Power supply system and method for controlling the power supply system

Abstract

A power supply system and a control method thereof are provided that prevent a power converter from stopping due to an overcurrent by preventing magnetic flux saturation in a transformer interposed between a power system and a load. [Solution] A power supply system that supplies power from a power system to a load via a transformer 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 via a transformer. The power supply system includes a switch S that is provided on a power line P for supplying power from the power system S to a load L and opens and closes the power line, a power converter 4 that is connected to the power line and converts DC power from the DC power source into AC power, and a power converter control unit 85 that controls the voltage output by the power converter when the power system is abnormal. The power converter control unit includes a voltage compensation control unit 852 that performs voltage compensation control, which is control that causes the power converter to output a compensation voltage that compensates for the voltage of the load when the switch is opened when the power system is abnormal.

Description

[Technical field]

[0001] The present invention relates to a power supply system and a method for controlling 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, the circuit breaker is closed, power is supplied from the power system via the transformer to the load, 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. Since the load voltage drops when the circuit breaker is opened, after the circuit breaker is opened, the power converter converts the DC power from the energy storage unit into AC power and supplies the AC power to the load. In this way, the above power supply system compensates for the load voltage when the power system is abnormal.

[0004] In the above power supply system, the load voltage drops from when the power system abnormality occurs until the breaker is completely opened, causing an imbalance in the transformer's magnetic flux. If the load voltage is compensated for in a state where the transformer's magnetic flux is biased, the transformer's magnetic flux saturates and an excitation current flows. This can cause the power converter to shut down due to an overcurrent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6677916 Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, the present invention has been made in consideration of the above problems, and has as its main object to prevent the power converter from stopping due to an overcurrent by preventing magnetic flux saturation of a transformer interposed between the power system and the load when compensating for the load voltage after the switch has been completely opened. [Means for solving the problem]

[0007] 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 via a transformer 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 via the transformer, and is characterized in that it comprises: 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 power converter that is connected to the power line and converts DC power from the DC power source to AC power; and a power converter control unit that controls a voltage output by the power converter when the power system is abnormal, and the power converter control unit comprises a voltage compensation control unit that performs voltage compensation control, which is control for causing the power converter to output a compensation voltage that compensates for the voltage of the load when opening of the switch is completed when the power system is abnormal; and a magnetic flux change correction unit that, when the voltage compensation unit performs the voltage compensation control, causes the power converter to output a correction voltage that corrects the load magnetic flux change, which indicates a change in magnetic flux of the load from the occurrence of the abnormality in the power system to the completion of opening of the switch, to be equal to or less than a predetermined value.

[0008] In such a power supply system, the magnetic flux change correction unit outputs a correction voltage to the power converter to correct the load magnetic flux change so that the load magnetic flux change is equal to or less than a predetermined value, thereby preventing magnetic flux saturation in the transformer between the power system and the load. As a result, the generation of an excitation current can be prevented, and therefore the power converter can be prevented from stopping due to an overcurrent.

[0009] Outputting a correction voltage that makes the load magnetic flux change zero can prevent magnetic flux saturation in the load transformer. However, compared to a correction voltage that makes the load magnetic flux change other than zero, the correction voltage becomes larger, and there is a risk of an overvoltage being output from the power converter. Therefore, it is preferable that the magnetic flux change correction unit corrects the load magnetic flux change so that the load magnetic flux change is greater than 0 and the magnetic flux of the load is smaller than the saturation magnetic flux of the load.

[0010] With this configuration, it is possible to prevent magnetic flux saturation of the load, and also to prevent an overvoltage from being output from the power converter to the load.

[0011] It is preferable that the power converter control unit further includes a current interruption control unit that performs current interruption control, which is control to interrupt the load from the power system when an abnormality occurs in the power system, and a control switching unit that switches the voltage compensation control after completion of the current interruption control, and that the magnetic flux change correction unit outputs the correction voltage to the power converter at the same time that the control switching unit switches from the current interruption control to the voltage compensation control.

[0012] With this configuration, the magnetic flux change correction unit outputs a correction voltage to the power converter at the same time that the control switching unit switches from current interruption control to voltage compensation control, thereby making it possible to more reliably prevent magnetic flux saturation of the load.

[0013] It is preferable that the power supply voltage measuring unit further includes a load voltage measuring unit that measures a voltage of the load, and the magnetic flux change correction unit calculates the load magnetic flux change based on the difference between the voltage of the load when the power system is assumed to be normal and the voltage of the load measured by the load voltage measuring unit.

[0014] With this configuration, the magnetic flux change correction unit calculates the load magnetic flux change based on the difference between the load voltage when the power system is assumed to be normal and the load voltage measured by the load voltage measuring unit, thereby making it possible to accurately calculate the load magnetic flux change.

[0015] Since the power converter is controlled to output a correction voltage in addition to a conventional compensation voltage, the absolute value of the voltage output by the power converter becomes larger by the amount of the correction voltage. Therefore, in order to prevent an overvoltage from being output from the power converter to a load, it is preferable to further include a voltage limiting unit that limits the output voltage of the power converter, which is the sum of the compensation voltage and the correction voltage, within a predetermined range.

[0016] A specific embodiment of the voltage limiting unit is one in which the upper limit value of the voltage limiting unit is 1.1 times the rated voltage of the power converter, and the lower limit value of the voltage limiting unit is -1.1 times the rated voltage of the power converter.

[0017] A control method for a power supply system that supplies power from the power system to a load via a transformer 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 via the transformer, the power supply system being provided on a power line for supplying power from the power system to the load and including a switch for opening and closing the power line, and a power converter connected to the power line and for converting DC power from the DC power supply to AC power, the control method for the power supply system including performing voltage compensation control, which is control for causing the power converter to output a compensation voltage that compensates for a voltage of the load when opening of the switch is completed when the power system is abnormal, and, when performing the voltage compensation control, causing the power converter to output a compensation voltage that corrects the load magnetic flux change, which indicates a change in magnetic flux of the load from the occurrence of the abnormality in the power system to the completion of opening of the switch, so that the load magnetic flux change is equal to or less than a predetermined value.

[0018] With this configuration, it is possible to obtain the same effects as the power supply system described above. Effect of the Invention

[0019] According to the present invention configured in this manner, when compensating for the load voltage after the switch has been completely opened, magnetic flux saturation of the transformer interposed between the power system and the load can be prevented, thereby preventing the power converter from shutting down due to an overcurrent. [Brief description of the drawings]

[0020] [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 schematic diagram showing functional blocks of a power converter control unit in the present embodiment. [Figure 4] 5A to 5C are schematic diagrams showing a method of correcting a magnetic flux change in the present embodiment. [Diagram 5] 13 shows a simulation result in this embodiment. [Figure 6] 13 shows a simulation result in this embodiment. [Figure 7] 13 shows a simulation result in this embodiment. [Figure 8] 13 shows a simulation result in a conventional example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] 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.

[0022] <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 in the electric power system S, such as a momentary sag, occurs, 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. In this embodiment, a load transformer Tr interposed between the electric power system S and the load L is provided on the power line P.

[0023] Specifically, as shown in FIG. 1 , the power supply system 100 includes a switch 2 that cuts off the power supply from a power system S to a load L, a DC power supply 3 that outputs DC power, a power converter 4 that converts the DC power of the DC power supply 3 into 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 load voltage measuring unit 6 that measures the load voltage that is the voltage of the load L, 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 power converter 4.

[0024] 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 AC power from the power system S to the load L is cut off, and when the switch 2 is closed, AC power is supplied from the power system S to the load L. As shown in Fig. 1, the low-voltage side of the switch 2 is connected to a load transformer Tr. Note that the switch 2 in this embodiment may be a semiconductor switch or a mechanical switch.

[0025] The DC power supply 3 is a battery such as a lead storage battery or 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 discharges and outputs DC power.

[0026] The 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 to supply the power to the load L. In this embodiment, the AC power output from the power converter 4 is supplied to the power line P via an injection transformer T. Note that although the power converter 4 is a single-phase inverter in this embodiment, it may be a three-phase inverter.

[0027] 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 measured 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.

[0028] The load voltage measuring unit 6 is provided on the low-voltage side of the switch 2 and on the primary side of the load transformer Tr. A measured load voltage, which is a load voltage measured by the load voltage measuring unit 6, is output to a parameter acquiring unit 81, which will be described later.

[0029] 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.

[0030] 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 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 power converter control unit 85 that controls the power converter 4.

[0031] 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 measured system voltage measured by the system voltage measuring unit 5, the measured load voltage measured by the load 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 measured system voltage and the measured load voltage.

[0032] 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.

[0033] The closing command output unit 83 judges whether the abnormality in the power system S has been recovered from based on the measured system voltage, and when it is judged that the abnormality in the power system S has been recovered from, 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 recovered from, and outputs a closing command to the switch control unit 84.

[0034] 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.

[0035] 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.

[0036] 3, the 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 voltage compensation control unit 852 that performs voltage compensation control, which is control for causing the power converter 4 to output 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 control switching unit 853 that switches between the current interruption control and the voltage compensation control, a magnetic flux change correction unit 854 that causes the power converter 4 to output a correction voltage that corrects the load magnetic flux change Δφ, which indicates a change in the magnetic flux of the load L from the occurrence of an abnormality in the power system S to the completion of the opening of the switch 2, to be equal to or less than a predetermined value when the voltage compensation control unit 852 performs the voltage compensation control, and a voltage limiting unit 855 that limits the voltage output by the power converter 4 to a predetermined range. 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.

[0037] The current cut-off control unit 851 performs feedback control of the current output from the power converter 4 in response to the output of the opening command so as to make the current flowing through the switch 2 zero. Specifically, the current cut-off 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. Then, the current cut-off control unit 851 multiplies the difference by a proportional gain Kp and causes the power converter 4 to output a voltage calculated by the multiplication.

[0038] The voltage compensation control unit 852 outputs a compensation voltage based on the difference between a voltage command value to be output by the power converter 4 in order to make the load voltage a predetermined voltage and the measured system voltage of the system voltage measurement unit 5. Note that the voltage command value used when the voltage compensation control unit 852 outputs the compensation voltage may be, but is not limited to, a voltage command value for making the load voltage equivalent to, for example, a rated voltage.

[0039] The control switching unit 853 switches from the current cutoff control to the voltage compensation control after the current cutoff control is completed. After the current cutoff control is completed here means that the opening of the switch 2 in the current cutoff control is completed.

[0040] As shown in Fig. 3, the magnetic flux change correction unit 854 calculates the load magnetic flux change Δφ based on the difference between an assumed load voltage, which is the voltage of the load L when it is assumed that the power system S is normal, and the measured load voltage of the load voltage measurement unit 6. Specifically, as shown in Figs. 3 and 4, the magnetic flux change correction unit 854 calculates the load magnetic flux change Δφ by integrating the difference between the assumed load voltage (the load voltage shown by the dashed line in Fig. 4) and the measured load voltage (the load voltage shown by the solid line in Fig. 4) from the time when an abnormality occurs in the power system S until the voltage compensation control unit 852 starts the voltage compensation control. Then, the magnetic flux change correction unit 854 calculates the correction voltage by, for example, performing PI control based on the deviation between the load magnetic flux change Δφ and a load magnetic flux change target value, which is a target value for preventing magnetic flux saturation of the load L.

[0041] Here, the magnetic flux change correction unit 854 calculates the correction voltage so that the load magnetic flux change Δφ is greater than 0 and the magnetic flux of the load L is smaller than the saturation magnetic flux of the load L. Specifically, as shown in Fig. 3 and Fig. 4, the magnetic flux change correction unit 854 calculates the correction voltage so that the load magnetic flux change Δφ during voltage compensation control is equal to or less than a predetermined value a at which magnetic flux saturation of the load L does not occur. Note that when the load magnetic flux change Δφ is equal to or less than the predetermined value a, the magnetic flux change correction unit 854 does not need to calculate the correction voltage.

[0042] 3, the voltage limiting unit 855 limits the output voltage of the power converter 4, which is the sum of the compensation voltage and the correction voltage, to a predetermined range. The predetermined range here has a lower limit value, for example, -1.1 times the rated voltage of the power converter 4, and an upper limit value, for example, 1.1 times the rated voltage of the power converter 4. If the output voltage is within the predetermined range, the voltage limiting unit 855 causes the power converter 4 to output the output voltage, and if the output voltage is outside the predetermined range, the voltage limiting unit 855 causes the power converter 4 to output a voltage of the lower limit value or a voltage of the upper limit value.

[0043] <Power supply system control operation> Next, the control operation of the power supply system 100 will be described.

[0044] (1) Power system S in normal operation The measured system voltage measured by the system voltage measuring unit 5 is output to the opening command output unit 82. The opening command output unit 82 compares the measured system voltage with a predetermined value.

[0045] When the power system S is normal, the switch 2 is turned on. Therefore, AC power is supplied from the power system S to the load L.

[0046] (2) When an abnormality occurs in power system S For example, when a voltage sag occurs and the system voltage falls below a predetermined value, the opening command output unit 82 determines that an abnormality has occurred in the power system S, and outputs an opening command to the switch control unit 84.

[0047] 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 cut-off control unit 851 controls the current output from the power converter 4 so as to make the current flowing through the switch 2 zero.

[0048] Here, from when the opening command is output until the opening of the switch 2 is completed, the magnetic flux of the load transformer Tr decreases with the occurrence of a momentary sag, as shown in Fig. 4. The magnetic flux change correction unit 854 calculates the load magnetic flux change Δφ based on the deviation between the assumed load voltage and the measured load voltage.

[0049] 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 control switching unit 853 switches from current cut-off control to voltage compensation control. As a result, the current cut-off control unit 851 completes the current cut-off control, and the voltage compensation control unit 852 calculates a compensation voltage and starts voltage compensation control.

[0050] At the same time that the control switching unit 853 switches from the current cutoff control to the voltage compensation control, the magnetic flux change correction unit 854 outputs a correction voltage so that the load magnetic flux change Δφ becomes equal to or smaller than a predetermined value a. Specifically, at the same time that the voltage compensation control unit 852 starts the voltage compensation control, the power converter 4 is controlled to output a correction voltage and a compensation voltage.

[0051] When the compensation voltage and the correction voltage are output, the voltage limiting unit 855 limits the output voltage so that the output voltage obtained by adding the compensation voltage and the correction voltage falls within a predetermined range. This causes the power converter 4 to output an output voltage within the predetermined range, or a voltage at the upper limit or lower limit of the predetermined range.

[0052] When the voltage of the load L is compensated and the power system S is restored from the abnormality, the power supply command output unit 83 outputs a power supply command. In response to the output of the power supply command, the switch control unit 84 closes the switch 2.

[0053] 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 power converter 4 is completed.

[0054] <Simulation results> Next, voltage and current waveforms in various power supply systems are shown by simulation. The accident condition in the following simulation is a three-phase short circuit accident with a momentary sag in which the voltage of the power system S drops by 100%.

[0055] Fig. 5 shows the simulation results when magnetic flux change correction unit 854 outputs a correction voltage to power converter 4 so as to make load magnetic flux change Δφ zero. In Fig. 5, the correction voltage is simply calculated so as to make load magnetic flux change Δφ zero, and no voltage limit is imposed on power converter 4. As shown in Fig. 5, it can be seen that by making load magnetic flux change Δφ zero, the bias of magnetic flux in load L is eliminated, and no excitation current is generated from power converter 4.

[0056] FIG. 6 shows a simulation result in the case where the magnetic flux change correction unit 854 outputs a correction voltage to the power converter 4 so that the load magnetic flux change Δφ is equal to or less than a predetermined value a at which magnetic flux saturation of the load L does not occur. In FIG. 6, the correction voltage is calculated only so that the load magnetic flux change Δφ is equal to a, and no voltage limiting is performed on the power converter 4. As shown in FIG. 6, it can be seen that by setting the load magnetic flux change Δφ to equal to or less than the predetermined value a, the magnetic flux bias of the load L is eliminated, and no excitation current is generated from the power converter 4. In addition, compared to the case where the power converter 4 outputs a correction voltage so that the load magnetic flux change Δφ is 0, the correction voltage is reduced, thereby reducing the voltage applied to the load L, and it was confirmed that the overvoltage of the load can be improved.

[0057] 7 shows the simulation results when the magnetic flux change correction unit 854 outputs a correction voltage to the power converter 4 so that the load magnetic flux change Δφ is equal to or less than the predetermined value a at which magnetic flux saturation of the load L does not occur, and the voltage limiting unit 855 limits the output voltage of the power converter 4. As shown in FIG. 7, it is understood that by setting the load magnetic flux change Δφ to equal to or less than the predetermined value a, the bias of the magnetic flux of the load L is eliminated and no excitation current is generated from the power converter 4. In addition, it was confirmed that the overvoltage of the load can be improved compared to the case where the voltage limiting unit 855 does not limit the output voltage of the power converter 4.

[0058] Fig. 8 shows the results of a simulation in which the load voltage is compensated for without correcting the load magnetic flux change Δφ, as in the conventional case. As shown in Fig. 8, the magnetic flux of the load transformer Tr becomes saturated, and an excitation current is generated. This causes an overcurrent to flow in the power converter 4, which may cause the power converter 4 to stop.

[0059] <Effects of this embodiment> According to the power supply system 100 of this embodiment, the magnetic flux change corrector 854 causes the power converter 4 to output a correction voltage so that the load magnetic flux change Δφ is equal to or smaller than a predetermined value, thereby preventing magnetic flux saturation of the transformer interposed between the power system S and the load L. As a result, generation of an excitation current can be prevented, and therefore, the power converter 4 can be prevented from stopping due to an overcurrent.

[0060] According to the power supply system 100 of this embodiment, the load magnetic flux change Δφ is corrected so that the load magnetic flux change Δφ is greater than 0 and the magnetic flux of the load L is smaller than the saturation magnetic flux of the load L, thereby preventing magnetic flux saturation of the load L and preventing an overvoltage from being output from the power converter 4 to the load L.

[0061] The magnetic flux change correction unit 854 calculates the load magnetic flux change Δφ based on the difference between the assumed load voltage when it is assumed that the power system S is normal and the measured load voltage, so that it is possible to accurately calculate the load magnetic flux change Δφ when the power system S is abnormal.

[0062] Since the voltage limiting unit 855 limits the output voltage of the power converter 4, which is the sum of the compensation voltage and the correction voltage, to within a predetermined range, it is possible to prevent an overvoltage from being output from the power converter 4 to the load L.

[0063] <Other embodiments> The present invention is not limited to the above-described embodiment.

[0064] In the above embodiment, the magnetic flux change correction unit 854 calculates the correction voltage so that the load magnetic flux change Δφ during voltage compensation control is equal to or less than the predetermined value a at which magnetic flux saturation of the load L does not occur, but the value by which the load magnetic flux change Δφ is corrected is not limited to this. For example, in order to eliminate bias in the magnetic flux of the load transformer Tr, the magnetic flux change correction unit 854 may correct the load magnetic flux change Δφ so as to make the load magnetic flux change Δφ zero.

[0065] In the above embodiment, the magnetic flux change correction unit 854 outputs the correction voltage to the power converter 4 at the same time that the control switching unit 853 switches from current interruption control to voltage compensation control, but the timing at which the magnetic flux change correction unit 854 outputs the correction voltage to the power converter 4 is not limited to this. If the load transformer Tr does not become magnetically saturated, the magnetic flux change correction unit 854 may output the correction voltage to the power converter 4 after a predetermined time has elapsed since the start of voltage compensation control.

[0066] In the above embodiment, the power converter control unit 85 includes the voltage limiting unit 855, but it is not necessary to include the voltage limiting unit 855. Even in this case, the magnetic flux change correcting unit 854 causes the power converter 4 to output a correction voltage, thereby making it possible to prevent magnetic flux saturation of the load transformer Tr interposed between the power system S and the load L.

[0067] In the above embodiment, the power supply system 100 is configured to include a system voltage measuring unit 5, a load voltage measuring unit 6, and a switch current measuring unit 7, but the load voltage measuring unit 6 and the switch current measuring unit 7 may be provided separately from the power supply system 100.

[0068] 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]

[0069] 100 Power System 2 Switch 3...DC power supply 4. Power Converter 5. System voltage measurement section 6 Load 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 Power converter control section 851 Current interruption control unit 852 Compensation voltage calculation unit 853 Control switching unit 854 Magnetic flux change compensation unit 855 Voltage limiter S...Power system L...Load P...Power line

Claims

1. A power supply system that supplies power from a power system to a load via a transformer 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 source to the load via the transformer, 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 power converter connected to the power line and converting DC power from the DC power supply into AC power; a power converter control unit that controls a voltage output by the power converter when an abnormality occurs in the power grid, The power converter control unit a voltage compensation control unit that performs voltage compensation control, which is control for causing the power converter to output a compensation voltage that compensates for a voltage of the load, when the opening of the switch is completed during an abnormality in the power system; a magnetic flux change correction unit that, when the voltage compensation control unit performs the voltage compensation control, causes the power converter to output a correction voltage that corrects the load magnetic flux change, such that a load magnetic flux change indicating a change in the magnetic flux of the load from the occurrence of an abnormality in the power system to the completion of opening of the switch is greater than 0 and the magnetic flux of the load is smaller than a saturation magnetic flux of the load.

2. The power converter control unit includes a current interruption control unit that performs current interruption control, which is control for interrupting the load from the power system when an abnormality occurs in the power system; A control switching unit that switches the voltage compensation control after the current interruption control is completed, The power supply system according to claim 1 , wherein the magnetic flux change correction unit causes the power converter to output the correction voltage at the same time that the control switching unit switches from the current cut-off control to the voltage compensation control.

3. A load voltage measurement unit for measuring a voltage of the load is further provided, The magnetic flux change correction unit includes:

2. The power supply system according to claim 1, wherein the load magnetic flux change is calculated based on a difference between a voltage of the load when the power system is assumed to be normal and a voltage of the load measured by the load voltage measuring unit.

4. 4. The power supply system according to claim 1, further comprising a voltage limiting unit that limits an output voltage of the power converter, which is a sum of the compensation voltage and the correction voltage, to within a predetermined range.

5. 5. The power supply system according to claim 4, wherein an upper limit value in the voltage limiting unit is a value 1.1 times a rated voltage of the power converter, and a lower limit value in the voltage limiting unit is a value -1.1 times a rated voltage of the power converter.

6. A control method for a power supply system, in which power is supplied from a power system to a load via a transformer when the power system is normal, and power supply from the power system to the load is cut off when an abnormality occurs in the power system, and power is supplied from a DC power source to the load via the transformer, 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 power converter connected to the power line to convert DC power from the DC power supply into AC power; The method for controlling a power supply system includes: performing a voltage compensation control that causes the power converter to output a compensation voltage that compensates for a voltage of the load when the opening of the switch is completed during an abnormality in the power system; a control method for a power supply system, causing the power converter to output a correction voltage that corrects the load magnetic flux change, which indicates a change in magnetic flux of the load from the occurrence of an abnormality in the power system to the completion of opening of the switch, so that the load magnetic flux change is greater than 0 and is smaller than a saturation magnetic flux of the load, when the voltage compensation control is performed.

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