Power conversion device and individual operation detection method

Abstract

To provide a power conversion device capable of detecting individual operation of a voltage-controlled type inverter, and an individual operation detection method.SOLUTION: A power conversion device includes an inverter circuit for converting DC power to AC power, an inverter having a reactor provides between the inverter circuit and a linkage point, and a control device for controlling the inverter as a voltage-controlled type inverter. The inverter outputs an output voltage with harmonic wave overlapped to the linkage point, the control device generates a first signal by multiplying an output current detection value of the inverter by the harmonic wave signal, generates a second signal by filtering the first signal, generates a third signal which is an absolute vale of the second signal, generates a fourth signal by low-pass filtering the third signal, and detects individual operation of the inverter based on the third signal and the fourth signal.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to a power conversion device and a stand-alone operation detection method.

Background Art

[0002] Conventionally, a stand-alone operation detection device for detecting the stand-alone operation of a distributed power source is known (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Inverters connectable to a power system include a current control type inverter that controls the input and output currents on the AC side and a voltage control type inverter that controls the output voltage on the AC side. However, the stand-alone operation detection device applied to the current control type inverter cannot be applied to voltage control type inverters such as GFM inverters.

[0005] The present disclosure provides a power conversion device and a stand-alone operation detection method capable of detecting the stand-alone operation of a voltage control type inverter including a GFM inverter.

Means for Solving the Problems

[0006] The power conversion device according to the first aspect includes an inverter that converts DC power into AC power, and an inductor provided between the inverter and the connection point, and a control device that controls the inverter as a voltage control type inverter. The inverter outputs an output voltage with superimposed harmonics to the connection point. The control device generates a first signal by multiplying a measured value of the output current of the inverter by the harmonic signal, generates a second signal by filtering the first signal, generates a third signal which is the absolute value of the second signal, generates a fourth signal by performing a low-pass filter process on the third signal, and detects the single operation of the inverter based on the third signal and the fourth signal.

[0007] A second aspect is the power conversion device of the first aspect, The control device generates a fifth signal by multiplying the fourth signal by a positive number less than 1, and detects the single operation of the inverter by comparing the third signal with the fifth signal.

[0008] A third aspect is the power conversion device of the second aspect, When the third signal is lower than the fifth signal, the control device determines that the inverter is in a single operation state.

[0009] A fourth aspect is the power conversion device of the second or third aspect, When the admittance between the connection point and the power grid is Y1 and the admittance of the load connected to the connection point is Y2, The positive number is greater than (the maximum value of Y2) / (the maximum value of Y1).

[0010] A fifth aspect is the power conversion device of any one of the first to fourth aspects, The control device generates the second signal by performing a moving average on the first signal.

[0011] A sixth aspect is the power conversion device of the fifth aspect, The moving average time of the moving average filter that calculates the moving average of the first signal is an integer multiple of the period of the harmonic signal, or a time longer than the period of the harmonic signal.

[0012] A seventh aspect is the power conversion device of any one of the first to fourth aspects, The control device generates the second signal by performing a low-pass filter process on the first signal.

[0013] An eighth aspect is the power conversion device of the seventh aspect, wherein a time constant of the low-pass filter that performs a low-pass filter process on the first signal is a time longer than a period of the harmonic signal.

[0014] A ninth aspect is the power conversion device of any one of the first to eighth aspects, wherein an amplitude of the harmonic superimposed on the output voltage is smaller than a product of a reactance between the inverter circuit and the connection point and a harmonic current output limit value from the inverter circuit to the connection point.

[0015] A single operation detection method of a tenth aspect is a single operation detection method of a voltage control type inverter having an inverter circuit that converts DC power into AC power and a reactor provided between the inverter circuit and a connection point, wherein an output voltage with a superimposed harmonic is output from the inverter to the connection point, a first signal obtained by multiplying a measured value of an output current of the inverter by the harmonic signal is generated, a second signal is generated by filtering the first signal, a third signal that is an absolute value of the second signal is generated, a fourth signal is generated by performing a low-pass filter process on the third signal, and a single operation of the inverter is detected based on the third signal and the fourth signal.

Advantages of the Invention

[0016] According to the present disclosure, it is possible to detect a single operation of a voltage control type inverter including a GFM inverter.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments will be described.

[0019] <Overall Schematic Configuration of the Power Conversion Device> FIG. 1 is a diagram showing a configuration example of a power conversion device according to the first embodiment. The power conversion device 2 shown in FIG. 1 is connected to the power grid 1 at the connection point N. The power grid 1 is a power grid that supplies the AC power generated at the power plant to the load 11 such as the facilities of the customer via the distribution line 10.

[0020] 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 GFM (Grid Forming) inverter. Since the GFM inverter is required to act as a voltage source, the control device 20 controls the inverter 5 as a voltage control type inverter.

[0021] The inverter 5 is a device that converts the input DC power into AC power. The inverter 5 is, for example, an inverter-connected power source (IBR: Inverter Based Resources) that converts DC power generated from renewable energy such as sunlight into AC power and operates in connection with the power system 1. The inverter 5 includes a power conversion unit 6, a reactor L1, and a switch 4.

[0022] The power conversion unit 6 converts the input DC power P AC * (for example, DC power generated from renewable energy) into AC power according to a pulse width modulation signal (PWM pulse signal V in ) which is an example of a command value supplied from the control device 20. The power conversion unit 6 outputs a voltage V AC * corresponding to an AC voltage according to the PWM pulse signal V AC . The power conversion unit 6 is connected to the connection point N via the reactor L1 and is connected to the power system 1 via the connection point N and the distribution line 10.

[0023] The reactor L1 is a passive element provided between the power conversion unit 6 and the connection point N. The reactor is also referred to as an inductor. The AC current output from the power conversion unit 6 via the reactor L1 flows to the connection point N as the output current i out of the inverter 5. The voltage V AC output from the power conversion unit 6 is converted into a sinusoidal voltage as the output voltage v out of the inverter 5 by the reactor L1 and the capacitor C. Also, the outflow of high-frequency current to the power system 1 is restricted by the reactor L1 and the capacitor C.

[0024] The reactor L1 is a component having reactance. The reactor L1 may be a reactor configured as a filter, may be a leakage reactance of a transformer, or may be both. The reactor L1 is not limited to these components.

[0025] Switch 4 is connected between the power system 1 and the power conversion unit 6. Switch 4 may be called a tie breaker.

[0026] When the power conversion device 2 is in the single operation state, the control device 20 detects this state and stops the operation of the inverter 5, or releases the switch 4 to stop the single operation state.

[0027] Specifically, when the power conversion device 2 is interconnected with the power system 1, the load 11 is supplied with power from both the power system 1 and the power conversion device 2. When the circuit breaker 9 inserted in series in the distribution line 10 is opened due to a system accident or the like while the power conversion device 2 is in interconnected operation, the power supply from the power system 1 stops. If the power conversion device 2 continues to operate alone after the power supply from the power system 1 stops, a voltage will continue to be applied to the power system connected to the load 11, so there may be safety problems in the work on the power system. Therefore, the power conversion device 2 has a function of performing a predetermined operation such as detecting a single operation separated from the power system 1 and cutting off the power supply to the load 11. Details of the single operation detection will be described later.

[0028] The inverter 5 is controlled by the control device 20 in a voltage control method (GFM control method) and operates as, for example, a virtual synchronous generator (VSG).

[0029] The control device 20 controls the output voltage v of the inverter 5 by controlling the voltage V output by the power conversion unit 6. AC The output voltage v corresponds to the voltage at the connection point N connected to the distribution line 10. The control device 20 generates a command value (for example, a PWM pulse signal V) of the voltage V output by the power conversion unit 6 based on the measured value of the output voltage v at the connection point N and the output current i flowing through the connection point N. out The output voltage v out is equivalent to the voltage at the connection point N connected to the distribution line 10. The control device 20 generates a command value (for example, a PWM pulse signal V) of the voltage V output by the power conversion unit 6 based on the measured value of the output voltage v at the connection point N and the output current i flowing through the connection point N. out The output voltage v out at the connection point N and the output current i AC flowing through the connection point N. AC * )

[0030] 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 also be realized by an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). Further, an analog circuit using an operational amplifier or the like may be used as part of the control device 20.

[0031] FIG. 2 is a diagram showing configuration examples of the inverter and the control device in the power conversion device of the first embodiment. FIG. 2 shows the circuit configuration of the inverter 5 and the functional blocks of the control device 20B. The power conversion device 2B is an example of the above-described power conversion device 2. The power conversion device 2B includes an inverter 5 and a control device 20B.

[0032] The inverter 5 includes a power conversion unit 6, a reactor L1, a capacitor C, and a switch 4. The power conversion unit 6 has a capacitor 7 and an inverter circuit 8.

[0033] 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. The DC voltage v dc corresponds to the voltage of the capacitor 7 (capacitor voltage).

[0034] The inverter circuit 8 is an inverter circuit that converts the 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 dc smoothed by the capacitor 7 into a voltage V AC corresponding to an AC voltage and outputs it.

[0035] The control device 20B controls the inverter 5 in a voltage control method (GFM control method). In this example, the control device 20B performs virtual synchronous generator control (VSG control) to control the inverter 5 so that it behaves like a synchronous generator. For example, the control device 20B includes an active power control unit 22, a reactive power control unit 23, an instantaneous voltage command unit 31, an adder 29, a PWM pulse generation unit 30, and a single operation detection unit 60.

[0036] [Active Power Control Unit] Based on the VSG control, the active power control unit 22 generates a command value (phase command value θ out ) of the phase θ of the three-phase output voltage v ref output from the inverter 5 to the power grid 1. The phase command value θ ref is the phase of the output voltage command value v out,ref generated by the instantaneous voltage command unit 31. The output voltage command value v out,ref is the command value of the three-phase output voltage v out output from the inverter 5 to the power grid 1.

[0037] The active power control unit 22 generates the phase command value θ ref based on, for example, the active power command value P out and the active power measurement value P ref .

[0038] The active power command value P ref is the command value of the active power output from the inverter 5 to the power grid 1. The active power measurement value P out is the measurement value of the actual active power output from the inverter 5 to the power grid 1. The active power measurement value P out is the measurement value at the connection point N between the reactor L1 and the power grid 1.

[0039] Figure 3 is a functional block diagram showing an example of the active power control unit in the control device. The active power control unit 22 includes adders 22a, 22b, 22f, multipliers 22c, 22g, 22l, and integrators 22d, 22n.

[0040] In the following description, when the inverter 5 operates as a virtual synchronous generator, the inertia constant is denoted as M and the damping constant is denoted as D.

[0041] The adder 22a subtracts the measured active power value P ref from the active power command value P out and outputs the result (P ref -P out ) to the adder 22b.

[0042] The adder 22b adds the input from the multiplier 22e to the input value (P ref -P out ) from the adder 22a and outputs the result to the multiplier 22c.

[0043] The multiplier 22c multiplies the input value from the adder 22b by 1 / M and outputs the result to the integrator 22d.

[0044] The integrator 22d integrates the input value from the multiplier 22c and outputs the result to the multiplier 22l.

[0045] The value obtained by the integration operation here (the output value of the integrator 22d) is the value obtained by normalizing the frequency ω of the output voltage v out of the inverter 5 with the nominal frequency ω n of the power grid 1. The nominal frequency ω n is, for example, in Japan, a value obtained by multiplying 50 Hz by 2π in eastern Japan and a value obtained by multiplying 60 Hz by 2π in western Japan.

[0046] The adder 22f subtracts the input value from the integrator 22d from 1 and outputs the result to the multiplier 22g. The input value to the adder 22f may be the value obtained by dividing the frequency ω of the output voltage v out measured at the connection point N by the nominal frequency ω n instead of the input value from the integrator 22d.

[0047] The multiplier 22g multiplies the input value from the adder 22f by the damping constant D of the VSG and outputs the result to the adder 22b.

[0048] The multiplier 22l outputs a value obtained by multiplying the input value from the integrator 22d by the nominal frequency ω n . The output value of the multiplier 22l corresponds to the command value of the frequency of the output voltage v out output from the inverter 5 to the power grid 1 (the frequency of the voltage V AC output from the inverter circuit 8).

[0049] The integrator 22n outputs the phase command value θ ref as a result of integrating the input value from the multiplier 22l.

[0050] [Reactive power control unit] In FIG. 2, the reactive power control unit 23 generates a command value for the amplitude V of the three-phase output voltage v out output from the inverter 5 to the power grid 1 (amplitude command value V ref ). The amplitude command value V ref is the amplitude of the output voltage command value v out,ref generated by the instantaneous voltage command unit 31.

[0051] The reactive power control unit 23 generates, for example, the amplitude command value V ref based on the reactive power command value Q out , the reactive power measurement value Q out,ref and the output voltage amplitude command value V ref .

[0052] The 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 the measured value of the reactive power actually output from the inverter 5 to the power grid 1. The reactive power measurement value Q out is the measured value at the connection point N between the reactor L1 and the power grid 1.

[0053] The output voltage amplitude command value V out,ref is the command value of the amplitude of the output voltage v out output from the inverter 5 to the power grid 1.

[0054] FIG. 4 is a functional block diagram showing an example of a reactive power control unit in the control device. The reactive power control unit 23 includes adders 23a, 23e, 23f, multipliers 23b, 23c, an integrator 23d, and a limiter 23g.

[0055] The adder 23a outputs the value obtained by subtracting the reactive power measurement value Q ref from the reactive power command value Q out to the multiplier 23b and the multiplier 23c.

[0056] The multiplier 23b multiplies the input value from the adder 23a by a gain K p,QV and outputs the result to the adder 23e. The gain K p,QV is a parameter for proportional control to suppress the difference between the reactive power measurement value Q out and the reactive power command value Q ref . The gain K p,QV is, for example, the proportional gain of a PI regulator (proportional-integral regulator) for Q-V loop control.

[0057] The multiplier 23c multiplies the input value from the adder 23a by a gain K i,QV and outputs the result to the integrator 23d. The gain K i,QV is a parameter for integral control to suppress the difference between the reactive power measurement value Q out and the reactive power command value Q ref . The gain K i,QV is, for example, the integral gain of a PI regulator (proportional-integral regulator) for Q-V loop control.

[0058] The integrator 23d outputs the result of time-integrating the input value from the multiplier 23c to the adder 23e.

[0059] The adder 23e outputs the value obtained by adding the input value from the multiplier 23b and the input value from the integrator 23d to the adder 23f.

[0060] The adder 23f outputs the value obtained by adding the input value from the adder 23e and the amplitude command value V out of the output voltage v out,ref to the limiter 23g.

[0061] The limiting unit 23g outputs the value obtained by limiting the input value from the adder 23f based on the set upper limit value and lower limit value as the amplitude command value V ref to output.

[0062] If the input value from the adder 23f is greater than or equal to the lower limit value V ref,LLIM and less than or equal to the upper limit value V ref,ULIM , the input value from the adder 23f is output as it is.

[0063] If the input value from the adder 23f is greater than the upper limit value V ref,ULIM , the upper limit value V ref,ULIM is output. If the input value from the adder 23f is less than the lower limit value V ref,LLIM , the lower limit value V ref,LLIM is output.

[0064] The output value of the limiting unit 23g corresponds to the command value of the amplitude V of the three-phase output voltage v out output from the inverter 5 to the power system 1 (amplitude command value V ref ).

[0065] [Instantaneous Voltage Command Unit] In FIG. 2, the instantaneous voltage command unit 31 derives the output voltage command value v ref which is the command value of the three-phase output voltage output from the inverter 5 to the power system 1 based on the amplitude command value V ref and the phase command value θ out,ref . The output voltage command value v out,ref is the command value of the three-phase instantaneous voltage output from the inverter 5 to the power system 1.

[0066] FIG. 5 is a functional block diagram showing an example of the instantaneous voltage command unit in the control device. The instantaneous voltage command unit 31 includes adders 31a, 31b, cosine functions 31c, 31d, 31e, multipliers 31f, 31g, 31h, and a multiplexer 31i.

[0067] The adder 31a subtracts (2π / 3) from the phase command value θ ref to obtain a value (θref Outputs -(2π / 3) to the cosine function 31d.

[0068] The adder 31b adds the phase command value θ ref and (2π / 3), and outputs the resulting value (θ ref + (2π / 3)) to the cosine function 31e.

[0069] The multiplier 31f multiplies the input value cos(θ ref ) from the cosine function 31c by the amplitude command value V ref and outputs the resulting value as the output voltage command value v out,ref,a for phase A.

[0070] The multiplier 31g multiplies the input value cos(θ ref - (2π / 3)) from the cosine function 31d by the amplitude command value V ref and outputs the resulting value as the output voltage command value v out,ref,b for phase B.

[0071] The multiplier 31h multiplies the input value cos(θ ref + (2π / 3)) from the cosine function 31e by the amplitude command value V ref and outputs the resulting value as the output voltage command value v out,ref,c for phase C.

[0072] The multiplexer 31i combines the output voltage command values v out,ref,a , v out,ref,b , v out,ref,c for each phase into a single signal and outputs the three-phase output voltage command value v out,ref output from the inverter 5 to the power system 1. In this example, the multiplexer 31i is used to bundle the three signals into one signal for ease of handling, but the signals may be sent to the next block as three separate signals without using the multiplexer 31i.

[0073] [Adder] In FIG. 2, the adder 29 adds the harmonic v out,ref to the output voltage command value v ν and outputs the resulting value as the PWM command value v PWM,ref . The harmonic v νis a harmonic signal generated by the single - operation detection unit 60 described later.

[0074] [PWM Pulse Generation Unit] In FIG. 2, the PWM pulse generation unit 30 compares the PWM command value v PWM,ref with a carrier signal such as a triangular wave to generate a PWM pulse signal V AC * including PWM pulses. Note that the pulse - width modulation method is not limited to the triangular - wave comparison modulation method, and generally used pulse - width modulation methods can be used. Also, it goes without saying that it is necessary to generate the required number of PWM pulses according to the configuration of the inverter circuit 8.

[0075] [Single - operation Detection Unit] In FIG. 2, the single - operation detection unit 60 detects the single - operation of the inverter 5. The single - operation detection unit 60 generates a harmonic v ν for detecting the single - operation of the inverter 5 (power conversion device 2), and outputs the detection result (judgment result d s ). When the single - operation of the inverter 5 is detected by the single - operation detection unit 60, the control device 20B takes measures such as opening the switch 4 or stopping the inverter 5 to eliminate the single - operation of the inverter 5 (power conversion device 2).

[0076] FIG. 6 is a functional block diagram showing an example of the single - operation detection unit in the control device. The single - operation detection unit 60 shown in FIG. 6 includes multipliers 61, 62, 67, a filter 63, an abs function 64, low - pass filters 65, 66, and a determination unit 68. The low - pass filter 65 may not be provided.

[0077] The multiplier 61 multiplies the ν - th harmonic signal s ν with an amplitude of 1 by an amplitude A ν to generate a ν - th harmonic v ν with an amplitude A ν , and the ν - th harmonic v νOutputs to the adder 29. ν is a number greater than 1 (excluding multiples of 3), and preferably a non-integer, to improve the detection accuracy of single operation. The ν-th harmonic signal s ν is a signal having a frequency ν times the rated frequency of the power system 1 (e.g., 50 Hz or 60 Hz).

[0078] Fig. 7 is a functional block diagram showing an example of the harmonic generation section in the control device. The harmonic generation section 70 generates a ν-th harmonic signal s ν with an amplitude of 1. The harmonic generation section 70 has a dq / abc conversion section 71 and a multiplier 72. The dq / abc conversion section 71 uses inverse Park transformation to convert the two binary values d and q in the dq rotating coordinate system into three-phase abc signals (the ν-th harmonic signal s ν ). The multiplier 72 multiplies the phase command value θ ref by ν to generate the angular position νθ ref in the dq rotating coordinate system, and outputs the angular position νθ ref to the dq / abc conversion section 71. The dq / abc conversion section 71 may have the same configuration as the instantaneous voltage command section 31 (see Fig. 5).

[0079] In Fig. 6, the adder 29 generates a PWM command value v out,ref by superimposing the ν-th harmonic v ν on the output voltage command value v PWM,ref . The output voltage command value v out,ref is the command value of the three-phase output voltage output from the inverter 5 to the power system 1. By generating the PWM command value v out,ref with the ν-th harmonic v ν superimposed thereon, the inverter 5 outputs the output voltage v PWM,ref with the harmonic v ν superimposed thereon to the connection point N. out

[0080] On the other hand, the multiplier 62 generates the first signal s1 by multiplying the ν-th harmonic signal s ν with an amplitude of 1 by the output current measurement value i out , and outputs the first signal s1 to the filter 63. The output current measurement value i out ​is the measured value of the three-phase output current output from the inverter 5 to the power system 1. Note that the multiplier 62 generates the first signal s1 for three phases, but it may also generate the first signal s1 for only one phase.

[0081] At the adder 29, the ν-th harmonic v out,ref is superimposed on the output voltage command value v ν so that the ν-th component is mixed into the output current measured value i out . The single operation detection unit 60 detects the single operation of the inverter 5 by evaluating the magnitude of the ν-th component mixed into the output current measured value i out .

[0082] The filter 63 generates the second signal s2 by filtering the first signal s1. The filter 63 performs a filtering process corresponding to the Fourier series expansion of the first signal s1 to extract the ν-th component included in the output current measured value i out .

[0083] The filter 63 is, for example, a moving average filter that calculates the moving average of the first signal s1. The moving average time of the moving average filter is set to, for example, an integer multiple of the period of the ν-th harmonic signal s ν , or a time sufficiently longer than the period of the ν-th harmonic signal s ν . The moving average time of the moving average filter is set to a time sufficiently shorter than a predetermined single operation detection time limit. By using the filter 63 as a moving average filter, the detection signal b described below with reduced pulsation of the ν-th component can be extracted.

[0084] The filter 63 may also be a low-pass filter that generates the second signal s2 by performing low-pass filter processing on the first signal s1, attenuating the high-frequency components of the first signal s1 more than the low-frequency components. In the case of a low-pass filter, its time constant is set to, for example, a time sufficiently longer than the period of the ν-th harmonic signal s ν . The time constant of the low-pass filter is set to a time sufficiently shorter than a predetermined single operation detection time limit. By using the filter 63 as a low-pass filter, the detection signal b described below with reduced pulsation of the ν-th component can be extracted.

[0085] The abs function 64 is an absolute value calculation unit that generates a third signal s3 which is the absolute value of the second signal s2. Since the second signal s2 can be a negative value, the absolute value of the second signal s2 is calculated.

[0086] The low-pass filter 65 outputs the detected signal b by performing low-pass filtering on the third signal s3, where the high-frequency components of the third signal s3 are attenuated more than the low-frequency components. If there is no low-pass filter 65, the detected signal b may be the same as the third signal s3.

[0087] The low-pass filter 66 generates a fourth signal s4 by performing low-pass filtering on the detected signal b. The time constant of the low-pass filter 66 is set to, for example, a time longer than a predetermined single-operation detection time limit.

[0088] The multiplier 67 generates a fifth signal a by multiplying the fourth signal s4 by a positive number c less than 1.

[0089] The determination unit 68 detects (determines) the single operation of the inverter 5 by comparing the detected signal b with the fifth signal a. When the inverter 5 is in a single operation state, a phenomenon occurs in which the harmonic admittance on the output side of the inverter 5 decreases. The determination unit 68 utilizes this phenomenon to detect (determine) the single operation of the inverter 5 by comparing the fifth signal b (or the third signal s3 if there is no low-pass filter 65) with the fifth signal a.

[0090] Thus, according to the power conversion device 2 according to the first embodiment (according to the single operation detection method executed by the control device 20B by the single operation detection unit 60), the single operation of the inverter 5 (power conversion device 2) can be detected.

[0091] When the single operation of the inverter 5 is detected by the single operation detection unit 60, the control device 20B takes measures such as opening the switch 4 or stopping the inverter 5 to eliminate the single operation of the inverter 5 (power conversion device 2).

[0092] FIG. 8 is a model diagram schematically showing an example of a power system including a power conversion device connected to a power system and a load.

[0093] Output voltage command value v out,ref The amplitude A of the superimposed harmonic v ν is set to a value smaller than, for example, the product of "reactance X related to the ν-th component" between the inverter circuit 8 and the connection point N and the harmonic current output limit value I ν from the inverter circuit 8 to the connection point N. Thereby, when the inverter 5 is connected to the power system 1, the ν-th harmonic current flowing out to the power system 1 can be kept below the harmonic current output limit value I max max

[0094] A positive number c less than 1 (FIG. 6) is set to a value larger than, for example, the ratio of the maximum value of the admittance Y2 of the load 11 that can be assumed in the single-operation state with respect to the ν-th component and the minimum value of the admittance Y1 of the distribution line 10 that can be assumed when the inverter 5 is connected to the power system 1. Thereby, it is possible to suppress the occurrence of detection failures such as missing the detection of single operation.

[0095] More specifically, in FIG. 8, the admittance Y1 represents the admittance of the distribution line 10 between the connection point N and the power system 1. The admittance Y2 represents the admittance of the load 11 connected to the connection point N. The voltage V ν represents the harmonic voltage superimposed on the output voltage of the inverter circuit 8. When the inverter 5 is connected to the power system 1, the harmonic current (Y1V ν ) flowing out from the inverter circuit 8 mainly flows to the power system 1 side. When the inverter 5 shifts to the single-operation state, the harmonic current (Y2V ν ) flowing out from the inverter circuit 8 flows only to the load 11, and the harmonic current (Y2V ν ​​) has a magnitude of about (Y2 / Y1) during connection. Therefore, by setting a positive number c less than 1 to a value greater than the ratio (= (maximum value of Y2) / (maximum value of Y1)), it is possible to suppress the occurrence of detection failures such as failing to detect the independent operation of the inverter 5 after the inverter 5 shifts to the independent operation state.

[0096] Fig. 9 is a diagram showing an example of the result of simulating the independent operation detection method. Fig. 9 shows a simulation by a model in which the inverter 5 of the GFM control method is connected to an infinite bus. The conditional values in the simulation are expressed in per-unit values standardized with a nominal frequency of 50 Hz, a line voltage of 6.6 kV, and a reference capacity of 60 MVA. Referring to Fig. 8, the bus voltage of the power system 1 during connection is set to 1.0 pu, the reactance of the line between the connection point N and the power system 1 is set to 0.1 pu, and the resistance of the line between the connection point N and the power system 1 is set to 0.01 pu. The output of the inverter circuit 8 is set to 1.0 + j0, and the load 11 is set to a capacitive load of 1.0 - j0.1. The reactance X between the inverter circuit 8 and the connection point N is set to j0.13 pu.

[0097] In Fig. 9, first, the frequency of the power system 1 is set to 50 Hz, and at time 1.0 s, the inverter 5 is connected to the power system 1 and the output of the inverter 5 is started. The frequency of the power system 1 is increased from time 10 s at 2 Hz / s to 52 Hz, and then returned to 50 Hz at -2 Hz / s at time 14 s. After that, the frequency of the power system 1 is decreased from time 20 s at -2 Hz / s to 48 Hz, and then returned to 50 Hz at 2 Hz / s at time 24 s. The reason for varying the frequency in this way is to confirm that even if the system frequency of the power system 1 fluctuates, it is not misjudged as an independent operation state. From time 25 s, the connection between the connection point N and the power system 1 is interrupted to shift the inverter 5 to the independent operation state.

[0098] Let ν be 2.8 and the positive number c be 0.4. The time constant of the low-pass filter 66 is set to 1.0 s.

[0099] After the transition to the single - operation state, the detection signal b drops sharply. In contrast, the fifth signal a (= the fourth signal s4 × positive number c) is generated by the configuration shown in FIG. 6, and thus drops more gently than the detection signal b. The single - operation detector 60 detects the single - operation of the inverter 5 by comparing the detection signal b with the fifth signal a (= the fourth signal s4 × positive number c). When it is detected that the detection signal b is lower than the fifth signal a, the single - operation detector 60 determines that the inverter 5 is in the single - operation state and asserts its determination flag. The time constant of the low - pass filter 66 is set to be longer than the single - operation detection time limit, so that sudden changes during the determination of the fifth signal a are suppressed, and false determination of single - operation is suppressed.

[0100] As described above, the embodiments have been explained. However, the above embodiments are presented as examples, and the present invention is not limited by the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, replacements, changes, 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 invention described in the claims and its equivalent scope.

[0101] For example, the amplitude command value V ref is not limited to being generated by reactive - power control as in the above - described embodiments. For example, the amplitude command value V ref may be generated by other controls such as constant - voltage control in which the amplitude command value V is set to a constant value.

Explanation of Reference Numerals

[0102] 1 Power grid 2, 2B Power conversion device 4 Switch 5 Inverter 6 Power conversion unit 7 Capacitor 8 Inverter circuit 9 Circuit breaker 10 Distribution line 11 Load 20, 20B Control device 22 Active - power control unit 23 Reactive power control unit 29 Adder 30 PWM pulse generation unit 31 Instantaneous voltage command unit 60 Stand-alone operation detection unit 70 Harmonic generation unit L1 Reactor N Connection point

Claims

1. An inverter having an inverter circuit that converts DC power into AC power and a reactor provided between the inverter circuit and a connection point, A control device that controls the inverter as a voltage-controlled inverter, and The inverter outputs an output voltage with harmonics superimposed thereon to the connection point, The control device generates a first signal by multiplying a measured value of the output current of the inverter by a signal of the harmonics, generates a second signal by filtering the first signal, generates a third signal that is an absolute value of the second signal, generates a fourth signal by performing a low-pass filter process on the third signal, and detects a single operation of the inverter based on the third signal and the fourth signal. A power conversion device.

2. The control device generates a fifth signal by multiplying the fourth signal by a positive number less than 1, and detects a single operation of the inverter by comparing the third signal with the fifth signal. The power conversion device according to claim 1.

3. The control device determines that the inverter is in a single operation state when the third signal is lower than the fifth signal. The power conversion device according to claim 2.

4. Let the admittance between the connection point and the power system be Y １ and the admittance of the load connected to the connection point be Y ２ When this is the case, The positive number is (the maximum value of Y ２ ) / (the maximum value of Y １ ), and the power conversion device according to claim 2, which is larger than that.

5. The control device generates the second signal by performing a moving average on the first signal. The power conversion device according to any one of claims 1 to 4.

6. The moving average time of the moving average filter that calculates the moving average of the first signal is an integer multiple of the period of the harmonic signal or a time longer than the period of the harmonic signal. The power conversion device according to claim 5.

7. The control device generates the second signal by performing a low-pass filter process on the first signal. The power conversion device according to any one of claims 1 to 4.

8. The time constant of the low-pass filter that performs a low-pass filter process on the first signal is a time longer than the period of the harmonic signal. The power conversion device according to claim 7.

9. The amplitude of the harmonics superimposed on the output voltage is smaller than the product of the reactance between the inverter circuit and the connection point and the harmonic current output limit value from the inverter circuit to the connection point. The power conversion device according to any one of claims 1 to 4.

10. A method for detecting a single operation of a voltage-controlled inverter having an inverter circuit that converts DC power into AC power and a reactor provided between the inverter circuit and a connection point, Output a harmonic-overlapped output voltage from the inverter to the connection point. A single-operation detection method for generating a first signal by multiplying a harmonic signal by a measured value of an output current of the inverter, generating a second signal by filtering the first signal, generating a third signal which is an absolute value of the second signal, generating a fourth signal by performing a low-pass filter process on the third signal, and detecting a single operation of the inverter based on the third signal and the fourth signal.

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