Power supply system, control method for power supply system, and control program for power supply system

Abstract

To provide a power supply system including a three-phase power converter for supplying AC power for compensating for the voltage of a load when an abnormality occurs in a power system, a compensation time during which the voltage of the load can be compensated being extended.SOLUTION: A power supply system 100 includes a switch 2 for opening and closing a power line P, a three-phase power converter 4 for converting DC power from a DC power source 3 into three-phase AC power and supplying the AC power to the power line, and a control device 8 having a three-phase power converter control unit for controlling the three-phase power converter. When the switch has been opened during abnormality of a power system, the three-phase power converter control unit calculates a compensation voltage that is a voltage for compensating for the load, acquires a DC voltage that is a voltage to be output by the DC power source, calculates a command voltage that is a voltage to be output by the three-phase power converter based on the compensation voltage and the DC voltage, calculates, based on the command voltage, a superimposed third harmonic that is to be superimposed on the command voltage, and superimposes the superimposed third harmonic on the command voltage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power supply system, a control method for the power supply system, and a control program for the power supply system.

Background Art

[0002] A conventional power supply system includes, for example, as shown in Patent Document 1, a circuit breaker provided in a power line for supplying power from a power grid to a load, and a power converter connected on the load side of the circuit breaker and converting the energy of an energy storage unit into AC power.

[0003] During normal operation of the power grid, this power supply system supplies power from the power grid to the load via the circuit breaker, and the power converter is stopped. On the other hand, during an abnormality in the power grid, the circuit breaker is opened to cut off the power supply from the power grid to the load, and AC power is supplied from the energy storage unit to the load via the power converter. Thereby, the voltage of the load is compensated during an abnormality in the power grid.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, in the above power supply system, a three-phase power converter may be used for the power converter. In this case, when the command voltage to be output to the three-phase power converter is larger than the maximum voltage that the three-phase power converter can output, the voltage waveform is distorted or the output voltage decreases. Therefore, when compensating the voltage of the load, it is necessary for the voltage to be output from the three-phase power converter in a state where the command voltage is smaller than the maximum voltage.

[0006] On the one hand, the maximum voltage is determined by the voltage output from the energy storage unit. Here, when compensating for the voltage of the load, the voltage output from the energy storage unit rapidly drops due to rapid discharge from the energy storage unit, and the maximum voltage rapidly drops. As a result, the command voltage immediately becomes larger than the maximum voltage, and the compensation time for compensating the voltage of the load becomes short.

[0007] Therefore, in order to reduce the amplitude of the command voltage, a configuration in which a third harmonic is superimposed on the command voltage is conceivable. In this case, during a three-phase short circuit, since the command voltage before superimposing the third harmonic is three-phase balanced, the third harmonic for reducing the amplitude of the command voltage can be accurately calculated.

[0008] However, during a two-phase short circuit, since the command voltage before superimposing the third harmonic is three-phase unbalanced, the third harmonic for reducing the amplitude of the command voltage cannot be accurately calculated. Therefore, during a two-phase short circuit, simply superimposing the third harmonic on the command voltage cannot extend the compensation time.

[0009] Therefore, the present invention has been made in view of the above problems, and in a power supply system including a three-phase power converter that supplies AC power to compensate for the voltage of a load during an abnormality in the power system, the main problem is to extend the compensation time capable of compensating for the voltage of the load regardless of whether it is three-phase balanced or three-phase unbalanced.

Means for Solving the Problem

[0010] That is, the power supply system according to the present invention supplies power from the power grid to a load during normal operation of the power grid, cuts off the power supply from the power grid to the load during abnormal operation of the power grid, and supplies power from a DC power supply to the load. The power supply system is provided on a power line for supplying power from the power grid to the load, and includes a switch for opening and closing the power line, a three-phase power converter for converting DC power from the DC power supply into three-phase AC power and supplying the power to the power line, and a three-phase power converter control unit for controlling the three-phase power converter. The three-phase power converter control unit includes a compensation voltage calculation unit for calculating a compensation voltage, which is a voltage for compensating the load, when the opening of the switch is completed during abnormal operation of the power grid, an instruction voltage calculation unit for obtaining a DC voltage output from the DC power supply and calculating an instruction voltage, which is a voltage to be output to the power converter, based on the compensation voltage and the DC voltage, and a third harmonic superimposition unit for calculating a superimposed third harmonic, which is a third harmonic for superimposing on the instruction voltage, based on the instruction voltage and superimposing the superimposed third harmonic on the instruction voltage. The third harmonic superimposition unit separates the instruction voltage into a positive-phase component and a negative-phase component, calculates a positive-phase third harmonic, which is a third harmonic corresponding to the positive-phase component, based on the amplitude and phase of the positive-phase component, calculates a negative-phase third harmonic, which is a third harmonic corresponding to the negative-phase component, based on the amplitude and phase of the negative-phase component, and calculates the superimposed third harmonic by synthesizing the positive-phase third harmonic and the negative-phase third harmonic.

[0011] With such a power supply system, the third harmonic superimposition unit separates the instruction voltage into a positive-phase component and a negative-phase component, calculates a positive-phase third harmonic and a negative-phase third harmonic, and calculates the superimposed third harmonic by synthesizing the positive-phase third harmonic and the negative-phase third harmonic. Therefore, regardless of whether the three-phase is balanced or unbalanced, the superimposed third harmonic for reducing the amplitude of the instruction voltage can be accurately calculated. Accordingly, regardless of whether the three-phase is balanced or unbalanced, the compensation time can be extended compared to the prior art. In addition, the three-phase power converter outputs three-phase AC, and since the third harmonics of each phase are canceled out in the line voltage, the voltage output by the power converter can be increased without increasing the distortion of the line voltage.

[0012] As a specific embodiment of the third harmonic superposition part, there is one that calculates the third harmonic by multiplying the amplitude of the command voltage by 1 / 6 and multiplying the phase of the command voltage by 3.

[0013] With such a configuration, the amplitude of the command voltage after superimposing the third harmonic can be minimized, so that the compensation time can be extended to the maximum extent.

[0014] The three-phase power converter is preferably connected in series to the power line.

[0015] With such a configuration, compared with the case where the three-phase power converter is connected in parallel to the power line, the loss of the three-phase power converter can be suppressed.

[0016] When compensating the voltage of the load during momentary voltage dips, a capacitor is often adopted as the DC power supply from the viewpoints of installation space, maintenance, or cost. However, compared with other DC power supplies such as lead-acid batteries, when the capacitor is discharged, as the capacitance of the capacitor decreases, the DC voltage output from the capacitor drops rapidly, and the maximum voltage of the three-phase power converter also drops. As a result, in the conventional power supply system, it is necessary to increase the capacitor capacitance to extend the compensation time. Therefore, the DC power supply is preferably a capacitor.

[0017] With such a configuration, the compensation time can be extended without increasing the capacitor capacitance. Specifically, when the capacitor capacitance is the same as that of the conventional case, the compensation time can be extended compared with the conventional case. Also, when the compensation time is the same as that of the conventional case, the capacitor capacitance can be reduced compared with the conventional case.

[0018] Also, a control method for a power supply system that supplies power from a power system to a load during normal operation of the power system, cuts off the power supply from the power system to the load during abnormal operation of the power system, and supplies power from a DC power supply to the load. The power supply system is provided on a power line for supplying power from the power system to the load, and includes a switch for opening and closing the power line, and a three-phase power converter connected in series to the power line for converting DC power from the DC power supply into three-phase AC power. The control method of the power supply system calculates a compensation voltage, which is a voltage for compensating the load, when the opening of the switch is completed during abnormal operation of the power system, obtains a DC voltage, which is the voltage output by the DC power supply, and calculates a command voltage, which is the voltage to be output to the three-phase power converter, based on the compensation voltage and the DC voltage. The command voltage is separated into a positive-phase component and a negative-phase component, and a positive-phase third harmonic, which is a third harmonic corresponding to the positive-phase component, is calculated based on the amplitude and phase of the positive-phase component, and a negative-phase third harmonic, which is a third harmonic corresponding to the negative-phase component, is calculated based on the amplitude and phase of the negative-phase component. By synthesizing the positive-phase third harmonic and the negative-phase third harmonic, a superimposed third harmonic, which is a third harmonic for superimposing on the command voltage, is calculated, and the superimposed third harmonic is superimposed on the command voltage. Furthermore, it is a control program for a power supply system that supplies power from a power grid to a load during normal operation of the power grid, cuts off the power supply from the power grid to the load during abnormal operation of the power grid, and supplies power from a DC power supply to the load. The power supply system is provided on a power line for supplying power from the power grid to the load, and includes a switch for opening and closing the power line, and a three-phase power converter connected in series to the power line for converting DC power from the DC power supply into three-phase AC power. The control program of the power supply system causes a computer to function as a compensation voltage calculation unit that calculates a compensation voltage, which is a voltage for compensating the load, when the opening of the switch is completed during abnormal operation of the power grid, a command voltage calculation unit that acquires a DC voltage, which is the voltage output by the DC power supply, and calculates a command voltage, which is the voltage to be output to the three-phase power converter, based on the compensation voltage and the DC voltage, and a third harmonic superimposition unit that calculates a superimposed third harmonic, which is a third harmonic for superimposing on the command voltage, based on the command voltage and superimposes the superimposed third harmonic on the command voltage. The third harmonic superimposition unit separates the command voltage into a positive-phase component and a negative-phase component, calculates a positive-phase third harmonic, which is a third harmonic corresponding to the positive-phase component, based on the amplitude and phase of the positive-phase component, calculates a negative-phase third harmonic, which is a third harmonic corresponding to the negative-phase component, based on the amplitude and phase of the negative-phase component, and calculates the superimposed third harmonic by synthesizing the positive-phase third harmonic and the negative-phase third harmonic.

[0019] With such a configuration, the same operational effects as those of the above power supply system can be obtained.

Advantages of the Invention

[0020] According to the present invention configured as described above, in a power supply system including a three-phase power converter that supplies AC power to compensate for the voltage of a load during abnormal operation of a power grid, regardless of whether it is three-phase balanced or three-phase unbalanced, the compensation time for compensating the voltage of the load can be extended.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0022] Hereinafter, an embodiment of the power supply system according to the present invention will be described with reference to the drawings. Note that, for the sake of clarity, any of the following figures may be appropriately omitted or exaggerated and schematically drawn. The same components are denoted by the same reference numerals, and the description thereof will be appropriately omitted.

[0023] <Device Configuration> The power supply system 100 in this embodiment is provided between the power grid S and the load L, and after cutting off the power supply from the power grid S to the load L in the event of an abnormality in the power grid S such as a short circuit accident in the power grid S, it compensates for the voltage of the load L. Note that the number of phases of the power supply system 100 in this embodiment is three-phase.

[0024] Specifically, as shown in FIG. 1, the power supply system 100 includes a switch 2 that cuts off the power supply from the power grid S to the load L, a DC power supply 3 that outputs DC power, a three-phase power converter 4 that converts the DC power of the DC power supply 3 into three-phase AC power and supplies it to the power line P, a system voltage measurement unit 5 that measures the system voltage which is the voltage of the power grid S, a DC voltage measurement unit 6 that measures the DC voltage which is the voltage output from the DC power supply 3, a switch current measurement unit 7 that measures the switch current which is the current flowing through the switch 2, and a control device 8 that controls the switch 2 and the three-phase power converter 4.

[0025] Switch 2 is provided on the power line P for supplying power from the power system S to the load L, and opens and closes the power line P. Specifically, when switch 2 is opened, the supply of three-phase AC power from the power system S to the load L is cut off, and when switch 2 is closed, three-phase AC power is supplied from the power system S to the load L. Note that the switch 2 in the present embodiment may be a semiconductor switch or a mechanical switch.

[0026] The DC power supply 3 is, for example, a capacitor that stores DC power during normal operation of the power system S. When the power system S is abnormal, the DC power supply 3 discharges and outputs DC power. Note that when the DC power supply 3 is a capacitor as compared with the case where the DC power supply 3 is a lead storage battery, as the capacitance of the capacitor decreases, the magnitude of the DC voltage output from the capacitor also rapidly decreases.

[0027] The three-phase power converter 4 is connected in series to the power line P, and converts the DC power from the DC power supply 3 into AC power and supplies it to the load L. In the present embodiment, the three-phase AC power output from the three-phase power converter 4 is supplied to the power line P via the series reactor R, the series capacitor C, and the injection transformer T in this order.

[0028] The system voltage measurement unit 5 is connected to each phase of the power line P via a system transformer (not shown), and measures the system voltage. The system voltage measured by the system voltage measurement unit 5 is output to a parameter acquisition unit 81 described later. In the present embodiment, the system voltage measurement unit 5 measures the voltage on the power system S side rather than the switch 2 so that an open command output unit 82 described later can quickly detect an abnormality in the power system S.

[0029] The DC voltage measurement unit 6 is provided on the output side of the DC power supply 3 and the input side of the three-phase power converter 4, and measures the DC voltage when it is output from the DC power supply 3 toward the three-phase power converter 4. The DC voltage measured by the DC voltage measurement unit 6 is output to a parameter acquisition unit 81 described later.

[0030] The switch current measurement unit 7 is provided on the power line P of each phase and measures the switch current. The switch current measured by the switch current measurement unit 7 is output to a parameter acquisition unit 81 described later.

[0031] The control device 8 is a dedicated or general-purpose computer equipped with a CPU, an internal memory, an input / output interface, an A / D converter, etc., and controls the switch 2 and the three-phase power converter 4 in the event of an abnormality in the power system S. Specifically, as shown in FIG. 2, the control device 8 includes a parameter acquisition unit 81 that acquires various parameters, a release command output unit 82 that outputs a release command to open the switch 2 when an abnormality in the power system S is detected, an input command output unit 83 that outputs an input command to close the switch 2 when the abnormality in the power system S has recovered, a switch control unit 84 that controls the opening and closing of the switch 2 based on the release command or the input command, and a three-phase power converter control unit 85 that controls the three-phase power converter 4.

[0032] The parameter acquisition unit 81 acquires various parameters measured by each measurement unit. In the present embodiment, the parameter acquisition unit 81 acquires at least one of the system voltage measured by the system voltage measurement unit 5, the DC voltage measured by the DC voltage measurement unit 6, and the switch current measured by the switch current measurement unit 7. During voltage compensation of the load L, the parameter acquisition unit 81 only needs to acquire at least the system voltage and the DC voltage.

[0033] The release command output unit 82 determines whether an abnormality has occurred in the power system S based on the system voltage, and outputs a release command to the switch control unit 84 when it is determined that an abnormality has occurred in the power system S. Specifically, when the system voltage becomes less than a predetermined value, the release command output unit 82 determines that there is an abnormality in the power system S and outputs a release command to the switch control unit 84. Here, the predetermined value is a voltage value for detecting momentary voltage dips.

[0034] The input command output unit 83 determines whether the abnormality of the power system S has been recovered based on the system voltage, and outputs an input command to the switch control unit 84 when it is determined that the abnormality of the power system S has been recovered. Specifically, after the release command is output, when the system voltage becomes equal to or higher than a predetermined value over a plurality of cycles, the input command output unit 83 determines that the abnormality of the power system S has been recovered and outputs an input command to the switch control unit 84.

[0035] The switch control unit 84 controls the opening and closing of the switch 2 using a drive circuit (not shown). Specifically, the switch control unit 84 receives a release command and performs control to release the switch 2. Then, when the release of the switch 2 is completed, the switch control unit 84 outputs a release completion signal, which is a signal indicating that the release of the switch 2 has been completed.

[0036] Also, the switch control unit 84 receives an input command and performs control to turn on the switch 2. Then, when the turn-on of the switch 2 is completed, the switch control unit 84 outputs an input completion signal, which is a signal indicating that the turn-on of the switch 2 has been completed.

[0037] As shown in FIG. 3, the three-phase power converter control unit 85 includes a current cutoff control unit 851 that performs current cutoff control, which is control to cut off the load L from the power system S when a release command is output; a compensation voltage calculation unit 852 that calculates a compensation voltage, which is a voltage for compensating the voltage of the load L that has decreased by the current cutoff control after the release of the switch 2 is completed; a command voltage calculation unit 853 that calculates a command voltage, which is a voltage to be output to the three-phase power converter 4 based on the compensation voltage and the DC voltage; a third harmonic superimposing unit 854 that calculates a third harmonic based on the command voltage and superimposes the third harmonic on the command voltage; and a PWM control unit 855 that compares the command voltage with a carrier wave and performs PWM control on the three-phase power converter 4. Here, the case where the release of the switch 2 is completed refers to the case where the switch control unit 84 outputs a release completion signal.

[0038] The current cutoff control unit 851 performs feedback control on the current output from the three-phase power converter 4 so that the current flowing through the switch 2 becomes 0 in accordance with the output of the opening command. Specifically, the current cutoff control unit 851 subtracts the switch current acquired by the parameter acquisition unit 81 from the command value of the switch current that makes the current flowing through the switch 2 zero, and multiplies the difference by the proportional gain Kp to calculate the command voltage to be output to the three-phase power converter 4 during current cutoff control.

[0039] The compensation voltage calculation unit 852 calculates a compensation voltage based on the difference between the voltage command value to be output to the three-phase power converter 4 and the system voltage in order to make the voltage of the load L a predetermined voltage. Note that the voltage command value used when the compensation voltage calculation unit 852 calculates the compensation voltage includes, but is not limited to, a voltage command value for making the voltage of the load L equivalent to, for example, the rated voltage.

[0040] The command voltage calculation unit 853 acquires the DC voltage from the parameter acquisition unit 81 and calculates the three-phase command voltage based on the compensation voltage and the DC voltage. Specifically, the command voltage calculation unit 853 calculates the amplitude of the command voltage by dividing the amplitude of the compensation voltage by one-half of the DC voltage.

[0041] The third harmonic superimposition unit 854 calculates a superimposed third harmonic, which is a third harmonic for superimposing on the three-phase command voltage, and superimposes the superimposed third harmonic on the three-phase command voltage. Specifically, the third harmonic superimposition unit 854 separates the command voltage into a positive-phase component and a negative-phase component, calculates a positive-phase third harmonic, which is a third harmonic corresponding to the positive-phase component, based on the amplitude and phase of the positive-phase component, and calculates a negative-phase third harmonic, which is a third harmonic corresponding to the negative-phase component, based on the amplitude and phase of the negative-phase component, and calculates the superimposed third harmonic by synthesizing the positive-phase third harmonic and the negative-phase third harmonic.

[0042] More specifically, the third harmonic superposition unit 854 converts the three-phase command voltage from uvw / αβ, and then separates the command voltage into a positive-phase component and a negative-phase component. Then, the third harmonic superposition unit 854 performs polar coordinate conversion on the positive-phase component of the command voltage to calculate the amplitude and phase of the positive-phase component. Then, the third harmonic superposition unit 854 multiplies the amplitude of the positive-phase component by 1 / 6 and multiplies the phase of the positive-phase component by 3, and performs polar coordinate conversion on the amplitude of the positive-phase component multiplied by 1 / 6 and the phase of the positive-phase component multiplied by 3 to calculate the positive-phase third harmonic.

[0043] Also, the third harmonic superposition unit 854 performs polar coordinate conversion on the negative-phase component of the command voltage to calculate the amplitude and phase of the negative-phase component. Then, the third harmonic superposition unit 854 multiplies the amplitude of the negative-phase component by 1 / 6 and multiplies the phase of the negative-phase component by 3, and performs polar coordinate conversion on the amplitude of the negative-phase component multiplied by 1 / 6 and the phase of the negative-phase component multiplied by 3 to calculate the negative-phase third harmonic.

[0044] Then, the third harmonic superposition unit 854 synthesizes the positive-phase third harmonic and the negative-phase third harmonic, and then performs uvw / αβ conversion to calculate the superimposed third harmonic. The third harmonic superposition unit 854 superimposes the calculated superimposed third harmonic on the three-phase command voltage.

[0045] The PWM control unit 855 compares the three-phase command voltage with the third harmonic superimposed with the carrier wave to perform PWM control on the three-phase power converter 4. Specifically, if the three-phase command voltage with the third harmonic superimposed is greater than the carrier wave, the PWM control unit 855 turns on the three-phase power converter 4, and if the three-phase command voltage with the third harmonic superimposed is less than the carrier wave, the PWM control unit 855 turns off the three-phase power converter 4.

[0046] <Control Operation of Power Supply System> Next, the control operation of the power supply system 100 will be described.

[0047] (1) During Normal Operation of Power Grid S The grid voltage measurement unit 5 measures the grid voltage, and the measured grid voltage is output to the release command output unit 82. The release command output unit 82 compares the grid voltage with a predetermined value.

[0048] When the power system S is normal, the system voltage is equal to or higher than a predetermined value, and the switch 2 is closed. Therefore, AC power is supplied from the power system S to the load L.

[0049] (2) When the power system S is abnormal For example, when an abnormality such as a two-wire short-circuit fault occurs in the power system S and the system voltage is less than the predetermined value, the release command output unit 82 outputs a release command to the switch control unit 84.

[0050] When the release command is output, the switch control unit 84 controls to open the switch 2 using the drive circuit. Also, the current interruption control unit 851 controls the current output from the three-phase power converter 4 so that the current flowing through the switch 2 becomes zero.

[0051] Then, when the opening of the switch 2 is completed, the switch control unit 84 outputs a switch completion signal. When the switch completion signal is output, the current interruption control unit 851 completes the current interruption control.

[0052] When the current interruption control is completed, the compensation voltage calculation unit 852 calculates the compensation voltage.

[0053] When the compensation voltage is calculated, the command voltage calculation unit 853 calculates the amplitudes of the three-phase command voltages based on the compensation voltage and the DC voltage.

[0054] When the amplitudes of the three-phase command voltages are calculated, the third harmonic superimposing unit 854 separates the command voltages into a positive-phase component and a negative-phase component. Then, the third harmonic superimposing unit 854 calculates the superimposed third harmonic by multiplying the amplitudes of the positive-phase component and the negative-phase component by 1 / 6 and multiplying the phases of the positive-phase component and the negative-phase component by 3. Then, the third harmonic superimposing unit 854 superimposes the superimposed third harmonic on the three-phase command voltages. As a result, the amplitudes of the three-phase command voltages are reduced to √3 / 2 times.

[0055] When the superimposed third harmonic is superimposed on the three-phase command voltage, the PWM control unit 855 compares the three-phase command voltage with the superimposed third harmonic and the carrier wave, and PWM-controls the three-phase power converter 4.

[0056] When the voltage compensation calculation unit 852 determines that the voltage of the load L has been compensated by the voltage compensation control and the abnormality of the power system S has been recovered, the input command output unit 83 outputs an input command. Along with the output of the input command, the switch control unit 84 closes switch 2.

[0057] When the closing of switch 2 is completed, the switch control unit 84 outputs a completion signal. In response to the output of the completion signal, the voltage compensation of the load L by the three-phase power converter 4 is completed.

[0058] <Simulation Results> Next, the voltage waveforms and current waveforms in various power systems are shown by simulation. In the following simulation, the load capacity is 2 MVA, the rated output voltage of the three-phase power converter 4 is 380 V, the capacitance of the capacitor constituting the DC power supply 3 is 2.34 μF, and the initial DC voltage of the capacitor constituting the DC power supply 3 is 725 V. Also, the accident condition is a momentary two-line short-circuit accident in which the voltage of the power system S drops by 100%.

[0059] Figure 4 shows the simulation results when the superimposed third harmonic calculated by separating the command voltage into the positive-phase component and the negative-phase component is superimposed on the command voltage. As can be seen from Figure 4, in the case of a two-phase short-circuit accident, the state where the ratio of the command voltage to the maximum voltage is less than 1 continues for 0.21 seconds after the start of the voltage compensation of the load L.

[0060] FIG. 5 shows the simulation results when the third harmonic is calculated from the command voltage without separating the command voltage into the positive-phase component and the negative-phase component, and the calculated third harmonic is superimposed on the command voltage. As can be seen from FIG. 5, in the case of a two-phase short-circuit accident, the state where the ratio of the command voltage to the maximum voltage is less than 1 continues for 0.12 seconds after the compensation of the voltage of the load L is started. Therefore, comparing FIGS. 4 and 5, it can be confirmed that in the case of a two-phase short-circuit accident, the compensation time can be extended more when calculating the superimposed third harmonic by separating the command voltage into the positive-phase component and the negative-phase component than when calculating the third harmonic from the command voltage without separating the command voltage into the positive-phase component and the negative-phase component.

[0061] <Effects of this Embodiment> According to the power supply system 100 in this embodiment, the third harmonic superimposing unit 854 separates the command voltage into the positive-phase component and the negative-phase component to calculate the positive-phase third harmonic and the negative-phase third harmonic, and calculates the superimposed third harmonic by synthesizing the positive-phase third harmonic and the negative-phase third harmonic. Therefore, regardless of whether it is three-phase balanced or three-phase unbalanced, the superimposed third harmonic that reduces the amplitude of the command voltage can be accurately calculated. Therefore, regardless of whether it is three-phase balanced or three-phase unbalanced, the compensation time can be extended compared to the prior art. In addition, the three-phase power converter 4 outputs three-phase alternating current, and since the third harmonic of each phase is canceled out in the line voltage, the voltage output by the three-phase power converter 4 can be increased without increasing the distortion of the line voltage.

[0062] Also according to this embodiment, the third harmonic superimposing unit 854 calculates the third harmonic by multiplying the amplitude of the command voltage by 1 / 6 and multiplying the phase of the command voltage by 3. Therefore, the amplitude of the command voltage after superimposing the third harmonic can be minimized, and the compensation time can be extended the longest.

[0063] In addition, according to the power supply system 100 of this embodiment, since the three-phase power converter 4 is connected in series to the power line P, the loss of the three-phase power converter 4 can be suppressed compared to the case where the three-phase power converter 4 is connected in parallel to the power line P.

[0064] Furthermore, according to the present embodiment, the compensation time can be extended without increasing the capacitor capacitance. Specifically, when the capacitor capacitance is the same as that of the prior art, according to the power supply system 100 of the present embodiment, the compensation time can be extended compared to the prior art. Also, when the compensation time is the same as that of the prior art, according to the power supply system 100 of the present embodiment, the capacitor capacitance can be reduced compared to the prior art.

[0065] <Other Embodiments> Note that the present invention is not limited to the above-described embodiment.

[0066] In the above-described embodiment, the third harmonic superposition unit 854 calculates the third harmonic by multiplying the amplitude of the three-phase command voltage by 1 / 6 and multiplying the phase of the three-phase command voltage by 3. However, the multiples of the amplitude and phase of the three-phase command voltage are not limited to this.

[0067] In the above-described embodiment, the three-phase power converter 4 is connected in series to the power line P. However, the three-phase power converter 4 may be connected in parallel to the power line P.

[0068] In the above-described embodiment, the DC power supply 3 is a capacitor. However, it may be another DC power supply such as a lead-acid battery. Even when the DC power supply 3 is a lead-acid battery, by superimposing the third harmonic on the command voltage, the amplitude of the voltage output from the three-phase power converter 4 is reduced, so that the compensation time can be extended.

[0069] In the above-described embodiment, the power supply system 100 includes the system voltage measurement unit 5, the DC voltage measurement unit 6, and the switch current measurement unit 7. However, the DC voltage measurement unit 6 and the switch current measurement unit 7 may be provided separately from the power supply system 100.

[0070] In the above-described embodiment, if it is only for extending the compensation time of the load L, the three-phase power converter control unit 85 may not include the current interruption control unit 851. Further, if it is only for extending the compensation time of the load L, the release command output unit 82, the input command output unit 83, and the switch control unit 84 may be provided in a control device different from the control device provided with the three-phase power converter control unit 85.

[0071] Needless to say, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit thereof.

Explanation of Reference Numerals

[0072] 100 ··· Power supply system 2 ··· Switch 3 ··· DC power supply 4 ··· Three-phase power converter 5 ··· System voltage measurement unit 6 ··· DC voltage measurement unit 7 ··· Switch current measurement unit 8 ··· Control device 81 ··· Parameter acquisition unit 82 ··· Release command output unit 83 ··· Input command output unit 84 ··· Switch control unit 85 ··· Three-phase power converter control unit 851 ··· Current interruption control unit 852 ··· Compensation voltage calculation unit 853 ··· Command voltage calculation unit 854 ··· Third harmonic superimposition unit 855 ··· PWM control unit S ··· Power grid L ··· Load P ··· Power line

Claims

1. A power supply system that supplies power from a power grid to a load during normal operation of the power grid, cuts off the power supply from the power grid to the load during abnormal operation of the power grid, and supplies power to the load from a DC power source, comprising: a switch provided on a power line for supplying power from the power grid to the load, the switch opening and closing the power line; a three-phase power converter that converts DC power from the DC power source into three-phase AC power and supplies the power to the power line; a three-phase power converter control unit that controls the three-phase power converter, wherein the three-phase power converter control unit: when the opening of the switch is completed during abnormal operation of the power grid, a compensation voltage calculation unit that calculates a compensation voltage that is a voltage for compensating the load; acquires a DC voltage that is the voltage output by the DC power source, and based on the compensation voltage and the DC voltage, a command voltage calculation unit that calculates a command voltage that is a voltage to be output to the three-phase power converter; a third harmonic superimposition unit that calculates a superimposed third harmonic, which is a third harmonic for superimposing on the command voltage, based on the command voltage, and superimposes the superimposed third harmonic on the command voltage, wherein the third harmonic superimposition unit separates the command voltage into a positive-phase component and a negative-phase component, calculates a positive-phase third harmonic, which is a third harmonic corresponding to the positive-phase component, based on the amplitude and phase of the positive-phase component, and calculates a negative-phase third harmonic, which is a third harmonic corresponding to the negative-phase component, based on the amplitude and phase of the negative-phase component, and calculates the superimposed third harmonic by synthesizing the positive-phase third harmonic and the negative-phase third harmonic. A power supply system.

2. The power supply system according to claim 1, wherein the third harmonic superimposition unit calculates the third harmonic by multiplying the amplitude of the command voltage by 1 / 6 and multiplying the phase of the command voltage by 3.

3. The power supply system according to claim 1, wherein the three-phase power converter is connected in series to the power line.

4. The power supply system according to claims 1 to 3, wherein the DC power source is a capacitor.

5. A control method for a power supply system that supplies power from a power grid to a load during normal operation of the power grid, cuts off the power supply from the power grid to the load during abnormal operation of the power grid, and supplies power to the load from a DC power source, wherein: the power supply system includes: a switch provided on a power line for supplying power from the power grid to the load, the switch opening and closing the power line; A three-phase power converter connected in series to the power line and converting DC power from the DC power source into three-phase AC power is provided. The control method of the power supply system is as follows. When the opening of the switch is completed during an abnormality in the power system, a compensation voltage, which is a voltage for compensating the load, is calculated. A DC voltage, which is the voltage output from the DC power source, is acquired, and based on the compensation voltage and the DC voltage, a command voltage, which is the voltage to be output to the three-phase power converter, is calculated. The command voltage is separated into a positive-phase component and a negative-phase component. Based on the amplitude and phase of the positive-phase component, a positive-phase third harmonic, which is the third harmonic corresponding to the positive-phase component, is calculated. At the same time, based on the amplitude and phase of the negative-phase component, a negative-phase third harmonic, which is the third harmonic corresponding to the negative-phase component, is calculated. By synthesizing the positive-phase third harmonic and the negative-phase third harmonic, a superimposed third harmonic, which is the third harmonic for superimposing on the command voltage, is calculated. A control method of a power supply system for superimposing the superimposed third harmonic on the command voltage.

6. A control program for a power supply system that supplies power from a power system to a load during normal operation of the power system, cuts off the power supply from the power system to the load during an abnormality in the power system, and supplies power from a DC power source to the load, The power supply system is as follows. A switch provided on a power line for supplying power from the power system to the load and opening and closing the power line, A three-phase power converter connected in series to the power line and converting DC power from the DC power source into three-phase AC power is provided. The control program of the power supply system is as follows. A function as a compensation voltage calculation unit that calculates a compensation voltage, which is a voltage for compensating the load, when the opening of the switch is completed during an abnormality in the power system, A function as a command voltage calculation unit that acquires a DC voltage, which is the voltage output from the DC power source, and calculates a command voltage, which is the voltage to be output to the three-phase power converter, based on the compensation voltage and the DC voltage, Causes the computer to exhibit a function as a third harmonic superimposing unit that calculates a superimposed third harmonic, which is a third harmonic for superimposing on the command voltage, based on the command voltage and superimposes the superimposed third harmonic on the command voltage. The third harmonic superposition unit separates the command voltage into a positive-phase component and a negative-phase component, calculates a positive-phase third harmonic, which is a third harmonic corresponding to the positive-phase component, based on the amplitude and phase of the positive-phase component, calculates a negative-phase third harmonic, which is a third harmonic corresponding to the negative-phase component, based on the amplitude and phase of the negative-phase component, and calculates the superimposed third harmonic by synthesizing the positive-phase third harmonic and the negative-phase third harmonic. A control program for a power supply system.

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