Electric power conversion apparatus

Abstract

An electric power conversion apparatus comprising an inverter that converts input DC power into AC power and a control device that controls the inverter, wherein the control device preferentially limits one current, out of an effective current and a reactive current output from the inverter, more than the other current so that an apparent current output from the inverter is equal to or less than a limit value.

Description

Power Conversion Device

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

[0002] Power converters that apply voltage-controlled virtual synchronous generator control may shut down due to converter overcurrent during grid disturbances or overloads, and a control method is needed to prevent this and continue operation. Virtual synchronous generator control is broadly classified into voltage-controlled and current-controlled types. In the case of current-controlled types, there is a method of limiting a current command value to control the current to an arbitrary value. However, in the case of voltage-controlled types, the method of limiting the voltage command value does not allow the current to be controlled to an arbitrary value, and therefore, depending on conditions such as grid impedance, an overcurrent may occur. 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).

[0003] Japanese Patent Application Laid-Open No. 2021-141704

[0004] The inverter controls the frequency and voltage of the grid by outputting active current to stabilize the frequency and reactive current to stabilize the voltage. When the grid frequency disturbance is large, it is desirable to output as much active current as possible, and when the grid voltage disturbance is large, it is desirable to output as much reactive current as possible.

[0005] However, if the active current output and the reactive current output are limited at the same rate, it will affect both frequency stabilization and voltage stabilization. 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 that can stabilize the frequency or voltage of a grid while suppressing overcurrent.

[0007] The power conversion device of the present disclosure includes an inverter that converts input DC power into AC power, and a control device that controls the inverter, and the control device limits one of the active current and reactive current output from the inverter in preference to the other current so that the apparent current output from the inverter is equal to or less than a limit value.

[0008] In the power conversion device of the present disclosure, when the amplitude of the output voltage from the inverter is disturbed, 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.

[0009] The power supply comprises an inverter that converts input DC power into AC power, and a control device that controls the inverter, wherein 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 is equal to or less than a limit value.

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

[0011] FIG. 1 is a diagram illustrating an example of a configuration of a power conversion device. FIG. 2 is a diagram illustrating examples of configurations of an inverter and a control device in the power conversion device of the first embodiment. FIG. 3 is a functional block diagram illustrating an example of a current command limiting unit. FIG. 4 is a vector diagram for explaining current command limiting in an apparent current limiting mode. FIG. 5 is a functional block diagram for explaining current command limiting in an active current limiting mode. FIG. 6 is a functional block diagram for explaining current command limiting in a reactive current limiting mode. FIG. 7 is a functional block diagram for explaining an example of a reactive current limiting unit. FIG. 8 is a functional block diagram for explaining an example of a mode selecting unit. FIG. 9 is a diagram illustrating examples of configurations of an inverter and a control device in a power conversion device of a second embodiment. FIG. 10 is a functional block diagram for explaining an example of a frequency control unit in the control device. FIG. 11 is a functional block diagram for explaining an example of a voltage amplitude control unit in the control device. FIG. 12 is a functional block diagram for explaining an example of an instantaneous voltage command unit in the control device. FIG. 13 is a functional block diagram for explaining an example of an instantaneous current command unit in the control device.

[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. The power conversion device 2 shown in Fig. 1 is connected to a power grid 1. The power grid 1 is a power system that supplies AC power generated at a power plant to consumer facilities via a distribution line 10.

[0014] The power conversion device 2 is a device that inputs and outputs power to and from the power grid 1. The power conversion device 2 includes an inverter 5 that inputs and outputs power to and from the power grid 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 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 The power converter 6 converts the DC power (e.g., DC power generated from renewable energy) into AC power. ＰＷＭ According to this, the voltage equivalent to the AC voltage v ＰＷＭ The power conversion unit 6 is connected to the power grid 1 via the filter 3 and the switch 4.

[0017] The filter 3 removes harmonic components from the current flowing between the power conversion unit 6 and the power grid 1. The filter 3 also removes harmonic components from the AC current i output from the power conversion unit 6. Ｌ The filter 3 receives the current i Ｌ The output current i with harmonic components removed from ｏｕｔ is output to the 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 grid 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 the 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 occurs in the reactor L1. This difference voltage and the impedance of the reactor L1 result in a current i flowing through the reactor L1. 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 distribution line 10. ｏｕｔ Frequency f ｏｕｔ , or the active power P ｏｕｔ and reactive power Q ｏｕｔ The voltage V ＰＷＭ By controlling ｏｕｔ It is a device that outputs the effective power P ｏｕｔ When positive, it is the active power output from the inverter 5 to the power grid 1, and when negative, it is the active power input from the power grid 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 an inverter and a control device in a power conversion device of the first embodiment. Fig. 2 shows the circuit configuration of the inverter 5 and functional blocks of a control device 20A. A power conversion device 2A of the first embodiment is an example of the power conversion device 2 described above. The power conversion device 2A includes an inverter 5 and a control device 20A. The control device 20A controls the inverter 5 using 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 converts DC power input from an external device such as a power generator into AC power. ｄｃ 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 effective 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. When a storage battery is provided on the DC side, the effective power setting value P ｓｅｔ may be set based on 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 ｏｕｔ is a measurement value at node N between the filter 3 and the power grid 1. The rated frequency setting value f ｎ，ｒｅｆ is the set value of the rated frequency of the power system 1. The rated frequency set value f ｎ，ｒｅｆ For example, in Japan, 50 Hz is used in eastern Japan and 60 Hz is used in western Japan.

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

[0033] The active power control unit 42 calculates the active power command value P ｒｅｆ and the active 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, which contributes to the active power output from the inverter 5 to the power grid 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 set value Q ｓｅｔ and the output voltage amplitude command value V ｏｕｔ，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 person. When performing constant power factor control with a solar inverter, the reactive power setting value Q ｓｅｔ is the power factor value set by a user and the currently output active power measurement 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 command value of the amplitude of

[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 the inverter 5 to the 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 is the reactive power measurement value Q ｏｕｔ is the reactive power command value Q ｒｅｆ PI control is performed to perform feedback control so that the reactive power measurement value Q ｏｕｔ is the reactive power Q output from the inverter 5 to the power system 1 ｏｕｔ is the measured value.

[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 a command value of the reactive current output from the inverter 5 to the power grid 1. The q-axis current command value i ｑ，ｒｅｆ is an example of a second current command value, which contributes to the reactive power output from the inverter 5 to the power grid 1.

[0038] 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 transform unit 27 converts the biaxial current command value (d-axis current command value i ｄ，ｒｅｆ，ＬＩＭ and the 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 3Ｌ 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 is the current measurement value i Ｌ is the output current command value i ｒｅｆ The current measurement value i can be configured as an ACR (Automatic Current Regulator) that performs feedback control so that the current measurement value i Ｌ is a measured value of the three-phase instantaneous current flowing from the inverter circuit 8 to the reactor L1 of the filter 3.

[0041] The instantaneous current control unit 28 determines the output current command value i ｒｅｆ and the 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 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 In order to correct the output voltage measurement value v ｏｕｔ is added by an adder 29 to

[0042] The adder 29 calculates the output voltage measurement value v ｏｕｔ to the output voltage correction value v Ｌ，ｒｅｆ The value obtained by adding the above is the PWM command value v ＰＷＭ，ｒｅｆ Output as

[0043] The PWM pulse generator 30 generates a PWM command value v ＰＷＭ，ｒｅｆ is compared with a carrier signal such as a triangular wave to obtain a PWM pulse signal V ＰＷＭThe 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 overcurrent flowing in the power grid 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 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 54.

[0046] The apparent current limiting unit 51 determines the d-axis current command limit value (d-axis current command limit value i ｄ，ＬＩＭ，１ and q-axis current command limit value i ｑ，ＬＩＭ，１ ) is generated. ｄ，ＬＩＭ，１ is the d-axis current command value i ｄ，ｒｅｆ is the value to be limited in the apparent current limit mode. 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] 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，ｓｅｔis 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 is 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-axis current command value before limiting (the d-axis current command value i ｄ，ｒｅｆ and the 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 limit 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 is multiplied by the current command suppression gain K to obtain 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 is multiplied by the current command suppression gain K to obtain the q-axis current command limit value i ｑ，ＬＩＭ，１ As a result, the apparent current command value before limiting i ｓ，ｒｅｆ The magnitude of the vector of the current command value is the radius (limit value I ＬＩＭ，ｓｅｔ The apparent current command value i 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 is 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, which is limited to be between 0 and 1, to the multipliers 51g and 51h. The multiplier 51g outputs the d-axis current command value i before the limiting ｄ，ｒｅｆ is multiplied by the current command suppression gain K to obtain the d-axis current command limit value I ｄ，ＬＩＭ，１ The multiplication unit 51h outputs the q-axis current command value i before limiting. ｑ，ｒｅｆ is multiplied by the current command suppression gain K to obtain the q-axis current command limit value I ｑ，ＬＩＭ，１ Output as

[0053] 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 i ｄ，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 active current limiting unit 52 determines 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. As a result, the apparent current command value before limiting i ｓ，ｒｅｆ The magnitude of the vector of the current command value is the radius (limit value I ＬＩＭ，ｓｅｔ The apparent current command value i 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 sets the lower limit (-I ＬＩＭ，ｓｅｔ ) or 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 limit value I ＬＩＭ，ｓｅｔ The q-axis current command limit value I ｑ，ＬＩＭ，２ Output as

[0057] 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. As a result, the apparent current command value before limiting iｓ，ｒｅｆ The magnitude of the vector of the current command value is the radius (limit value I ＬＩＭ，ｓｅｔ The apparent current command value i 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 that contributes to the reactive current is limited preferentially, and therefore the d-axis current command value that contributes 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 sets the lower limit (-I ＬＩＭ，ｓｅｔ ) or above the upper limit (+I ＬＩＭ，ｓｅｔ ) The d-axis current command value i ｄ，ｒｅｆ The 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 limit value I ＬＩＭ，ｓｅｔ The d-axis current command limit value I ｄ，ＬＩＭ，３ Output as

[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 example of the configuration 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 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，１is the d-axis current limit value I ｄ，ＬＩＭ and the q-axis current command limit value I ｑ，ＬＩＭ，１ is 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 within 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 d-axis current command limiting value I ｄ，ＬＩＭ，３ is the d-axis current limit value I ｄ，ＬＩＭ and the q-axis current command limit value I ｑ，ＬＩＭ，３ is the q-axis current limit value I ｑ，ＬＩＭ As 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, and 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 is the d-axis current limit value I ｄ，ＬＩＭ and the q-axis current command limit value I ｑ，ＬＩＭ，２ is 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, and therefore the voltage of the power system 1 can be stabilized by the output of the reactive current while suppressing overcurrent.

[0065] The mode selection unit 54 selects the active current limit mode or the reactive current limit mode when it detects that the amplitude of the output voltage from the inverter 5 is outside a predetermined amplitude range and that the frequency of the output voltage from the inverter 5 is outside a predetermined frequency range.

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

[0067] For example, if the amplitude of the output voltage from the inverter 5 is 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, if 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 and sets a value obtained by adding a positive sign to the absolute value as the d-axis upper limit value, and a value obtained by adding a negative sign to the absolute value as the d-axis lower limit value. ｄ，ｒｅｆ is limited to the d-axis lower limit value or more and the d-axis upper limit value or less, and the limited value is set as the d-axis current command value i ｄ，ｒｅｆ，ＬＩＭSimilarly, the current command limiting unit 40 outputs the q-axis current limit value I ｑ，ＬＩＭ The current command limiting unit 40 calculates the absolute value of the q-axis current command value i and sets a value obtained by adding a positive sign to the absolute value as the q-axis upper limit value, and a value obtained by adding a negative sign to the absolute value as the q-axis lower limit value. ｑ，ｒｅｆ is limited to the q-axis lower limit value or more and the q-axis upper limit value or less, and the limited value is set as the q-axis current command value i ｑ，ｒｅｆ，ＬＩＭ Output as

[0070] Therefore, according to the first embodiment, the control device 20A includes 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 an inverter and a control device in a power conversion device of a second embodiment. In the second embodiment, the description of the configuration, actions, and effects 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 blocks of the control device 20B. A 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 Unit] The frequency control unit 22 controls the voltage v output from the inverter circuit 8. ＰＷＭ The 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 ＰＷＭThe 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 inverter circuit 8 are closer to each other, i.e., the frequency synchronization control. 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, calculates the active power command value P ｒｅｆ , the 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. ｏｕｔ is a measured value of the active power actually output from the inverter 5 to the power grid 1. ｏｕｔ is the measurement at node N between the filter 3 and the power grid 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 grid 1.

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

[0078] Fig. 12 is a functional block diagram showing an example of a frequency control unit in the control device. The frequency control unit 22 shown in Fig. 12 is a part that performs frequency control in the GFM control. The frequency control unit 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, when the inverter 5 operates as a virtual synchronous generator, the unit inertia constant is H and the unit damping constant is D.

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

[0081] The adder 22b adds the input value (P ｒｅｆ -P ｏｕｔ The value obtained by subtracting the input from the adder 22k from the sum of the two inputs 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 the 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 the 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 subtracts the input value from the multiplier 22e from the input value from the integrator 22d, and outputs the result 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] The multiplier 22h is a rated frequency setting value f ｎ，ｒｅｆ The rated frequency setting value f of the 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 is the rotational speed of the rotor, which is the rated frequency setting value f ｎ，ｒｅｆ The high-speed governor gain is one of the parameters used to adjust the speed.

[0090] The adder 22k adds the input value from the multiplier 22g and the input value from the multiplier 22j and outputs the result 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 A frequency command value f for controlling the frequency of 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 Unit] In FIG. 11, the voltage amplitude control unit 23 controls the voltage v output from the inverter circuit 8. ＰＷＭ where v ＰＷＭ The amplitude of v ＰＷＭThe voltage amplitude control unit 23 controls 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 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 is derived.

[0094] The voltage amplitude control unit 23, for example, determines the reactive power command value Q ｒｅｆ , reactive power measurement value Q ｏｕｔ and the 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 reactive power output from the inverter 5 to the power grid 1. ｏｕｔ is a measurement value of the reactive power actually output from the inverter 5 to the power grid 1. ｏｕｔ is the measurement at node N between the filter 3 and the power grid 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 command value of the amplitude of

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

[0098] The adder 23a calculates the reactive power command value Q ｒｅｆ From the reactive power measurement value Q ｏｕｔ The value obtained by subtracting the value from the multiplier 23 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 Kｐ，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 result to the adder 23f.

[0103] The adder 23f calculates the input value from the adder 23e and the output voltage v ｏｕｔ Amplitude command value V ｏｕｔ，ｒｅｆ The sum of the above 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 Output as

[0105] The limiting unit 23g determines whether the input value from the adder 23f is a lower limit value V ｒｅｆ，ＬＬＩＭ or more, and the upper limit value 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 determines whether the input value from the adder 23f is an upper limit value V ｒｅｆ，ＵＬＩＭ If it is greater than the upper limit V ｒｅｆ，ＵＬＩＭThe 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 ｒｅｆ is equivalent to

[0108] [Instantaneous Voltage Command Section] In FIG. 11, the instantaneous voltage command section 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 the three-phase instantaneous voltages output from the inverter 5 to the power grid 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 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 the 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 the phase command value θ ｒｅｆ and (2π / 3) (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 value multiplied by this is the output voltage command value v of phase A. ｏｕｔ，ｒｅｆ，ａ Output as

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

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

[0115] The multiplexer 31i outputs the output voltage command value v ｏｕｔ，ｒｅｆ，ａ , v ｏｕｔ，ｒｅｆ，ｂ , v ｏｕｔ，ｒｅｆ，ｃ 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，ｒｅｆ In 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 Transformation Unit] In FIG. 11, the dq transformation unit 21 converts a phase command value θ ｒｅｆ The output current measurement value i, which is a measurement value of the three-phase output current output from the inverter 5 to the power grid 1, is calculated using the ｏｕｔ 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 ＰＷＭThese are the d-axis component and the q-axis component in a rotating coordinate system that rotates at an angular frequency corresponding to the frequency command value of the rotational frequency.

[0118] [Instantaneous Current Command Section] In FIG. 11, the instantaneous current command section 25 controls the d-axis current i ｄ，ｏｕｔ , q-axis current i ｑ，ｏｕｔ , frequency command value f ｒｅｆ and amplitude command value V ｒｅｆ Based on this, the d-axis current command value i ｄ，ｒｅｆ and the q-axis current command value i ｑ，ｒｅｆ The d-axis current command value i ｄ，ｒｅｆ and the q-axis current command value i ｑ，ｒｅｆ is the current i output from the inverter circuit 8 to the filter 3 Ｌ The 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 the inverter 5 to the power grid 1 ｏｕｔ Since there is no large deviation between the q-axis current command value i and the q-axis current command value i, the q-axis current command value i 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 the inverter 5 to the power grid 1 ｏｕｔ Since there is no large deviation between these two, the inverter 5 contributes to the reactive power output 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 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 converts the d-axis current i ｄ，ｏｕｔ The d-axis current command value i ｄ，ｒｅｆ Output as

[0121] The limiting unit 25u converts the d-axis current i ｄ，ｏｕｔ is equal to or greater than the lower limit value id, ref, LLIM and equal to or less than the upper limit value id, ref, ULIM, the d-axis current i ｄ，ｏｕｔis output as is.

[0122] The limiting unit 25u converts the d-axis current i ｄ，ｏｕｔ is greater than the upper limit values ​​id, ref, ULIM, the limiting unit 25u outputs the upper limit values ​​id, ref, ULIM. ｄ，ｏｕｔ If is smaller than the lower limit values ​​id, ref, LLIM, the lower limit values ​​id, ref, LLIM are 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 these two is output to the adder 25h.

[0125] The adder 25h receives the q-axis current i ｑ，ｏｕｔ and the input value from the multiplier 25g are added together and the result 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 Output as

[0127] If the input value from the adder 25h is equal to or greater than the lower limit value iq, ref, LLIM and equal to or less than the upper limit value iq, ref, ULIM, the limiting unit 25v outputs the input value from the adder 25h as is.

[0128] The limiting unit 25v outputs the upper limit values ​​iq, ref, ULIM if the input value from the adder 25h is greater than the upper limit values ​​iq, ref, ULIM. If the input value from the adder 25h is smaller than the lower limit values ​​iq, ref, LLIM, the limiting unit 25v outputs the lower limit values ​​iq, ref, LLIM.

[0129] [Current Command Limiting Unit] In FIG. 11, 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 of the second embodiment may have the same configuration as the current command limiting unit 40 of the first embodiment.

[0130] [Inverse dq Transformation Unit] In FIG. 11, the inverse dq transformation unit 27 transforms the biaxial current command value (d-axis current command value i ｄ，ｒｅｆ，ＬＩＭ and the 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 Unit] In FIG. 11, 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 is the current measurement value i Ｌ is the output current command value i ｒｅｆ The current measurement value i can be configured as an ACR (Automatic Current Regulator) that performs feedback control so that the current measurement value i Ｌ is a measured value of the three-phase instantaneous current flowing from the inverter circuit 8 to the reactor L1 of the filter 3.

[0132] The instantaneous current control unit 28 determines the output current command value i ｒｅｆ and the 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，ｒｅｆThe 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 v ｏｕｔ，ｒｅｆ is added by an adder 29 to

[0133] Fig. 16 is a functional block diagram showing an example of an instantaneous current control unit in the control device. The instantaneous current control unit 28 shown in Fig. 16 is a part that performs instantaneous current control as part of GFM control. The instantaneous current control unit 28 includes 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 measured current value of A phase i Ｌ，ａ , B-phase current measurement value i Ｌ，ｂ and the C-phase current measurement value 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 without being bundled, in which case the demultiplexer 28a is not required.

[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 the 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 subtracts the input value from the multiplier 28d from the current measurement value i of the B phase and outputs the result to the adder 28i. Ｌ，ｂThe adder 28g subtracts the input value from the multiplier 28d from the current measurement value i of the C phase and outputs the result to the adder 28j. Ｌ，ｃ The input value from the multiplier 28d is subtracted from the sum, and the resulting value is output to the adder 28k.

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

[0139] The adder 28i calculates the output current command value i of the A phase. ｒｅｆ，ａ The adder 28j subtracts the input value from the adder 28e from the B-phase output current command value i ｒｅｆ，ｂ The adder 28k subtracts 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 28a and outputs the result to the multiplier 28n.

[0140] The multiplier 28l multiplies the input value from the adder 28i by a gain K ＡＣＲ The value multiplied by this is the A phase output voltage correction value v Ｌ，ｒｅｆ，ａ The multiplier 28m multiplies the input value from the adder 28j by a gain K ＡＣＲ The value multiplied by this is the B phase output voltage correction value v Ｌ，ｒｅｆ，ｂ The multiplier 28n multiplies the input value from the adder 28k by a gain K ＡＣＲ The value multiplied by this is the C phase output voltage correction value v Ｌ，ｒｅｆ，ｃ The gain K ＡＣＲ is the current measurement value i Ｌ and the output current command value i ｒｅｆ The gain K is a parameter for controlling the difference between ＡＣＲ is, for example, the P gain (proportional gain) when the ACR control is configured using a P regulator.

[0141] The multiplexer 28o receives the output voltage correction values ​​v for each phase, which are input from the multipliers 28l, 28m, and 28n, respectively. Ｌ，ｒｅｆ，ａ , v Ｌ，ｒｅｆ，ｂ , v Ｌ，ｒｅｆ，ｃ are combined into one signal to obtain the three-phase output voltage correction value v Ｌ，ｒｅｆ Here, as in the case described above, a configuration without using a multiplexer is also 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 the above is the PWM command value v ＰＷＭ，ｒｅｆ Output as

[0143] [PWM Pulse Generator] In FIG. 11, the PWM pulse generator 30 generates a PWM command value v ＰＷＭ，ｒｅｆ is compared with a carrier signal such as a triangular wave to obtain 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 includes 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] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

[0146] This international application claims priority based on Japanese Patent Application No. 2023-122541, filed on July 27, 2023, the entire contents of which are incorporated herein by reference.

[0147] REFERENCE SIGNS LIST 1 Power system 2 Power conversion device 3 Filter 4 Switch 5 Inverter 6 Power conversion section 7 Capacitor 8 Inverter circuit 10 Distribution line 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 generation section 31 Instantaneous voltage command section 32 DC voltage control section 33 Power correction section 34 Subtractor 35 Adder 40 Current command limiting section 41 Active power command section 42 Active power control section 43 Reactive power command section 44 Reactive power control section 51 Apparent current limiting section 52 Active current limiting section 53 Reactive current limiting section 54 Mode selection section

Claims

1. A power conversion device comprising: an inverter that converts input DC power into AC power; and a control device that controls the inverter, wherein the control device limits one of the active current and reactive current output from the inverter in preference to the other current, so that the apparent current output from the inverter is equal to or lower 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 the amplitude of the output voltage from the inverter is disturbed.

3. A power conversion device as described in claim 1, wherein the control device limits the active current in 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. The power conversion device according to claim 1, wherein the control device reduces the active current with a gain greater than that of 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.

5. The power conversion device according to claim 1, wherein 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 when the frequency of the output voltage from the inverter is disturbed.

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

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

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

9. A power conversion device according to any one of claims 1 to 8, wherein the control device selects whether to give priority to limiting the active current or the reactive current in accordance with a signal from outside the control device.

10. A power conversion device as described in claim 9, wherein the control device selects, in accordance with the external signal, whether to give priority to limiting the active current or the reactive current when the amplitude of the output voltage from the inverter is disturbed and when the frequency of the output voltage from the inverter is disturbed.

11. A power conversion device comprising: an inverter that converts input DC power into AC power; and a control device that controls the inverter, wherein 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 is equal to or lower than a limit value.

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 becomes equal to or less than the limit value.

13. A power conversion device as described in 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. A power conversion device as described in 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 less than the limit value.

Images