Control device, power supply system and control method

Abstract

This prevents the current flowing from the power converter from becoming an overcurrent. [Solution] A control device that controls a power converter that supplies power to a power line when an opening / closing switch that opens and closes a power line for supplying power from a power system to a load is opened, and includes a first voltage command value calculation unit that calculates a first voltage command value that is a command value for a voltage output by the power converter, a first virtual impedance output unit that acquires a power converter current flowing from the power converter and outputs a first virtual impedance that imagines an impedance of the power converter based on a slope that indicates a time change of the power converter current, a virtual voltage drop calculation unit that calculates a virtual voltage drop calculated from the first virtual impedance and the power converter current when the first virtual impedance is output, and a second voltage command value output unit that outputs a second voltage command value obtained by subtracting the virtual voltage drop from the first voltage command value, to control the power converter.

Description

[Technical field]

[0001] The present invention relates to a control device, a power supply system, and a control method. [Background technology]

[0002] Conventionally, there has been proposed a control device that controls a power converter to disconnect the power converter from the power system and compensate for the load in the event of a power outage or momentary voltage drop (hereinafter also referred to as a voltage drop). For example, as shown in Patent Document 1, when a voltage drop occurs, this type of control device drives a power converter that is provided in parallel with a thyristor switch circuit provided between the power system and the load in order to forcibly extinguish the thyristor switch circuit. After forcibly extinguishing the thyristor switch circuit, the control device drives the power converter to supply compensating AC equivalent to the voltage drop in the power system to the load, thereby compensating for the drop in the load voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Utility model registration No. 2578802 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the above-mentioned power converter may be connected in parallel with the thyristor switch circuit via a capacitive load or a phase-leading capacitor for power factor adjustment. In this case, if a transient current is temporarily generated from the power system or the load, the current flowing from the power converter may become an overcurrent.

[0005] Furthermore, even when the thyristor switch circuit is forcibly extinguished to compensate for a drop in the load voltage, there is a risk that the current flowing from the power converter will become an overcurrent due to, for example, the introduction of a capacitive load.

[0006] The present invention has been made in consideration of the above problems, and has as its main object to prevent the current flowing from a power converter from becoming an overcurrent. [Means for solving the problem]

[0007] That is, the control device of the present invention is a control device that controls a power converter that supplies power to a power line when an opening / closing switch that opens and closes a power line for supplying power from a power system to a load is opened, and is characterized by comprising: a first voltage command value calculation unit that calculates a first voltage command value that is a command value for a voltage output by the power converter; a first virtual impedance output unit that acquires a power converter current flowing from the power converter and outputs a first virtual impedance that imagines an impedance of the power converter based on a slope that indicates a time change of the power converter current; a virtual voltage drop calculation unit that calculates a virtual voltage drop calculated from the first virtual impedance and the power converter current when the first virtual impedance is output; and a second voltage command value output unit that outputs a second voltage command value obtained by subtracting the virtual voltage drop from the first voltage command value to control the power converter.

[0008] Moreover, a control method according to the present invention is a control method for controlling a power converter supplying power to a power line when an opening / closing switch that opens and closes a power line for supplying power from a power system to a load is opened, the control method comprising the steps of: calculating a first voltage command value that is a command value for a voltage to be output by the power converter; acquiring a power converter current flowing from the power converter; and outputting a first virtual impedance that imagines an impedance of the power converter based on a slope that represents a time change of the power converter current; when the first virtual impedance is output, calculating a virtual voltage drop calculated from the first virtual impedance and the power converter current; and outputting a second voltage command value obtained by subtracting the virtual voltage drop from the first voltage command value, thereby controlling the power converter.

[0009] With this configuration, the virtual voltage drop due to the first virtual impedance is calculated, and the second voltage command value obtained by subtracting the virtual voltage drop from the first voltage command value is output, so the voltage output from the power converter is smaller than when the power converter is controlled based only on the first voltage command value. As a result, the current flowing from the power converter is reduced, making it possible to prevent an overcurrent from flowing from the power converter. In particular, with this configuration, since the first virtual impedance is output based on a slope representing a time change in the power converter current, it is possible to predict the occurrence of an overcurrent based on the slope. As a result, when the power converter current changes suddenly, the power converter is controlled to suppress the change in the power converter current, thereby preventing an overcurrent from occurring.

[0010] It is preferable that the first virtual impedance output unit outputs the first virtual impedance when the slope exceeds a slope threshold that is a threshold value of the slope, and sets the first virtual impedance to 0 when the slope is equal to or less than the slope threshold.

[0011] With this configuration, the first virtual impedance is output when the slope exceeds the slope threshold, so that it is possible to prevent the occurrence of an overcurrent in a situation where the slope exceeds the slope threshold and the occurrence of an overcurrent is more likely. Also, when the slope is equal to or less than the slope threshold, the first virtual impedance becomes 0, so that it is possible to prevent the voltage of the power converter from being unnecessarily suppressed.

[0012] It is preferable that the power converter further includes a second virtual impedance output unit that acquires the power converter current and, when the power converter current exceeds a threshold current of the power converter, outputs a second virtual impedance that imagines an impedance of the power converter, and when the first virtual impedance or the second virtual impedance is output, the virtual voltage drop calculation unit calculates a composite virtual impedance by combining the first virtual impedance and the second virtual impedance, and calculates the virtual voltage drop using the composite virtual impedance and the power converter current.

[0013] With this configuration, even if the power converter current exceeds the threshold current, the voltage output by the power converter is suppressed, so that the power converter current is suppressed when the power converter current actually becomes excessive, thereby making it possible to more reliably suppress overcurrent.

[0014] It is desirable that the second virtual impedance output section sets a lower limit value of the second virtual impedance to zero.

[0015] With this configuration, since the lower limit value of the second virtual impedance is 0, it is possible to prevent the first voltage command value from being unnecessarily subtracted when the power converter current is below the threshold current. Therefore, it is possible to prevent the voltage of the power converter from being unnecessarily reduced, and it is possible to accurately compensate the voltage of the load.

[0016] Further, specific examples of the power converter current acquired by the first virtual impedance output unit include the effective value of the three-phase power converter current, the effective value of the single-phase power converter current, or the instantaneous value of the power converter current.

[0017] Here, when the first virtual impedance output unit acquires an instantaneous value of the power converter current and determines whether or not the instantaneous value exceeds the gradient threshold, it is possible that a malfunction occurs due to the fundamental wave frequency. Therefore, in order to prevent malfunction of the first virtual impedance output unit due to the fundamental frequency, when the first virtual impedance output unit acquires an instantaneous value of the power converter current and calculates the slope, it is desirable that the slope threshold be the maximum value of the slope at the fundamental frequency.

[0018] A power supply system that is provided between a power system and a load and supplies power to the load can include an open / close switch that opens and closes a power line for supplying power from the power system to the load, a power converter that supplies power to the power line when the open / close switch is opened, and the control device. With this configuration, it is possible to obtain the same effects as the above-mentioned control device. Effect of the Invention

[0019] According to the present invention configured in this manner, it is possible to prevent the current flowing from the power converter from becoming an overcurrent. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic diagram of a power supply system according to an embodiment of the present invention; [Diagram 2] 2 is a schematic diagram showing functional blocks of a control device in the embodiment. FIG. [Diagram 3] FIG. 2 is a diagram showing a control block of a control device in the embodiment. [Figure 4] 13 is a simulation result using a conventional control device. [Diagram 5] 4 shows the results of a simulation using the control device in the same embodiment. [Figure 6] FIG. 11 is a diagram showing a control block of a control device according to another embodiment. [Figure 7] FIG. 11 is a diagram showing a control block of a control device according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] An embodiment of a power supply system including a control device according to the present invention will be described below with reference to the drawings. Note that in any of the drawings shown below, some parts may be omitted or exaggerated and illustrated in a schematic manner for ease of understanding. Identical components are given the same reference numerals and descriptions thereof will be omitted as appropriate.

[0022] <Overall configuration of power supply system> As shown in Fig. 1, a power supply system 100 in this embodiment is provided between a power system 10 and a load 20, and supplies power to the load 20. In this embodiment, when the power system 10 is normal, the power supply system 100 electrically connects the power system 10 and the load 20, thereby supplying power from the power system 10 to the load 20. On the other hand, when an abnormality such as a power outage or an instantaneous voltage drop (hereinafter also referred to as a momentary voltage drop) occurs in the power system 10, the power supply system 100 cuts off the power supply from the power system 10 to the load 20, and compensates for the voltage of the load 20. Note that the power supply system 100 in this embodiment supplies three-phase power, but the number of phases is not particularly limited.

[0023] Specifically, the power supply system 100 includes an open / close switch 3 that opens and closes a power line L for supplying power from a power system 10 to a load 20, a system voltage measurement unit 4 that measures a system voltage that is the voltage of the power system 10, a switch current measurement unit 5 that measures a switch current that is a current flowing through the open / close switch 3, a power converter 6 that is connected to the power line L in parallel with the open / close switch 3, and a control device 7 that controls the open / close switch 3 or the power converter 6. Each unit will be described below.

[0024] The open / close switch 3 is provided on the power line L, and when the open / close switch 3 is turned on, the power system 10 and the load 20 are electrically connected, and when the open / close switch 3 is turned off, the power system 10 and the load 20 are electrically disconnected. In this embodiment, the open / close switch 3 is a thyristor switch, and a control device 7 described later controls the power converter 6 to turn on or off the thyristor switch.

[0025] The system voltage measuring unit 4 is connected to the power line L via a potential transformer, and measures the voltage on the power system 10 side of the open / close switch 3. Specifically, the system voltage measuring unit 4 is connected via a potential transformer to the power system 10 side of the parallel circuit made up of the open / close switch 3 and the power converter 6. The system voltage obtained by the system voltage measuring unit 4 is input to the control device 7, which will be described later, and is used to control the open / close switch 3 or the power converter 6.

[0026] The switch current measuring unit 5 is provided in a parallel circuit made up of the open / close switch 3 and the power converter 6, and measures the switch current. Specifically, the switch current measuring unit 5 measures the current flowing through the power line L in which the open / close switch 3 is provided, in the parallel circuit made up of the open / close switch 3 and the power converter 6.

[0027] The power converter 6 is provided in parallel with the open / close switch 3 via an injection transformer T, and converts DC power from a power storage device (not shown) such as a secondary battery (storage battery) into AC power. The power converter 6 is configured using, for example, semiconductor switching elements, and is controlled by a control device 7.

[0028] In addition, a power converter current I, which is a current flowing from the power converter 6, is fed to the closed circuit formed by the injection transformer T and the power converter 6. inv The power converter current measuring unit 8 is provided to measure the power converter current I inv is input to the control device 7 described later.

[0029] The control device 7 controls the open / close switch 3 or the power converter 6 when an abnormality occurs in the power system 10. Here, the control device 7 is a general-purpose or dedicated computer equipped with a CPU, memory, input / output interface, etc., and performs the following functions by making the CPU and peripheral devices cooperate in accordance with a predetermined program stored in the memory.

[0030] Specifically, the control device 7 includes a parameter acquisition unit 71 that acquires various parameters, a switching control unit 72 that controls the switching of the switching switch 3, and a first voltage command value V ref1a first virtual impedance output unit 74 that calculates a first virtual impedance R1 that is a first virtual impedance obtained by imagining the impedance of the power converter 6; a second virtual impedance output unit 75 that calculates a second virtual impedance R2 that is a second virtual impedance obtained by imagining the impedance of the power converter 6; and a virtual voltage drop ΔV 0 A virtual voltage drop calculation unit 76 calculates a second voltage command value V ref2 Each of the functional units will be described below.

[0031] The parameter acquisition unit 71 acquires various parameters for controlling the open / close switch 3 or the power converter 6. The various parameters referred to here include the system voltage, the switch current, the power converter current I inv , the power converter current I inv The threshold current I limit , and the three-phase power converter current I inv The effective value of the threshold current I limit may be set by input from the user, or may be stored in advance.

[0032] The switching control unit 72 controls the opening / closing switch 3 and the power converter 6 to open the opening / closing switch 3 when an abnormality occurs in the power system 10, and also controls the opening / closing switch 3 and the power converter 6 to close the opening / closing switch 3 when the system voltage is restored.

[0033] Specifically, when the parameter acquisition unit 71 acquires a system voltage that exceeds a predetermined range, the switching control unit 72 outputs an extinguishing command signal to extinguish the opening / closing switch 3, thereby controlling the current output by the power converter 6. Specifically, the switching control unit 72 acquires the switch current measured by the switch current measurement unit 5, and controls the power converter 6 so as to set the switch current to 0 A. Note that the system voltage exceeding the predetermined range referred to here refers to a case where the system voltage is, for example, 20% or less or 107% or more of the rated voltage.

[0034] When the parameter acquisition unit 71 acquires the restored system voltage, the switching control unit 72 outputs an ignition command signal for igniting the opening / closing switch 3 to control the current output by the power converter 6. Note that the restored system voltage here refers to a state in which the system voltage is equivalent to the rated voltage and continues for a certain period of time.

[0035] The first voltage command value calculation unit 73 calculates the first voltage command value V ref1 The target value of the load voltage referred to here is, for example, the rated voltage.

[0036] The first virtual impedance output unit 74 outputs the power converter current I inv and calculate the power converter current I inv The first virtual impedance output unit 74 outputs the first virtual impedance R1 based on a slope indicating a time change of the impedance R1. Specifically, the first virtual impedance output unit 74 outputs the first virtual impedance R1 when the slope exceeds a slope threshold, and sets the first virtual impedance R1 to 0 when the slope is equal to or smaller than the slope threshold.

[0037] The output of the first virtual impedance R1 by the first virtual impedance output section 74 will be described below.

[0038] The first virtual impedance output unit 74 receives the three-phase power converter current I from the parameter acquisition unit 71 at a predetermined sampling period. inv Get the effective value of .

[0039] The first virtual impedance output unit 74 outputs the three-phase power converter current I inv and the three-phase power converter current I at a time point earlier than the measurement, for example, the previous sampling period. inv The power converter current I inv That is, in this embodiment, the slope of the power converter current I inv The slope of the time change of the power converter current I inv In this embodiment, the first virtual impedance output section 74 calculates the difference between the effective value at the current time and the effective value one sample earlier, but may calculate the difference between the effective value at the current time and the effective value two samples earlier, or may calculate the difference between the effective value one sample earlier and the effective value two samples earlier in addition to calculating the difference between the effective value at the current time and the effective value one sample earlier.

[0040] When the slope is calculated, the first virtual impedance output unit 74 converts the slope into a first virtual impedance R1 by multiplying the slope by a proportional constant Kp. inv In order to suppress the change in

[0041] Furthermore, the first virtual impedance output unit 74 determines whether the slope exceeds a slope threshold. inv In order to detect a sudden increase in the slope, the slope threshold is set to a positive value. When the slope exceeds the slope threshold, the first virtual impedance output unit 74 outputs the first virtual impedance R1, which is a positive value, to the virtual voltage drop calculation unit 76. On the other hand, when the slope is equal to or smaller than the slope threshold, the first virtual impedance output unit 74 sets the first virtual impedance R1 to 0 and outputs it to the virtual voltage drop calculation unit 76.

[0042] The second virtual impedance output unit 75 outputs the power converter current I inv and calculate the power converter current I invis the threshold current I limit Specifically, the second virtual impedance output unit 75 outputs the second virtual impedance R2 when the power converter current I inv and the threshold current I limit Based on the difference between these, a second virtual impedance R2 is output.

[0043] More specifically, the second virtual impedance output unit 75 receives the three-phase power converter current I inv The second virtual impedance output unit 75 acquires the effective value of the threshold current I limit Get the.

[0044] The second virtual impedance output unit 75 outputs the power converter current I inv and the threshold current I limit The second virtual impedance R2 is calculated by performing PI control based on the difference between the power converter current I inv is the threshold current I limit If it exceeds this value, the second virtual impedance output section 75 outputs the second virtual impedance R2, which is a positive value, to the virtual voltage drop calculation section .

[0045] On the other hand, the power converter current I inv is the threshold current I limit If the second virtual impedance R2 is equal to or less than 0, a negative value is input to the PI control. Here, the second virtual impedance output unit 75 sets the lower limit of the second virtual impedance R2 to 0. Therefore, when a negative value is input to the PI control, the second virtual impedance output unit 75 sets the second virtual impedance R2 to 0 and outputs it to the virtual voltage drop calculation unit 76.

[0046] When the first virtual impedance R1 or the second virtual impedance R2 is output, the virtual voltage drop calculation unit 76 calculates a virtual voltage drop ΔV 0Here, the virtual voltage drop calculation unit 76 calculates a combined virtual impedance R by combining the first virtual impedance R1 and the second virtual impedance R2. The virtual voltage drop calculation unit 76 then calculates the combined virtual impedance R and the power converter current I inv By multiplying by , the virtual voltage drop ΔV 0 Calculate.

[0047] The second voltage command value output unit 77 outputs the first voltage command value V ref1 and virtual voltage drop ΔV 0 Based on this, the second voltage command value V ref2 The second voltage command value V ref2 is the first voltage command value V ref1 Virtual voltage drop ΔV from 0 The second voltage command value output unit 77 outputs the second voltage command value V ref2 Based on this, the power converter 6 determines the second voltage command value V ref2 The power converter 6 is controlled so as to output the following.

[0048] <Power supply system operation> Next, the operation of power supply system 100 including control device 7 configured as above will be described.

[0049] When the power system 10 is normal, the open / close switch 3 is turned on and power is supplied from the power system 10 to the load 20. In addition, the system voltage measurement unit 4 measures the system voltage, and the parameter acquisition unit 71 acquires the measured system voltage.

[0050] When it is determined that the system voltage measured by the system voltage measurement unit 4 exceeds a predetermined range, the control device 7 determines that an abnormality has occurred in the power system 10. Specifically, when the system voltage acquired by the parameter acquisition unit 71 exceeds a predetermined range, the switching control unit 72 controls the opening / closing switch 3 and the power converter 6 to open the opening / closing switch 3. Furthermore, the parameter acquisition unit 71 acquires, in addition to the system voltage, a three-phase power converter current I inv has been obtained.

[0051] When the current flowing through the opening / closing switch 3 becomes 0 A, the opening / closing control section 72 determines that the opening of the opening / closing switch 3 is completed. Then, the opening control section 72 outputs an opening completion signal indicating that the opening of the opening / closing switch 3 is completed to the first voltage command value calculation section 73. The first voltage command value calculation section 73 acquires the opening completion signal and calculates the first voltage command value V ref1 Calculate.

[0052] First voltage command value V ref1 When is calculated, the first virtual impedance output unit 74 and the second virtual impedance output unit 75 calculate the first virtual impedance R1 and the second virtual impedance R2, respectively, in a manner similar to the calculation of the first virtual impedance R1 and the calculation of the second virtual impedance R2 described above.

[0053] Here, the first virtual impedance output unit 74 outputs the power converter current I inv and, if the slope exceeds a slope threshold, outputs a positive first virtual impedance R1 to the virtual voltage drop calculation unit 76. On the other hand, if the slope is equal to or smaller than the slope threshold, the first virtual impedance output unit 74 sets the first virtual impedance R1 to 0 and outputs it to the virtual voltage drop calculation unit 76.

[0054] In addition, the second virtual impedance output unit 75 outputs the power converter current I inv is the threshold current I limit If the power converter current I inv is the threshold current I limit If it is equal to or less than this, the second virtual impedance R2 is set to 0 and output to the virtual voltage drop calculation unit 76.

[0055] When the first virtual impedance R1 or the second virtual impedance R2 is output, the virtual voltage drop calculation unit 76 calculates the virtual voltage drop ΔV 0Specifically, the virtual voltage drop calculation unit 76 calculates the virtual voltage drop ΔV 0 The first virtual impedance R1 and the second virtual impedance R2 are combined in the same manner as in the calculation of the first virtual impedance R1 and the second virtual impedance R2 to calculate a combined virtual impedance R. The combined virtual impedance R1 and the power converter current I inv By multiplying the virtual voltage drop ΔV 0 Calculate.

[0056] Virtual voltage drop ΔV 0 When the first voltage command value V ref1 and virtual voltage drop ΔV 0 Based on this, the second voltage command value V ref2 Specifically, the second voltage command value output unit 77 calculates the second voltage command value V ref2 The first voltage command value V ref1 Virtual voltage drop ΔV from 0 The voltage command value obtained by subtracting ref2 and the power converter 6 outputs the second voltage command value V ref2 The power converter 6 is controlled so as to output the following.

[0057] When the system voltage is restored, the switching control unit 72 controls the switching switch 3 and the power converter 6 to close the switching switch 3. Specifically, the switching control unit 72 sets the current output by the power converter 6 to zero, and closes the switching switch 3 to electrically connect the power system 10 and the load 20.

[0058] <Example> Below, a simulation result using a control device in a conventional example and a simulation result using the control device 7 in this embodiment are shown. In either case, the inverter voltage indicates the voltage output by the power converter 6, and the inverter current indicates the current output by the power converter 6.

[0059] In the conventional example, when an abnormality such as an accident occurs in the power system 10 and the open / close switch 3 is opened, the control device controls the voltage output by the power converter 6 based on the difference between the target value of the load voltage and the measured value of the system voltage. In this case, when a temporary transient current occurs from the power system 10 or the load 20, the difference between the target value of the load voltage and the measured value of the system voltage becomes large. As a result, as shown in Fig. 4, an overcurrent occurs in which the inverter current becomes equal to or exceeds the rated current (1 pu).

[0060] On the other hand, in the control device 7 of this embodiment, when an abnormality such as an accident occurs in the power system 10 and the open / close switch 3 is opened, the first voltage command value calculation unit 73 calculates the first voltage command value V ref1 The virtual voltage drop calculation unit 76 calculates the virtual impedance Z 0 Virtual voltage drop ΔV based on 0 Then, the second voltage command value output unit 77 calculates the first voltage command value V ref1 and virtual voltage drop ΔV 0 Based on this, the second voltage command value V ref2 As a result, as shown in Fig. 5, the inverter current is controlled to be equal to or less than the rated current (1 pu), and no overcurrent occurs.

[0061] <Effects of this embodiment> According to this embodiment, the virtual voltage drop ΔV based on the synthetic virtual impedance R 0 Calculate the first voltage command value V ref1 Virtual voltage drop ΔV from 0 The second voltage command value V ref2 is output, the first voltage command value V ref1 In comparison with the case where the power converter 6 is controlled based only on the output voltage, the voltage output from the power converter 6 is reduced. As a result, the current flowing from the power converter 6 is reduced, so that it is possible to prevent an overcurrent from flowing from the power converter 6.

[0062] In particular, according to this embodiment, the power converter current I invSince the first virtual impedance R1 is output based on the slope representing the time change of the power converter current I inv When the power converter current I inv By controlling the power converter 6 so as to suppress the change in the input current, it is possible to prevent an overcurrent from occurring.

[0063] According to the present embodiment, the first virtual impedance R1 is output when the slope exceeds the slope threshold, so that it is possible to prevent the occurrence of an overcurrent in a situation where the occurrence of an overcurrent is more likely. Also, when the slope is equal to or less than the slope threshold, the first virtual impedance R1 is not output, so that it is possible to prevent the voltage output by the power converter 6 from being unnecessarily suppressed.

[0064] Furthermore, according to this embodiment, the power converter current I inv is the threshold current I limit Even if the power converter current I inv When the power converter current I inv As a result, overcurrent can be more reliably suppressed.

[0065] Moreover, according to the present embodiment, the lower limit value of the second virtual impedance R2 is 0, so that the power converter current I inv is the threshold current I limit If the first voltage command value V ref1 Therefore, it is possible to prevent the voltage of the power converter 6 from being unnecessarily reduced, and the voltage of the load 20 can be compensated for with high accuracy.

[0066] <Other embodiments> The present invention is not limited to the above-described embodiment.

[0067] In the above embodiment, the first virtual impedance output unit 74 or the second virtual impedance output unit 75 outputs the three-phase power converter current Iinv 6, the first virtual impedance output unit 74 or the second virtual impedance output unit 75 acquires the effective value of the power converter current I inv and outputting the first virtual impedance Ru1 or the second virtual impedance Ru2 in each phase.

[0068] As shown in FIG. 7, the first virtual impedance output unit 74 or the second virtual impedance output unit 75 outputs the power converter current I inv Here, the instantaneous value of the power converter current I inv By calculating the absolute value of the power converter current I inv In this case, in order to prevent malfunction of the first virtual impedance output section 74 due to the fundamental frequency, it is preferable to set the slope threshold to a value equal to or greater than the maximum value of the slope at the fundamental frequency expressed by the following equation 1.

[0069]

number

[0070] where fn is the fundamental frequency and fs is the power converter current I inv is the frequency at which the signal was acquired.

[0071] In this embodiment, the control device 7 is configured to include both the first virtual impedance output section 74 and the second virtual impedance output section 75, but it may also be configured to include only the first virtual impedance output section 74, or may be configured to include only the second virtual impedance output section 75.

[0072] In this embodiment, the open / close switch 3 is a thyristor switch, but may be another type of switch, such as a semiconductor switch, a mechanical switch, or a hybrid switch of these.

[0073] In the present embodiment, the power supply system 100 is configured to include the switch current measuring unit 5, but may be configured not to include the switch current measuring unit 5. For example, the power supply system 100 may cause the switch current to converge to 0 A or to intersect with 0 A.

[0074] Furthermore, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0075] 100 Power System 10...Electric power system 20 Load 3 Open / Close Switch 4. System voltage measurement section 5 Switch current measurement section 6 Power Converter 7. Control device 71 Parameter acquisition section 72 Opening and closing control section 73 First voltage command value calculation unit 74 First virtual impedance output section 75 Second virtual impedance output section 76 Virtual voltage drop calculation section 77 Second voltage command value output section L...Power line T: Injection transformer

Claims

1. A control device for controlling a power converter that supplies power to a power line when an open / close switch that opens and closes a power line for supplying power from a power system to a load is opened, comprising: a first voltage command value calculation unit that calculates a first voltage command value that is a command value of a voltage output by the power converter; a first virtual impedance output unit that acquires a power converter current flowing from the power converter and outputs a first virtual impedance that is a virtual impedance of the power converter based on a gradient that indicates a time change of the power converter current; a second virtual impedance output unit that acquires the power converter current, and outputs a second virtual impedance that is a virtual impedance of the power converter when the power converter current exceeds a threshold current of the power converter; a virtual voltage drop calculation unit that calculates a composite virtual impedance by combining the first virtual impedance and the second virtual impedance when the first virtual impedance or the second virtual impedance is output, and calculates a virtual voltage drop based on the composite virtual impedance and the power converter current; a second voltage command value output unit that outputs a second voltage command value obtained by subtracting the virtual voltage drop from the first voltage command value to control the power converter.

2. 2. The control device according to claim 1, wherein the first virtual impedance output unit outputs the first virtual impedance when the slope exceeds a slope threshold that is a threshold value of the slope, and sets the first virtual impedance to 0 when the slope is equal to or less than the slope threshold.

3. The control device according to claim 1 , wherein the second virtual impedance output unit sets a lower limit value of the second virtual impedance to zero.

4. 2. The control device according to claim 1, wherein the power converter current acquired by the first virtual impedance output unit is an effective value of the three-phase power converter current, an effective value of the single-phase power converter current, or an instantaneous value of the power converter current.

5. 3 . The control device according to claim 2 , wherein when the first virtual impedance output unit obtains an instantaneous value of the power converter current to calculate the slope, the slope threshold value is a maximum value of the slope at a fundamental frequency.

6. A power supply system provided between a power system and a load, for supplying power to the load, comprising: an open / close switch for opening and closing a power line for supplying power from the power system to a load; a power converter that supplies power to the power line when the open / close switch is opened; A power supply system comprising the control device according to claim 1 or 2.

7. 1. A control method for controlling a power converter that supplies power to a power line when an open / close switch that opens and closes a power line for supplying power from a power system to a load is opened, comprising: Calculating a first voltage command value which is a command value of a voltage output by the power converter; acquiring a power converter current flowing from the power converter, and outputting a first virtual impedance obtained by virtualizing an impedance of the power converter based on a gradient representing a time change of the power converter current; acquiring a current of the power converter, and outputting a second virtual impedance obtained by virtualizing an impedance of the power converter when the power converter current exceeds a threshold current of the power converter; When the first virtual impedance or the second virtual impedance is output, a composite virtual impedance is calculated by combining the first virtual impedance and the second virtual impedance, and a virtual voltage drop is calculated based on the composite virtual impedance and the power converter current; A control method for controlling the power converter by outputting a second voltage command value obtained by subtracting the virtual voltage drop from the first voltage command value.

8. A control device for controlling a power converter that supplies power to a power line when an opening / closing switch that opens and closes a power line for supplying power from a power system to a load is opened, comprising: a first voltage command value calculation unit that calculates a first voltage command value that is a command value of a voltage output by the power converter; a first virtual impedance output unit that acquires a power converter current flowing from the power converter and outputs a first virtual impedance that is a virtual impedance of the power converter based on a gradient that indicates a time change of the power converter current; a virtual voltage drop calculation unit that calculates a virtual voltage drop calculated based on the first virtual impedance and the power converter current when the first virtual impedance is output; a second voltage command value output unit that outputs a second voltage command value obtained by subtracting the virtual voltage drop from the first voltage command value to control the power converter, the first virtual impedance output unit outputs the first virtual impedance when the gradient exceeds a gradient threshold that is a threshold value of the gradient, and sets the first virtual impedance to 0 when the gradient is equal to or less than the gradient threshold; The control device, wherein, when the first virtual impedance output unit obtains an instantaneous value of the power converter current to calculate the slope, the slope threshold is a maximum value of the slope at a fundamental wave frequency.

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