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

Abstract

To provide a power supply system equipped with a three-phase power converter that supplies AC power to compensate for the voltage of a load when an abnormality occurs in a power system, a compensation time when a two-wire short circuit occurs being further extended.SOLUTION: A power supply system cuts off power supply from a power system in the event of an abnormality and supplies power from a DC power source, and includes a switch for opening and closing a power line for a load from the power system, a three-phase power converter for converting power from the DC power source and supplies it to the power line, and a three-phase power converter control unit 85. A three-phase power converter control unit 851 opens the switch in the event of an abnormality in a power system, and includes a compensation voltage calculation unit 852 that calculates a compensation voltage for the load, a command voltage calculation unit 853 that calculates a command voltage based on the compensation voltage and the DC voltage, a third-order harmonic superposition unit 854 that calculates a superimposed third-order harmonic and superimposes it on the command voltage, and a fundamental wave superposition unit 855 that calculates the amplitude difference between respective phases using the superimposed command voltage on which the superimposed third-order harmonic has been superimposed, calculates a fundamental wave that reduces the amplitude difference, and superimposes it on the superimposed command voltage.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

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

[0003] In this power supply system, when the power grid is normal, power is supplied to the load from the power grid via a circuit breaker, and the power converter is stopped. On the other hand, when an abnormality occurs 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 to the load from the energy storage unit via the power converter. In this way, the voltage of the load is compensated for when an abnormality occurs in the power grid. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6677916 Summary of the Invention [Problem to be solved by the invention]

[0005] In some cases, the power converter in the power supply system described above uses a three-phase power converter. In this case, if the command voltage output from the three-phase power converter becomes larger than the maximum voltage that the three-phase power converter can output, the voltage waveform will be distorted and the output voltage will decrease. Therefore, when compensating for the load voltage, the three-phase power converter needs to output a voltage with a command voltage smaller than the maximum voltage.

[0006] On the other hand, the maximum voltage is determined by the voltage output from the energy storage unit. When compensating for the load voltage, a sudden discharge from the energy storage unit causes a sudden drop in the voltage output from the energy storage unit, which in turn causes a sudden drop in the maximum voltage. As a result, the command voltage quickly becomes larger than the maximum voltage, shortening the compensation time for compensating for the load voltage.

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

[0008] However, when two wires are shorted, the command voltage before the third harmonic is superimposed is three-phase unbalanced, so the third harmonic to reduce the amplitude of the command voltage cannot be accurately calculated. Therefore, when two wires are shorted, simply superimposing the third harmonic on the command voltage cannot extend the compensation time.

[0009] In particular, when two wires are shorted, the command voltages are three-phase unbalanced, so there is an amplitude difference between each phase, and the limit of the compensation time is determined by the maximum amplitude. After extensive research, the inventors of the present invention discovered that if the maximum amplitude of the command voltage could be reduced, the compensation time when two wires are shorted could be further extended, and arrived at the present invention.

[0010] The present invention has been made in view of the above problems, and has as its main object to further extend the compensation time in the event of a two-wire short circuit in a power supply system equipped with a three-phase power converter that supplies AC power to compensate for the load voltage when an abnormality occurs in the power grid. [Means for solving the problem]

[0011] That is, the power supply system according to the present invention is a power supply system that supplies power from the power system to a load when the power system is normal, and cuts off the power supply from the power system to the load when the power system is abnormal, and supplies power to the load from a DC power supply, and is provided with a switch that is provided on a power line for supplying power from the power system to the load and opens and closes the power line, a three-phase power converter that converts DC power from the DC power supply into three-phase AC power and supplies it to the power line, and a three-phase power converter control unit that controls the three-phase power converter, and the three-phase power converter control unit controls a voltage that compensates for the load when the switch has been opened during the abnormality of the power system. a command voltage calculation unit that acquires a DC voltage that is a voltage output by the DC power supply and calculates a command voltage that is a voltage to be output to the three-phase power converter based on the compensation voltage and the DC voltage; a third harmonic superimposing unit that calculates a superimposed third harmonic that is a third harmonic to be superimposed on the command voltage and superimposes the superimposed third harmonic on the command voltage; and a fundamental wave superimposing unit that calculates an amplitude difference between each phase in a superimposed command voltage that is the command voltage after the superimposed third harmonic has been superimposed, calculates a fundamental wave that reduces the amplitude difference between the each phase, and superimposes the fundamental wave on the superimposed command voltage.

[0012] In such a power supply system, the amplitude difference between each phase is calculated from the superimposed command voltage after the superimposed third harmonic is superimposed, a fundamental wave that reduces the amplitude difference between each phase is calculated, and the fundamental wave is superimposed on the superimposed command voltage, thereby reducing the maximum amplitude of the superimposed command voltage. As a result, the compensation time can be further extended when two lines are shorted. Furthermore, even if the fundamental wave is superimposed on the command voltage and then compensated for, the voltage of the load does not fluctuate, so the superposition of the fundamental wave does not affect the voltage of the load when compensating for the voltage of the load. Furthermore, since a three-phase power converter outputs three-phase AC and the third harmonics of each phase are cancelled out in the line voltage, the voltage output by the power converter can be increased without increasing the distortion of the line voltage.

[0013] The fundamental wave superimposing unit preferably calculates a fundamental wave that makes the amplitude difference between the phases zero.

[0014] With this configuration, the amplitude difference between the phases becomes zero, so the compensation time can be extended to the longest possible time.

[0015] It is preferable that the fundamental wave superimposing unit separates the superimposed command voltage into a positive sequence component and a negative sequence component, and calculates the amplitude difference between the phases based on the positive sequence component and the negative sequence component.

[0016] With this configuration, the fundamental wave superimposing unit separates the superimposed command voltage into a positive-phase component and a negative-phase component and calculates the amplitude difference between each phase based on the positive-phase component and the negative-phase component, so that the amplitude difference between each phase of the superimposed command voltage can be calculated more accurately when two wires are shorted. As a result, the compensation time when two wires are shorted can be calculated accurately and the compensation time can be extended more than before.

[0017] It is preferable that the third-order harmonic superimposing unit separates the command voltage into a positive-phase component and a negative-phase component, calculates a positive-phase third harmonic that 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 that 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.

[0018] With this configuration, the third harmonic superimposing unit separates the command voltage into positive-phase and negative-phase components to calculate the positive-phase and negative-phase third harmonics, and then calculates the superimposed third harmonic by combining the positive-phase and negative-phase third harmonics. Therefore, regardless of whether the three-phase is balanced or unbalanced, it is possible to accurately calculate the superimposed third harmonic that reduces the amplitude of the command voltage. Therefore, regardless of whether the three-phase is balanced or unbalanced, it is possible to extend the compensation time more than before.

[0019] The three-phase power converter is preferably connected in series to the power line.

[0020] With this configuration, the voltage output from the three-phase power converter only needs to compensate for the voltage drop in the power grid, compared to when the three-phase power converter is connected in parallel to the power line, thereby reducing DC power consumption.

[0021] When compensating for load voltage sags, a capacitor is often used in a DC power supply due to considerations of installation space, maintenance, and cost. However, compared to other DC power supplies, such as lead-acid batteries, when a capacitor discharges, the DC voltage output from the capacitor drops sharply as the capacitor's capacitance decreases, resulting in a drop in the maximum voltage of the three-phase power converter. As a result, in conventional power supply systems, the capacitor capacitance must be increased to extend the compensation time. Therefore, it is preferable that the DC power supply be a capacitor.

[0022] With this configuration, the compensation time can be extended without increasing the capacitor capacitance. Specifically, if the capacitor capacitance is the same as in the past, the compensation time can be extended compared to the past. Also, if the compensation time is the same as in the past, the capacitor capacitance can be reduced compared to the past.

[0023] Also, there is provided a control method for a power supply system that supplies power from the power system to a load when the power system is normal, and cuts off the power supply from the power system to the load when an abnormality occurs in the power system, and supplies power to the load from a DC power supply, wherein the power supply system is provided on a power line for supplying power from the power system to the load, and includes a switch that opens and closes the power line, and a three-phase power converter that is connected in series to the power line and converts DC power from the DC power supply into three-phase AC power, and the control method for the power supply system includes calculating a compensation voltage that is a voltage that compensates for the load when opening of the switch is completed during the abnormality in the power system, and outputting the compensation voltage from the DC power supply. a DC voltage, which is a voltage, is acquired, and a command voltage, which is a voltage to be output from the three-phase power converter, is calculated based on the compensation voltage and the DC voltage; the command voltage is separated into a positive-phase component and a negative-phase component; 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; the positive-phase third harmonic and the negative-phase third harmonic are synthesized to calculate a superimposed third harmonic, which is a third harmonic to be superimposed on the command voltage, and the superimposed third harmonic is superimposed on the command voltage. Furthermore, there is provided a control program for a power supply system that supplies power from the power system to a load when the power system is normal, and that cuts off the power supply from the power system to the load when an abnormality occurs in the power system, and supplies power to the load from a DC power supply, the power supply system including a switch that is provided on a power line for supplying power from the power system to the load and that opens and closes the power line, and a three-phase power converter that is connected in series to the power line and that converts DC power from the DC power supply into three-phase AC power, the control program for the power supply system including a compensation voltage calculation unit that calculates a compensation voltage that is a voltage that compensates for the load when opening of the switch is completed when an abnormality occurs in the power system, and a compensation voltage calculation unit that acquires a DC voltage that is a voltage output by the DC power supply, and calculates the compensation voltage and the DC power supply. The computer is caused to perform two functions: a command voltage calculation unit that calculates, based on a voltage, a command voltage that is a voltage to be output from the three-phase power converter; and a third-harmonic superimposition unit that calculates, based on the command voltage, a superimposed third harmonic that is a third harmonic to be superimposed 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 that 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 that 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 combining the positive-phase third harmonic and the negative-phase third harmonic.

[0024] With this configuration, it is possible to obtain the same effects as the above-described power supply system. [Effects of the Invention]

[0025] 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 load voltage when an abnormality occurs in the power grid, the compensation time in the event of a two-wire short circuit can be further extended. [Brief explanation of the drawings]

[0026] [Figure 1]1 is a schematic diagram showing the configuration of a power supply system according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram showing functional blocks of a control device according to the present embodiment. [Figure 3] FIG. 2 is a diagram showing functional blocks of a three-phase power converter control unit in the present embodiment. [Figure 4] 10 is a simulation result showing a voltage waveform when a fundamental wave is superimposed on a post-superimposition command voltage in the same embodiment. [Figure 5] 10 is a simulation result showing a voltage waveform and a current waveform when a fundamental wave is superimposed on a post-superimposition command voltage in the same embodiment. [Figure 6] 10 shows simulation results for an example and a comparative example. [Figure 7] 10 is a simulation result showing voltage waveforms and current waveforms in a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0027] An embodiment of a power supply system according to the present invention will be described below with reference to the drawings. Note that, for ease of understanding, some parts may be omitted or exaggerated in schematic form in all of the drawings shown below. Identical components are designated by the same reference numerals, and their descriptions will be omitted where appropriate.

[0028] <Device configuration> The power supply system 100 in this embodiment is provided between an electric power system S and a load L, and when an abnormality occurs in the electric power system S, such as a short circuit accident in the electric power system S, the power supply from the electric power system S to the load L is cut off, and then the voltage of the load L is compensated for. The number of phases of the power supply system 100 in this embodiment is three.

[0029] Specifically, as shown in FIG. 1 , the power supply system 100 includes a switch 2 that cuts off the power supply from a power system S to a 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 a power line P, a system voltage measurement unit 5 that measures the system voltage, which is the voltage of the power system 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.

[0030] The switch 2 is provided on a 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 the 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 the switch 2 is closed, the three-phase AC power is supplied from the power system S to the load L. Note that the switch 2 in this embodiment may be a semiconductor switch or a mechanical switch.

[0031] The DC power supply 3 is, for example, a capacitor that stores DC power when the power system S is normal. When an abnormality occurs in the power system S, the DC power supply 3 is discharged and DC power is output. Compared to when the DC power supply 3 is a lead storage battery, when the DC power supply 3 is a capacitor, the magnitude of the DC voltage output from the capacitor also drops sharply as the capacitance of the capacitor drops.

[0032] The three-phase power converter 4 is connected in series to the power line P and converts DC power from the DC power supply 3 into AC power to supply the 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 an interconnection reactor R, an interconnection capacitor C, and an injection transformer T in this order.

[0033] The system voltage measurement unit 5 is connected to the power lines P of each phase 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, which will be described later. In this embodiment, the system voltage measurement unit 5 measures the voltage on the power system S side relative to the switch 2 so that an opening command output unit 82, which will be described later, can detect an abnormality in the power system S early.

[0034] The DC voltage measuring unit 6 is provided on the output side of the DC power supply 3 and on the input side of the three-phase power converter 4, and measures the DC voltage output from the DC power supply 3 to the three-phase power converter 4. The DC voltage measured by the DC voltage measuring unit 6 is output to a parameter acquiring unit 81, which will be described later.

[0035] The switch current measuring 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 measuring unit 7 is output to a parameter acquiring unit 81, which will be described later.

[0036] The control device 8 is a dedicated or general-purpose computer equipped with a CPU, 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 opening command output unit 82 that outputs an opening command to open the switch 2 when an abnormality in the power system S is detected, a closing command output unit 83 that outputs a closing command to close the switch 2 when the abnormality in the power system S is recovered from, a switch control unit 84 that controls the opening and closing of the switch 2 based on the opening command or the closing command, and a three-phase power converter control unit 85 that controls the three-phase power converter 4.

[0037] The parameter acquisition unit 81 acquires various parameters measured by each measurement unit. In this 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. When compensating for the voltage of the load L, it is sufficient for the parameter acquisition unit 81 to acquire at least the system voltage and the DC voltage.

[0038] The open command output unit 82 determines whether an abnormality has occurred in the power grid S based on the grid voltage, and if it determines that an abnormality has occurred in the power grid S, it outputs an open command to the switch control unit 84. Specifically, if the grid voltage falls below a predetermined value, the open command output unit 82 determines that an abnormality has occurred in the power grid S, and outputs an open command to the switch control unit 84. The predetermined value here is a voltage value for detecting a momentary sag.

[0039] The closing command output unit 83 determines whether the abnormality in the power system S has been recovered based on the system voltage, and if it determines that the abnormality in the power system S has been recovered, outputs a closing command to the switch control unit 84. Specifically, if the system voltage has been equal to or higher than a predetermined value over multiple cycles after an opening command has been output, the closing command output unit 83 determines that the abnormality in the power system S has been recovered, and outputs a closing command to the switch control unit 84.

[0040] The switch control unit 84 uses a drive circuit (not shown) to control the opening and closing of the switch 2. Specifically, the switch control unit 84 receives an opening command and performs control to open the switch 2. When the opening of the switch 2 is complete, the switch control unit 84 outputs an opening completion signal, which is a signal indicating that the opening of the switch 2 is complete.

[0041] Furthermore, the switch control unit 84 receives a closing command and performs control to close the switch 2. Then, when the closing of the switch 2 is completed, the switch control unit 84 outputs a closing completion signal indicating that the closing of the switch 2 is completed.

[0042] 3 , the three-phase power converter control unit 85 includes a current interruption control unit 851 that performs current interruption control, which is control to interrupt the load L from the power grid S, when an opening command is output, a compensation voltage calculation unit 852 that calculates a compensation voltage that compensates for the voltage of the load L that has dropped due to the current interruption control after the opening of the switch 2 is completed, a command voltage calculation unit 853 that calculates a command voltage that is a voltage to be output by the three-phase power converter 4, based on the compensation voltage and the DC voltage, a third harmonic superimposition unit 854 that calculates a third harmonic based on the command voltage and superimposes the third harmonic on the command voltage, a fundamental wave superimposition unit 855 that superimposes a fundamental wave, and a PWM control unit 856 that compares the command voltage with the carrier wave and PWM controls the three-phase power converter 4. Note that the case where the opening of the switch 2 is completed here refers to the case where the switch control unit 84 outputs an opening completion signal.

[0043] In response to the output of the opening command, the current interruption control unit 851 performs feedback control of the current output from the three-phase power converter 4 so as to set the current flowing through the switch 2 to 0. Specifically, the current interruption control unit 851 subtracts the switch current acquired by the parameter acquisition unit 81 from the switch current command value that sets the current flowing through the switch 2 to 0, and multiplies the difference by a proportional gain Kp to calculate a command voltage to be output from the three-phase power converter 4 during current interruption control.

[0044] The compensation voltage calculation unit 852 calculates a compensation voltage based on the difference between the system voltage and a voltage command value to be output from the three-phase power converter 4 in order to make the voltage of the load L a predetermined voltage. Note that the voltage command value used by the compensation voltage calculation unit 852 when calculating the compensation voltage may be, but is not limited to, a voltage command value for making the voltage of the load L equivalent to, for example, a rated voltage.

[0045] 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 half the DC voltage.

[0046] The third-order harmonic superimposing unit 854 calculates a superimposed third harmonic, which is a third harmonic to be superimposed on a three-phase command voltage, and superimposes the superimposed third harmonic on the three-phase command voltage. Specifically, the third-order harmonic superimposing 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, 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 combining the positive-phase third harmonic and the negative-phase third harmonic.

[0047] More specifically, the third harmonic superimposing unit 854 performs a UVW / αβ transformation on the three-phase command voltage, and then separates the command voltage into a positive-phase component and a negative-phase component. The third harmonic superimposing unit 854 then performs a polar coordinate transformation on the positive-phase component command voltage to calculate the amplitude and phase of the positive-phase component. The third harmonic superimposing unit 854 then reduces the amplitude of the positive-phase component by six times and triples the phase of the positive-phase component, and then performs a polar coordinate transformation on the reduced amplitude and tripled phase of the positive-phase component to calculate the positive-phase third harmonic.

[0048] The third harmonic superimposing unit 854 also converts the command voltage of the negative-phase-sequence component into polar coordinates to calculate the amplitude and phase of the negative-phase-sequence component. The third harmonic superimposing unit 854 then reduces the amplitude of the negative-phase-sequence component to 1 / 6 and triples the phase of the negative-phase-sequence component, and then converts the reduced amplitude and tripled phase of the negative-phase-sequence component into polar coordinates to calculate the negative-phase-sequence third harmonic.

[0049] The third-order harmonic superimposing unit 854 then combines the positive-phase third harmonic and the negative-phase third harmonic, and performs UV / αβ conversion to calculate a superimposed third harmonic. The third-order harmonic superimposing unit 854 superimposes the calculated superimposed third harmonic on the three-phase command voltage.

[0050] The fundamental wave superimposing unit 855 calculates a fundamental wave based on a superimposed command voltage, which is a command voltage after the superimposed third harmonic has been superimposed, and superimposes the fundamental wave on the superimposed command voltage. Specifically, the fundamental wave superimposing unit 855 calculates the amplitude difference between each phase in the superimposed voltage, calculates a fundamental wave having an amplitude that reduces the amplitude difference between each phase, and superimposes the fundamental wave on the superimposed command voltage. In this embodiment, the fundamental wave having an amplitude that reduces the amplitude difference between each phase is a fundamental wave having an amplitude that reduces the amplitude difference between each phase to zero, and particularly, a fundamental wave having an amplitude that reduces the amplitude difference between two shorted phases and one non-shorted phase to zero when two phases are shorted.

[0051] More specifically, the fundamental wave superimposing unit 855 performs a UV / W / αβ conversion on the three-phase superimposed command voltage, and then separates the superimposed command voltage into a positive-phase component and a negative-phase component. The third harmonic superimposing unit 854 then performs a polar coordinate conversion on the positive-phase component and the negative-phase component of the superimposed command voltage, and calculates the amplitude and phase of each of the positive-phase component and the negative-phase component of the superimposed command voltage.

[0052] The fundamental wave superimposing unit 855 then calculates an amplitude difference by subtracting the amplitudes corresponding to the two shorted phases from the amplitude corresponding to the one non-shorted phase, based on the amplitudes and phases of the positive-phase and negative-phase components of the superimposed command voltage. The fundamental wave superimposing unit 855 then calculates a fundamental wave having an amplitude that makes the amplitude difference zero. The fundamental wave superimposing unit 855 then performs polar coordinate transformation and UVW / αβ transformation on the fundamental wave, and then superimposes it on each phase of the superimposed command voltage.

[0053] The PWM control unit 856 compares the three-phase command voltages on which the third harmonic is superimposed with the carrier wave, and PWM controls the three-phase power converter 4. Specifically, if the three-phase command voltages on which the third harmonic is superimposed are greater than the carrier wave, the PWM control unit 856 turns on the three-phase power converter 4, and if the three-phase command voltages on which the third harmonic is superimposed are smaller than the carrier wave, the PWM control unit 856 turns off the three-phase power converter 4.

[0054] <Power supply system control operation> Next, the control operation of the power supply system 100 will be described.

[0055] (1) Normal operation of power system S The system voltage measurement unit 5 measures the system voltage, and outputs the measured system voltage to the opening command output unit 82. The opening command output unit 82 compares the system voltage with a predetermined value.

[0056] When the power system S is normal, the system voltage is equal to or higher than a predetermined value, and the switch 2 is turned on. Therefore, AC power is supplied from the power system S to the load L.

[0057] (2) When an abnormality occurs in power system S For example, when an abnormality such as a two-line short circuit occurs in the power system S and the system voltage is lower than a predetermined value, the opening command output unit 82 outputs an opening command to the switch control unit 84.

[0058] When the open command is output, the switch control unit 84 controls the drive circuit to open the switch 2. Furthermore, the current cut-off 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.

[0059] 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 cut-off control unit 851 completes the current cut-off control.

[0060] When the current cutoff control is completed, the compensation voltage calculation unit 852 calculates the compensation voltage.

[0061] Once the compensation voltages are calculated, the command voltage calculation unit 853 calculates the amplitudes of the three-phase command voltages based on the compensation voltages and the DC voltages.

[0062] Once the amplitudes of the three-phase command voltages have been calculated, the third-order harmonic superimposing unit 854 separates the command voltages into positive-phase and negative-phase components. The third-order harmonic superimposing unit 854 then calculates a superimposed third harmonic by multiplying the amplitudes of the positive-phase and negative-phase components by six times and tripling their phases. The third-order harmonic superimposing unit 854 then superimposes the superimposed third harmonic on the three-phase command voltages. This reduces the amplitude of the command voltage after superimposition by √3 / 2, minimizing the amplitude of the command voltage after the third harmonic has been superimposed and maximizing the compensation time.

[0063] The fundamental wave superimposing unit 855 then separates the superimposed command voltage into a positive-phase component and a negative-phase component, and calculates the amplitude difference between the two short-circuited phases and the one non-short-circuited phase based on the positive-phase component and the negative-phase component of the superimposed command voltage. The fundamental wave superimposing unit 855 then calculates a fundamental wave having an amplitude that makes the amplitude difference zero, and superimposes the fundamental wave on each phase of the superimposed command voltage.

[0064] When the fundamental wave is superimposed on each phase of the superimposed command voltage, the PWM control unit 856 compares the superimposed command voltage on which the fundamental wave is superimposed with the carrier wave, and performs PWM control on the three-phase power converter 4.

[0065] When the voltage of the load L is compensated by the voltage compensation control by the compensation voltage calculation unit 852 and the power grid S is restored to normal, the power supply command output unit 83 outputs a power supply command. In response to the output of the power supply command, the switch control unit 84 closes the switch 2.

[0066] When the closing of the switch 2 is completed, the switch control unit 84 outputs a closing completion signal. Upon receiving the output of the closing completion signal, the voltage compensation of the load L by the three-phase power converter 4 is completed.

[0067] <Simulation results> Next, voltage and current waveforms in various power supply systems are shown by simulation. In the following simulations, the load capacity is 2MVA, the rated output voltage of the three-phase power converter 4 is 380V, the capacitance of the capacitor constituting the DC power supply 3 is 2.34μF, and the initial DC voltage of the capacitor constituting the DC power supply 3 is 725V. The fault condition is a momentary sag two-wire short-circuit fault in which the voltage of the power system S drops by 100%.

[0068] FIG. 4 shows the simulation results when a fundamental wave is superimposed on the post-superimposition command voltage after a third harmonic is superimposed on each phase of the command voltage. As shown in FIG. 4, after the third harmonic is superimposed on each phase of the command voltage and before the fundamental wave is superimposed, there is an amplitude difference in the post-superimposition command voltage between the two shorted phases and the one non-shorted phase. Therefore, as shown in FIG. 4, a fundamental wave having an amplitude that makes this amplitude difference zero is calculated, and this fundamental wave is superimposed on each phase of the post-superimposition command voltage. As a result, as can be seen from FIG. 4, it was confirmed that the amplitude difference between each phase in the post-superimposition command voltage after the fundamental wave is superimposed is zero.

[0069] Figure 5 shows the simulation results of the voltage and current waveforms when the fundamental wave is superimposed on the post-superimposition command voltage. As can be seen from Figure 5, the compensation time is 0.21 seconds when the fundamental wave is not superimposed on the post-superimposition command voltage, while the compensation time is 0.26 seconds when the fundamental wave is superimposed on the post-superimposition command voltage. This confirms that the compensation time can be further extended compared to conventional methods by making the amplitude difference between each phase zero in the post-superimposition command voltage after the fundamental wave is superimposed. Furthermore, as can be seen from Figure 5, the voltage waveform of the load does not fluctuate after the fundamental wave is superimposed on the post-superimposition command voltage. Therefore, it was confirmed that superimposing the fundamental wave on the post-superimposition command voltage does not affect the load voltage.

[0070] Figure 6 shows the simulation results showing the compensation time when the amount of fundamental wave superimposed on the superimposed command voltage is changed. In Figure 6, the vertical axis represents the compensation limit time, which indicates the maximum value of the compensation time, and the horizontal axis represents the ratio of the amplitude of the one phase that is not short-circuited to the amplitude of the two short-circuited phases, with the superimposition amount of the fundamental wave having an amplitude that makes the amplitude difference between the two short-circuited phases and the one phase that is not short-circuited being 0, set to 100%. As can be seen from Figure 6, it was confirmed that the compensation limit time is maximized when the superimposition amount of the fundamental wave is 100%.

[0071] Figure 7 shows the simulation results of the voltage waveform and current waveform when the superimposition amount of the fundamental wave is 50% and 150% in Figure 6. As can be seen from Figure 7, in both cases where the superimposition amount of the fundamental wave is 50% and 150%, it was confirmed that the compensation limit time was 0.23 seconds, which was shorter than when the superimposition amount of the fundamental wave was 100%. 7, the voltage waveform of the load after superimposing the fundamental wave on the post-superimposition command voltage does not fluctuate, whether the superimposition amount of the fundamental wave is 50% or 150%. Therefore, it was confirmed that superimposing the fundamental wave on the post-superimposition command voltage does not affect the voltage of the load.

[0072] <Effects of this embodiment> In the power supply system 100 of this embodiment, the fundamental wave superimposing unit 855 calculates the amplitude difference between each phase from the superimposed command voltage after superimposing the superimposed third harmonic, calculates a fundamental wave that reduces the amplitude difference between each phase, and superimposes the fundamental wave on the superimposed command voltage. As a result, the maximum amplitude of the superimposed command voltage can be reduced, and therefore the compensation time can be further extended when two lines are short-circuited. Furthermore, even if the fundamental wave is superimposed on the command voltage after superimposition, no disturbance occurs in the voltage of the load, so the influence of the fundamental wave superimposition on the voltage of the load can be suppressed. Furthermore, since the three-phase power converter 4 outputs three-phase AC and the third harmonics of each phase are cancelled out in the line voltage, the voltage output by the power converter can be increased without increasing the distortion of the line voltage.

[0073] <Other embodiments> The present invention is not limited to the above-described embodiment.

[0074] In the above embodiment, the fundamental wave superimposing unit 855 calculates a fundamental wave having an amplitude that makes the difference between the amplitude of the two shorted phases and the amplitude of the one phase that is not shorted zero, but this is not limited to this. The fundamental wave superimposing unit 855 may calculate a fundamental wave having an amplitude that reduces the amplitude difference between the phases of the command voltage after superimposition, and may, for example, calculate a fundamental wave that makes the difference between the amplitude of the two shorted phases and the amplitude of the one phase that is not shorted zero.

[0075] In the above embodiment, the fundamental wave superimposing unit 855 calculates the amplitude difference between each phase by separating the superimposed command voltage into a positive-phase component and a negative-phase component, but this is not limiting. The fundamental wave superimposing unit 855 is only required to calculate the amplitude of each phase of the superimposed command voltage, and is not necessarily required to separate the superimposed command voltage into a positive-phase component and a negative-phase component.

[0076] In the above embodiment, the third-order harmonic superimposing unit 854 is configured to calculate the superimposed third harmonic by separating the command voltage into a positive-phase component and a negative-phase component, but the calculation of the superimposed third harmonic is not limited to this. For example, the third-order harmonic superimposing unit 854 may calculate the superimposed third harmonic by performing a UV / αβ transformation and a polar coordinate transformation on the three-phase command voltage to calculate the amplitude and phase of the command voltage, without separating the command voltage into a positive-phase component and a negative-phase component.

[0077] In the above embodiment, the third-order harmonic superimposing unit 854 calculates the third-order harmonic by multiplying the amplitude of the three-phase command voltage by a factor of six and multiplying the phase of the three-phase command voltage by a factor of three, but the multiplication factors of the amplitude and phase of the three-phase command voltage are not limited to this.

[0078] In the above embodiment, the three-phase power converter 4 is connected in series to the power line P, but the three-phase power converter 4 may be connected to the power line P in parallel.

[0079] In the above embodiment, the DC power supply 3 is a capacitor, but 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, the amplitude of the voltage output from the three-phase power converter 4 is reduced by superimposing the third harmonic on the command voltage, so that the compensation time can be extended.

[0080] In the above embodiment, the power supply system 100 is configured to include a system voltage measurement unit 5, a DC voltage measurement unit 6, and a 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.

[0081] In the above embodiment, if the only purpose is to extend the compensation time of the load L, the three-phase power converter control unit 85 does not need to include the current interruption control unit 851. Furthermore, if the only purpose is to extend the compensation time of the load L, the opening command output unit 82, the closing command output unit 83, and the switch control unit 84 may be provided in a control device other than the control device in which the three-phase power converter control unit 85 is provided.

[0082] 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 of the present invention. [Explanation of symbols]

[0083] 100 Power Supply System 2 Switch 3...DC power supply 4. Three-phase power converter 5. System voltage measurement section 6 DC voltage measurement section 7 Switch current measurement section 8. Control device 81 Parameter acquisition section 82...Open command output section 83 ... Closing command output section 84 Switch control section 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 superposition section 855 Fundamental wave superposition section 856 PWM control unit S...Power system L...Load P...Power line

Claims

1. A power supply system that supplies power from an electric power system to a load when the electric power system is normal, and cuts off the power supply from the electric power system to the load when an abnormality occurs in the electric power system, and supplies power to the load from a DC power supply, 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 that converts DC power from the DC power supply into three-phase AC power and supplies the AC power to the power line; a three-phase power converter control unit that controls the three-phase power converter; The three-phase power converter control unit a compensation voltage calculation unit that calculates a compensation voltage that is a voltage that compensates for the load when the switch is completely opened during an abnormality in the power grid; a command voltage calculation unit that acquires a DC voltage that is a voltage output by the DC power supply, and 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; a third-order harmonic superimposing unit that calculates a superimposed third-order harmonic that is a third-order harmonic to be superimposed on the command voltage and superimposes the superimposed third-order harmonic on the command voltage; a fundamental wave superimposing unit that calculates an amplitude difference between each phase in a superimposed command voltage, which is a command voltage after the superimposed third harmonic has been superimposed, calculates a fundamental wave that reduces the amplitude difference between each phase, and superimposes the fundamental wave on the superimposed command voltage.

2. The power supply system according to claim 1 , wherein the fundamental wave superimposing unit calculates a fundamental wave that makes the amplitude difference between the phases zero.

3. 2. The power supply system according to claim 1, wherein the fundamental wave superimposing unit separates the superimposed command voltage into a positive-phase component and a negative-phase component, and calculates the amplitude difference between the phases based on the positive-phase component and the negative-phase component.

4. 2. The power supply system according to claim 1, wherein the third harmonic superimposing unit separates the command voltage into a positive-phase component and a negative-phase component, calculates a positive-phase third harmonic that is a third harmonic corresponding to the positive-phase component based on an amplitude and a phase of the positive-phase component, calculates a negative-phase third harmonic that is a third harmonic corresponding to the negative-phase component based on an amplitude and a phase of the negative-phase component, and calculates the superimposed third harmonic by combining the positive-phase third harmonic and the negative-phase third harmonic.

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

6. 6. The power supply system according to claim 1, wherein the DC power supply is a capacitor.

7. A control method for a power supply system that supplies power from a power system to a load when the power system is normal, and cuts off power supply from the power system to the load when an abnormality occurs in the power system, and supplies power to the load from a DC power supply, 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 that converts DC power from the DC power supply into three-phase AC power and supplies the power to the power line, The method for controlling a power supply system includes: calculating a compensation voltage that is a voltage that compensates for the load when the switch is completely opened during an abnormality in the power system; acquiring a DC voltage that is a voltage output by the DC power supply, and outputting the DC voltage to the three-phase power converter based on the compensation voltage and the DC voltage; calculating a superimposed third harmonic that is a third harmonic to be superimposed on the command voltage; and superimposing the superimposed third harmonic on the command voltage; a control method for a power supply system, the control method comprising: calculating an amplitude difference between each phase in a superimposed command voltage, which is a command voltage after the superimposed third harmonic has been superimposed; calculating a fundamental wave that reduces the amplitude difference between each phase; and superimposing the fundamental wave on the superimposed command voltage.

8. A control program for a power supply system that supplies power from a power system to a load when the power system is normal, and cuts off power supply from the power system to the load when an abnormality occurs in the power system, and supplies power from a DC power supply to the load, 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 that converts DC power from the DC power supply into three-phase AC power and supplies the power to the power line, a control program for the power supply system, a function as a compensation voltage calculation unit that calculates a compensation voltage that is a voltage that compensates for the load when the switch is completely opened during an abnormality in the power system; a function as a command voltage calculation unit that acquires a DC voltage that is a voltage output by the DC power supply and outputs the command voltage to the three-phase power converter based on the compensation voltage and the DC voltage; a function as a third-order harmonic superimposing unit that calculates a superimposed third-order harmonic that is a third-order harmonic to be superimposed on the command voltage and superimposes the superimposed third-order harmonic on the command voltage; a fundamental wave superimposition unit that calculates an amplitude difference between each phase in a superimposed command voltage, which is a command voltage after the superimposed third harmonic has been superimposed, calculates a fundamental wave that reduces the amplitude difference between each phase, and superimposes the fundamental wave on the superimposed command voltage.

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