Control circuit and control method for power converter

Abstract

This control circuit for a power converter calculates a current target value in such a way that: using a value set as a virtual impedance between an AC power supply system and a virtual prime mover generator when it is assumed that the AC power supply system and the virtual prime mover generator are connected, an internal induced voltage in the virtual prime mover generator is calculated from a current flowing through the virtual impedance when active power output from the virtual prime mover generator is an active power target value and reactive power output from the virtual prime mover generator is a reactive power target value; and a current flowing through the virtual impedance when it is assumed that the AC power supply system and the virtual prime mover generator are connected is calculated from a deviation of the internal induced voltage target value with respect to a voltage in AC wiring.

Description

Control circuit and control method for power converter

[0001] This disclosure relates to a control circuit and control method for a power converter.

[0002] In power systems such as microgrids, where an AC power system and energy storage equipment including a battery are interconnected, a power converter is connected between the AC power system and the battery to convert the AC power from the AC power system to DC power and to convert the DC power from the battery to AC power.

[0003] Such power converters include GFL inverters (Grid Following inverters), which operate the power converter as a current source, and GFM inverters (Grid Forming inverters), which operate the power converter as a voltage source. GFL inverters do not have the ability to adjust power in response to load fluctuations in the connected AC power system, and therefore cannot contribute to the stabilization of the AC power system. Furthermore, there is room for improvement in ensuring stable independent operation when the energy storage equipment is disconnected from the AC power system. On the other hand, GFM inverters have the ability to adjust power in response to load fluctuations in the connected AC power system and contribute to the stabilization of the AC power system. Furthermore, they can perform stable independent operation when the energy storage equipment is disconnected from the AC power system. However, there is a risk of overcurrent occurring due to instantaneous potential differences caused by sudden changes in grid voltage, and there is room for improvement in ensuring continued operation.

[0004] For example, Patent Document 1 discloses a configuration in which the control mode of a power converter can be switched between a mode that performs an operation mode that is not based on inertial force and a mode that performs an operation based on inertial force. In other words, in the configuration of Patent Document 1, the power converter can be switched to function as either a GFL inverter or a GFM inverter depending on the grid conditions.

[0005] Japanese Patent Application Publication No. 2023-137734

[0006] However, the configuration described in Patent Document 1 above is complex because the control method is switched depending on the situation. Furthermore, there is no mention of the energy storage equipment operating independently when it is disconnected from the AC power system. For this reason, there is room for improvement in ensuring that the power converter can stably operate independently when the energy storage equipment is disconnected from the AC power system in a power system where the AC power system and the energy storage equipment are interconnected.

[0007] This disclosure aims to solve the above problems and to provide a control circuit and control method for a power converter of an energy storage facility connected to an AC power grid, which can operate stably independently even when the energy storage facility is disconnected from the AC power grid, with a simple configuration.

[0008] A control circuit for a power converter according to an aspect of the present disclosure is a control circuit for a power converter that performs power conversion between a capacitor and an AC power supply system. The control circuit acquires the voltage, frequency in an AC wiring connecting the AC power supply system and the power converter, and the current output from the power converter to the AC wiring. An effective power target value is calculated by an effective power target value calculation process including an operation of multiplying a first deviation, which is a deviation of the frequency with respect to a frequency target value, by a coefficient indicating the first droop characteristic so that a relationship between the frequency and the effective power output from the power converter to the AC wiring has a predetermined first droop characteristic. An ineffective power target value is calculated by an ineffective power target value calculation process including an operation of multiplying a second deviation, which is a deviation of the voltage with respect to a voltage target value, by a coefficient indicating the second droop characteristic so that a relationship between the voltage and the ineffective power output from the power converter to the AC wiring has a predetermined second droop characteristic. An internal induced voltage target value is calculated by an internal induced voltage target value calculation process that calculates the internal induced voltage target value from a current flowing through the virtual impedance when an effective power output from the virtual prime mover generator is the effective power target value and an ineffective power output from the virtual prime mover generator is the ineffective power target value, assuming that the AC power supply system and a virtual prime mover generator are connected. A current target value is calculated by a current target value calculation process including an operation of calculating a current flowing through the virtual impedance when it is assumed that the AC power supply system and the virtual prime mover generator are connected from a deviation of the internal induced voltage target value with respect to the voltage in the AC wiring. The voltage target value is calculated by a voltage target value calculation process that calculates the voltage target value from a deviation of the current target value with respect to the current output to the AC wiring, and a drive signal for the power converter is generated according to the voltage target value.

[0009] 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 a capacitor and an AC power system, comprising: obtaining the voltage, frequency, and current output from the power converter to the AC wiring connecting the AC power system and the power converter; calculating an active power target value by an active power target value calculation process that includes multiplying a first deviation, which is the deviation of the frequency from a frequency target value, by a coefficient indicating the first drooping characteristic, so that the relationship between the frequency and the active power of the power converter output by the power converter to the AC wiring has a predetermined first drooping characteristic; calculating a reactive power target value by an reactive power target value calculation process that includes multiplying a second deviation, which is the deviation of the voltage from a voltage target value, by a coefficient indicating the second drooping characteristic, so that the relationship between the voltage and the reactive power of the power converter output by the power converter to the AC wiring has a predetermined second drooping characteristic; and assuming that the AC power system and a virtual prime mover are connected. In this case, an internal induced voltage target value is calculated by an internal induced voltage target value calculation process that uses a value set as the virtual impedance between the AC power system and the virtual prime mover, and calculates the internal induced voltage target value in the virtual prime mover from the current flowing through the virtual impedance when the active power output from the virtual prime mover is the active power target value and the reactive power output from the virtual prime mover is the reactive power target value. A current target value is calculated by a current target value calculation process that includes a calculation to determine the current flowing through the virtual impedance assuming that the AC power system and the virtual prime mover are connected, based on the deviation of the internal induced voltage target value with respect to the voltage in the AC wiring. A voltage target value is calculated by a voltage target value calculation process that calculates the voltage target value from the deviation of the current target value with respect to the current output to the AC wiring, and a drive signal for the power converter is generated according to the voltage target value.

[0010] According to this disclosure, a power converter for an energy storage facility connected to an AC power grid can be configured simply to enable stable independent operation even when the energy storage facility is disconnected from the AC power grid.

[0011] FIG. 1 is a block diagram showing a schematic configuration of a power storage facility including a control circuit of a power converter according to an embodiment of the present disclosure. FIG. 2 is a block diagram showing a configuration of an active power target value calculation unit in the control circuit shown in FIG. 1. FIG. 3 is a block diagram showing a configuration of a reactive power target value calculation unit in the control circuit shown in FIG. 1. FIG. 4 is a block diagram showing a configuration of an internal induced voltage target value calculation unit in the control circuit shown in FIG. 1. FIG. 5 is a block diagram showing a configuration of a current target value calculation unit in the control circuit shown in FIG. 1. FIG. 6 is a block diagram showing a configuration of a voltage target value calculation unit in the control circuit shown in FIG. 1. FIG. 7 is a block diagram showing a configuration of a drive signal generation unit in the control circuit shown in FIG. 1. FIG. 8 is a graph showing temporal changes in active power, reactive power, system voltage, system frequency, and effective current value in the first simulation. FIG. 9 is a graph showing temporal changes in active power, reactive power, system voltage, system frequency, and effective current value in the second simulation. FIG. 10 is a graph showing temporal changes in active power, reactive power, system voltage, and system frequency in the third simulation.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following, elements having the same or identical functions throughout all the drawings are denoted by the same reference numerals, and redundant descriptions thereof are omitted.

[0013] [System Configuration] FIG. 1 is a block diagram showing a schematic configuration of a power storage facility including a control circuit of a power converter according to an embodiment of the present disclosure. As shown in FIG. 1, the power storage facility 1 in the present embodiment includes a capacitor 3 and a power converter 4. The power converter 4 is connected to an AC power supply system 2 such as a commercial power supply system via an AC wiring 5. The capacitor 3 and the power converter 4 are connected by a DC wiring 6. In the present embodiment, a case where the AC power supply system 2 is a three-phase AC system is exemplified.

[0014] The power storage device 3 includes secondary batteries, electric double-layer capacitors, fuel cells, etc. The power converter 4 is equipped with multiple power semiconductor elements and rapidly switches the power semiconductor elements on and off to convert the DC power from the power storage device 3 into AC power and output it to the AC wiring 5, or converts the AC power from the AC power supply system 2 into DC power to store energy in the power storage device 3. A control circuit 10 for controlling the on / off state of the power semiconductor elements is connected to the power converter 4.

[0015] The energy storage device 1 is equipped with 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 the control circuit 10.

[0016] The control circuit 10 includes a computer such as a microcontroller or a personal computer. For example, the control circuit 10 includes a CPU, main memory such as RAM, a communication interface, and so on.

[0017] The functions of the elements disclosed herein can be performed using general-purpose processors, dedicated processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, or circuits or processing circuits that include a combination thereof and are configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuits. In this specification, a circuit, unit, or means is hardware that performs the enumerated functions, or hardware programmed to perform the enumerated functions. The hardware may be hardware disclosed herein, or other known hardware that is programmed or configured to perform the enumerated functions. If the hardware is a processor which is considered a type of circuit, then the circuit, unit, means, or part is a combination of hardware and software, and the software is used to configure the hardware or processor.

[0018] The control circuit 10 comprises control blocks including a voltage calculation unit 11, a current calculation unit 12, an active power target value calculation unit 13, a reactive power target value calculation unit 14, an internal induced voltage target value calculation unit 17, a current target value calculation unit 18, a voltage target value calculation unit 15, and a drive signal generation unit 16. As described above, each of these control blocks is considered a processing circuit or circuit. The control circuit 10 executes the processing in each control block. As a result, the control circuit 10 controls the power converter 4, which can seamlessly transition between grid-connected operation with the AC power system 2 and independent operation of the energy storage equipment 1. Each control block will be described in detail below.

[0019] [Voltage Calculation Unit] The voltage calculation unit 11 calculates the instantaneous voltage v of each phase detected by the voltage detector 7. ａ ,v ｂ ,v ｃ The voltage Vac in the AC wiring 5 is calculated using the following formula. Note that the voltage Vac in the AC wiring 5 represents the effective value of the voltage in a three-phase AC system.

[0020]

[0021] Further, the voltage calculation unit 11 calculates the frequency fac and phase φ in the AC wiring 5 by a known PLL (Phase Lock Loop) calculation. ａｃ Also, the voltage calculation unit 11 calculates the instantaneous voltage v of each phase ａ , v ｂ , v ｃ and phase φ ａｃ to calculate the voltages on the coordinate axes of the rotating coordinate system of the AC voltage, that is, the d-axis voltage Vd and q-axis voltage Vq, by the following formula. Note that the coefficients in the following formula are not limited to (2 / 3) １／２ and other values may also be used. Thus, in this embodiment, the control circuit 10 obtains the voltages Vd, Vq and frequency fac in the AC wiring 5 from the instantaneous voltages v ａ , v ｂ , v ｃ detected by the voltage detector 7.

[0022]

[0023] [Current calculation unit] The current calculation unit 12 calculates the AC current Iac output from the power converter 4 to the AC wiring 5 from the instantaneous currents i of each phase ａ , i ｂ , i ｃ detected by the current detector 8 by the following formula. Note that the current Iac output to the AC wiring 5 means the effective value of the current in the three-phase AC.

[0024]

[0025] Also, the current calculation unit 12 calculates the d-axis current Id and q-axis current Iq, which are the currents on the coordinate axes of the rotating coordinate system of the AC current, from the instantaneous currents i of each phase ａ , i ｂ , i ｃ detected by the current detector 8 and the phase φac calculated by the voltage calculation unit 11 by the following formula. Note that the coefficients in the following formula are not limited to (2 / 3) １／２ and other values may also be used. Thus, in this embodiment, the control circuit 10 calculates the instantaneous currents i ａ , i ｂ , i ｃThe currents Id and Iq in the AC wiring 5 are obtained from this.

[0026]

[0027] [Active Power Target Value Calculation Unit] Figure 2 is a block diagram showing the configuration of the active power target value calculation unit in the control circuit shown in Figure 1. As shown in Figure 2, the active power target value calculation unit 13 calculates the active power target value Pac_ref by performing an active power target value calculation process. For this purpose, in this embodiment, the active power target value calculation unit 13 includes gain multipliers 31, 34, adder 32, subtractor 33, 37, low-pass filter 35, and differential arithmetic unit 36.

[0028] The active power target value calculation unit 13 performs a calculation by multiplying the first deviation Δfac, which is the deviation of frequency fac with respect to the frequency target value fac_ref, by a coefficient (1 / Kdr) that indicates the first droop characteristic, so that the relationship between the frequency fac and the active power Pac of the power converter output by the power converter 4 to the AC wiring 5 has a predetermined first droop characteristic. The first droop characteristic means that when the active power Pac of the power converter increases, the frequency fac decreases, and when the active power Pac of the power converter decreases, the frequency fac increases.

[0029] In this embodiment, the active power target value calculation unit 13 calculates the frequency target value fac_ref from a predetermined active power command value Pac_cmd and a predetermined frequency command value fac_cmd. The active power command value Pac_cmd and the frequency command value fac_cmd may be fixed values ​​set in advance or variable values ​​input from an external source each time. The active power target value calculation unit 13 calculates the frequency target value fac_ref by adding the frequency command value fac_cmd to the value obtained by multiplying the active power command value Pac_cmd by the reciprocal of the coefficient showing the first drooping characteristic (Kdr).

[0030] For this purpose, the gain multiplier 31 multiplies the active power command value Pac_cmd by the reciprocal of the coefficient that exhibits the first drooping characteristic (Kdr). The adder 32 adds the frequency command value fac_cmd to the output of the gain multiplier 31. The subtractor 33 outputs the first deviation Δfac by subtracting the frequency fac of the AC wiring 5 from the frequency target value fac_ref, which is the output of the adder 32. The gain multiplier 34 multiplies the output of the subtractor 33 by the coefficient that exhibits the first drooping characteristic (1 / Kdr).

[0031] The output Pac_m of the gain multiplier 34 is a proportional control component that maintains the frequency fac of the AC wiring 5 at the frequency target value fac_ref. This mimics the function of a governor in a prime mover. Therefore, the configurations 31, 32, 33, and 34 in the active power target value calculation unit 13 constitute a governor model circuit 13a.

[0032] In this embodiment, the active power target value calculation unit 13 multiplies the frequency fac by a virtual unit inertia constant M, the value obtained by passing it through a predetermined low-pass filter 35, and calculates the derivative of the multiplied value as the virtual inertia force Pac_i. For example, the low-pass filter 35 into which the frequency fac is input includes a first-order lag filter. The differential calculator 36 multiplies the output of the low-pass filter 35 by the virtual unit inertia constant M and then performs a differential operation.

[0033] The virtual unit inertia constant M is determined from the equation of motion shown below for a virtual prime mover, assuming that a virtual prime mover is connected to the AC power system 2 instead of the power converter 4. In the following equation, ω is the rotational speed and Pg is the power output of the prime mover. The right-hand side of the following equation is a linear approximation of the torque of the prime mover near its rated rotational speed.

[0034]

[0035] The virtual inertial force Pac_i, which is the output of the differential calculator 36, simulates the inertial force generated in a prime mover. Therefore, configurations 35 and 36 in the active power target value calculation unit 13 constitute a pseudo-inertial model circuit 13b. By including the component of the virtual inertial force Pac_i in the active power target value Pac_ref, the active power target value Pac_ref can be appropriately adjusted in response to frequency fluctuations during grid-connected operation.

[0036] Here, the low-pass filter 35 suppresses excessive fluctuations in the virtual inertial force Pac_i caused by large fluctuations in the measured value of frequency fac due to system disturbances such as phase jumps in the AC wiring 5. In particular, since the pseudo-inertia model circuit 13b includes a differential arithmetic unit 36, if a large change in frequency fac is directly differentiated, an excessive virtual inertial force Pac_i will be output. Therefore, by passing frequency fac through the low-pass filter 35 before inputting it to the differential arithmetic unit 36, large fluctuations in the input value of the differential arithmetic unit 36 ​​are suppressed, and the output of an excessive virtual inertial force Pac_i is suppressed.

[0037] The active power target value calculation unit 13 calculates the active power target value Pac_ref by subtracting the value of the virtual inertial force Pac_i from the value Pac_m, which is obtained by multiplying the first deviation Δfac by a coefficient (1 / Kdr) that indicates the first drooping characteristic. That is, the subtractor 37 calculates the active power target value Pac_ref by subtracting the virtual inertial force Pac_i, which is the output of the differential arithmetic unit 36, from the output Pac_m of the gain multiplier 34.

[0038] [Reactive Power Target Value Calculation Unit] Figure 3 is a block diagram showing the configuration of the reactive power target value calculation unit in the control circuit shown in Figure 1. As shown in Figure 3, the reactive power target value calculation unit 14 calculates the reactive power target value Qac_ref by performing reactive power target value calculation processing. In this embodiment, the reactive power target value calculation unit 14 includes gain multipliers 41, 44, an adder 42, and a subtractor 43.

[0039] The reactive power target value calculation unit 14, in the reactive power target value calculation process, performs a calculation by multiplying the second deviation ΔVac, which is the deviation of voltage Vac with respect to the voltage target value Vac_ref, by a coefficient (1 / Kdra) that indicates the second drooping characteristic, so that the relationship between the voltage Vac in the AC wiring 5 and the power converter reactive power Qac output by the power converter 4 to the AC wiring 5 has a predetermined second drooping characteristic. The second drooping characteristic means that when the power converter reactive power Qac increases, the voltage Vac decreases, and when the power converter reactive power Qac decreases, the voltage Vac increases.

[0040] In this embodiment, the reactive power target value calculation unit 14 calculates the voltage target value Vac_ref from a predetermined reactive power command value Qac_cmd and a predetermined voltage command value Vac_cmd. The reactive power command value Qac_cmd and the voltage command value Vac_cmd may be fixed values ​​set in advance or variable values ​​input from an external source each time. The reactive power target value calculation unit 14 calculates the voltage target value Vac_ref by adding the voltage command value Vac_cmd to the value obtained by multiplying the reactive power command value Qac_cmd by the reciprocal of the coefficient showing the second drooping characteristic (Kdra).

[0041] For this purpose, the gain multiplier 41 multiplies the reactive power command value Qac_cmd by the reciprocal of the coefficient that exhibits the second drooping characteristic (Kdra). The adder 42 adds the voltage command value Vac_cmd to the output of the gain multiplier 41. The subtractor 43 outputs the second deviation ΔVac by subtracting the voltage Vac in the AC wiring 5 from the voltage target value Vac_ref, which is the output of the adder 42. The gain multiplier 44 calculates the reactive power target value Qac_ref by multiplying the output of the subtractor 43 by the coefficient that exhibits the second drooping characteristic (1 / Kdra).

[0042] [Internal Induced Voltage Target Value Calculation Unit] Figure 4 is a block diagram showing the configuration of the internal induced voltage target value calculation unit in the control circuit shown in Figure 1. As shown in Figure 4, the internal induced voltage target value calculation unit 17 calculates the internal induced voltage target value, i.e., the d-axis internal induced voltage target value Ed_ref and the q-axis internal induced voltage target value Eq_ref, by performing internal induced voltage target value calculation processing.

[0043] First, let's consider the case where a virtual prime mover is connected to AC power system 2. Let the virtual impedance between AC power system 2 and the virtual prime mover be r + jx, where r is the resistance component and x is the re-auction component. The internal induced voltage of the virtual prime mover is Eac Ｖ Let = Ed + jEq, and the rated voltage in AC power system 2 be Vac Ｖ Let = Vd + jVq = 1 (Vd = 1, Vq = 0), and at this time, the current flowing from the virtual prime mover to the AC power system 2 is Iac Ｖ Let = Id + jIq. Note that the voltage Vac of AC power system 2. Ｖ The reason for fixing this value at the rated value of 1 is that the system voltage will approximately match the rated value when the AC power system 2 is stable.

[0044] The circuit equation for a circuit including such an AC power system 2 and a virtual prime mover is: Eac Ｖ -Vac Ｖ =(r+jx)Iac Ｖ This is expressed as follows. From the above, the circuit equation can be rewritten as follows: Ed + jEq = (rId - xIq + 1) + j(rIq + xId) ... (6) Also, when P is the active power output from the virtual prime mover to the AC power system 2, and Q is the reactive power output from the virtual prime mover to the AC power system 2, these powers P and Q and the current Iac flowing from the virtual prime mover to the AC power system 2 Ｖ The relationship is P + jQ = Vac Ｖ Iac ＊ It is expressed as follows: Note that Iac in this formula ＊ The current Iac Ｖ It is the complex conjugate of and Iac ＊ = Id - jIq. From the above, Vac Ｖ Since = 1, this equation can be rewritten as follows: P + jQ = Id + j(-Iq) ... (7)

[0045] Substituting P = Id and Q = -Iq into equation (6) from equation (7) above, we derive Ed + jEq = (rP + xQ + 1) + j(xP - rQ). From this, the internal induced voltage of the d axis of the virtual prime mover is expressed as Ed = rP + xQ + 1, and the internal induced voltage of the q axis of the virtual prime mover is expressed as Eq = xP - rQ. From the above, using the active power target value Pac_ref calculated by the active power target value calculation unit 13 and the reactive power target value Qac_ref calculated by the reactive power target value calculation unit 14, the internal induced voltage target values ​​Ed_ref and Eq_ref for each axis of the virtual prime mover can be calculated.

[0046] The internal induced voltage target value calculation unit 17 calculates the internal induced voltage target values ​​Ed_ref and Eq_ref from the active power target value Pac_ref and the reactive power target value Qac_ref based on the logic described above. For this purpose, the internal induced voltage target value calculation unit 17 includes gain multipliers 71, 72, 73, 74, adders 75, 76, and subtractors 77.

[0047] Gain multiplier 71 multiplies the reactive power target value Qac_ref by a virtual reactance value x. Gain multiplier 72 multiplies the reactive power target value Qac_ref by a virtual resistance value r. Gain multiplier 73 multiplies the active power target value Pac_ref by a virtual resistance value r. Gain multiplier 74 multiplies the active power target value Pac_ref by a virtual reactance value x.

[0048] The adder 75 adds the output of the gain multiplier 71 to the voltage command value Vac_cmd of the AC power supply system 2. The voltage command value Vac_cmd is set to the value of the rated voltage Vac, i.e., 1. However, the value of the voltage command value Vac_cmd may be set to a significant fixed value other than 1. The adder 76 adds the output of the gain multiplier 73 to the output of the adder 75. As a result, the adder 76 outputs r・Pac_ref + x・Qac_ref + 1 as the d-axis internal induced voltage target value Ed_ref. The subtractor 77 subtracts the output of the gain multiplier 72 from the output of the gain multiplier 74. As a result, the subtractor 77 outputs x・Pac_ref - r・Qac_ref as the q-axis internal induced voltage target value Eq_ref.

[0049] In this way, the internal induced voltage target value calculation unit 17 calculates the internal induced voltage target values ​​Ed_ref and Eq_ref in the virtual prime mover using the value (r+jx) set as the virtual impedance between the AC power system 2 and the virtual prime mover, assuming that the AC power system 2 and the virtual prime mover are connected. At this time, the internal induced voltage target value calculation unit 17 calculates the internal induced voltage target values ​​Ed_ref and Eq_ref in the virtual prime mover from the current Iac flowing through the virtual impedance when the active power output from the virtual prime mover is the active power target value Pac_ref and the reactive power output from the virtual prime mover is the reactive power target value Qac_ref.

[0050] [Current Target Value Calculation Unit] Figure 5 is a block diagram showing the configuration of the current target value calculation unit in the control circuit shown in Figure 1. As shown in Figure 5, the current target value calculation unit 18 calculates the current target value, i.e., the d-axis current target value Id_ref and the q-axis current target value Iq_ref, by performing current target value calculation processing. The current calculation processing includes a calculation to determine the current flowing through the virtual impedance (r+jx) assuming that the AC power system 2 and a virtual prime mover are connected, based on the deviation of the internal induced voltage target values ​​Ed_ref and Eq_ref with respect to the voltages Vd and Vq in the AC wiring 5.

[0051] As described above, the circuit equation for the circuit including the AC power system 2 and the virtual prime mover generator is: Eac Ｖ -Vac Ｖ =(r+jx)・Iac Ｖ It is expressed as follows: Therefore, the internal induced voltage Eac Ｖ The internal induced voltage target values ​​are Ed_ref and Eq_ref, and the voltage of AC power system 2 is Vac Ｖ When the current targets are Vd and Vq, let Id_ref and Iq_ref be the target currents. Then the above circuit equation becomes Ed_ref + jEq_ref - (Vd + jVq) = (r + jx) * (Id_ref + jIq_ref). When this equation is rearranged by separating the real and imaginary parts, the target currents Id_ref and Iq_ref are expressed by the following equations.

[0052]

[0053] The current target value calculation unit 18 calculates current target values ​​Id_ref and Iq_ref from the internal induced voltage target values ​​Ed_ref and Eq_ref and the voltages Vd and Vq in the AC wiring 5 based on the above logic. For this purpose, the current target value calculation unit 18 includes subtractors 81, 82, and 88, gain multipliers 83, 84, 85, and 86, and an adder 87.

[0054] Subtractor 81 subtracts the d-axis voltage Vd in the AC wiring 5 from the d-axis internal induced voltage target value Ed_ref and outputs the d-axis voltage deviation ΔVd. Subtractor 82 subtracts the q-axis voltage Vq in the AC wiring 5 from the q-axis internal induced voltage target value Eq_ref and outputs the q-axis voltage deviation ΔVq. Gain multiplier 83 multiplies the d-axis voltage deviation ΔVd output from subtractor 81 by r / (r ２ +x ２ The gain multiplier 84 multiplies the d-axis voltage deviation ΔVd output from the subtractor 81 by x / (r ２ +x ２ The gain multiplier 85 multiplies the q-axis voltage deviation ΔVq output from the subtractor 82 by x / (r). ２ +x ２ The gain multiplier 86 multiplies the q-axis voltage deviation ΔVq output from the subtractor 82 by r / (r). ２ +x ２ Multiply by ).

[0055] The adder 87 adds the output of gain multiplier 85 to the output of gain multiplier 83. As a result, the output of adder 87 is the result of the calculation in equation (8) above. The subtractor 88 subtracts the output of gain multiplier 84 from the output of gain multiplier 86. As a result, the output of subtractor 88 is the result of the calculation in equation (9) above.

[0056] The virtual impedance r+jx is defined as the sum of the internal impedance rs+jxs of the capacitor 3 and the external impedance rl+jxl between the capacitor 3 and the AC power system 2. However, the actual internal impedance rs+jxs of the capacitor 3 is almost equal to zero, and the total impedance r+jx is almost equal to the external impedance rl+jxl between the capacitor 3 and the AC power system 2. Nevertheless, in this embodiment, the total impedance r+jx, which is the sum of the internal impedance rs+jxs of the capacitor 3 and the external impedance rl+jxl between the capacitor 3 and the AC power system 2, is used.

[0057] In particular, by virtually increasing the internal impedance rs + jxs of the capacitor 3 to obtain the total impedance r + jx, and then using this virtual impedance to calculate the target current values ​​Id_ref and Iq_ref, stable operation becomes possible. This is because, when multiple power converters 4 are operated in parallel, even a small voltage difference between the power converters 4 can cause a significant disruption to the output balance because the impedance of the power converters 4 is low. By virtually increasing the internal impedance of the capacitor 3, the impedance of the power converters 4 becomes higher, preventing the output balance from becoming unstable due to voltage differences. For example, if the internal impedance rs + jxs is practically almost zero, a considerable degree of stabilization can be achieved by setting the resistance component to 0.1 PU and the reactance component to 0.4 PU in the total impedance.

[0058] Furthermore, the current target value calculation unit 18 assumes that a virtual prime mover is connected to the AC power system 2 via the AC wiring 5 instead of the power converter 4, and estimates the current value output to the AC wiring 5 when the virtual prime mover generates an internal electromotive force calculated by the internal induced voltage target value calculation unit 17. This suppresses the increase in the apparent impedance of the power converter 4, which would otherwise cause system instability during grid-connected operation with the AC power system 2 or during parallel operation of power converters 4.

[0059] Furthermore, the current target value calculation unit 18 performs a first limiting process to limit the d-axis current target value Id_ref to a predetermined first range. The current target value calculation unit 18 also performs a second limiting process to limit the q-axis current target value Iq_ref to a predetermined second range. For this purpose, the current target value calculation unit 18 further includes upper and lower limiters 89 and 90. The upper and lower limiter 89 limits the value output from the adder 87 to a first range between a predetermined upper limit and a predetermined lower limit and outputs the d-axis current target value Id_ref. The upper and lower limiter 90 limits the value output from the subtractor 88 to a second range between a predetermined upper limit and a predetermined lower limit and outputs the q-axis current target value Iq_ref.

[0060] [Voltage Target Value Calculation Unit] Figure 6 is a block diagram showing the configuration of the voltage target value calculation unit in the control circuit shown in Figure 1. As shown in Figure 6, the voltage target value calculation unit 15 calculates the voltage target values, namely the d-axis voltage target value Vd_ref and the q-axis voltage target value Vq_ref, by performing voltage target value calculation processing. For this purpose, in this embodiment, the voltage target value calculation unit 15 includes subtractors 52, 57, proportional-integral operators 53, 58, adders 54, 59, and upper and lower limiters 55, 60.

[0061] The voltage target value calculation unit 15 receives the currents Id and Iq, voltages Vd and Vq, and current target values ​​Id_ref and Iq_ref in the AC wiring 5 as input.

[0062] The voltage target value calculation unit 15 calculates the voltage target values ​​Vd_ref and Vq_ref from the d-axis current deviation ΔId with respect to the d-axis current Id in the d-axis current target value Id_ref and the q-axis current deviation ΔIq with respect to the q-axis current Iq in the q-axis current target value Iq_ref. The subtractor 52 subtracts the d-axis current Id from the d-axis current target value Id_ref and outputs the d-axis current deviation ΔId. The proportional-integral calculator 53 performs a proportional-integral operation on the d-axis current deviation ΔId, which is the output of the subtractor 52, to calculate the d-axis voltage target value Vdo_ref based on the d-axis current deviation ΔId. Similarly, the subtractor 57 subtracts the q-axis current Iq from the q-axis current target value Iq_ref and outputs the q-axis current deviation ΔIq. The proportional-integral unit 58 calculates the q-axis voltage target value Vqo_ref based on the q-axis current deviation ΔIq, which is the output of the subtractor 57, by performing a proportional-integral operation.

[0063] Based on the above, the relationship between the voltage target values ​​Vdo_ref and Vqo_ref and the current target values ​​Id_ref and Iq_ref, based on the current deviations ΔId and ΔIq for each axis, can be expressed as follows using the currents Id and Iq, the gains Kd and Kq in the proportional-integral operation, and the time constants Tid and Tiq. Note that the gains Kd and Kq may be the same or different values. Also, the time constants Tid and Tiq may be the same or different values.

[0064]

[0065] The adder 54 adds a d-axis limiting voltage Vdl, which limits the d-axis voltage Vd to a predetermined third range, to the d-axis voltage target value Vdo_ref based on the d-axis current deviation ΔId. The upper and lower limiter 55 outputs the d-axis limiting voltage Vdl, which limits the d-axis voltage Vd to a third range between a predetermined upper limit and a predetermined lower limit. The voltage target value calculation unit 15 outputs the output of the adder 54 as the d-axis voltage target value Vd_ref. For example, the upper limit of the third range in the upper and lower limiter 55 is 1 when the rated voltage of the d-axis voltage Vd is 1, and the lower limit is 0. The upper and lower limits of the third range are not limited to these values, but it is preferable that the upper limit is 1 or less.

[0066] Similarly, the adder 59 adds a q-axis limiting voltage Vql, which limits the q-axis voltage Vq to a predetermined fourth range, to the voltage target value Vqo_ref based on the q-axis current deviation ΔIq. The upper and lower limiters 60 output the q-axis limiting voltage Vql, which limits the q-axis voltage Vq to a fourth range between a predetermined upper limit and a predetermined lower limit. The voltage target value calculation unit 15 outputs the output of the adder 59 as the q-axis voltage target value Vq_ref. For example, the fourth range in the upper and lower limiters 60 can be appropriately set according to the energy storage equipment 1. However, it is preferable that the fourth range includes 0 when the rated voltage of the q-axis voltage Vq is 1.

[0067] If the d-axis voltage Vd is added directly to the d-axis voltage target value Vdo_ref based on the d-axis current deviation ΔId, independent operation is not possible. In this case, during independent operation, the d-axis voltage Vd output by the power converter 4 is input directly to the adder 54, so the d-axis voltage Vd is added to the d-axis voltage target value Vdo_ref based on the d-axis current deviation ΔId. As a result, the voltage target value calculation unit 15 keeps increasing the d-axis voltage target value Vd_ref in the adder 54. Therefore, independent operation cannot be performed continuously from grid-connected operation.

[0068] In contrast, according to this embodiment, since the d-axis limiting voltage Vdl is applied to the d-axis voltage target value Vdo_ref based on the d-axis current deviation ΔId, it is possible to prevent the d-axis voltage target value Vd_ref from continuously rising during independent operation. Therefore, with this configuration, it is possible to switch between grid-connected operation and independent operation without changing the control method, while improving the responsiveness of current control when instantaneous voltage drops occur. Furthermore, by performing integral calculations as well as proportional calculations when calculating the d-axis voltage target value Vdo_ref based on the d-axis current deviation ΔId, a d-axis voltage target value Vd_ref is generated such that the d-axis current Id converges appropriately near the rating. As a result, appropriate control can be implemented even when the d-axis voltage Vd applied to the d-axis voltage target value Vdo_ref based on the d-axis current deviation ΔId is limited.

[0069] In this embodiment, the q-axis limiting voltage Vql is added to the voltage target value Vqo_ref based on the q-axis current deviation ΔIq, but it is not necessary to add the q-axis limiting voltage Vql. For example, both the upper and lower limits of the upper and lower limiters 60 may be set to 0. Alternatively, the adder 59 and the upper and lower limiters 60 may be omitted.

[0070] [Drive Signal Generation Unit] Figure 7 is a block diagram showing the configuration of the drive signal generation unit in the control circuit shown in Figure 1. As shown in Figure 5, the drive signal generation unit 16 receives the phase φac and voltage target values ​​Vd_ref and Vq_ref in the AC wiring 5 as input. The drive signal generation unit 16 calculates the instantaneous voltage v of each phase of the AC wiring 5, which is a three-phase AC, from the voltage target values ​​Vd_ref and Vq_ref. ａ ,v ｂ ,v ｃ Target value v ａ＿ｒｅｆ ,v ｂ＿ｒｅｆ ,v ｃ＿ｒｅｆ Calculate.

[0071] For this purpose, the drive signal generation unit 16 includes a dq-abc converter 61 and a signal converter 62. The dq-abc converter 61 calculates the target value v of the instantaneous voltage of each phase of the AC wiring 5 based on the following equation from the voltage target values ​​Vd_ref and Vq_ref. ａ＿ｒｅｆ ,v ｂ＿ｒｅｆ ,v ｃ＿ｒｅｆ Calculate the following. Note that the coefficient in the following equation is (2 / 3). １／２ It is not limited to this value; other values ​​are also acceptable.

[0072]

[0073] The calculated target value of instantaneous voltage v ａ＿ｒｅｆ ,v ｂ＿ｒｅｆ ,v ｃ＿ｒｅｆ This is input to the signal converter 62. The signal converter 62 receives the target value v of the instantaneous voltage. ａ＿ｒｅｆ ,v ｂ＿ｒｅｆ ,v ｃ＿ｒｅｆBased on this, a drive signal So is generated for switching the power converter 4. For example, the drive signal So is a PWM control signal. The drive signal generation unit 16 outputs the drive signal So thus generated. 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.

[0074] [Effects] According to this embodiment, the active power target value Pac_ref is calculated so that the relationship between the frequency fac and the active power Pac output by the power converter 4 to the AC wiring 5 has a predetermined first drooping characteristic, and the reactive power target value Qac_ref is calculated so that the relationship between the voltage Vac in the AC wiring 5 and the reactive power Qac output by the power converter 4 to the AC wiring 5 has a predetermined second drooping characteristic. The current target values ​​Id_ref and Iq_ref are calculated from the calculated active power target value Pac_ref and reactive power target value Qac_ref. In this case, in order to calculate the current target values ​​Id_ref and Iq_ref that take into account the voltage Vac = Vd + jVq in the AC wiring 5, the internal induced voltage target values ​​Ed_ref and Eq_ref in the virtual prime mover are calculated by assuming that the AC power system 2 and a virtual prime mover are connected. The current target values ​​Id_ref and Iqref are calculated from the deviations of the calculated internal induced voltage target values ​​Ed_ref and Eq_ref from the voltages Vd and Vq in the AC wiring 5.

[0075] In this way, the current target values ​​Id_ref and I_ref are calculated to reflect the actual voltage fluctuations in the AC wiring 5, thus increasing the responsiveness of the power converter 4 to current fluctuations due to load fluctuations in the AC wiring 5. Therefore, in the power converter 4 during independent operation, the responsiveness of the current Iac output to the AC wiring 5 by the power converter 4 to load fluctuations in the AC wiring 5 can be increased, and the amount of voltage Vac fluctuation in the AC wiring 5 can be reduced. As described above, according to this embodiment, with a simple configuration, the power converter 4 can stably operate independently even when the energy storage equipment 1 is disconnected from the AC power system 2.

[0076] Furthermore, according to this embodiment, in order to calculate the internal induced voltage target values ​​Ed_ref and Eq_ref, the value of the virtual impedance (r + jx) between the AC power system 2 and the virtual prime mover generator is set assuming that the AC power system 2 and the virtual prime mover generator are connected. The d-axis internal induced voltage target value Ed_ref is calculated by adding the value obtained by multiplying the active power target value Pac_ref by the virtual resistance value r in the virtual impedance, the value obtained by multiplying the reactive power target value Qac_ref by the virtual reactance value x in the virtual impedance, and a predetermined fixed value. Also, the q-axis internal induced voltage target value Eq_ref is calculated by subtracting the value obtained by multiplying the reactive power target value Qac_ref by the virtual resistance value r in the virtual impedance from the value obtained by multiplying the active power target value Pac_ref by the virtual reactance value x in the virtual impedance. Therefore, the voltage target value used as a reference for calculating the current target values ​​Id_ref and Iq_ref can be set to a value that simulates a virtual prime mover, based on the circuit equation between the AC power system 2 and the virtual prime mover, thereby ensuring load fluctuation stability similar to that of a real prime mover.

[0077] Furthermore, according to this embodiment, the d-axis current target value Id_ref is limited to a first range by the upper and lower limiter 89, and the q-axis current target value Iq_ref is limited to a second range by the upper and lower limiter 90.

[0078] As described above, the reactive power target value calculation unit 14 receives feedback from the voltage Vac in the AC wiring 5. Therefore, if a momentary voltage drop occurs in the AC power supply system 2, the low voltage Vac is fed back to the reactive power target value calculation unit 14, and the reactive power target value Qac_ref becomes excessive. If the current target values ​​Id_ref and Iq_ref are calculated based on this reactive power target value Qac_ref, the values ​​will be excessive, and there is a risk that the power converter 4 will trip.

[0079] Furthermore, the active power target value calculation unit 13 receives feedback from the frequency fac in the AC wiring 5. Therefore, if the frequency fac in the AC power supply system 2 fluctuates significantly, the active power target value Pac_ref becomes excessive. If the current target values ​​Id_ref and Iq_ref are calculated based on this active power target value Pac_ref, their values ​​will also become excessive, potentially causing the power converter 4 to trip.

[0080] In contrast, according to this embodiment, the d-axis current target value Id_ref and the q-axis current target value Iq_ref are limited, so even if a momentary voltage drop or large frequency fluctuation occurs in the AC power system 2, excessive current target values ​​Id_ref and Iq_ref are suppressed. Therefore, according to this embodiment, grid connection operation can be continued even if a momentary voltage drop occurs during grid connection operation without changing the circuit configuration and control method. Furthermore, when the voltage in the AC power system 2 recovers, the current target values ​​Id_ref and Iq_ref are generated from the active power target value Pac_ref corresponding to the frequency fac in the AC wiring 5 and the reactive power target value Qac_ref corresponding to the voltage Vac in the AC wiring 5. Therefore, according to this embodiment, the AC power system 2 can be quickly restored from a voltage drop state when the voltage recovers without changing the circuit configuration and control method.

[0081] The upper and lower limits of the upper and lower limiters 89 and 90 in the current target value calculation unit 18 described above can be determined based on the maximum rated current of the power semiconductor element used in the power converter 4. For example, if the maximum rated current of the power semiconductor element is set to twice the rated value of the current output by the power converter 4, the upper limits of the upper and lower limiters 89 and 90 can be determined so that the current value during normal operation is lower than twice that value, for example, less than 1.5 times. If the rated power factor of the power converter 4 is 90%, and the rated value of the current output by the power converter 4 is 1, then the rated active power of the power converter is 0.9, and the rated reactive power is 0.43 (= (1 - 0.9) ２ ) １／２ These are the upper and lower limit values ​​of the upper and lower limiters 38 and 45, which have a margin over these rated values.

[0082] For example, in the current target value calculation unit 18, the upper limit of the upper and lower limiter 89 that limits the d-axis current target value Id_ref is set to 1.2, and the lower limit is set to -1.2. Also, for example, in the current target value calculation unit 18, the upper limit of the upper and lower limiter 90 that limits the q-axis current target value Iq_ref is set to 0.6, and the lower limit is set to -0.6. In this case, the current output from the power converter 4 is -1.34 (= -1.2 ２ +0.6 ２ ) １／２ ) and 1.34 (= (1.2 ２ +0.6 ２ ) １／２ It is restricted between ) and ).

[0083] Thus, the first range R1 of the upper and lower limiter 89 that limits the d-axis current target value Id_ref can be set to -A < R1 < A. Here, A can be a value greater than 1 and less than 2 (1 < A < 2) when the rated value of the power output from the power converter 4 is 1. Also, the second range R2 of the upper and lower limiter 90 that limits the q-axis current target value Iq_ref can be set to -B < R2 < B. Here, B can be a value greater than 0 and less than 1 (0 < B < 1) when the rated value of the power output from the power converter 4 is 1.

[0084] This allows the power output from the power converter 4 to be limited to a value smaller than the rated value, and even if an instantaneous voltage drop occurs in the AC power supply system 2, the occurrence of overcurrent can be appropriately suppressed. Note that the first range R1 limited by the upper and lower limiters 89 or the second range R2 limited by the upper and lower limiters 90 are not limited to those described above.

[0085] Furthermore, according to this embodiment, a proportional control component Pac_m is calculated such that the relationship between the frequency fac in the AC wiring 5 and the active power Pac of the power converter output by the power converter 4 has a predetermined first drooping characteristic. At the same time, the value obtained by passing the frequency fac through a predetermined low-pass filter 35 is multiplied by a virtual unit inertia constant M, and the derivative of the multiplied value is calculated as the virtual inertia force Pac_i. By subtracting the virtual inertia force Pac_i from the proportional control component Pac_m, the target active power value Pac_ref is calculated, and the power converter 4 is controlled so that the d-axis current Id of the AC wiring 5 matches the d-axis current target value Id_ref corresponding to the target active power value Pac_Ref.

[0086] This allows the power converter 4 to be provided with an inertial force that enables it to flexibly respond to power fluctuations in the AC power system 2 during grid-connected operation, as well as to frequency fluctuations. Furthermore, by passing the frequency fac through the low-pass filter 35 before the differential calculation to generate the virtual inertial force Pac_i, and by limiting the calculated active power target value Pac_ref to a predetermined second range by the upper and lower limiter 38, the generation of an excessively large active power target value Pac_ref is suppressed even when frequency fluctuations are large. As a result, even when a pseudo-inertia model is applied to the active power target value calculation unit 13, it is possible to calculate a stable active power target value Pac_ref and a d-axis current target value Id_ref. Therefore, stable operation can be achieved while providing an inertial force to the power converter 4.

[0087] Furthermore, according to this embodiment, the voltage target values ​​Vd_ref and Vq_ref are calculated by adding limiting voltages Vdl and Vql, which restrict the corresponding currents to a predetermined range, to the voltage target values ​​Vdo_ref and Vqo_ref, which are based on the current deviations ΔId and ΔIq of the respective axis currents Id and Iq with respect to the current target values ​​Id and Iq. By adding the limited voltages Vdl and Vql to the voltage target values ​​Vdo_ref and Vqo_ref based on the current deviations ΔId and ΔIq, it is possible to achieve independent operation in which the energy storage equipment 1 operates independently of the AC power system 2, while improving responsiveness in the event of an instantaneous voltage drop in the AC power system 2, without changing the control method.

[0088] Thus, according to this embodiment, it is possible to seamlessly switch between grid-connected operation and independent operation with a simple configuration without changing the control method.

[0089] [Simulation Results] (1) Simulation 1 Regarding the Occurrence of Instantaneous Voltage Drop Below, as the first simulation, the results of a simulation in which an instantaneous voltage drop occurs due to a three-phase short circuit in the AC power supply system 2 during grid-connected operation in the energy storage equipment 1 of the above embodiment are shown below. In the first simulation, a simulation was performed on the behavior when an instantaneous voltage drop occurs in the AC power supply system 2 with a residual voltage of 20% and a duration of 0.3 seconds. In the first simulation, an instantaneous voltage drop occurs at time t1 after the start of the simulation, and the voltage in the AC power supply system 2 recovers at time t2, 0.3 seconds after time t1.

[0090] Furthermore, in this simulation, various parameters in each configuration are set as follows: The coefficient (1 / Kdr) showing the first drooping characteristic in the gain multiplier 34 of the active power target value calculation unit 13 is 20. That is, the gain Kdr of the gain multiplier 31 is 0.05. Also, the time constant T of the low-pass filter 35 is 0.1, and the virtual unit inertia constant M is 2. Also, the coefficient (1 / Kdra) showing the second drooping characteristic in the gain multiplier 44 of the reactive power target value calculation unit 14 is 2.5. That is, the gain Kdra of the gain multiplier 41 is 0.4. Also, the upper limit value of the upper and lower limit limiter 89 of the current target value calculation unit 18 is 1.2, and the lower limit value is -1.2. Also, the upper limit value of the upper and lower limit limiter 90 is 0.5, and the lower limit value is -0.5.

[0091] Furthermore, the proportional gain in the proportional-integral calculators 53 and 58 of the voltage target value calculation unit 15 is Kd = Kq = 1.0, and the integral gain is Kd / Tid = Kq / Tiq = 40. Also, the upper limit of the upper and lower limiter 55 is 0.9, and the lower limit is 0. The upper and lower limits of the upper and lower limiter 60 are both 0. In other words, in this simulation, the q-axis limiting voltage Vql is not added to the voltage target value Vqo_ref based on the q-axis current deviation ΔIq.

[0092] Figure 8 is a graph showing the time evolution of active power, reactive power, system voltage, system frequency, and RMS current in the first simulation. The graphs for active power, reactive power, system voltage, system frequency, and RMS current shown in Figure 8 represent each value with the value at rated power set to 1, while the graph for reactive power shown in Figure 8 represents the value with the value at rated power set to 0. On the horizontal axis of the graph in Figure 8, one division represents 0.1 seconds.

[0093] When a momentary voltage drop occurs at time t1, the active power decreases and the reactive power increases. However, the reactive power does not rise excessively and stabilizes within 0.1 seconds from time t1. Also, although the effective current increases at time t1, no overcurrent exceeding twice the rated current occurs and remains stable.

[0094] Furthermore, when the grid voltage is restored at time t2, the reactive power rises temporarily, but the increase is not excessive, and it returns to a steady state, i.e., the state before time t1, within 0.1 seconds from time t2. The effective current also does not exceed twice the rated current after time t2, and returns to the state before time t1 within 0.1 seconds from time t2.

[0095] For example, the FRT requirement stipulated in the grid connection regulations (JEAC9701-2019) includes the requirement that "when the remaining voltage is 20% or more, operation shall continue in the event of a voltage drop of 0.3 seconds without phase change, and after the voltage recovers in the AC power system, the output shall recover to 80% or more of the output before the voltage drop within 0.1 seconds." As described above, in the first simulation, it can be said that operation can continue even if a voltage drop occurs at time t1. Furthermore, it can be said that the output recovers to 80% or more of the output before the voltage drop within 0.1 seconds from time t2, when the voltage recovers. Therefore, it can be said that the energy storage equipment 1 in this embodiment satisfies the above FRT requirement when a three-phase short circuit occurs.

[0096] (2) Simulation 2 regarding the occurrence of instantaneous voltage drops Next, as a second simulation, the results of a simulation in which an instantaneous voltage drop occurs due to a line-to-line short circuit in the AC power supply system 2 during grid-connected operation in the energy storage equipment 1 of the above embodiment are shown below. In the second simulation as well, an instantaneous voltage drop similar to that in the first simulation occurs at time t1 after the start of the simulation, and the voltage in the AC power supply system 2 recovers at time t2, 0.3 seconds after time t1. In this simulation as well, various parameters in each configuration are set to the same values ​​as in the first simulation.

[0097] Figure 9 is a graph showing the time evolution of active power, reactive power, system voltage, system frequency, and RMS current in the second simulation. The graphs for active power, reactive power, system voltage, system frequency, and RMS current shown in Figure 9 represent each value with the value at rated operation set to 1, while the graph for reactive power shown in Figure 9 represents the value with the value at rated operation set to 0. On the horizontal axis of the graph in Figure 9, one division represents 0.1 seconds.

[0098] In this simulation, the behavior was similar to that of the first simulation shown in Figure 6, except that the values ​​were oscillating during the voltage drop from time t1 to time t2. That is, even when an instantaneous voltage drop occurred at time t1, the reactive power did not rise excessively and stabilized within 0.1 seconds from time t1. Also, although the effective current increased at time t1, no overcurrent exceeding twice the rated current occurred and it remained stable. Furthermore, when the grid voltage was restored at time t2, the increase in reactive power was not excessive and returned to the state before time t1 within 0.1 seconds from time t2. The effective current also did not experience any overcurrent exceeding twice the rated current after time t2 and returned to the state before time t1 within 0.1 seconds from time t2.

[0099] Thus, in the second simulation, it can be said that operation can continue even if a voltage drop occurs at time t1. Furthermore, it can be said that the output recovers to more than 80% of the output before the voltage drop within 0.1 seconds from time t2, when the voltage recovers. Therefore, it can be said that the energy storage equipment 1 in this embodiment satisfies the above FRT requirements when a line short circuit occurs.

[0100] (3) Simulation of Standalone Operation Next, as a third simulation, the results of a simulation in which the load is changed during standalone operation of the energy storage equipment 1 of the above embodiment are shown below. In the third simulation, the simulation is started in a no-load state, and at time t3 after the start of the simulation, the load has increased to about 0.5 times the rated value in terms of active power. In this simulation as well, the various parameters in each configuration are set to the same values ​​as in the first simulation.

[0101] Figure 10 is a graph showing the time evolution of active power, reactive power, grid voltage, and grid frequency in the third simulation. On the horizontal axis of the graph in Figure 10, one division represents 0.1 seconds.

[0102] As shown in Figure 10, even during autonomous operation, the same configuration and control method can be used to ensure continued operation without the grid voltage becoming excessive. In particular, even if the load fluctuates at time t3, the grid voltage can be maintained at the same value as before time t3 after time t3.

[0103] (4) Summary of Simulations From the results of the first and second simulations, it can be seen that, according to the control method of the energy storage equipment 1 in the above embodiment, operation is possible in both independent operation and grid-connected operation without changing the circuit configuration or control method, and even if a momentary voltage drop occurs during grid-connected operation, grid-connected operation can be continued, and the voltage can be quickly recovered from the voltage drop state when the voltage in the AC power system 2 recovers. Furthermore, from the results of the third simulation, it can be seen that, according to the control method of the energy storage equipment 1 in the above embodiment, it can operate stably even if the load fluctuates during independent operation.

[0104] While embodiments of this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various improvements, changes, and modifications are possible without departing from the spirit of this disclosure.

[0105] [Other Embodiments] For example, in the above embodiment, the case in which the AC wiring 5 in the energy storage equipment 1 is a three-phase system was described, but it is not limited to this. For example, even if the AC wiring 5 is a single-phase two-wire system or a single-phase three-wire system, a similar energy storage equipment 1 can be constructed, except that the methods of various calculations differ depending on the system type.

[0106] Furthermore, in the above embodiment, in order to enable a seamless transition between independent operation and grid-connected operation, an example was given in which a d-axis limiting voltage is applied to the d-axis voltage target value Vdo_ref based on the d-axis current deviation ΔId, and a q-axis limiting voltage is applied to the voltage target value Vqo_ref based on the q-axis current deviation ΔIq. However, in order to continue grid-connected operation even if an instantaneous voltage drop occurs during grid-connected operation, and to quickly recover from the voltage drop state when the voltage in the AC power system 2 recovers, such control methods do not necessarily have to be implemented.

[0107] Furthermore, although the above embodiment illustrates a control mode in which the active power target value calculation unit 13 has a pseudo-inertia model circuit 13b, the pseudo-inertia model circuit 13b may be omitted.

[0108] [Summary of the Disclosure] [Aspect 1] A control circuit for a power converter according to one aspect of the Disclosure is a control circuit for a power converter that performs power conversion between a capacitor and an AC power system, and acquires the voltage, frequency and current output from the power converter to the AC wiring connecting the AC power system and the power converter, calculates an active power target value by an active power target value calculation process that includes multiplying a first deviation, which is the deviation of the frequency from a frequency target value, by a coefficient indicating the first drooping characteristic, so that the relationship between the frequency and the active power of the power converter output by the power converter to the AC wiring has a predetermined first drooping characteristic, and calculates a reactive power target value by an reactive power target value calculation process that includes multiplying a second deviation, which is the deviation of the voltage from a voltage target value, by a coefficient indicating the second drooping characteristic, so that the relationship between the voltage and the reactive power of the power converter output by the power converter to the AC wiring has a predetermined second drooping characteristic, and assumes that the AC power system and a virtual prime mover are connected. In this process, an internal induced voltage target value is calculated by an internal induced voltage target value calculation process that uses a value set as the virtual impedance between the AC power system and the virtual prime mover, and calculates the internal induced voltage target value in the virtual prime mover from the current flowing through the virtual impedance when the active power output from the virtual prime mover is the active power target value and the reactive power output from the virtual prime mover is the reactive power target value. A current target value is calculated by a current target value calculation process that includes a calculation to determine the current flowing through the virtual impedance assuming that the AC power system and the virtual prime mover are connected, based on the deviation of the internal induced voltage target value with respect to the voltage in the AC wiring. A voltage target value is calculated by a voltage target value calculation process that calculates the voltage target value from the deviation of the current target value with respect to the current output to the AC wiring, and a drive signal for the power converter is generated according to the voltage target value.

[0109] According to the above configuration, the current target value is calculated to reflect the actual voltage fluctuations in the AC wiring, thereby increasing the responsiveness of the power converter to current fluctuations caused by load fluctuations in the AC wiring. Therefore, in a power converter operating independently, the responsiveness of the current output to the AC wiring from the power converter to load fluctuations in the AC wiring can be increased, and the amount of voltage fluctuation in the AC wiring can be reduced. Thus, according to this embodiment, in a power converter for an energy storage facility connected to an AC power system, a simple configuration allows the power converter to operate stably independently even when the energy storage facility is disconnected from the AC power system.

[0110] [Aspect 2] The control circuit described in Aspect 1 may calculate the d-axis internal induced voltage target value by adding the value obtained by multiplying the active power target value by the virtual resistance value in the virtual impedance, the value obtained by multiplying the reactive power target value by the virtual reactance value in the virtual impedance, and a predetermined fixed value in the internal induced voltage target value calculation process, and then subtract the value obtained by multiplying the reactive power target value by the virtual resistance value in the virtual impedance from the value obtained by multiplying the active power target value by the virtual reactance value in the virtual impedance.

[0111] According to the above configuration, the voltage target value used as a reference for calculating the current target value can be set to a value that simulates a virtual prime mover, based on the circuit equation between the AC power system and the virtual prime mover, thereby ensuring load fluctuation stability similar to that of a real prime mover.

[0112] [Aspect 3] The control circuit described in aspect 1 or 2 may, in the current target value calculation process, perform a first restriction process to limit the d-axis current target value corresponding to the current target value to a predetermined first range, and a second restriction process to limit the q-axis current target value corresponding to the current target value to a predetermined second range.

[0113] With the above configuration, the d-axis current target value and the q-axis current target value are limited, so even if instantaneous voltage drops or large frequency fluctuations occur in the AC power system, excessive current target values ​​are suppressed. Therefore, with the above configuration, grid connection operation can be continued even if an instantaneous voltage drop occurs during grid connection operation. Furthermore, with the above configuration, without changing the circuit configuration or control method, the AC power system can quickly recover from a voltage drop state when voltage recovery occurs.

[0114] [Aspect 4] The control circuit described in any of aspects 1 to 3 may calculate the target active power value in the active power target value calculation process by multiplying the frequency by a virtual unit inertia constant, calculating the derivative of the multiplied value as a virtual inertial force, and subtracting the value of the virtual inertial force from the value obtained by multiplying the first deviation by a coefficient indicating the first drooping characteristic.

[0115] According to the above configuration, the power converter can be provided with the ability to adjust supply and demand in response to power fluctuations in the AC power system during grid-connected operation, as well as with inertia to flexibly respond to frequency fluctuations. Furthermore, by passing the frequency through a low-pass filter before the differential calculation to generate the virtual inertia, the generation of excessive virtual inertia is suppressed even when frequency fluctuations are large. As a result, even when a pseudo-inertia model is applied to the active power target value calculation unit, a stable calculation of the active power target value can be achieved. Therefore, stable operation can be achieved while providing inertia to the power converter.

[0116] [Aspect 5] In the control circuit described in aspect 4, the low-pass filter may include a first-order lag filter.

[0117] [Aspect 6] The control circuit described in any of aspects 1 to 5 may, in the voltage target value calculation process, calculate the d-axis voltage from the instantaneous voltage value in the AC wiring, calculate the d-axis current from the instantaneous current value in the AC wiring, calculate the d-axis current deviation which is the deviation of the d-axis current target value corresponding to the current target value with respect to the d-axis current, and add a d-axis limiting voltage which limits the d-axis voltage to a predetermined third range to the d-axis voltage target value calculated based on the d-axis current deviation. This makes it possible to achieve independent operation, in which the power supply system is operated independently of the AC power supply system, while improving responsiveness in the event of an instantaneous voltage drop in the AC power supply system, without changing the control method.

[0118] [Aspect 7] The control circuit described in aspect 6 may calculate the d-axis voltage target value by performing a proportional-integral operation on the d-axis current deviation in the voltage target value calculation process. By performing an integral operation as well as a proportional operation when calculating the voltage target value based on the d-axis current deviation, a d-axis voltage target value is generated such that the d-axis current converges appropriately near the rating. As a result, appropriate control can be performed even when the d-axis voltage applied to the voltage target value based on the d-axis current deviation is limited.

[0119] [Aspect 8] The control circuit described in aspect 6 or 7 may, in the voltage target value calculation process, calculate the q-axis voltage from the instantaneous voltage value in the AC wiring, calculate the q-axis current from the instantaneous current value in the AC wiring, calculate the q-axis current deviation which is the deviation of the q-axis current target value corresponding to the current target value with respect to the q-axis current, and add a q-axis limiting voltage which limits the q-axis voltage to a predetermined fourth range to the q-axis voltage target value calculated based on the q-axis current deviation. This makes it possible to achieve independent operation, in which the power supply system is operated independently of the AC power supply system, while improving responsiveness when an instantaneous voltage drop occurs in the AC power supply system, without changing the control method.

[0120] [Aspect 9] In the control circuit described in aspect 3, the first range R1 may be set to -A < R1 < A and 1 < A < 2 when the rated value of the power or current output by the power converter is 1, and the second range R2 may be set to -B < R2 < B and 0 < B < 1 when the rated value of the power or current output by the power converter is 1. This makes it possible to limit the power output from the power converter to a value smaller than the rated value, and even if an instantaneous voltage drop occurs in the AC power system, the occurrence of overcurrent can be appropriately suppressed.

[0121] [Aspect 10] 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 a capacitor and an AC power system, wherein the method obtains the voltage, frequency, and current output from the power converter to the AC wiring connecting the AC power system and the power converter, calculates an active power target value by an active power target value calculation process that includes multiplying a first deviation, which is the deviation of the frequency from a frequency target value, by a coefficient indicating the first drooping characteristic, so that the relationship between the frequency and the active power of the power converter output by the power converter to the AC wiring has a predetermined first drooping characteristic, calculates a reactive power target value by an reactive power target value calculation process that includes multiplying a second deviation, which is the deviation of the voltage from a voltage target value, by a coefficient indicating the second drooping characteristic, so that the relationship between the voltage and the reactive power of the power converter output by the power converter to the AC wiring has a predetermined second drooping characteristic, and assumes that the AC power system and a virtual prime mover are connected. In this case, an internal induced voltage target value is calculated by an internal induced voltage target value calculation process that uses a value set as the virtual impedance between the AC power system and the virtual prime mover, and calculates the internal induced voltage target value in the virtual prime mover from the current flowing through the virtual impedance when the active power output from the virtual prime mover is the active power target value and the reactive power output from the virtual prime mover is the reactive power target value. A current target value is calculated by a current target value calculation process that includes a calculation to determine the current flowing through the virtual impedance assuming that the AC power system and the virtual prime mover are connected, based on the deviation of the internal induced voltage target value with respect to the voltage in the AC wiring. A voltage target value is calculated by a voltage target value calculation process that calculates the voltage target value from the deviation of the current target value with respect to the current output to the AC wiring, and a drive signal for the power converter is generated according to the voltage target value.

[0122] 2. AC power supply system 3. Energy storage 4. Power converter 5. AC wiring 10. Control circuit

Claims

1. A control circuit for a power converter that performs power conversion between a power storage device and an AC power system, comprising: acquiring the voltage, frequency, and current output from the power converter to the AC wiring connecting the AC power system and the power converter; calculating an active power target value by an active power target value calculation process that includes multiplying a first deviation, which is the deviation of the frequency from a frequency target value, by a coefficient indicating the first drooping characteristic, so that the relationship between the frequency and the active power of the power converter output by the power converter to the AC wiring has a predetermined first drooping characteristic; and calculating a reactive power target value by an reactive power target value calculation process that includes multiplying a second deviation, which is the deviation of the voltage from a voltage target value, by a coefficient indicating the second drooping characteristic, so that the relationship between the voltage and the reactive power of the power converter output by the power converter to the AC wiring has a predetermined second drooping characteristic. A control circuit that calculates an internal induced voltage target value in the virtual prime mover by an internal induced voltage target value calculation process, which uses a value set as the virtual impedance between the AC power system and the virtual prime mover, assuming that the AC power system and the virtual prime mover are connected, and calculates an internal induced voltage target value in the virtual prime mover from the current flowing through the virtual impedance when the active power output from the virtual prime mover is the active power target value and the reactive power output from the virtual prime mover is the reactive power target value; calculates a current target value by a current target value calculation process that includes a calculation to calculate the current flowing through the virtual impedance assuming that the AC power system and the virtual prime mover are connected, based on the deviation of the internal induced voltage target value with respect to the voltage in the AC wiring; calculates a voltage target value by a voltage target value calculation process that calculates a voltage target value from the deviation of the current target value with respect to the current output to the AC wiring; and generates a drive signal for the power converter according to the voltage target value.

2. The control circuit according to claim 1, wherein in the internal induced voltage target value calculation process, the d-axis internal induced voltage target value is calculated by adding the value obtained by multiplying the active power target value by the virtual resistance value in the virtual impedance, the value obtained by multiplying the reactive power target value by the virtual reactance value in the virtual impedance, and a predetermined fixed value, and the q-axis internal induced voltage target value is calculated by subtracting the value obtained by multiplying the reactive power target value by the virtual resistance value in the virtual impedance from the value obtained by multiplying the active power target value by the virtual reactance value in the virtual impedance.

3. The control circuit according to claim 1 or 2, wherein in the current target value calculation process, a first restriction process is performed to restrict the d-axis current target value corresponding to the current target value to a predetermined first range, and a second restriction process is performed to restrict the q-axis current target value corresponding to the current target value to a predetermined second range.

4. The control circuit according to claim 1 or 2, wherein in the active power target value calculation process, the active power target value is calculated by multiplying the frequency by a virtual unit inertia constant, calculating the derivative of the multiplied value as a virtual inertial force, and subtracting the value of the virtual inertial force from the value obtained by multiplying the first deviation by a coefficient indicating the first drooping characteristic.

5. The control circuit according to claim 4, wherein the low-pass filter includes a first-order lag filter.

6. The control circuit according to claim 1 or 2, wherein in the voltage target value calculation process, a d-axis voltage is calculated from the instantaneous voltage value in the AC wiring; a d-axis current is calculated from the instantaneous current value in the AC wiring; a d-axis current deviation is calculated which is the deviation of the d-axis current target value corresponding to the current target value with respect to the d-axis current; and a d-axis limiting voltage, which limits the d-axis voltage to a predetermined third range, is added to the d-axis voltage target value calculated based on the d-axis current deviation.

7. The control circuit according to claim 6, wherein, in the voltage target value calculation process, the d-axis current deviation is used to calculate the d-axis voltage target value.

8. The control circuit according to claim 6, wherein in the voltage target value calculation process, a q-axis voltage is calculated from the instantaneous voltage value in the AC wiring; a q-axis current is calculated from the instantaneous current value in the AC wiring; a q-axis current deviation is calculated which is the deviation of the q-axis current target value corresponding to the current target value with respect to the q-axis current; and a q-axis limiting voltage, which limits the q-axis voltage to a predetermined fourth range, is added to the q-axis voltage target value calculated based on the q-axis current deviation.

9. The control circuit according to claim 3, wherein the first range R1 is set to -A < R1 < A and 1 < A < 2 when the rated value of the power or current output by the power converter is 1, and the second range R2 is set to -B < R2 < B and 0 < B < 1 when the rated value of the power or current output by the power converter is 1.

10. A control method for a power converter that performs power conversion between a power storage device and an AC power system, comprising: acquiring the voltage, frequency, and current output from the power converter to the AC wiring connecting the AC power system and the power converter; calculating an active power target value by an active power target value calculation process that includes multiplying a first deviation, which is the deviation of the frequency from a frequency target value, by a coefficient indicating the first drooping characteristic, so that the relationship between the frequency and the active power of the power converter output by the power converter to the AC wiring has a predetermined first drooping characteristic; and calculating a reactive power target value by an reactive power target value calculation process that includes multiplying a second deviation, which is the deviation of the voltage from a voltage target value, by a coefficient indicating the second drooping characteristic, so that the relationship between the voltage and the reactive power of the power converter output by the power converter to the AC wiring has a predetermined second drooping characteristic. A control method comprising: calculating an internal induced voltage target value by an internal induced voltage target value calculation process that calculates an internal induced voltage target value in the virtual prime mover from the current flowing through the virtual impedance when the active power output from the virtual prime mover is the active power target value and the reactive power output from the virtual prime mover is the reactive power target value, assuming that the AC power system and a virtual prime mover are connected; calculating a current target value by a current target value calculation process that includes a calculation of the current flowing through the virtual impedance assuming that the AC power system and a virtual prime mover are connected, based on the deviation of the internal induced voltage target value with respect to the voltage in the AC wiring; calculating a voltage target value by a voltage target value calculation process that calculates a voltage target value from the deviation of the current target value with respect to the current output to the AC wiring; and generating a drive signal for the power converter according to the voltage target value.

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