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 that is installed on a power line P for supplying power L from a power system S to a load and opens and closes the power line, a three-phase power converter 4 that is connected in series to the power line and converts DC power from a DC power source into three-phase AC power, and a control device 8 including a three-phase power converter control unit for controlling the three-phase power converter. When opening of the switch is completed during abnormality of the power system, the three-phase power converter control unit calculates a compensation voltage which is a voltage for compensating for the load, obtains a DC voltage output by the DC power source, calculates a command voltage to be output by the three-phase power converter based on the compensation voltage and the DC voltage, calculates a third-order harmonic based on the command voltage, and superimposes the third-order 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 for converting the energy of an energy storage unit into AC power.

[0003] In this power supply system, when the power grid is normal, power is supplied from the power grid to the load through the circuit breaker, and the power converter is stopped. On the other hand, when the power grid is abnormal, 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 through the power converter. Thereby, the voltage of the load is compensated when the power grid is abnormal.

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 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 decreases due to rapid discharge from the energy storage unit, and the maximum voltage rapidly decreases. 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, 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 grid, the main object is to extend the compensation time capable of compensating for the voltage of the load.

Means for Solving the Problems

[0008] That is, the power supply system according to the present invention is a power supply system that supplies power from the power grid to the load during normal operation of the power grid, cuts off the power supply from the power grid to the load during an abnormality in the power grid, and supplies power from a DC power source to the load. It 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 connected in series to the power line for converting DC power from the DC power source into three-phase AC power, 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 an abnormality in the power grid, an acquisition unit for acquiring a DC voltage, which is a voltage output from the DC power source, and a command voltage calculation unit for calculating a command voltage, which is a voltage to be output to the three-phase power converter, based on the compensation voltage and the DC voltage, and a third harmonic superimposing unit for calculating a third harmonic based on the command voltage and superimposing the third harmonic on the command voltage.

[0009] In such a power supply system, compared with the conventional configuration in which the third harmonic is not superimposed on the command voltage, the amplitude of the command voltage after superimposing the third harmonic is reduced. Therefore, by outputting the command voltage after superimposing the third harmonic to the power converter, the state where the command voltage is smaller than the maximum voltage becomes longer, so that the compensation time can be extended more than before. In addition, the three-phase power converter outputs three-phase alternating current, and since the third harmonics of each phase cancel each other out in the line voltage, the voltage output by the power converter can be increased without increasing the distortion of the line voltage.

[0010] As a specific aspect of the third harmonic superimposing section, an example is calculating the third harmonic by multiplying the amplitude of the command voltage by 1 / 6 and multiplying the phase of the command voltage by 3.

[0011] 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.

[0012] 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 decreases. 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.

[0013] 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 more than before. 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.

[0014] Also, 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 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 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 grid, 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. Then, a third harmonic is calculated based on the command voltage, and the third harmonic is superimposed on the command voltage. Furthermore, 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 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, and a third harmonic superimposition unit that calculates a third harmonic based on the command voltage and superimposes the third harmonic on the command voltage.

[0015] With such a configuration, the same operational effects as those of the above power supply system can be obtained.

Advantages of the Invention

[0016] 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 an abnormality in the power system, it is possible to extend the compensation time for compensating the voltage of the load.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0018] 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 figures shown below may be appropriately omitted or exaggerated and schematically drawn. The same reference numerals are assigned to the same components, and the description thereof will be appropriately omitted.

[0019] <Device Configuration> The power supply system 100 in this embodiment is provided between the power grid S and the load L. When an abnormality occurs in the power grid S, such as a short - circuit accident in the power grid S, after cutting off the power supply from the power grid S to the load L, 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.

[0020] 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 power 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.

[0021] The switch 2 is provided on the power line P for supplying power from the power grid S to the load L and opens and closes the power line P. Specifically, when the switch 2 is opened, the supply of three - phase AC power from the power grid S to the load L is cut off, and when the switch 2 is closed, three - phase AC power is supplied from the power grid S to the load L. Note that the switch 2 in this embodiment may be a semiconductor switch or a mechanical switch.

[0022] The DC power supply 3 is, for example, a capacitor that stores DC power when the power grid S is normal. When an abnormality occurs in the power grid S, the DC power supply 3 discharges and outputs DC power. Note that when the DC power supply 3 is a capacitor, compared with the case where the DC power supply 3 is a lead - acid battery, as the capacitance of the capacitor decreases, the magnitude of the DC voltage output from the capacitor also rapidly decreases.

[0023] The three-phase power converter 4 is connected in series to the power line P, converts the DC power from the DC power supply 3 into AC power, and supplies power to the load L. In this 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.

[0024] 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 this embodiment, the system voltage measurement unit 5 measures the voltage on the power system S side of the switch 2 so that the open command output unit 82 described later can quickly detect an abnormality in the power system S.

[0025] 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 the parameter acquisition unit 81 described later.

[0026] The switch current measurement unit 7 is provided on each phase of the power line P and measures the switch current. The switch current measured by the switch current measurement unit 7 is output to the parameter acquisition unit 81 described later.

[0027] 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 when an abnormality occurs 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, an open command output unit 82 that outputs an open 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 open command or the input command, and a three-phase power converter control unit 85 that controls the three-phase power converter 4.

[0028] 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. Note that when compensating for the voltage of the load L, the parameter acquisition unit 81 only needs to acquire at least the system voltage and the DC voltage.

[0029] The opening command output unit 82 determines whether an abnormality has occurred in the power system S based on the system voltage, and outputs an opening 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 opening command output unit 82 determines that there is an abnormality in the power system S and outputs an opening command to the switch control unit 84. Note that the predetermined value mentioned here is the voltage value for detecting momentary voltage dips.

[0030] The closing command output unit 83 determines whether the abnormality in the power system S has recovered based on the system voltage, and outputs a closing command to the switch control unit 84 when it is determined that the abnormality in the power system S has recovered. Specifically, after the opening command is output, when the system voltage becomes equal to or greater than a predetermined value over a plurality of cycles, the closing command output unit 83 determines that the abnormality in the power system S has recovered and outputs a closing command to the switch control unit 84.

[0031] 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 the opening command and performs control to open the switch 2. When the opening of the switch 2 is completed, the switch control unit 84 outputs an opening completion signal, which is a signal indicating that the opening of the switch 2 is completed.

[0032] Also, the switch control unit 84 receives the closing command and performs control to close the switch 2. When the closing of the switch 2 is completed, the switch control unit 84 outputs a closing completion signal, which is a signal indicating that the closing of the switch 2 is completed.

[0033] As shown in FIG. 3, when an opening command is output, the three-phase power converter control unit 85 performs current interruption control for interrupting the load L from the power system S by a current interruption control unit 851, and after the opening of the switch 2 is completed, a compensation voltage calculation unit 852 calculates a compensation voltage, which is a voltage for compensating the voltage of the load L reduced by the current interruption control, a command voltage calculation unit 853 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 calculates a third harmonic based on the command voltage and superimposes the third harmonic on the command voltage, and a PWM control unit 855 compares the command voltage with a carrier wave to perform PWM control on the three-phase power converter 4. Here, the case where the opening of the switch 2 is completed means the case where the switch control unit 84 outputs an opening completion signal.

[0034] The current interruption 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 interruption 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 interruption control.

[0035] 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. The voltage command value used by the compensation voltage calculation unit 852 when calculating 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.

[0036] The command voltage calculation unit 853 acquires the DC voltage from the parameter acquisition unit 81 and calculates three-phase command voltages 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.

[0037] The third harmonic superposition unit 854 calculates the third harmonic for superimposing on the three-phase command voltage, and superimposes the calculated third harmonic on the three-phase command voltage. Specifically, the third harmonic superposition unit 854 performs uvw / αβ conversion and polar coordinate conversion on the three-phase command voltage to calculate the amplitude and phase of the command voltage. Then, the third harmonic superposition unit 854 multiplies the amplitude of the command voltage by 1 / 6 and triples the phase of the command voltage, and performs polar coordinate conversion and uvw / αβ conversion on the 1 / 6-fold amplitude and 3-fold phase to calculate the third harmonic. Furthermore, the third harmonic superposition unit 854 superimposes the calculated third harmonic on the three-phase command voltage.

[0038] The PWM control unit 855 compares the three-phase command voltage with the third harmonic superimposed and the carrier wave, and performs 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.

[0039] <Control Operation of Power Supply System> Next, the control operation of the power supply system 100 will be described.

[0040] (1) When the power grid S is normal The grid voltage measurement unit 5 measures the grid voltage, and the measured grid voltage is output to the opening command output unit 82. The opening command output unit 82 compares the grid voltage with a predetermined value.

[0041] Note that when the power grid S is normal, the grid voltage is equal to or higher than the predetermined value, and the switch 2 is closed. Therefore, AC power is supplied from the power grid S to the load L.

[0042] (2) When the power grid S is abnormal When the grid voltage is less than the predetermined value, the opening command output unit 82 determines that the power grid S is abnormal and outputs an opening command to the switch control unit 84.

[0043] When an open command is output, the switch control unit 84 controls the opening of switch 2 using a drive circuit. Also, the current cutoff control unit 851 controls the current output from the three-phase power converter 4 so that the current flowing through switch 2 becomes zero.

[0044] When the opening of switch 2 is completed, the switch control unit 84 outputs a switch completion signal. When the switch completion signal is output, the current cutoff control unit 851 completes the current cutoff control.

[0045] When the current cutoff control is completed, the compensation voltage calculation unit 852 calculates the compensation voltage.

[0046] When the compensation voltage is calculated, the command voltage calculation unit 853 calculates the amplitude of the three-phase command voltage based on the compensation voltage and the DC voltage.

[0047] When the amplitude of the three-phase command voltage is calculated, the third harmonic superimposition unit 854 calculates the third harmonic by reducing the amplitude of the command voltage to 1 / 6 and tripling the phase of the command voltage. Then, the third harmonic superimposition unit 854 superimposes the calculated third harmonic on the three-phase command voltage. As a result, the amplitude of the three-phase command voltage is reduced to √3 / 2 times.

[0048] When the third harmonic is superimposed on the three-phase command voltage, the PWM control unit 855 compares the three-phase command voltage with the carrier wave on which the third harmonic is superimposed and performs PWM control on the three-phase power converter 4.

[0049] When the input command output unit 83 determines that the voltage of the load L has been compensated by the voltage compensation control by the compensation voltage calculation unit 852 and the abnormality of the power system S has been restored, 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.

[0050] When the closing of switch 2 is completed, the switch control unit 84 outputs a closing completion signal. In response to the output of the closing completion signal, the voltage compensation of the load L by the three-phase power converter 4 is completed.

[0051] <Simulation Results> Next, the voltage waveform and current waveform in power supply systems of various aspects 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 three-phase short-circuit accident with an instantaneous voltage drop of 100% in the power grid S.

[0052] Figure 4 shows the simulation results when the third harmonic is not superimposed on the command voltage when compensating the voltage of the load L. In this case, the maximum voltage that the three-phase power converter 4 can output is calculated by Equation (1) below.

[0053]

Equation

[0054] As can be seen from Figure 4, the state where the ratio of the command voltage to the maximum voltage is less than 1 continues for 0.08 seconds after starting the compensation of the voltage of the load L. Also, in this case, the compensation limit voltage, which is the limit voltage output by the DC power supply 3 when the voltage of the load L can be compensated, is approximately 620 V.

[0055] Figure 5 shows the simulation results when the third harmonic is superimposed on the command voltage when compensating the voltage of the load L as shown in the present embodiment. By superimposing the third harmonic calculated by making the amplitude of the command voltage 1 / 6 times and the phase of the command voltage 3 times on the command voltage, the amplitude of the command voltage after superimposing the third harmonic becomes √3 / 2 times. As a result, the maximum voltage that the three-phase power converter 4 can output is calculated by Equation (2) below.

[0056]

Equation

[0057] As can be seen from FIG. 5, the state where the ratio of the command voltage to the maximum voltage is less than 1 continues for 0.14 seconds after the start of the voltage compensation of the load L. Therefore, it was confirmed that the compensation time can be extended compared to the compensation time in the conventional example. The three-phase power converter 4 can compensate the voltage of the load L for 0.14 seconds after the start of the voltage compensation of the load L. Also, the compensation limit voltage in this embodiment is about 537V, which is smaller than the compensation limit voltage in the conventional example. Therefore, it was confirmed that the utilization rate of the DC power supply 3 can be improved.

[0058] Further, FIG. 6 is a table and a graph comparing the compensation times when the capacitance of the capacitor constituting the DC power supply 3 is the same in the conventional example and the embodiment. The accident condition in FIG. 6 is an instantaneous three-phase short-circuit accident in which the voltage of the power system S drops between 10% and 100%. As can be seen from FIG. 6, it can be seen that the larger the voltage drop width of the power system S, the larger the ratio of the compensation time of the embodiment to the compensation time of the conventional example. That is, it was confirmed that the larger the voltage drop width of the power system S, the longer the compensation time of the embodiment compared to the conventional example.

[0059] Furthermore, FIG. 7 is a table showing the capacitance of the capacitor in the embodiment required to satisfy the compensation time of the conventional example. The accident condition in FIG. 7 is the same as in FIG. 6, which is an instantaneous three-phase short-circuit accident in which the voltage of the power system S drops between 10% and 100%. As can be seen from FIG. 7, it can be seen that the larger the voltage drop width of the power system S, the smaller the capacitance of the capacitor in the embodiment compared to the capacitance of the capacitor in the conventional example. That is, it was confirmed that the larger the voltage drop width of the power system S, the more the capacitance of the capacitor can be reduced in the embodiment compared to the conventional example.

[0060] <Effects of this Embodiment> According to the power supply system 100 in this embodiment, compared with the conventional configuration in which the third harmonic is not superimposed on the command voltage, the amplitude of the command voltage after superimposing the third harmonic is reduced. Therefore, by outputting the command voltage after superimposing the third harmonic to the three-phase power converter 4, the state where the command voltage is smaller than the maximum voltage becomes longer, so the compensation time can be extended more than before. In addition, the three-phase power converter 4 outputs three-phase alternating current, and since the third harmonics of each phase cancel each other 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.

[0061] Also according to this embodiment, the third harmonic superimposing section 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 to the longest.

[0062] Furthermore, according to this embodiment, 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, according to the power supply system 100 of this embodiment, the compensation time can be extended more than before. Also, when the compensation time is the same as that of the conventional case, according to the power supply system 100 of this embodiment, the capacitor capacitance can be reduced more than before.

[0063] <Other Embodiments> Note that the present invention is not limited to the above embodiments.

[0064] In the above embodiment, the third harmonic superimposing section 854 calculates the third harmonic by multiplying the amplitudes of the three-phase command voltages by 1 / 6 and multiplying the phases of the three-phase command voltages by 3. However, the multiples of the amplitudes and phases of the three-phase command voltages are not limited to this.

[0065] In the above embodiment, the DC power supply 3 was a capacitor, but it may be other DC power supplies 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 the compensation time can be extended.

[0066] In the above embodiment, the power supply system 100 included the system voltage measurement unit 5, the DC voltage measurement unit 6, and the switch current measurement unit 7, but the DC voltage measurement unit 6 and the switch current measurement unit 7 may be provided separately from the power supply system 100.

[0067] In the above embodiment, if it is only for extending the compensation time of the load L, the three-phase power converter control unit 85 does not necessarily need to include the current cutoff control unit 851. Also, 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.

[0068] Needless to say, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit thereof.

Explanation of Reference Numerals

[0069] 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 cutoff control unit 852 ··· Compensation voltage calculation unit 853 ··· Command voltage calculation unit 854 ··· Third harmonic superimposing unit 855 ··· PWM control unit S ··· Power system L ··· Load P ··· Power line

Claims

1. 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 abnormal condition of the power system, and supplies power to the load from a DC power supply, comprising: a switch provided on a power line for supplying power from the power system to the load, the switch opening and closing the power line; a three-phase power converter connected in series to the power line, the three-phase power converter converting DC power from the DC power supply into three-phase AC power; a three-phase power converter control unit that controls the three-phase power converter, wherein the three-phase power converter control unit comprises 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 abnormal condition of the power system; a command voltage calculation unit that obtains a DC voltage, which is the voltage output from the DC power supply, and calculates a command voltage, which is a voltage to be output to the three-phase power converter, based on the compensation voltage and the DC voltage; a power supply system having a third harmonic superimposing unit that calculates a third harmonic based on the command voltage and superimposes the third harmonic on the command voltage.

2. The power supply system according to claim 1, wherein the third harmonic superimposing 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 or 2, wherein the DC power supply is a capacitor.

4. 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 an abnormal condition of the power system, and supplies power to the load from a DC power supply, wherein the power supply system comprises a switch provided on a power line for supplying power from the power system to the load, the switch opening and closing the power line; a three-phase power converter connected in series to the power line, the three-phase power converter converting DC power from the DC power supply into three-phase AC power, and the control method for the power supply system comprises calculating a compensation voltage, which is a voltage for compensating the load, when the opening of the switch is completed during an abnormal condition of the power system; obtaining a DC voltage, which is the voltage output from the DC power supply, and calculating a command voltage, which is a voltage to be output to the three-phase power converter, based on the compensation voltage and the DC voltage; calculating a third harmonic based on the command voltage and superimposing the third harmonic on the command voltage.

5. 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 abnormal operation of the power system, and supplies power from a DC power supply to the load, comprising: The power supply system includes: a switch provided on a power line for supplying power from the power system to the load, the switch opening and closing the power line; a three-phase power converter connected in series to the power line, the three-phase power converter converting DC power from the DC power supply into three-phase AC power; The control program of the power supply system includes: 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 abnormal operation of the power system; a function as a command voltage calculation unit that acquires a DC voltage, which is a voltage output by the DC power supply, and calculates a command voltage, which is a voltage to be output to the three-phase power converter, based on the compensation voltage and the DC voltage; A control program for a power supply system that causes a computer to exhibit a function as a third harmonic superimposition unit that calculates a third harmonic based on the command voltage and superimposes the third harmonic on the command voltage.

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