of v a_ref ,v b_ref ,v c_ref Specifically, the voltage command values ​​Vd_cmd and Vq_cmd are input to a dq-abc conversion unit 94. The dq-abc conversion unit 94 calculates the target value v of the instantaneous voltage of each phase of the AC wiring 5 from the voltage command values ​​Vd_cmd and Vq_cmd based on the following equation: a_ref ,v b_ref ,vc_ref Calculate.

[0067]

number

[0068] The calculated target value of the instantaneous voltage, v a_ref ,v b_ref ,v c_ref is input to the signal converter 95. The signal converter 95 converts the target value v of the instantaneous voltage a_ref ,v b_ref ,v c_ref The drive signal So for switching the power converter 4 is generated based on the drive signal So. For example, the drive signal So is a PWM control signal. The drive signal generation unit 85 outputs the drive signal So generated in this manner. The drive signal So is input to the power converter 4, and the output voltage to the AC wiring 5 is controlled based on the drive signal So.

[0069] [effect] According to this embodiment, in order to simulate the power that a virtual generator would output to the AC wiring 5 if it were connected to the AC wiring 5 instead of the power converter 4, the internal electromotive force target value Ef_ref and the internal phase difference angle θ of the virtual generator are calculated, and the current output from the virtual generator is estimated from the internal electromotive force target value Ef_ref, the internal phase difference angle θ, and the voltages Vd and Vq in the AC wiring 5. If a system fault or the like occurs in the power supply system 1 and an instantaneous voltage drop occurs, the estimated value of this current becomes excessively large. Therefore, if the power converter 4 is driven using the estimated current value as a current command value as is, the power converter 4 may trip or be damaged due to an overcurrent. As a result, it becomes impossible to continue operation during an instantaneous voltage drop and to quickly recover from the voltage drop state when the voltage in the AC power supply system 2 recovers.

[0070] Therefore, in this embodiment, the power converter 4 is driven using current command values ​​Id_cmd, Iq_cmd obtained by limiting the current target values ​​Id_ref, Iq_ref estimated as the currents output from the virtual generators to within a first range using limiters 90, 91. This makes it possible to suppress overcurrents during momentary voltage drops. Furthermore, since the d-axis limit voltage Vdl, which limits the d-axis voltage Vd to within a second range, is added to the feedback loop of the d-axis current command value Id_cmd, it is possible to improve the responsiveness of current control during momentary voltage drops and prevent tripping due to overcurrent.

[0071] As described above, in this embodiment, the estimated value of the current output from the virtual generator is limited by the limiters 90, 91, and therefore the power output from the power converter 4 is also limited. In this embodiment, the frequency target value fac_ref in the virtual generator is estimated from the first deviation D1, which is the deviation of the active power Pac from a predetermined active power command value Pac_cmd, and the internal phase difference angle θ is calculated from the frequency target value fac_ref.

[0072] Therefore, if the active power Pac is limited during an instantaneous voltage drop, the first deviation D1 increases, and the frequency target value fac_ref also increases. As a result, during an instantaneous voltage drop, the internal phase difference angle θ becomes larger than the theoretical value, causing large power fluctuations in the power supply system 1 when the system recovers from the voltage drop state. This may prevent the AC power supply system 2 from recovering from the voltage drop state quickly.

[0073] Therefore, in this embodiment, a power correction value Pac_cmp is calculated from fourth deviations D4d=Id_cmp, D4q=Iq_cmp, which are deviations of the current command values ​​Id_cmd, I_cmd from the current target values ​​Id_ref, Iq_ref, and the voltages Vd, Vq in the AC wiring 5. The calculated power correction value Pac_cmp is subtracted from the first deviation D1 used to calculate the frequency target value fac_ref. This suppresses an increase in the frequency target value fac_ref that accompanies a decrease in power output due to limitation by the limiters 90, 91, and also suppresses an increase in the internal phase difference angle θ that occurs during a momentary voltage drop. This suppresses power oscillations when the voltage in the AC power supply system 2 recovers, allowing the power converter 4 to quickly recover from a voltage drop state.

[0074] In conventional virtual generator model control, in order to enable switching between grid-connected operation and stand-alone operation without changing the control method, current feedback is performed using PI control in the drive signal generation unit, and the voltage command values ​​Vd_cmd and Vq_cmd are calculated by adding the d-axis voltage Vd=1 and the q-axis voltage Vq=0 as additive terms to the grid voltage. While this makes it possible to switch between grid-connected operation and stand-alone operation without changing the control method, there is a risk that tracking will be delayed if a momentary voltage drop occurs, resulting in a transient excessive current flow.

[0075] In contrast to this, in the present embodiment, the drive signal generation unit 85 adds a voltage obtained by limiting the voltage in the AC wiring 5 as an additive term to the grid voltage. That is, the drive signal generation unit 85 adds the d-axis limit voltage Vdl to the result of a proportional-plus-integral calculation on the fifth deviation D5d related to the d-axis current, D5d=Id_cmd-Id. This makes it possible to switch between grid-connected operation and stand-alone operation without changing the control method, as with conventional virtual generator model control, and also improves the responsiveness of current control when a momentary voltage drop occurs.

[0076] Another method for realizing continuous operation during a momentary voltage drop and rapid recovery from the voltage drop state is to detect the occurrence of a momentary voltage drop and temporarily switch the control method. However, this requires additional equipment to detect the occurrence of a momentary voltage drop. On the other hand, according to this embodiment, there is no need to change the control method even when a momentary voltage drop occurs. Therefore, since there is no need to detect the occurrence of a momentary voltage drop, it is possible to realize continuous operation during a momentary voltage drop and rapid recovery from the voltage drop state when the voltage in the AC power system recovers without requiring additional equipment in the power supply system 1.

[0077] [Simulation Results] (1) Simulation of momentary voltage drop Below, as a first simulation, the results of a simulation in which an instantaneous voltage drop occurs in the power supply system 1 of the above embodiment are shown. In the first simulation, as an example, a simulation was carried out on the behavior of the power supply system 1 shown in FIG. 1 in the event of an instantaneous voltage drop of 20% residual voltage and lasting for 0.3 seconds in the AC power supply system 2, and the results were compared with a comparative example. In the first simulation, an instantaneous voltage drop occurs 5 seconds after the start of the simulation, and the voltage in the AC power supply system 2 recovers after a further 0.3 seconds.

[0078] The comparative example differs in that correction by the power correction value Pac_cmp is not performed in the power supply system 1 shown in Fig. 1, and that addition of the d-axis limit voltage Vdl, which is a limit voltage addition term, and subtraction of the interference components XqIq, XdId are not performed in the current feedback control, but PI control is performed on fifth deviations D5d, D5q related to the current in the AC wiring 5. Note that, even in the comparative example, current limitation by limiters 90, 91 in the current command value calculation unit 84 shown in Fig. 5 is performed.

[0079] 7 is a graph showing the change in output power over time in the first simulation. According to the graph of output power Pc in the comparative example, after the voltage in the AC power supply system 2 recovers 5.3 seconds after the start of the simulation, the output power Pc of the power converter swings significantly into the negative region. This is thought to be because, as can be seen from the simulation results of the internal phase difference angle described below, the increase in the internal phase difference angle that occurred during the instantaneous voltage drop became excessive, causing a loss of synchronization. For this reason, for example, one of the FRT requirements defined in the Grid Interconnection Regulations (JEAC9701), which requires that the output in the AC power supply system recover to 80% or more of the output before the voltage drop within 0.1 seconds after the voltage recovery, cannot be satisfied.

[0080] On the other hand, according to the graph of output power Pe in the example, no step-out phenomenon occurs, and power fluctuations after voltage recovery are kept low. As a result, the FRT requirements are met. This is thought to be due to the fact that power compensation control using the power correction value Pac_cmp suppresses increases in the frequency target value fac_ref and the internal phase difference angle θ during momentary voltage drops.

[0081] FIG. 8 is a graph showing the change in frequency over time in the first simulation. The frequency in the graph in FIG. 8 is a value corresponding to the frequency fac obtained by the voltage calculation unit 71. According to the graph of the frequency frc in the comparative example, when there is an instantaneous voltage drop, the output power is suppressed by limiting the current command value, and the frequency frc increases. Furthermore, after the voltage recovers, a step-out phenomenon occurs, resulting in a further increase in the frequency frc.

[0082] On the other hand, the graph of frequency fre in the example shows that the increase in frequency fre is suppressed by power compensation control using the power correction value Pac_cmp. Even after voltage recovery, no step-out phenomenon occurs, and although frequency fre decreases temporarily, it then returns to a value close to the original frequency in a short period of time.

[0083] FIG. 9 is a graph showing the change in the internal phase difference angle over time in the first simulation. Comparing the graph of the internal phase difference angle θc in the comparative example with the graph of the internal phase difference angle θe in the example, the internal phase difference angle θc in the comparative example changes more significantly during an instantaneous voltage drop. Furthermore, in the comparative example, the internal phase difference angle θc changes instantaneously from a positive value to a negative value after the voltage recovers. This indicates that because the change in the internal phase difference angle θc in the comparative example during an instantaneous voltage drop is steep, the phase difference cannot be restored when the voltage recovers, leading to a loss of synchronization.

[0084] On the other hand, according to the graph of the internal phase difference angle θe in the example, after the voltage recovery, the internal phase difference angle θe returns to its original state. This is thought to be due to the effect of power compensation control using the power correction value Pac_cmp.

[0085] Fig. 10 is a graph showing the time variation of the d-axis current command value and the d-axis current of the example in the first simulation. Fig. 11 is a graph showing the time variation of the d-axis current command value and the d-axis current of the comparative example in the first simulation. Fig. 12 is a graph showing the time variation of the output current from the power converter in the first simulation. The output current in the graph of Fig. 12 is a value equivalent to the AC current Iac output from the power converter 4 to the AC wiring 5, obtained by the above formula (3).

[0086] According to the graph of the comparative example shown in FIG. 11, the d-axis current Idc cannot follow the d-axis current command value Idcc during an instantaneous voltage drop. That is, even though the d-axis current command value Idcc is limited by the limiter, the d-axis current Idc exceeds the d-axis current command value Idcc. In contrast, according to the graph of the embodiment shown in FIG. 10, the d-axis current Ide can almost follow the d-axis current command value Idce. This is thought to be due to the addition of the d-axis limit voltage Vdl, which is a limit voltage addition term, to the current feedback loop.

[0087] Regarding the current command value shown in Fig. 12, the graph of the current command value Ic in the comparative example shows that immediately after an instantaneous voltage drop, the current command value Ic exceeds 2.5 times the rated current. Therefore, at this point, there is a possibility that the power converter may trip due to an overcurrent. On the other hand, the graph of the current command value Ie in the example shows that the current command value Ie is appropriately limited even during an instantaneous voltage drop.

[0088] (2) Simulation of transition from grid-connected operation to isolated operation Below, as a second simulation, the results of a simulation in which switching from grid-connected operation to independent operation is performed in the power supply system 1 of the above embodiment are shown. In the second simulation, an example and a comparative example (hereinafter referred to as comparative example 1) similar to those in the first simulation were used to verify whether the switching from grid-connected operation to independent operation achieved in comparative example 1 can be achieved in the example as well. Furthermore, a simulation in which switching from grid-connected operation to independent operation is performed in the power supply system 1 of the above embodiment was also performed using comparative example 2, in which the voltage addition term added to the current feedback loop is not limited. In both examples, the simulation was performed in which switching from grid-connected operation to independent operation was performed 5 seconds after the start of the simulation.

[0089] Fig. 13 is a graph showing the time changes of AC voltage and frequency in AC wiring based on the results of the second simulation for the example. Fig. 14 is a graph showing the time changes of AC voltage and frequency in AC wiring based on the results of the second simulation for the comparative example 1. The AC voltage in these graphs is a value corresponding to the AC voltage Vac obtained by the above formula (1). The frequency in these graphs is a value corresponding to the frequency fac obtained by the voltage calculation unit 71.

[0090] According to the graph of AC voltage Vc1 and frequency fc1 of Comparative Example 1 shown in FIG. 14, when switching from grid-connected operation to isolated operation, the AC voltage Vc1 and frequency fc1 fluctuate slightly due to fluctuations in the power output from the power converter, etc. This is a response expected in virtual generator model control. The graph of AC voltage Ve and frequency fe of the example shown in FIG. 13 also shows results similar to those of the graph of Comparative Example 1 shown in FIG. 14. Therefore, it is believed that the power supply system 1 of the example can also switch from grid-connected operation to isolated operation without any problems, just like Comparative Example 1.

[0091] 15 is a graph showing the time changes in AC voltage and frequency in the AC wiring based on the results of the second simulation for Comparative Example 2. In Comparative Example 2, after parallel-off between the AC power supply system 2 and the power converter 4 occurs 5 seconds after the start of the simulation, both the AC voltage Vc2 and the frequency fc2 become abnormal values, indicating that autonomous operation is not possible.

[0092] (3) Summary of the simulation From the results of the above two simulations, it can be seen that the control mode of the power supply system 1 in the above embodiment makes it possible to switch between independent operation and grid-connected operation without changing the control method, and that even if a momentary voltage drop occurs during grid-connected operation, grid-connected operation can be continued and a quick recovery from the voltage drop state can be achieved when the voltage in the AC power supply system 2 recovers.

[0093] [Other embodiments] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various improvements, changes, and modifications are possible within the scope of the spirit of the present disclosure.

[0094] For example, in the above embodiment, the AC wiring 5 in the power supply system 1 is a three-phase system, but this is not limiting. For example, even if the AC wiring 5 is a single-phase two-wire system or a single-phase three-wire system, a similar power supply system 1 can be constructed, except that the various calculation methods differ depending on the system type.

[0095] Furthermore, in the above embodiment, the drive signal generator 85 adds the d-axis limit voltage Vdl to the feedback loop of the d-axis current Id, but in addition to or instead of this, the q-axis limit voltage Vql may be added to the feedback loop of the q-axis current Iq. That is, the drive signal generator 85 may generate the q-axis voltage command value Vq_ref by adding, as a limit voltage, the q-axis limit voltage Vql that limits the q-axis voltage Vq within a predetermined third range to a value based on the deviation D5q=Iq_cmd-Iq of the q-axis current Iq from the q-axis current command value Iq_cmd.

[0096] In the above embodiment, the second range, which is the limit range of the d-axis voltage Vd for generating the d-axis limit voltage Vd1, is set to be between 0 and 1, where 1 is the rated voltage of the d-axis voltage Vd. However, this is not limited to this. However, the second range is preferably set to be equal to or less than 1, where 1 is the rated voltage of the d-axis voltage Vd. Furthermore, when a q-axis limit voltage Vql is added to the feedback loop of the q-axis current Iq, the d-axis limit voltage Vdl may be a fixed value, such as 1, where 1 is the rated voltage of the d-axis voltage Vd. Furthermore, the third range, which is the limit range of the q-axis voltage Vq for generating the q-axis limit voltage Vq1, can be set appropriately depending on the power supply system 1. However, the third range is preferably set to be a range that includes 0, where 1 is the rated voltage of the q-axis voltage Vq.

[0097] In addition, in the above embodiment, an example was shown in which the drive signal generation unit 85 performs a calculation to subtract the interference component XqIq from the fifth deviation D5d regarding the d-axis current Id and add the interference component XdId to the fifth deviation D5q regarding the q-axis current Iq in order to perform decoupling processing between the d-axis and q-axes, but the subtraction of the interference component XqIq and the addition of the interference component XdId are not necessary.

[0098] Summary of this disclosure A controller of a power converter according to one aspect of the present disclosure is a controller of a power converter that performs power conversion between an energy storage facility and an AC power supply system, and the controller acquires a voltage and a frequency in AC wiring that connects the AC power supply system and the power converter, and a current output from the power converter to the AC wiring, calculates a frequency target value by a frequency target value calculation process that includes an operation of multiplying a value based on a first deviation that is a deviation of the power converter active power from a predetermined active power command value by a coefficient that indicates the first drooping characteristic, so that a relationship of frequency with respect to power converter active power output by the power converter to the AC wiring has a predetermined first drooping characteristic, calculates an internal phase difference angle by integrating a second deviation that is a deviation of the frequency in the AC wiring from the frequency target value, and ... with respect to a predetermined reactive power command value. calculates an internal electromotive voltage target value by adding a predetermined reference voltage to a value based on a third deviation that is a deviation of the power converter reactive power output by the power converter; calculates a current target value from the internal phase difference angle, the internal electromotive voltage target value, and a voltage in the AC wiring, and generates a current command value by limiting the current target value to within a predetermined first range; calculates a power correction value from a fourth deviation that is a deviation of the current command value from the current target value and the voltage in the AC wiring, and corrects the frequency target value by correcting the first deviation using the power correction value; generates a limit voltage that limits the voltage in the AC wiring to within a predetermined limit range; and generates a voltage command value by adding the limit voltage to a value based on a fifth deviation that is a deviation of the current output to the AC wiring from the current command value.

[0099] According to the above configuration, the power converter is driven using a current command value that limits a current target value estimated as a current output from the virtual generator to within a first range. This makes it possible to suppress overcurrent during a momentary voltage drop. Furthermore, because a limit voltage that limits the voltage in the AC wiring to within a predetermined limit range is added to the feedback loop of the current command value, it is possible to improve the responsiveness of current control during a momentary voltage drop and prevent tripping due to overcurrent.

[0100] Furthermore, in the above configuration, a power correction value is calculated from a fourth deviation, which is the deviation of the current command value from the current target value, and the voltage in the AC wiring. The calculated power correction value is subtracted from the first deviation for calculating the frequency target value. As a result, the current command value is limited to the current target value estimated as the current output from the virtual generator, and an increase in the frequency target value associated with a decrease in power output due to the output power being determined based on the limited current command value is suppressed. As a result, an increase in the internal phase difference angle that occurs during a momentary voltage drop is suppressed. Therefore, the occurrence of power oscillations is suppressed when the voltage in the AC power supply system recovers, allowing for rapid recovery from a voltage drop state.

[0101] In the above configuration, a voltage that limits the voltage in the AC wiring to a predetermined limit range is added as an additive term to the voltage added to the current feedback loop for generating the drive signal. This makes it possible to switch between grid-connected operation and stand-alone operation without changing the control method, as with conventional virtual generator model control, and improves the responsiveness of current control when a momentary voltage drop occurs.

[0102] The current command value may include a d-axis current command value and a q-axis current command value, and the controller may calculate a d-axis voltage and a q-axis voltage from an instantaneous value of a voltage in the AC wiring, calculate a d-axis current and a q-axis current from an instantaneous value of a current in the AC wiring, generate a d-axis voltage command value by adding a d-axis limit voltage that limits the d-axis voltage within a predetermined second range as the limit voltage to a value based on a deviation of the d-axis current from the d-axis current command value, and generate a q-axis voltage command value based on a deviation of the q-axis current from the q-axis current command value.

[0103] The magnitude of the d-axis limit voltage may be 0 or more and 1 or less, where 1 is the rated voltage of the d-axis voltage. [Explanation of symbols]

[0104] 2 AC power system 3. Energy storage facilities 4 Power Converter 10 Controller 71 Voltage calculation unit 72 Current calculation section 80 Frequency target value calculation unit 82 Internal phase difference angle calculation section 83 Internal electromotive voltage target value calculation unit 84 Current command value calculation unit 85 Drive signal generation unit

Claims

1. A controller for a power converter that performs power conversion between a power storage facility and an AC power supply system, acquiring a voltage and a frequency in an AC wiring that connects the AC power supply system and the power converter, and a current output from the power converter to the AC wiring; calculating a frequency target value by a frequency target value calculation process including a calculation of multiplying a value based on a first deviation, which is a deviation of the power converter active power from a predetermined active power command value, by a coefficient indicating the first drooping characteristic so that a relationship between the frequency and the power converter active power output by the power converter to the AC wiring has the predetermined first drooping characteristic; calculating an internal phase difference angle by integrating a second deviation, which is a deviation of the frequency in the AC wiring from the frequency target value; calculating an internal electromotive voltage target value by adding a predetermined reference voltage to a value based on a third deviation, which is a deviation of the power converter reactive power output by the power converter to the AC wiring from a predetermined reactive power command value; calculating a current target value from the internal phase difference angle, the internal electromotive voltage target value, and a voltage in the AC wiring; generating a current command value by limiting the current target value to within a predetermined first range; calculating a power correction value from a fourth deviation, which is a deviation of the current command value from the current target value, and a voltage in the AC wiring; correcting the first deviation using the power correction value to correct the frequency target value; a controller that generates a limit voltage that limits the voltage in the AC wiring to a predetermined limit range, and generates a voltage command value by adding the limit voltage to a value based on a fifth deviation that is a deviation of the current output to the AC wiring from the current command value, thereby generating a drive signal for the power converter.

2. the current command value includes a d-axis current command value and a q-axis current command value, The controller calculating a d-axis voltage and a q-axis voltage from the instantaneous value of the voltage in the AC wiring; calculating a d-axis current and a q-axis current from the instantaneous value of the current in the AC wiring; generating a d-axis voltage command value by adding a d-axis limit voltage, which limits the d-axis voltage within a predetermined second range as the limit voltage, to a value based on a deviation of the d-axis current from the d-axis current command value; The controller according to claim 1 , wherein the controller generates a value based on a deviation of the q-axis current from the q-axis current command value as a q-axis voltage command value.

3. The controller according to claim 2 , wherein the magnitude of the d-axis limit voltage is equal to or greater than 0 and equal to or less than 1, where 1 is a rated voltage of the d-axis voltage.

4. A control method for a power converter that performs power conversion between a power storage facility and an AC power supply system, comprising: acquiring a voltage and a frequency in an AC wiring that connects the AC power supply system and the power converter, and a current output from the power converter to the AC wiring; calculating a frequency target value by a frequency target value calculation process including a calculation of multiplying a value based on a first deviation, which is a deviation of the power converter active power from a predetermined active power command value, by a coefficient indicating the first drooping characteristic so that a relationship between the frequency and the power converter active power output by the power converter to the AC wiring has the predetermined first drooping characteristic; calculating an internal phase difference angle by integrating a second deviation, which is a deviation of the frequency in the AC wiring from the frequency target value; calculating an internal electromotive voltage target value by adding a predetermined reference voltage to a value based on a third deviation, which is a deviation of the power converter reactive power output by the power converter to the AC wiring from a predetermined reactive power command value; calculating a current target value from the internal phase difference angle, the internal electromotive voltage target value, and a voltage in the AC wiring; generating a current command value by limiting the current target value to within a predetermined first range; calculating a power correction value from a fourth deviation, which is a deviation of the current command value from the current target value, and a voltage in the AC wiring; correcting the first deviation using the power correction value to correct the frequency target value; a limiting voltage that limits the voltage in the AC wiring to a predetermined second range is generated, and a voltage command value is generated by adding the limiting voltage to a value based on a fifth deviation that is a deviation of the current output to the AC wiring from the current command value, thereby generating a drive signal for the power converter.

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