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 the voltage of a load when an abnormality occurs in the power grid, a compensation time during which the voltage of the load can be compensated is extended. [Solution] A power supply system 100 includes a switch 2 that opens and closes a power line P, a three-phase power converter 4 that converts DC power from a DC power source 3 into three-phase AC power and supplies the power to the power line, and a control device 8 having a three-phase power converter control unit that controls the three-phase power converter. When opening of the switch is completed during an abnormality in the power system, the three-phase power converter control unit calculates a compensation voltage that is a voltage that compensates for a load, acquires a DC voltage that is a voltage output by a DC power source, calculates a command voltage that is a voltage to be output by the three-phase power converter based on the compensation voltage and the DC voltage, calculates a superimposed third harmonic that is a third harmonic to be superimposed on the command voltage based on the command voltage, and superimposes the superimposed third harmonic on the 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] Therefore, the present invention has been made in consideration of the above problems, and has as its main object to extend the compensation time during which the load voltage can be compensated for, 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, regardless of whether the power grid is three-phase balanced or three-phase unbalanced. [Means for solving the problem]

[0010] That is, the power supply system according to the present invention 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 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 supply 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 includes 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 a compensation voltage acquisition unit that acquires a DC voltage that is a voltage output by the DC power supply. and a third harmonic superimposing unit that calculates a superimposed third harmonic, which is a third harmonic to be superimposed on the command voltage, based on the command voltage, and superimposes the superimposed third harmonic on the command voltage, 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, which 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, 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.

[0011] In such a power supply system, 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. In addition, 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.

[0012] A specific embodiment of the third harmonic superimposing section may be one that calculates the third harmonic by multiplying the amplitude of the command voltage by a factor of six and multiplying the phase of the command voltage by three.

[0013] With this configuration, the amplitude of the command voltage after the third harmonic is superimposed can be minimized, and the compensation time can be extended to the longest.

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

[0015] With this configuration, the loss in the three-phase power converter can be reduced compared to a case in which the three-phase power converter is connected in parallel to the power line.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] With this configuration, it is possible to obtain the same effects as the power supply system described above. Effect of the Invention

[0020] 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, the compensation time during which the load voltage can be compensated can be extended, regardless of whether the power grid is three-phase balanced or three-phase unbalanced. [Brief description of the drawings]

[0021] [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] 4 is a simulation result showing voltage waveforms and current waveforms when a three-phase power converter control unit in the embodiment controls the three-phase power converter. [Diagram 5] 13 is a simulation result in a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] 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.

[0023] <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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The control device 8 is a dedicated or general-purpose computer equipped with a CPU, an internal memory, an input / output interface, an A / D converter, etc., and controls the switch 2 and the three-phase power converter 4 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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 from 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, and a PWM control unit 855 that compares the command voltage with a 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] The PWM control unit 855 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 855 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 855 turns off the three-phase power converter 4.

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

[0047] (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.

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

[0049] (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 .

[0050] 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.

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

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

[0053] 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.

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

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

[0056] 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.

[0057] 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.

[0058] <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%.

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

[0060] Figure 5 shows the simulation results when the third harmonic is calculated from the command voltage without separating the command voltage into positive and negative phase components, and the calculated third harmonic is superimposed on the command voltage. As can be seen from Figure 5, in the event of a two-phase short circuit fault, the state in which the ratio of the command voltage to the maximum voltage is less than 1 continues for 0.12 seconds after the start of compensation for the voltage of the load L. Therefore, by comparing Figures 4 and 5, it was confirmed that in the event of a two-phase short circuit fault, the compensation time can be extended when the command voltage is separated into positive and negative phase components to calculate the superimposed third harmonic, compared to the case in which the command voltage is not separated into positive and negative phase components and the third harmonic is calculated from the command voltage.

[0061] <Effects of this embodiment> According to the power supply system 100 of this embodiment, the third harmonic superimposing unit 854 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 synthesizing 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. In addition, 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 three-phase power converter 4 can be increased without increasing the distortion of the line voltage.

[0062] Furthermore, according to this embodiment, the third harmonic superimposing unit 854 calculates the third harmonic by multiplying the amplitude of the command voltage by a factor of six and tripling the phase of the command voltage, so that the amplitude of the command voltage after the third harmonic is superimposed can be minimized and the compensation time can be extended to the longest.

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

[0064] Furthermore, according to this embodiment, the compensation time can be extended without increasing the capacitor capacity. Specifically, when the capacitor capacity is the same as in the past, the power supply system 100 of this embodiment can extend the compensation time more than in the past. Moreover, when the compensation time is the same as in the past, the power supply system 100 of this embodiment can reduce the capacitor capacity more than in the past.

[0065] <Other embodiments> The present invention is not limited to the above-described embodiment.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] Furthermore, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0072] 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 ···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 superimposing unit that calculates a superimposed third harmonic, which is a third harmonic to be superimposed on the command voltage, based on the command voltage, and superimposes the superimposed third harmonic on the command voltage, 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, and calculates a negative phase third harmonic which is a third harmonic corresponding to the negative phase component based on the amplitude and phase of the negative phase component, and calculates the superimposed third harmonic by synthesizing the positive phase third harmonic and the negative phase third harmonic.

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

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

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

5. 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 connected in series to the power line and converting DC power from the DC power supply into three-phase AC power; 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; separating the command voltage into a positive-phase component and a negative-phase component, calculating 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, and calculating 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 calculating a superimposed third harmonic that is a third harmonic to be superimposed on the command voltage by synthesizing the positive-phase third harmonic and the negative-phase third harmonic; The method for controlling a power supply system further comprises: superimposing the superimposed third harmonic on the command voltage.

6. A control program for a power supply system that supplies power from a power system to a load 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 connected in series to the power line and converting DC power from the DC power supply into three-phase AC power; 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 third harmonic superimposing unit that calculates a third harmonic to be superimposed on the command voltage based on the command voltage and superimposes the third harmonic on the command voltage; a third harmonic superimposing unit that 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 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.

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