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

Abstract

In a power supply system including a three-phase power converter that supplies AC power to compensate for a load voltage when an abnormality occurs in the power grid, the compensation time in the event of a two-wire short circuit is further extended. [Solution] A power supply system that cuts off power supply from a power grid when an abnormality occurs and supplies power from a DC power source includes a switch that opens and closes a power line from the power grid to a load, a three-phase power converter that converts 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 when an abnormality occurs in the power grid, 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 harmonic superposition unit 854 that calculates a superimposed third harmonic and superimposes it on the command voltage, and a fundamental wave superposition unit 855 that calculates an amplitude difference between each phase using a superimposed command voltage on which the superimposed third harmonic is superimposed, calculates a fundamental wave that reduces the amplitude difference, and superimposes it on the superimposed command voltage.

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 system is normal, power is supplied from the power system to the load via a circuit breaker and the power converter is stopped. On the other hand, when the power system is abnormal, the circuit breaker is opened to cut off the power supply from the power system to the load, and AC power is supplied from the energy storage unit to the load via the power converter. In this way, the voltage of the load is compensated when the power system is abnormal. [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 the above power supply system, a three-phase power converter may be used as the power converter. In this case, if a command voltage to be 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 drop. Therefore, when compensating for the voltage of the load, it is necessary for the three-phase power converter 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 voltage of the load, the voltage output from the energy storage unit drops suddenly due to the sudden discharge from the energy storage unit, and the maximum voltage also drops suddenly. As a result, the command voltage quickly becomes larger than the maximum voltage, and the compensation time during which the voltage of the load can be compensated for becomes shorter.

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

[0008] However, when two lines are shorted, the command voltage before the third harmonic is superimposed is a three-phase unbalanced voltage, so that the third harmonic for reducing the amplitude of the command voltage cannot be accurately calculated. Therefore, when two lines are shorted, the compensation time cannot be extended by simply superimposing the third harmonic on the command voltage.

[0009] In particular, when two lines are shorted, the command voltage is three-phase unbalanced, so there is an amplitude difference between the phases, and the limit of the compensation time is determined by the maximum amplitude value. As a result of extensive research, the inventors of the present application came to the conclusion that if the maximum amplitude of the command voltage can be reduced, the compensation time when two lines are shorted can be further extended, and arrived at the present invention.

[0010] Therefore, the present invention has been made in consideration 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 including a three-phase power converter that supplies AC power to compensate for the voltage of a load 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 a 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 source, and includes 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 source into three-phase AC power and supplies the power 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 compensation circuit that compensates for the load when opening of the switch is completed during the power system abnormality. 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 superposition 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 superposition unit that calculates an amplitude difference between each phase in a superimposed command voltage that is the command voltage after the superimposed third harmonic is superimposed, calculates a fundamental wave that reduces the amplitude difference between 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 used to compensate for the load voltage, the load voltage does not fluctuate, and therefore the fundamental wave superimposition does not affect the load voltage when compensating for the load voltage. 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 distortion in the line voltage.

[0013] It is preferable that the fundamental wave superimposing section calculates a fundamental wave that makes the amplitude difference between the phases zero.

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

[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 of each phase 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 of each phase based on the positive phase component and the negative phase component, so that the amplitude difference of each phase of the superimposed command voltage can be calculated more accurately when two lines are shorted. As a result, the compensation time when two lines are shorted can be calculated accurately and the compensation time can be extended more than before.

[0017] It is preferable that 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 which is a third harmonic corresponding to the positive phase component based on the amplitude and phase of the positive phase component, calculates a negative phase third harmonic which is a third harmonic corresponding to the negative phase component based on the amplitude and phase of the negative phase component, and calculates the superimposed third harmonic by synthesizing the positive phase third harmonic and the negative phase third harmonic.

[0018] With this configuration, the third harmonic superimposing unit separates the command voltage into a positive-phase component and a negative-phase component to calculate the positive-phase third harmonic and the negative-phase third harmonic, and calculates the superimposed third harmonic by combining the positive-phase third harmonic and the negative-phase third harmonic, so that it is possible to accurately calculate the superimposed third harmonic that reduces the amplitude of the command voltage regardless of whether the three-phase is balanced or unbalanced. 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 lines, so consumption of DC power can be reduced.

[0021] When compensating for the voltage of a load during a voltage sag, a capacitor is often used as a DC power supply from the viewpoints of installation space, maintenance, and cost. However, compared to other DC power supplies such as lead-acid batteries, when a capacitor is discharged, as the capacitance of the capacitor decreases, the DC voltage output from the capacitor drops rapidly, and the maximum voltage of the three-phase power converter also drops. As a result, in conventional power supply systems, it is necessary to increase the capacitance of the capacitor in order to extend the compensation time. Therefore, it is preferable that the DC power supply is a capacitor.

[0022] With this configuration, the compensation time can be extended without increasing the capacitance of the capacitor. Specifically, when the capacitance of the capacitor is the same as in the past, the compensation time can be extended more than in the past. Also, when the compensation time is the same as in the past, the capacitance of the capacitor can be reduced more than in 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 the power system is abnormal, 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 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, the control method for the power supply system including a step of: calculating a compensation voltage that is a voltage that compensates for the load when opening of the switch is completed during the abnormality of 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 by 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. Further, 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 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 source, 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 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 source 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 the power system is abnormal, and ... by acquiring a DC voltage that is a voltage output by the DC power source, and converting the compensation voltage and the DC power source into a three-phase AC power when the switch is opened when the power system is abnormal. The computer is caused to perform a function as a command voltage calculation unit that calculates, based on a voltage, a command voltage that is a voltage to be output to the three-phase power converter, and a function as a third harmonic superposition 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, wherein the third harmonic superposition unit separates the command voltage into a positive phase component and a negative phase component, calculates a positive phase third harmonic 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.

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

[0025] According to the present invention configured in this manner, 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, it is possible to further extend the compensation time in the event of a two-wire short circuit. [Brief description of the drawings]

[0026] [Figure 1]1 is a schematic diagram showing a configuration of a power supply system according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a diagram showing functional blocks of a control device according to the present embodiment. [Diagram 3] FIG. 2 is a diagram showing functional blocks of a three-phase power converter control unit in the present embodiment. [Figure 4] 13 is a simulation result showing a voltage waveform when a fundamental wave is superimposed on a post-superimposition command voltage in the embodiment. [Diagram 5] 11 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 embodiment. [Figure 6] 1 shows simulation results in an example and a comparative example. [Figure 7] 11 is a simulation result showing voltage waveforms and current waveforms in a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] An embodiment of a power supply system according to the present invention will be described below with reference to the drawings. Note that in any of the drawings shown below, some parts may be omitted or exaggerated and illustrated in a schematic manner for ease of understanding. Identical components are given the same reference numerals and descriptions thereof will be omitted as appropriate.

[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. Note that 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 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 measuring unit 5 that measures the system voltage that is the voltage of the power system S, a DC voltage measuring unit 6 that measures the DC voltage that is the voltage output from the DC power supply 3, a switch current measuring unit 7 that measures the switch current that 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 a power system S to a 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 the power system S is abnormal, 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 capacity 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 source 3 into AC power and supplies it 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 measuring 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 measuring unit 5 is output to a parameter acquiring unit 81, which will be described later. In this embodiment, the system voltage measuring unit 5 measures the voltage on the power system S side rather than 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 in 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, 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 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 acquiring unit 81 acquires various parameters measured by each measuring unit. In this embodiment, the parameter acquiring unit 81 acquires at least one of the system voltage measured by the system voltage measuring unit 5, the DC voltage measured by the DC voltage measuring unit 6, and the switch current measured by the switch current measuring unit 7. During voltage compensation of the load L, it is sufficient for the parameter acquiring unit 81 to acquire at least the system voltage and the DC voltage.

[0038] The opening command output unit 82 judges whether or not an abnormality has occurred in the power system S based on the system voltage, and when it is judged that an abnormality has occurred in the power system S, it outputs an opening command to the switch control unit 84. Specifically, when the system voltage falls below a predetermined value, the opening command output unit 82 judges that an abnormality has occurred in the power system S, and outputs an opening command to the switch control unit 84. Note that the predetermined value referred to here is a voltage value for detecting a momentary sag.

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

[0041] Furthermore, upon receiving a closing command, the switch control unit 84 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 for interrupting the load L from the power system S, when an opening command is output, a compensation voltage calculation unit 852 that calculates a compensation voltage that is a voltage for compensating 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 to 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. 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] The current interruption control unit 851 performs feedback control of the current output from the three-phase power converter 4 in response to the output of an opening command so as to make the current flowing through the switch 2 zero. Specifically, the current interruption control unit 851 subtracts the switch current acquired by the parameter acquisition unit 81 from a switch current command value for making the current flowing through the switch 2 zero, 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 to 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 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 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 synthesizing the positive-phase third harmonic and the negative-phase third harmonic.

[0047] More specifically, the third harmonic superimposing unit 854 performs uvw / αβ conversion 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 polar coordinate conversion on the command voltage of the positive-phase component to calculate the amplitude and phase of the positive-phase component. The third harmonic superimposing unit 854 then multiplies the amplitude of the positive-phase component by 6 times and triples the phase of the positive-phase component, and calculates a positive-phase third harmonic by polar coordinate conversion on the amplitude of the positive-phase component multiplied by 6 times and the phase of the positive-phase component multiplied by 3 times.

[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 multiplies the amplitude and phase of the negative phase-sequence component by 6 times and 3 times, respectively, and calculates the negative phase third harmonic by converting the 1 / 6 multiplied amplitude and tripled phase of the negative phase-sequence component into polar coordinates.

[0049] The third harmonic superimposing unit 854 then synthesizes the positive-phase third harmonic and the negative-phase third harmonic, and then performs uvw / αβ conversion to calculate a superimposed third harmonic. The third 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 the superimposed command voltage, which is the command voltage after the superimposed third harmonic wave is superimposed, and superimposes the fundamental wave on the superimposed command voltage. Specifically, the fundamental wave superimposing unit 855 calculates the amplitude difference of each phase in the superimposed voltage, calculates a fundamental wave having an amplitude that reduces the amplitude difference of 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 of each phase is a fundamental wave having an amplitude that makes the amplitude difference of each phase zero, and in particular, a fundamental wave having an amplitude that makes the amplitude difference between two short-circuited phases and one phase that is not short-circuited zero when two phases are short-circuited.

[0051] More specifically, the fundamental wave superimposing unit 855 performs uvw / 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 performs polar coordinate conversion on the positive-phase component and the negative-phase component in the superimposed command voltage, and calculates the amplitude and phase of each of the positive-phase component and the negative-phase component in the superimposed command voltage.

[0052] Then, the fundamental wave superimposing unit 855 calculates an amplitude difference obtained by subtracting the amplitude corresponding to the two shorted phases from the amplitude corresponding to the one non-shorted phase based on the amplitude and phase of each of the positive and negative phase components in the superimposed command voltage.The fundamental wave superimposing unit 855 then calculates a fundamental wave having an amplitude that makes the amplitude difference 0.The fundamental wave superimposing unit 855 then performs polar coordinate conversion and uvw / αβ conversion 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) Power system S in normal operation The system voltage measuring 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 falls below a predetermined value, the opening command output unit 82 outputs an opening command to the switch control unit 84 .

[0058] When the opening command is output, the switch control unit 84 performs control to open the switch 2 using the drive circuit. In addition, the current interruption control unit 851 controls the current output from the three-phase power converter 4 so as to make the current flowing through the switch 2 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 interruption control is completed, the compensation voltage calculation unit 852 calculates the compensation voltage.

[0061] When 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 voltage.

[0062] When the amplitude of the three-phase command voltage is calculated, the third harmonic superimposing unit 854 separates the command voltage into a positive phase component and a negative phase component. The third harmonic superimposing unit 854 then calculates a superimposed third harmonic by multiplying the amplitude of each of the positive phase component and the negative phase component by 1 / 6 and multiplying the phase of each by 3. The third harmonic superimposing unit 854 then superimposes the superimposed third harmonic on the three-phase command voltage. As a result, the amplitude of the command voltage after superimposition is reduced to √3 / 2, so that the amplitude of the command voltage after superimposition of the third harmonic can be minimized and the compensation time can be extended to the longest.

[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 phase that is not short-circuited 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 of 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 closing command output unit 83 determines that the abnormality in the power system S has been restored, the closing command output unit 83 outputs a closing command. In response to the output of the closing 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 simulation, 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 accident condition is a two-wire short circuit accident with a momentary sag in which the voltage of the power system S drops by 100%.

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

[0069] Figure 5 shows the simulation results showing the voltage waveform and current waveform when the fundamental wave is superimposed on the superimposed 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 superimposed command voltage, whereas the compensation time is 0.26 seconds when the fundamental wave is superimposed on the superimposed command voltage. From this, it was confirmed that the compensation time can be further extended compared to the conventional method by making the amplitude difference between each phase zero in the superimposed command voltage after the fundamental wave is superimposed. In addition, as can be seen from Fig. 5, the voltage waveform of the load does not change after the fundamental wave is superimposed on the post-superimposition command voltage. Therefore, it was confirmed that the load voltage is not affected even if the fundamental wave is superimposed on the post-superimposition command voltage.

[0070] Figure 6 shows the results of a simulation showing the compensation time when the amount of the fundamental wave superimposed on the superimposed command voltage is changed. In Figure 6, the vertical axis represents the compensation limit time indicating 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 amount of superimposition 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 set to 0 being 100%. As can be seen from Figure 6, it was confirmed that the compensation limit time is maximized when the amount of superimposition of the fundamental wave is 100%.

[0071] Fig. 7 shows the simulation results showing the voltage waveforms and current waveforms when the superimposition amount of the fundamental wave in Fig. 6 is 50% and 150%. As can be seen from Fig. 7, in both cases where the superimposition amount of the fundamental wave is 50% and 150%, it was confirmed that the compensation limit time is 0.23 seconds, which is shorter than when the superimposition amount of the fundamental wave is 100%. In addition, as can be seen from Fig. 7, the voltage waveform of the load after superimposing the fundamental wave on the post-superimposition command voltage does not change whether the superimposition amount of the fundamental wave is 50% or 150%. Therefore, it was confirmed that even if the fundamental wave is superimposed on the post-superimposition command voltage, it 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 the superimposed third harmonic is superimposed, 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 value of the 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 that the effect of superimposing the fundamental wave 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 two short-circuited phases and the amplitude of one non-shorted phase zero, but this is not limited thereto. The fundamental wave superimposing unit 855 only needs to calculate a fundamental wave having an amplitude that reduces the amplitude difference between each phase of the superimposed command voltage, and may calculate, for example, a fundamental wave in which the difference between the amplitude of two short-circuited phases and the amplitude of one non-shorted phase is not zero.

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

[0076] In the above embodiment, the third 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 harmonic superimposing unit 854 may calculate the superimposed third harmonic by performing a UVW / αβ conversion and a polar coordinate conversion 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 harmonic superimposing unit 854 calculates the third 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 multiples 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. However, 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 if 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 measuring unit 5, a DC voltage measuring unit 6, and a switch current measuring unit 7, but the DC voltage measuring unit 6 and the switch current measuring 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 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 section 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 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, 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 source into three-phase AC power and supplies the AC power to the power line; 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 that calculates a compensation voltage that is a voltage that compensates for the load when the opening of the switch is completed during an abnormality in 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 by the three-phase power converter based on the compensation voltage and the DC voltage; a third harmonic superposition unit that calculates a superposed third harmonic, which is a third harmonic to be superposed on the command voltage, and superposes the superposed third 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 the command voltage after the superimposed third harmonic is 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 an 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 of each phase 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 synthesizing 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 with 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, which 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, 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 source 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 opening of the switch is completed during an abnormality in the power system; acquiring a DC voltage that is a voltage output by the DC power supply, and calculating 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; Calculating a superimposed third harmonic, which 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, comprising: calculating an amplitude difference between each phase in a superimposed command voltage, which is a command voltage after the superimposed third harmonic is 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 source into three-phase AC power and supplies the power to the power line, The control program for the power supply system includes: a function of a compensation voltage calculation unit that calculates a compensation voltage that is a voltage that compensates for the load when the opening of the switch is completed during an abnormality in the power system; a function of 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 function as a third harmonic superposition unit that calculates a superposed third harmonic, which is a third harmonic to be superposed on the command voltage, and superposes the superposed third harmonic on the command voltage; a control program for a power supply system, which causes a computer to perform a function as a fundamental wave superposition unit that calculates an amplitude difference between each phase in a superimposed command voltage, which is a command voltage after the superimposed third harmonic is 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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