Power conversion device

Abstract

To stabilize the frequency or voltage of a power system while suppressing excess current.SOLUTION: A power conversion device includes an inverter that converts input direct current power to alternating current power and a control device that controls the inverter. The control device limits one current more preferentially than the other current of an active current and a reactive current output from the inverter so that an apparent current output from the inverter is less than or equal to a limit value.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device. [Background technology]

[0002] A power converter that applies voltage-controlled virtual synchronous generator control may stop due to converter overcurrent during system disturbance or overload, and a control method is required to suppress this and continue operation. Virtual synchronous generator control is roughly divided into voltage-controlled and current-controlled types, and in the case of the current-controlled type, there is a method of limiting a current command value and controlling the current to an arbitrary value. However, in the case of the voltage-controlled type, the method of suppressing the voltage command value does not allow the current to be controlled to an arbitrary value, so that an overcurrent may occur depending on conditions such as system impedance. Therefore, a power conversion device is known that performs voltage-controlled virtual synchronous generator control during normal operation and suppresses the overcurrent by current control when an output overcurrent occurs (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-141704 Summary of the Invention [Problem to be solved by the invention]

[0004] The inverter control has a function for stabilizing the frequency and voltage of the system by outputting active current to stabilize the frequency and outputting reactive current to stabilize the voltage. When the frequency disturbance of the system is large, it is desirable to output active current as much as possible, and when the voltage disturbance of the system is large, it is desirable to output reactive current as much as possible.

[0005] However, if the active current output and the reactive current output are uniformly limited at the same ratio, it will affect both the frequency stabilization and the voltage stabilization. Therefore, for example, even if the grid frequency is stable, the active current will be limited, and even if the grid voltage is stable, the reactive current will be limited.

[0006] The present disclosure provides a power conversion device capable of stabilizing the frequency or voltage of a grid while suppressing overcurrent. [Means for solving the problem]

[0007] The power conversion device of the present disclosure includes: An inverter that converts input DC power into AC power; A control device for controlling the inverter, The control device limits one of the active current and the reactive current output from the inverter by giving priority to the other current so that the apparent current output from the inverter is equal to or less than a limit value.

[0008] The power conversion device of the present disclosure includes: The control device may limit the active current with priority over the reactive current so that the apparent current is equal to or less than the limit value when the amplitude of the output voltage from the inverter is disturbed.

[0009] An inverter that converts input DC power into AC power; A control device for controlling the inverter, The control device reduces one of the active current and reactive current output from the inverter with a larger gain than the other current so that the apparent current output from the inverter becomes equal to or less than a limit value. Effect of the Invention

[0010] According to the present disclosure, it is possible to stabilize the frequency or voltage of a grid while suppressing overcurrent. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a configuration example of a power conversion device. [Diagram 2] 2 is a diagram illustrating an example of the configuration of an inverter and a control device in the power conversion device of the first embodiment. FIG. [Diagram 3] FIG. 4 is a functional block diagram illustrating an example of a current command limiting unit. [Figure 4] 11 is a vector diagram for explaining a current command limit in an apparent current limit mode; [Diagram 5] FIG. 4 is a functional block diagram illustrating an example of an apparent current limiting unit. [Figure 6] 11 is a vector diagram for explaining a current command limit in an active current limit mode; [Figure 7] FIG. 4 is a functional block diagram illustrating an example of an active current limiting unit. [Figure 8] 11 is a vector diagram for explaining a current command limit in a reactive current limit mode; [Figure 9] FIG. 4 is a functional block diagram illustrating an example of a reactive current limiting unit. [Figure 10] FIG. 4 is a functional block diagram illustrating an example of a mode selection unit. [Figure 11] 6 is a diagram illustrating an example of the configuration of an inverter and a control device in a power conversion device according to a second embodiment. FIG. [Figure 12] FIG. 2 is a functional block diagram illustrating an example of a frequency control unit in the control device. [Figure 13] FIG. 2 is a functional block diagram illustrating an example of a voltage amplitude control unit in the control device. [Figure 14] FIG. 2 is a functional block diagram illustrating an example of an instantaneous voltage command unit in the control device. [Figure 15] FIG. 2 is a functional block diagram showing an example of an instantaneous current command unit in the control device. [Figure 16] FIG. 2 is a functional block diagram showing an example of an instantaneous current control unit in the control device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The following describes the embodiments.

[0013] <Overall schematic configuration of power conversion device> Fig. 1 is a diagram showing an example of the configuration of a power conversion device. A power conversion device 2 shown in Fig. 1 is connected to a power system 1. The power system 1 is a power system that supplies AC power generated at a power plant to consumer equipment via a distribution line 10.

[0014] The power conversion device 2 is a device that inputs and outputs electric power to and from the power system 1. The power conversion device 2 includes an inverter 5 that inputs and outputs electric power to and from the power system 1, and a control device 20 that operates the inverter 5 as a GFL (Grid Following) inverter or a GFM (Grid Forming) inverter.

[0015] The inverter 5 is a device that converts input DC power into AC power. The inverter 5 is, for example, an inverter-based resource (IBR) that converts DC power generated from renewable energy such as solar power into AC power and operates in connection with the power grid 1. The inverter 5 includes a power conversion unit 6, a filter 3, and a switch 4.

[0016] The power conversion unit 6 converts a pulse width modulation signal (PWM pulse signal V PWM ) according to the input DC power P in (e.g., DC power generated from renewable energy) into AC power. The power conversion unit 6 converts the PWM pulse signal V PWM According to the above, the voltage v equivalent to the AC voltage PWM The power conversion unit 6 is connected to the power system 1 via the filter 3 and the switch 4.

[0017] The filter 3 removes harmonic components of the current flowing between the power conversion unit 6 and the power system 1. The filter 3 includes a filter for filtering the AC current i L is input. The filter 3 outputs the current i L The output current i with the harmonic components removed from out is output to power grid 1.

[0018] The filter 3 is, for example, an LCL filter including a reactor L1, a reactor L2, and a capacitor C. The reactor L1 and the reactor L2 are connected in series with each other. The reactor L1 is connected to the output side of the power conversion unit 6, and the reactor L2 is connected to the power system 1 side.

[0019] One end of the capacitor C is connected between the reactor L1 and the reactor L2. The other end of the capacitor C is connected to a neutral point of the three phases (not shown). The other end of the capacitor C may be grounded. Also, instead of such a Y connection (star connection), a Δ connection (delta connection) may be used.

[0020] Since the reactor L1 is present between the power conversion unit 6 and the capacitor C, a difference voltage between the output voltage of the power conversion unit 6 and the voltage of the capacitor C is generated in the reactor L1. This difference voltage and the impedance of the reactor L1 give the current i L Using this property, the control device 20 determines the voltage v output from the power conversion unit 6. PWM By controlling the current i L can be controlled.

[0021] The switch 4 is connected between the power system 1 and the power conversion unit 6. The switch 4 is sometimes called an interconnection switch.

[0022] When the power system 1 is in a normal state, the switch 4 is on, and the inverter 5 can exchange power with the power system 1. When an abnormality such as a failure occurs in the power system 1, the switch 4 switches from on to off, and the inverter 5 is disconnected from the power system 1. The on / off state of the switch 4 is controlled by, for example, the control device 20.

[0023] Specifically, the inverter 5 generates an output voltage v at a node N connected to the power distribution line 10. out Frequency f out , or active power P out and reactive power Q outDepending on the output of the voltage v PWM By controlling out The device outputs the effective power P out When the value is positive, it is the active power output from the inverter 5 to the power system 1, and when the value is negative, it is the active power input from the power system 1 to the inverter 5.

[0024] The functions of the control device 20 are realized by a processor such as a CPU (Central Processing Unit) operating according to a program stored in a memory. The functions of the control device 20 may be realized by a FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). The functions of the control device 20 may also be realized by an analog circuit using an operational amplifier or the like.

[0025] First Embodiment Fig. 2 is a diagram showing an example of the configuration of the inverter and the control device in the power conversion device of the first embodiment. Fig. 2 shows a circuit configuration of the inverter 5 and a functional block of the control device 20A. The power conversion device 2A of the first embodiment is an example of the above-mentioned power conversion device 2. The power conversion device 2A includes the inverter 5 and the control device 20A. The control device 20A controls the inverter 5 by a current control method.

[0026] The inverter 5 includes a power conversion unit 6, a filter 3, and a switch 4. The power conversion unit 6 includes a capacitor 7 and an inverter circuit 8.

[0027] The capacitor 7 smoothes the DC voltage input from an external device such as a power generation device that generates power using renewable energy such as sunlight, and stores the input energy. dc corresponds to the voltage of the capacitor 7 (capacitor voltage).

[0028] The inverter circuit 8 is an inverter circuit that converts DC power input from an external device such as a power generation device into AC power. The inverter circuit 8 converts the DC voltage v smoothed by the capacitor 7 into AC power. dc The AC voltage V PWM Convert it to and output it.

[0029] The control device 20A controls the inverter 5 by a current control method. The control device 20A includes an active power command unit 41, an active power control unit 42, a reactive power command unit 43, a reactive power control unit 44, a current command limiting unit 40, an inverse dq transformation unit 27, an instantaneous current control unit 28, an adder 29, and a PWM pulse generating unit 30.

[0030] The active power command unit 41 outputs an active power command value P ref The active power command unit 41 generates, for example, an active power set value P set , frequency measurement value f out and rated frequency setting value f n,ref Based on this, the active power command value P ref Calculate and output.

[0031] Active power setting value P set is the active power P out This is a reference value and is a value that is set by a person. When the DC side power generating device electrically connected to the capacitor 7 is a solar cell, the active power setting value P set is set to a value equal to or less than the effective power that the solar cell can generate. set may be automatically set by a control (MPPT: Maximum Power Point Tracking) that automatically determines the maximum power point at which the amount of power generated by the solar cell can be maximized. If a storage battery is provided on the DC side, the effective power setting value P set may be set according to the state of charge (SOC) of the storage battery. out is the output voltage v that is actually output from the inverter 5 to the power grid 1. out The frequency measurement value f outis the measured value at node N between filter 3 and power grid 1. The rated frequency setting value f n,ref is the set value of the rated frequency of power system 1. The rated frequency set value f n,ref For example, in Japan, eastern Japan uses 50Hz and western Japan uses 60Hz.

[0032] The active power control unit 42 controls the active power P out The active power control unit 42 controls the active power command value P ref , the active power P output from the inverter 5 to the power grid 1 out The active power control unit 42 performs instantaneous power control to bring the active power P out is sampled as the instantaneous active power, and the sampled value, the active power measurement value P out is the active power command value P ref In PI control, P stands for proportional control and I stands for integral control. out is the active power P output from the inverter 5 to the power grid 1. out are the measured values.

[0033] The active power control unit 42 determines the active power command value P ref and the effective power measurement value P out Based on this, the active power measurement value P out is the active power command value P ref The d-axis current command value i d,ref The d-axis current command value i d,ref is the command value of the active current output from the inverter 5 to the power grid 1. The d-axis current command value i d,ref is an example of a first current command value, and contributes to the active power output from the inverter 5 to the power system 1.

[0034] The reactive power command unit 43 outputs a reactive power command value Q ref The reactive power command unit 43 generates, for example, a reactive power setting value Q set and output voltage amplitude command value Vout,ref Based on this, the reactive power command value Q ref Calculate and output.

[0035] Reactive power setting value Q set is the reactive power Q out This is the reference value and is set by a human. When performing constant power factor control with a solar inverter, the reactive power setting value Q set is the power factor value set by the user and the measured active power value P out The output voltage amplitude command value V may be set to a value of the reactive power to be output, which is calculated based on the value of out,ref is the output voltage v output from the inverter 5 to the power grid 1. out is the amplitude command value.

[0036] The reactive power control unit 44 controls the reactive power Q output from the inverter 5 to the power system 1. out The reactive power control unit 44 controls the reactive power command value Q ref , the reactive power Q output from inverter 5 to power grid 1 out The reactive power control unit 44 performs instantaneous power control to bring the reactive power Q out is sampled as the instantaneous active power, and the sampled value, the reactive power measurement value Q out is the reactive power command value Q ref The reactive power measurement value Q out is the reactive power Q output from inverter 5 to power grid 1. out are the measured values.

[0037] The reactive power control unit 44 determines the reactive power command value Q ref and reactive power measurement value Q out Based on this, the reactive power measurement value Q out is the reactive power command value Q ref The q-axis current command value i q,ref The q-axis current command value i q,ref is the command value of the reactive current output from the inverter 5 to the power grid 1. The q-axis current command value i q,refis an example of a second current command value, and contributes to the reactive power output from the inverter 5 to the power grid 1.

[0038] In order to suppress an overcurrent flowing in the power grid 1, the current command limiting unit 40 limits the d-axis current command value i d,ref The d-axis current command value i d,ref,LIM and the q-axis current command value i q,ref The q-axis current command value i q,ref,LIM The current command limiting unit 40 will be described in detail later.

[0039] The inverse dq transformation unit 27 converts the biaxial current command value (d-axis current command value i d,ref,LIM and q-axis current command value i q,ref,LIM ) is the three-phase output current command value i ref The output current command value i ref is the current i output from the inverter circuit 8 to the filter 3. L are the command values ​​for the three phases.

[0040] The instantaneous current control unit 28 controls the current i output from the inverter circuit 8 to the filter 3. L The instantaneous current control unit 28 controls the output current command value i ref The current i output from the inverter circuit 8 to the filter 3 L The instantaneous current control unit 28 performs instantaneous current control to bring the current i L is sampled as an instantaneous current, and the sampled value, the current measurement value i L is the output current command value i ref It can be configured as an ACR (Automatic Current Regulator) that performs feedback control so that the measured current value i L are measured values ​​of instantaneous three-phase currents flowing from the inverter circuit 8 to the reactor L1 of the filter 3.

[0041] The instantaneous current control unit 28 controls the output current command value i ref and current measurement value i L Based on this, the current measurement value i L is the output current command value i refThe output voltage correction value v L,ref The output voltage correction value v L,ref is the output voltage measurement value v, which is the measurement value of the three-phase output voltage output from the inverter 5 to the power grid 1. out To correct the output voltage measurement value v out is added by adder 29.

[0042] The adder 29 outputs the measured output voltage v out to the output voltage correction value v L,ref The value obtained by adding PWM,ref The output is as follows:

[0043] The PWM pulse generating unit 30 generates a PWM command value v PWM,ref is compared with a carrier signal such as a triangular wave to generate a PWM pulse signal V PWM The pulse width modulation method is not limited to the triangular wave comparison modulation method, and any commonly used pulse width modulation method can be used. It goes without saying that the required number of PWM pulses must be generated depending on the configuration of the inverter circuit 8.

[0044] 3 is a functional block diagram showing an example of a current command limiting unit. The current command limiting unit 40 has a plurality of current limiting modes (apparent current limiting mode, active current limiting mode, and reactive current limiting mode) that can be switched during operation of the inverter 5 in order to suppress an overcurrent flowing through the power system 1. The current command limiting unit 40 switches the current limiting mode manually or automatically. For example, the current command limiting unit 40 basically operates in the apparent current limiting mode and the output voltage v out If it detects that the amplitude fluctuation of v exceeds the standard, it operates in active current limit mode and reduces the output voltage v out If it detects that the frequency fluctuation exceeds the standard, it will operate in reactive current limit mode.

[0045] The current command limiting unit 40 includes an apparent current limiting unit 51, an active current limiting unit 52, a reactive current limiting unit 53, and a mode selecting unit .

[0046] The apparent current limiting unit 51 is a d-axis current command limiting value (d-axis current command limiting value i d,LIM,1 and q-axis current command limit value i q,LIM,1 ) is generated. The d-axis current command limit value i d,LIM,1 is the d-axis current command value i d,ref This is the value that limits the q-axis current command limit value i q,LIM,1 is the q-axis current command value i q,ref is the value at which the apparent current is limited in the apparent current limit mode.

[0047] FIG. 4 is a vector diagram for explaining the current command limit in the apparent current limit mode. The apparent current limiting unit 51 limits the apparent current command value i s,ref is the limit value I LIM,set The d-axis current command value i d,ref and the q-axis current command value i q,ref is limited by the same ratio. LIM,set is set to be equal to or greater than the operational rating of the inverter 5 and equal to or less than the hardware rating of the inverter 5.

[0048] Apparent current command value i s,ref teeth, i s,ref =√((i d,ref ) 2 +(i q,ref ) 2 ) The following relation holds true.

[0049] The apparent current limiting unit 51 limits the d- and q-axis current command values ​​(d-axis current command value i d,ref and q-axis current command value i q,ref ) to obtain the apparent current command value i before limiting. s,ref The apparent current limiting unit 51 calculates the limiting value I LIM,set The apparent current command value i before limiting s,ref The apparent current limiting unit 51 calculates the current command suppression gain K by dividing the d-axis current command value i d,ref By multiplying by the current command suppression gain K, the d-axis current command limit value i d,LIM,1 The apparent current limiting unit 51 calculates the q-axis current command value i before limiting.q,ref By multiplying by the current command suppression gain K, the q-axis current command limit value i q,LIM,1 This calculates the apparent current command value i s,ref The magnitude of the current command vector is the radius (limit value I LIM,set The apparent current command value i is restricted to the circle s,ref,LIM Therefore, overcurrent is suppressed.

[0050] In this way, the control device 20A reduces the active current and the reactive current with the same gain so that the apparent current becomes equal to or less than the limit value.

[0051] 5 is a functional block diagram showing an example of the apparent current limiting unit 51. The apparent current limiting unit 51 includes multiplication units 51a and 51b, an addition unit 51c, a calculation unit 51d, a division unit 51e, a limiting unit 51f, and multiplication units 51g and 51h.

[0052] The multiplication units 51a and 51b, the addition unit 51c, and the calculation unit 51d calculate the d-axis current command value i d,ref and the q-axis current command value i q,ref ) and the apparent current command value i s,ref The division unit 51e calculates a predetermined limit value I LIM,set The apparent current command value i before limiting s,ref The limiting unit 51f outputs the current command suppression gain K limited to be between 0 and 1 to the multipliers 51g and 51h. The multiplier 51g outputs the d-axis current command value i d,ref The d-axis current command limit value I d,LIM,1 The multiplication unit 51h outputs the q-axis current command value i q,ref The q-axis current command limit value I q,LIM,1 The output is as follows:

[0053] FIG. 6 is a vector diagram for explaining the current command limit in the active current limit mode. The active current limiting unit 52 limits the apparent current command value i s,ref is the limit value i LIM,set The d-axis current command value id,ref The q-axis current command value i q,ref The q-axis current command value i q,ref is the limit value i LIM,set Since the q-axis current command value i q,ref The active current limiting unit 52 does not limit the limit value I LIM,set The q-axis current command limit value I q,LIM,2 The active current limiting unit 52 outputs the apparent current command value i s,ref is the limit value I LIM,set The d-axis current command limit value I d,LIM,2 (d-axis current command value i d,ref,LIM ) is calculated. This allows the apparent current command value before limiting i s,ref The magnitude of the current command vector is the radius (limit value I LIM,set The apparent current command value i is restricted to the circle s,ref,LIM Therefore, overcurrent is suppressed.

[0054] In this way, the control device 20A reduces the active current with a larger gain than the reactive current so that the apparent current is equal to or less than the limit value. As a result, the d-axis current command value that contributes to the active current is limited preferentially, and the q-axis current command value that contributes to the reactive current for stabilizing the voltage is set to be larger than the d-axis current command value.

[0055] 7 is a functional block diagram showing an example of the active current limiting unit 52. The active current limiting unit 52 includes multiplication units 52a and 52b, an addition unit 52c, a calculation unit 52d, and a limiting unit 52f.

[0056] The limiting section 52f is a lower limit value (-I LIM,set ) and above the upper limit (+I LIM,set ) The q-axis current command value i q,ref The multiplication units 52a and 52b, the addition unit 52c, and the calculation unit 52d output the apparent current command value i s,ref is the limit value I LIM,set The d-axis current command limit value I d,LIM,2 (d-axis current command value i d,ref,LIM The active current limiting unit 52 calculates the limiting value I LIM,set The q-axis current command limit value Iq,LIM,2 The output is as follows:

[0057] FIG. 8 is a vector diagram for explaining the current command limit in the reactive current limit mode. The reactive current limiting unit 53 limits the apparent current command value i s,ref is the limit value i LIM,set The q-axis current command value i q,ref The d-axis current command value i d,ref The d-axis current command value i d,ref is the limit value i LIM,set Since the d-axis current command value i d,ref The reactive current limiting unit 53 does not limit the limit value I LIM,set The d-axis current command limit value I q,LIM,3 The reactive current limiting unit 53 outputs the apparent current command value i s,ref is the limit value I LIM,set The q-axis current command limit value I q,LIM,3 (q-axis current command value i q,ref,LIM ) is calculated. This allows the apparent current command value before limiting i s,ref The magnitude of the current command vector is the radius (limit value I LIM,set The apparent current command value i is restricted to the circle s,ref,LIM Therefore, overcurrent is suppressed.

[0058] In this way, the control device 20A reduces the reactive current with a larger gain than the active current so that the apparent current is equal to or less than the limit value. As a result, the q-axis current command value contributing to the reactive current is limited preferentially, and the d-axis current command value contributing to the active current for stabilizing the frequency is set to be larger than the q-axis current command value.

[0059] 9 is a functional block diagram showing an example of the reactive current limiting unit 53. The reactive current limiting unit 53 includes multiplication units 53a and 53b, an addition unit 53c, a calculation unit 53d, and a limiting unit 53f.

[0060] The limiting section 53f is a lower limit value (-I LIM,set ) and above the upper limit (+I LIM,set ) The d-axis current command value i d,refThe multiplication units 53a and 53b, the addition unit 53c, and the calculation unit 53d output the apparent current command value i s,ref is the limit value I LIM,set The q-axis current command limit value I q,LIM,3 (q-axis current command value i q,ref,LIM The reactive current limiting unit 53 calculates the limiting value I LIM,set The d-axis current command limit value I d,LIM,3 The output is as follows:

[0061] Fig. 10 is a functional block diagram showing an example of a mode selection unit 54. The mode selection unit 54 shown in Fig. 10 is one configuration example of the mode selection unit 54 shown in Fig. 3. The mode selection unit 54 manually or automatically switches between current limiting modes (apparent current limiting mode, active current limiting mode, and reactive current limiting mode).

[0062] The mode selection unit 54 selects the apparent current limiting mode when it is detected that the amplitude of the output voltage from the inverter 5 does not deviate from a predetermined amplitude range and that the frequency of the output voltage from the inverter 5 does not deviate from a predetermined frequency range. In this case, the mode selection unit 54 selects the apparent current limiting mode when it is detected that the d-axis current command limiting value I d,LIM,1 The d-axis current limit value I d,LIM and the q-axis current command limit value I q,LIM,1 The q-axis current limit value I q,LIM As a result, the active current and reactive current are reduced with the same gain so that the apparent current is equal to or less than the limit value, thereby suppressing overcurrent.

[0063] The mode selection unit 54 selects the reactive current limiting mode when it is detected that the amplitude of the output voltage from the inverter 5 is not outside a predetermined amplitude range and the frequency of the output voltage from the inverter 5 is outside a predetermined frequency range. In this case, the mode selection unit 54 selects the reactive current limiting mode when it is detected that the amplitude of the output voltage from the inverter 5 is outside a predetermined frequency range. d,LIM,3 The d-axis current limit value I d,LIM and the q-axis current command limit value I q,LIM,3 The q-axis current limit value I q,LIMAs a result, the reactive current is reduced with a larger gain than the active current so that the apparent current is equal to or less than the limit value, so that the frequency of the power system 1 can be stabilized by the output of the active current while suppressing overcurrent.

[0064] The mode selection unit 54 selects the active current limit mode when it is detected that the amplitude of the output voltage from the inverter 5 is outside a predetermined amplitude range and the frequency of the output voltage from the inverter 5 is not outside a predetermined frequency range. In this case, the mode selection unit 54 selects the active current limit mode when it is detected that the d-axis current command limit value I d,LIM,2 The d-axis current limit value I d,LIM and the q-axis current command limit value I q,LIM,2 The q-axis current limit value I q,LIM As a result, the active current is reduced with a larger gain than the reactive current so that the apparent current is equal to or less than the limit value, so that the voltage of the power system 1 can be stabilized by the output of the reactive current while suppressing overcurrent.

[0065] When the amplitude of the output voltage from the inverter 5 is detected to be outside a predetermined amplitude range and the frequency of the output voltage from the inverter 5 is detected to be outside a predetermined frequency range, the mode selection unit 54 selects the active current limit mode or the reactive current limit mode.

[0066] The mode selection unit 54 selects which of the active current and the reactive current is to be limited preferentially in accordance with a signal from outside the control device 20. When the signal is a signal that prioritizes voltage stabilization of the power system 1, the mode selection unit 54 selects the current limiting mode based on the upper table shown in FIG. 10 in order to limit the active current with priority over the reactive current. In this case, when it is detected that the amplitude of the output voltage from the inverter 5 is outside a predetermined amplitude range and the frequency of the output voltage from the inverter 5 is outside a predetermined frequency range, the mode selection unit 54 selects the active current limiting mode. On the other hand, when the signal is a signal that prioritizes frequency stabilization of the power system 1, the mode selection unit 54 selects the current limiting mode based on the lower table shown in FIG. 10 in order to limit the reactive current with priority over the active current. In this case, when it is detected that the amplitude of the output voltage from the inverter 5 is outside a predetermined amplitude range and the frequency of the output voltage from the inverter 5 is outside a predetermined frequency range, the mode selection unit 54 selects the reactive current limiting mode.

[0067] For example, when the amplitude of the output voltage from the inverter 5 falls outside a predetermined amplitude range, the mode selection unit 54 may determine that the amplitude of the output voltage from the inverter 5 is disturbed, and in this case, may determine that a voltage disturbance has occurred in the power system 1. The method of determining the occurrence of a voltage disturbance is not limited to this.

[0068] For example, when the frequency of the output voltage from the inverter 5 falls outside a predetermined frequency range, the mode selection unit 54 may determine that the frequency of the output voltage from the inverter 5 has been disturbed, and in this case, may determine that a frequency disturbance has occurred in the power system 1. The method of determining the occurrence of a frequency disturbance is not limited to this.

[0069] In FIG. 3, the current command limiting unit 40 determines the d-axis current limit value I d,LIM The current command limiting unit 40 calculates the absolute value of the d-axis current command value i d,refis limited to the d-axis lower limit value or less than the d-axis upper limit value, and the limited value is set as the d-axis current command value i d,ref,LIM Similarly, the current command limiting unit 40 outputs the q-axis current limiting value I q,LIM The current command limiting unit 40 calculates the absolute value of the q-axis current command value i q,ref is limited to the q-axis lower limit or lower than the q-axis upper limit, and the limited value is set as the q-axis current command value i q,ref,LIM The output is as follows:

[0070] Therefore, according to the first embodiment, the control device 20A has a current command limiting unit 40 that limits one of the active current and the reactive current output from the inverter 5 with priority over the other current so that the apparent current output from the inverter 5 is equal to or less than a limit value. This makes it possible to stabilize the frequency or voltage of the power system 1 while suppressing overcurrent.

[0071] <Second embodiment> FIG. 11 is a diagram showing an example of the configuration of the inverter and the control device in the power conversion device of the second embodiment. In the second embodiment, the description of the configuration, action, and effect similar to those of the first embodiment will be omitted by citing the above description. FIG. 11 shows the circuit configuration of the inverter 5 and the functional block of the control device 20B. The power conversion device 2B of the second embodiment is an example of the above-mentioned power conversion device 2. The power conversion device 2B includes an inverter 5 and a control device 20B.

[0072] The control device 20B controls the inverter 5 by a voltage control method. The control device 20B includes a frequency control unit 22, a voltage amplitude control unit 23, an instantaneous voltage command unit 31, a dq conversion unit 21, an instantaneous current command unit 25, an inverse dq conversion unit 27, an instantaneous current control unit 28, an adder 29, and a PWM pulse generation unit 30.

[0073] [Frequency control section] The frequency control unit 22 controls the voltage v output from the inverter circuit 8. PWMThe frequency control unit 22 controls the frequency of the output voltage v output from the inverter 5 to the power grid 1. out The voltage v output from the inverter circuit 8 is PWM The frequency control unit 22 controls the frequency of the voltage v output from the inverter circuit 8 so that the frequencies of the voltage v and the PWM The frequency command value f ref and the voltage v output from the inverter circuit 8 PWM The phase command value θ ref and are derived.

[0074] The frequency control unit 22, for example, determines an effective power command value P ref , active power measurement value P out , frequency measurement value f out and rated frequency setting value f n,ref Based on this, the frequency command value f ref and phase command value θ ref Calculate and output.

[0075] Active power command value P ref is the command value of the active power output from the inverter 5 to the power system 1. The active power measurement value P out is a measurement value of the active power actually output from the inverter 5 to the power system 1. out is the measurement at node N between the filter 3 and the power system 1.

[0076] Frequency measurement value f out is the output voltage v that is actually output from the inverter 5 to the power grid 1. out The frequency measurement value f out is the measurement at node N between the filter 3 and the power system 1.

[0077] Rated frequency setting value f n,ref is the set value of the rated frequency of power system 1. The rated frequency set value f n,ref For example, in Japan, eastern Japan uses 50Hz and western Japan uses 60Hz.

[0078] Fig. 12 is a functional block diagram showing an example of a frequency control section in the control device. The frequency control section 22 shown in Fig. 12 is a section that performs frequency control in the GFM control. The frequency control section 22 has adders 22a, 22b, 22f, 22i, and 22k, multipliers 22c, 22e, 22g, 22h, 22j, and 22l, and integrators 22d and 22n.

[0079] In the following description, the unit inertia constant and the unit damping constant are assumed to be H and D, respectively, when the inverter 5 operates as a virtual synchronous generator.

[0080] The adder 22a calculates the active power command value P ref to the active power measurement value P out The value obtained by subtracting (P ref -P out ) to the adder 22b.

[0081] The adder 22b receives the input value (P ref -P out The input from the adder 22k is subtracted from the sum of the two, and the result is output to the multiplier 22c.

[0082] The multiplier 22c multiplies the input value from the adder 22b by 1 / (2H) and outputs the result to the integrator 22d (H is a unit inertia constant).

[0083] The integrator 22d integrates the input value from the multiplier 22c and outputs the result to the multiplier 22l.

[0084] The multiplier 22e multiplies the output voltage v out The frequency measurement value f out The rated frequency setting value f of inverter 5 n The output value of the multiplier 22e is the output voltage v out The frequency measurement value f out The rated frequency setting value f n This is a value converted into a unit.

[0085] The adder 22f outputs a value obtained by subtracting the input value from the multiplier 22e from the input value from the integrator 22d to the multiplier 22g.

[0086] The multiplier 22g multiplies the input value from the adder 22f by a unit damping constant D and outputs the result to the adder 22k.

[0087] Multiplier 22h is the rated frequency setting value f n,ref The rated frequency setting value f of inverter 5 n The output value of the multiplier 22h is the rated frequency setting value f of the power system 1. n,ref The rated frequency setting value f n This is a value converted into a unit.

[0088] The adder 22i subtracts the input value from the multiplier 22h from the input value from the integrator 22d, and outputs the result to the multiplier 22j.

[0089] The multiplier 22j multiplies the input value from the adder 22i by a gain K GOV The value multiplied by the gain K is output to the adder 22k. GOV The rotation speed of the rotor is set to the rated frequency f n,ref The fast governor gain is one of the parameters used to adjust the speed so as to keep the

[0090] The adder 22k outputs a value obtained by adding the input value from the multiplier 22g and the input value from the multiplier 22j to the adder 22b.

[0091] The multiplier 22l multiplies the input value from the integrator 22d by the rated frequency setting value f of the inverter 5. n The output value of the multiplier 22l is the output voltage v output from the inverter 5 to the power grid 1. out The voltage v output from the inverter circuit 8 is controlled so that the frequency of PWM The frequency command value f ref is equivalent to.

[0092] The integrator 22n executes a calculation to integrate the value obtained by multiplying the input value from the multiplier 22l by 2π. By this calculation, the integrator 22n obtains the phase command value θ ref Output.

[0093] [Voltage amplitude control section] In FIG. 11, a voltage amplitude control unit 23 controls a voltage v output from an inverter circuit 8. PWM where v PWM The amplitude of v PWM The voltage amplitude control unit 23 controls the output voltage v out The amplitude of the voltage v output from the inverter circuit 8 PWM The voltage amplitude control unit 23 controls the voltage v output from the inverter circuit 8 so that the amplitude of the voltage v PWM The amplitude command value V ref Derive.

[0094] The voltage amplitude control unit 23, for example, determines a reactive power command value Q ref , reactive power measurement value Q out and output voltage amplitude command value V out,ref Based on this, the amplitude command value V ref Calculate and output.

[0095] Reactive power command value Q ref is the command value of the reactive power output from the inverter 5 to the power grid 1. The reactive power measurement value Q out is a measurement value of the reactive power actually output from the inverter 5 to the power system 1. The reactive power measurement value Q out is the measurement at node N between the filter 3 and the power system 1.

[0096] Output voltage amplitude command value V out,ref is the output voltage v output from the inverter 5 to the power grid 1. out is the amplitude command value.

[0097] Fig. 13 is a functional block diagram showing an example of a voltage amplitude control section in the control device. Voltage amplitude control section 23 shown in Fig. 13 is a section that performs voltage amplitude control of the GFM control. Voltage amplitude control section 23 has adders 23a, 23e, and 23f, multipliers 23b and 23c, an integrator 23d, and a limiting section 23g.

[0098] The adder 23a calculates the reactive power command value Q ref to reactive power measurement value Q out The value obtained by subtracting 1 from 2 is output to the multiplier 23b and the multiplier 23c.

[0099] The multiplier 23b multiplies the input value from the adder 23a by a gain K p,QV The value multiplied by the gain K is output to the adder 23e. p,QV is the reactive power measurement value Q out and reactive power command value Q ref This is a parameter for proportional control to suppress the difference between the gain K p,QV is, for example, the proportional gain of a PI regulator (proportional-integral regulator) for QV droop control.

[0100] The multiplier 23c multiplies the input value from the adder 23a by a gain K i,QV The value multiplied by the gain K is output to the integrator 23d. i,QV is the reactive power measurement value Q out and reactive power command value Q ref This is a parameter for integral control to suppress the difference between the gain K i,QV is, for example, the integral gain of a PI regulator (proportional-integral regulator) for QV droop control.

[0101] The integrator 23d performs time integration of the input value from the multiplier 23c and outputs the result to the adder 23e.

[0102] The adder 23e adds the input value from the multiplier 23b and the input value from the integrator 23d, and outputs the sum to the adder 23f.

[0103] The adder 23f calculates the input value from the adder 23e and the output voltage v out The amplitude command value Vout,ref The sum of these is output to the limiting unit 23g.

[0104] The limiting unit 23g limits the input value from the adder 23f based on the set upper and lower limit values, and sets the limit value as the amplitude command value V ref The output is as follows:

[0105] The limiting unit 23g is configured to limit the input value from the adder 23f to the lower limit value V ref,LLIM Above the upper limit V ref,ULIM If it is equal to or less than this, the input value from the adder 23f is output as is.

[0106] The limiting unit 23g is configured to limit the input value from the adder 23f to the upper limit value V ref,ULIM If it is greater than V ref,ULIM The limiting unit 23g outputs the lower limit V ref,LLIM If it is smaller than the lower limit V ref,LLIM Output.

[0107] The output value of the limiting unit 23g is the output voltage v out The voltage v output from the inverter circuit 8 is controlled so that the amplitude of PWM The amplitude command value V for controlling the amplitude of ref is equivalent to.

[0108] [Instantaneous voltage command section] In FIG. 11, an instantaneous voltage command unit 31 outputs an amplitude command value V ref and phase command value θ ref Based on this, the output voltage command value v out,ref The output voltage command value v out,ref are command values ​​of three-phase instantaneous voltages output from the inverter 5 to the power system 1.

[0109] Fig. 14 is a functional block diagram showing an example of an instantaneous voltage command unit in the control device. The instantaneous voltage command unit 31 shown in Fig. 14 is a part that performs instantaneous voltage command calculation processing in the GFM control. The instantaneous voltage command unit 31 has adders 31a and 31b, cosine functions 31c, 31d, and 31e, multipliers 31f, 31g, and 31h, and a multiplexer 31i.

[0110] The adder 31a calculates a phase command value θ ref The value obtained by subtracting (2π / 3) from (θ ref -(2π / 3)) is output to the cosine function 31d.

[0111] The adder 31b calculates a phase command value θ ref The sum of (θ ref +(2π / 3)) is output to the cosine function 31e.

[0112] The multiplier 31f multiplies the input value cos(θ ref ) to the amplitude command value V ref The output voltage command value v of phase A is out,ref,a The output is as follows:

[0113] The multiplier 31g multiplies the input value cos(θ ref -(2π / 3)) to the amplitude command value V ref The output voltage command value v of phase B is out,ref,b The output is as follows:

[0114] The multiplier 31h multiplies the input value cos(θ ref +(2π / 3)) to the amplitude command value V ref The output voltage command value v out,ref,c The output is as follows:

[0115] The multiplexer 31i outputs the output voltage command value v out,ref,a ,v out,ref,b ,v out,ref,c These are combined into one signal, and the three-phase output voltage command value v output from the inverter 5 to the power grid 1 is out,refIn this example, the three signals are combined into one signal by the multiplexer 31i to make them easier to handle, but the signals may be sent to the next block as three separate signals without using the multiplexer 31i.

[0116] [dq conversion section] In FIG. 11, the dq conversion unit 21 converts a phase command value θ ref Using the above, the output current measurement value i out The current on the two axes (d-axis current i d,out and q-axis current i q,out ) and output the measured output current value i out is a measured value of the output current actually output from the inverter 5 to the power grid 1.

[0117] d-axis current i d,out is the active current component that contributes to the active power output from the inverter 5 to the power grid 1. The q-axis current i q,out is a reactive current component that contributes to the reactive power output from the inverter 5 to the power grid 1. The d-axis current i d,out and q-axis current i q,out are the frequency command values ​​f ref (The voltage v output from the inverter circuit 8 PWM These are the d-axis and q-axis components in a rotating coordinate system that rotates at an angular frequency corresponding to the frequency command value of

[0118] [Instantaneous current command section] In FIG. 11, the instantaneous current command unit 25 controls the d-axis current i d,out , q-axis current i q,out , frequency command value f ref and the amplitude command value V ref Based on this, the d-axis current command value i d,ref and q-axis current command value i q,ref The d-axis current command value i d,ref and q-axis current command value i q,ref is the current i output from the inverter circuit 8 to the filter 3. LThe d-axis current command value i d,ref is an example of a first current command value, and the current i L is the output current i from inverter 5 to power grid 1 out Since there is no significant deviation from the above, it contributes to the effective power output from the inverter 5 to the power grid 1. q,ref is an example of a second current command value, and the current i L is the output current i from inverter 5 to power grid 1 out Since there is no large deviation between these two, the inverter 5 contributes to the reactive power output from the inverter 5 to the power grid 1.

[0119] Fig. 15 is a functional block diagram showing an example of an instantaneous current command unit in the control device. The instantaneous current command unit 25 shown in Fig. 15 is a part that performs instantaneous current command value calculation processing in the GFM control. The instantaneous current command unit 25 has a multiplier 25f, a multiplier 25g, an adder 25h, a limiting unit 25u, and a limiting unit 25v.

[0120] The limiting unit 25u limits the d-axis current i d,out The d-axis current command value i d,ref The output is as follows:

[0121] The limiting unit 25u limits the d-axis current i d,out is the lower limit i d,ref,LLIM The upper limit value i d,ref,ULIM If the above is true, the d-axis current i d,out is output as is.

[0122] The limiting unit 25u limits the d-axis current i d,out is the upper limit i d,ref,ULIM If it is greater than i, d,ref,ULIM The limiting unit 25u outputs the d-axis current i d,out is the lower limit i d,ref,LLIM If it is smaller than i, d,ref,LLIM Output.

[0123] The multiplier 25f multiplies the frequency command value f ref to gain K Ci The value multiplied by the gain K is output to the multiplier 25g. Ci is a coefficient for calculating the current flowing through the capacitor C of the filter 3.

[0124] The multiplier 25g multiplies the input value from the multiplier 25f by the amplitude command value V ref The product of this multiplication is output to an adder 25h.

[0125] The adder 25h receives the q-axis current i q,out The value obtained by adding this to the input value from the multiplier 25g is output to the limiting unit 25v.

[0126] The limiting unit 25v limits the input value from the adder 25h based on the set upper and lower limits, and sets the limit value as the q-axis current command value i q,ref The output is as follows:

[0127] The limiting unit 25v is configured to limit the input value from the adder 25h to the lower limit value i q,ref,LLIM The upper limit value i q,ref,ULIM If it is equal to or less than this, the input value from the adder 25h is output as is.

[0128] The limiting unit 25v is configured to limit the input value from the adder 25h to the upper limit value i q,ref,ULIM If it is greater than i q,ref,ULIM The limiting unit 25v outputs the lower limit value i q,ref,LLIM If it is smaller than i, q,ref,LLIM Output.

[0129] [Current command limiting section] In FIG. 11, a current command limiting unit 40 limits the d-axis current command value i d,ref The d-axis current command value i d,ref,LIM and the q-axis current command value i q,ref The q-axis current command value i q,ref,LIMThe current command limiting unit 40 of the second embodiment may have the same configuration as the current command limiting unit 40 of the first embodiment.

[0130] [Inverse dq transformation section] In FIG. 11, the inverse dq transformation unit 27 converts the current command value of two axes (the d-axis current command value i d,ref,LIM and q-axis current command value i q,ref,LIM ) is the three-phase output current command value i ref The output current command value i ref is the current i output from the inverter circuit 8 to the filter 3. L are the command values ​​for the three phases.

[0131] [Instantaneous current control section] In FIG. 11, an instantaneous current control unit 28 controls a current i output from the inverter circuit 8 to the filter 3. L The instantaneous current control unit 28 controls the output current command value i ref The current i output from the inverter circuit 8 to the filter 3 L The instantaneous current control unit 28 performs instantaneous current control to bring the current i L is sampled as an instantaneous current, and the sampled value, the current measurement value i L is the output current command value i ref It can be configured as an ACR (Automatic Current Regulator) that performs feedback control so that the measured current value i L are measured values ​​of instantaneous three-phase currents flowing from the inverter circuit 8 to the reactor L1 of the filter 3.

[0132] The instantaneous current control unit 28 controls the output current command value i ref and current measurement value i L Based on this, the current measurement value i L is the output current command value i ref The output voltage correction value v L,ref The output voltage correction value v L,ref is the output voltage command value v, which is the command value of the three-phase output voltage output from the inverter 5 to the power grid 1. out,ref In order to correct the output voltage command value vout,ref is added by adder 29.

[0133] Fig. 16 is a functional block diagram showing an example of an instantaneous current control section in the control device. The instantaneous current control section 28 shown in Fig. 16 is a section that performs instantaneous current control in the GFM control. The instantaneous current control section 28 has demultiplexers 28a and 28h, adders 28b, 28c, 28e, 28f, 28g, 28i, 28j, and 28k, multipliers 28d, 28l, 28m, and 28n, and a multiplexer 28o.

[0134] The demultiplexer 28a outputs a current measurement value i, which is a measurement value of the filter current flowing from the power conversion unit 6 to the filter 3. L The current measurement value of A phase i L,a , B phase current measurement value i L,b and the measured current value of phase C i L,c This example is expanded to i L In order to make the signal easier to handle, the signals of each phase are bundled together, and the signals are expanded by the demultiplexer 28a. L These signals may be treated as three separate signals rather than being bundled, in which case demultiplexer 28a is not necessary.

[0135] The adders 28b and 28c calculate the three-phase current measurement values ​​i L,a ,i L,b ,i L,c The sum of these is output to multiplier 28d.

[0136] The multiplier 28d multiplies the three-phase current measurement value i L,a ,i L,b ,i L,c The sum of these is divided by 3 and the result is output to adders 28e, 28f, and 28g.

[0137] The adder 28e calculates the A-phase current measurement value i L,a The adder 28f outputs the value obtained by subtracting the input value from the multiplier 28d from the current measurement value i of the B phase. L,bThe adder 28g outputs the value obtained by subtracting the input value from the multiplier 28d from the current measurement value i L,c The multiplier 28c subtracts the input value from the multiplier 28d from the sum and outputs the result to the adder 28k.

[0138] The demultiplexer 28h detects the current i output from the inverter circuit 8 to the filter 3. L The output current command value i ref The output current command value i ref,a ,B-phase output current command value i ref,b and the output current command value i ref,c Expand to.

[0139] The adder 28i calculates the output current command value i ref,a The adder 28j outputs the value obtained by subtracting the input value from the adder 28e from the B-phase output current command value i ref,b The adder 28k outputs the value obtained by subtracting the input value from the adder 28f from the C-phase output current command value i ref,c The adder 28g subtracts the input value from the adder 28c and outputs the result to the multiplier 28n.

[0140] The multiplier 28l applies a gain K ACR The output voltage correction value v of phase A is calculated by multiplying the value by L,ref,a The multiplier 28m outputs the gain K ACR The value multiplied by this is the B phase output voltage correction value v L,ref,b The multiplier 28n outputs the gain K ACR The value multiplied by this is the output voltage correction value v of phase C. L,ref,c The gain K ACR is the measured current value i L and the output current command value i ref This is a parameter for controlling the difference between the gain K ACR is, for example, the P gain (proportional gain) when the ACR control is configured with a P regulator.

[0141] The multiplexer 28o receives the output voltage correction values ​​v of each phase, which are input from the multipliers 28l, 28m, and 28n, respectively. L,ref,a , v L,ref,b ,v L,ref,c These are combined into one signal to produce the three-phase output voltage correction value v L,ref Here, too, similarly to the above case, a configuration without using a multiplexer is possible.

[0142] [Adder] In FIG. 11, an adder 29 calculates an output voltage command value v out,ref to the output voltage correction value v L,ref The value obtained by adding PWM,ref The output is as follows:

[0143] [PWM pulse generation section] In FIG. 11, the PWM pulse generating unit 30 generates a PWM command value v PWM,ref is compared with a carrier signal such as a triangular wave to generate a PWM pulse signal V PWM The pulse width modulation method is not limited to the triangular wave comparison modulation method, and any commonly used pulse width modulation method can be used. It goes without saying that the required number of PWM pulses must be generated depending on the configuration of the inverter circuit 8.

[0144] Therefore, according to the second embodiment, the control device 20B has a current command limiting unit 40 that limits one of the active current and the reactive current output from the inverter 5 with priority over the other current so that the apparent current output from the inverter 5 is equal to or less than a limit value. This makes it possible to stabilize the frequency or voltage of the power system 1 while suppressing overcurrent.

[0145] As described above, the embodiment has been described, but the above embodiment is presented as an example, and the present invention is not limited to the above embodiment. The above embodiment can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0146] 1 Power system 2. Power conversion device 3. Filters 4 Switch 5. Inverter 6 Power conversion section 7 Capacitor 8 Inverter Circuit 10 Power Lines 20 Control device 21 dq conversion section 22 Frequency control section 23 Voltage amplitude control section 25 Instantaneous current command section 27 Inverse dq conversion section 28 Instantaneous current control section 29 Adder 30 PWM pulse generator 31 Instantaneous voltage command unit 32 DC voltage control section 33 Power correction section 34 Subtractor 35 Adder 40 Current command limiting section 41 Active power command unit 42 Active power control section 43 Reactive Power Command Unit 44 Reactive power control section 51 Apparent current limiter 52 Active current limiter 53 Reactive current limiting section 54 Mode selection section

Claims

1. An inverter that converts input DC power into AC power; A control device for controlling the inverter, The control device is a power conversion device that limits one of the active current and reactive current output from the inverter in priority over the other current so that the apparent current output from the inverter is equal to or less than a limit value.

2. The power conversion device according to claim 1 , wherein the control device limits the active current with priority over the reactive current so that the apparent current is equal to or less than the limit value when an amplitude of the output voltage from the inverter is disturbed.

3. 2. The power conversion device according to claim 1, wherein the control device limits the active current with priority over the reactive current so that the apparent current is equal to or less than the limit value when the amplitude of the output voltage from the inverter falls outside a predetermined amplitude range.

4. 2. The power conversion device according to claim 1, wherein the control device reduces the active current with a gain larger than that of the reactive current so that the apparent current is equal to or smaller than the limit value when an amplitude of the output voltage from the inverter is disturbed.

5. 2 . The power conversion device according to claim 1 , wherein, when a frequency of the output voltage from the inverter is disturbed, the control device limits the reactive current with priority over the active current so that the apparent current is equal to or less than the limit value.

6. 2. The power conversion device according to claim 1, wherein when a frequency of the output voltage from the inverter falls outside a predetermined frequency range, the control device limits the reactive current in priority to the active current so that the apparent current is equal to or less than the limit value.

7. 2. The power conversion device according to claim 1, wherein the control device reduces the reactive current with a larger gain than the active current so that the apparent current is equal to or less than the limit value when a frequency of the output voltage from the inverter is disturbed.

8. The control device includes: When an amplitude of an output voltage from the inverter is disturbed, the active current is limited in priority over the reactive current so that the apparent current is equal to or less than the limit value; The power conversion device according to claim 1 , wherein, when a frequency of the output voltage from the inverter is disturbed, the reactive current is limited with priority over the active current so that the apparent current is equal to or less than the limit value.

9. The power conversion device according to claim 1 , wherein the control device selects, in accordance with a signal from outside the control device, which of the active current and the reactive current is to be limited with priority.

10. 10. The power conversion device according to claim 9, wherein when an amplitude of the output voltage from the inverter is disturbed and a frequency of the output voltage from the inverter is disturbed, the control device selects, in accordance with the external signal, which of the active current and the reactive current is to be limited with priority.

11. An inverter that converts input DC power into AC power; A control device for controlling the inverter, The control device is a power conversion device that reduces one of the active current and reactive current output from the inverter with a larger gain than the other current so that the apparent current output from the inverter is equal to or less than a limit value.

12. 12. The power conversion device according to claim 11, wherein the control device selects whether to reduce the one current with a larger gain than the other current, or to reduce the one current and the other current with the same gain, so that the apparent current is equal to or less than the limit value.

13. 13. The power conversion device according to claim 11 or 12, wherein the control device selects whether to reduce the active current with a larger gain than the reactive current or to reduce the reactive current with a larger gain than the active current so that the apparent current is equal to or less than the limit value.

14. 13. The power conversion device according to claim 11 or 12, wherein the control device selects whether to reduce the active current and the reactive current with the same gain, to reduce the active current with a gain larger than that of the reactive current, or to reduce the reactive current with a gain larger than that of the active current, so that the apparent current is equal to or smaller than the limit value.

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