Power supply system

Abstract

To suppress a load overvoltage generated when a system voltage is recovered, in a power supply system for compensating for reduction in the system voltage from a power converter.SOLUTION: A power supply system includes: an on-off switch that opens and closes a power line for supplying power from a power system to a load; a power converter that is connected to the power line so as to be parallel to the on-off switch, converts DC power into AC power, and supplies the AC power to the load; an AC filter provided between the power converter and the power line so as to be in parallel with the on-off switch; a reactor element connected so as to be in parallel with the on-off switch and in series with the AC filter; and a control unit configured to control the on-off switch and the power converter. When abnormality occurs in the power system, the control unit opens the on-off switch and drives the power converter to perform compensation control for compensating for decrease in a voltage of the load, and when the power system recovers, closes the on-off switch and stops the power converter.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power supply system. [Background technology]

[0002] Conventionally, power supply systems have been proposed that control a power converter to disconnect the power supply from the power system and compensate for a load in the event of a power outage or momentary voltage drop (hereinafter also referred to as a voltage drop). As shown in Patent Document 1, for example, this type of power supply system opens an open / close switch that opens and closes a power line connecting the power system and the load when a voltage drop or other such abnormality occurs in the power system, and drives a power converter provided in parallel with the open / close switch via an injection transformer to supply a compensating voltage equivalent to the voltage drop in the power system to the load, thereby compensating for a drop in the load voltage. When the power system is restored, this type of power supply system closes the open / close switch again and stops the power converter to block the gate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Utility model registration No. 2578802 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, some of the power supply systems described above have an AC filter connected in parallel to the open / close switch on the primary side of the injection transformer (i.e., between the injection transformer and the power line) to absorb harmonic currents that are generated when converting between AC and DC. In such power supply systems, when power is restored to the power system, a surge current caused by a steep recovery voltage flows to the load via the AC filter. At this time, due to measurement delays and delays caused by the inductance of the injection transformer, the compensation voltage from the power converter cannot keep up with the sudden increase in system voltage, which can result in a load overvoltage.

[0005] Therefore, the present invention has been made in consideration of the above problems, and has as its main object to suppress a load overvoltage that occurs when the system voltage recovers in a power supply system that compensates for a drop in the system voltage from a power converter. [Means for solving the problem]

[0006] That is, the power supply system of the present invention includes an open / close switch that opens and closes a power line for supplying power from the power system to the load, a power converter connected to the power line so as to be in parallel to the open / close switch and that converts DC power to AC power for supplying power to the load, an AC filter provided between the power converter and the power line so as to be in parallel to the open / close switch, a reactor element connected in parallel to the open / close switch and in series to the AC filter, and a control unit that controls the open / close switch and the power converter, wherein when an abnormality occurs in the power system, the control unit opens the open / close switch and drives the power converter to perform compensation control to compensate for a voltage drop in the load, and when power is restored to the power system, the control unit closes the open / close switch and stops the power converter.

[0007] Such a power supply system includes a reactor element connected in parallel to the open / close switch and in series to the AC filter. Therefore, when power is restored to the power system, the surge current associated with the steep recovery voltage can be absorbed by the reactor element, thereby suppressing the load overvoltage that occurs when the system voltage is restored.

[0008] A specific embodiment of the power supply system in which the effects of the present invention are prominently exhibited is one in which the power converter is provided in parallel with the open / close switch via an injection transformer, and the AC filter is provided between the injection transformer and the power line. Effect of the Invention

[0009] According to the present invention thus configured, in a power supply system in which a drop in system voltage is compensated for by a power converter, it is possible to suppress a load overvoltage that occurs when the system voltage is restored. [Brief description of the drawings]

[0010] [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. 13 is a diagram showing a simulation result using a conventional power supply system. [Diagram 3] FIG. 13 is a diagram showing a simulation result using a conventional power supply system. [Figure 4] FIG. 4 is a diagram showing a simulation result using the power supply system of the embodiment. [Diagram 5] FIG. 4 is a diagram showing a simulation result using the power supply system of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a power supply system according to the present invention will be described with reference to the drawings.

[0012] As shown in Fig. 1, a power supply system 100 in this embodiment is provided between a power system 10 and a load 20, and supplies power to the load 20. In this embodiment, when the power system 10 is normal, the power supply system 100 electrically connects the power system 10 and the load 20, thereby supplying power from the power system 10 to the load 20. On the other hand, when an abnormality such as a power outage or an instantaneous voltage drop (hereinafter also referred to as a momentary sag) occurs in the power system 10, the power supply system 100 cuts off the power supply from the power system 10 to the load 20, and compensates for the voltage drop of the load 20. Note that the power supply system 100 in this embodiment supplies three-phase power, but the number of phases is not particularly limited.

[0013] Specifically, the power supply system 100 includes an open / close switch 3 that opens and closes a power line L for supplying power from a power system 10 to a load 20, a system voltage measurement unit 4 that measures a system voltage that is the voltage of the power system 10, a switch current measurement unit 5 that measures a switch current that is a current flowing through the open / close switch 3, a power converter 6 that is connected to the power line L in parallel with the open / close switch 3, and a control unit 7 that controls the open / close switch 3 and the power converter 6. Each unit will be described below.

[0014] The open / close switch 3 is provided on the power line L, and when the open / close switch 3 is turned on, the power system 10 and the load 20 are electrically connected, and when the open / close switch 3 is turned off, the power system 10 and the load 20 are electrically disconnected. In this embodiment, the open / close switch 3 is a thyristor switch, and the thyristor switch is turned on or off by a control unit 7 described later controlling the power converter 6. However, the open / close switch 3 is not limited to this, and may be a semiconductor switch, a mechanical switch, or a hybrid switch of these.

[0015] The system voltage measuring unit 4 is connected to the power line L via a potential transformer, and measures the voltage on the power system 10 side of the open / close switch 3. Specifically, the system voltage measuring unit 4 is connected via a potential transformer to the power system 10 side of the parallel circuit made up of the open / close switch 3 and the power converter 6. The system voltage obtained by the system voltage measuring unit 4 is input to a control unit 7, which will be described later, and is used to control the open / close switch 3 and the power converter 6.

[0016] The switch current measuring unit 5 is provided in a parallel circuit made up of the open / close switch 3 and the power converter 6, and measures the switch current. Specifically, the switch current measuring unit 5 measures the current flowing through the power line L in which the open / close switch 3 is provided, in the parallel circuit made up of the open / close switch 3 and the power converter 6.

[0017] The power converter 6 is provided in parallel with the open / close switch 3 via an injection transformer T, and converts DC power from a power storage device (not shown) such as a secondary battery (storage battery) into AC power. The power converter 6 is configured using, for example, a plurality of semiconductor switching elements, and is controlled by a control unit 7.

[0018] Furthermore, an AC filter 8 connected in parallel to the open / close switch 3 is provided between the injection transformer T and the power line L. That is, the AC filter 8 is connected in parallel to the open / close switch 3 and the power converter 6, and is provided on the power line L side of the injection transformer T (i.e., the primary side of the injection transformer T). This AC filter 8 absorbs harmonic currents generated when AC and DC are converted in the power converter 6, and is composed of a resistor element 81 and a capacitor element 82 connected in series to each other.

[0019] In this embodiment, a reactor element 9 for suppressing load overvoltage is provided between the open / close switch 3 and the AC filter 8. The reactor element 9 is connected in parallel to the open / close switch 3 and in series to the AC filter 8. The reactor element 9 may be provided on the power system 10 side of the AC filter 8, or on the load 20 side.

[0020] The control unit 7 controls the open / close switch 3 and the power converter 6. Here, the control unit 7 is a general-purpose or dedicated computer equipped with a CPU, memory, input / output interface, etc., and performs the following functions by making the CPU and peripheral devices cooperate in accordance with a predetermined program stored in the memory.

[0021] When an abnormality occurs in the power system 10, the control unit 7 performs voltage compensation control by controlling the open / close switch 3 and the power converter 6. Specifically, the control unit 7 acquires the system voltage of the power system 10 from the system voltage measurement unit 4, and when the acquired system voltage is outside a predetermined range, it determines that an abnormality has occurred in the power system 10 and starts controlling the open / close switch 3 and the power converter 6. Note that in this embodiment, the control unit 7 performs PWM control by repeatedly turning the power converter 6 on and off to control the voltage output from the power converter 6, but is not limited to this. Hereinafter, a control operation of the control unit 7 when an abnormality occurs in the power system 10 will be described.

[0022] Specifically, when an abnormality (specifically, a drop in the system voltage) occurs in the power system 10, the control unit 7 opens the open / close switch 3 and performs voltage compensation control to compensate for the drop in the system voltage from the power converter 6. The control unit 7 outputs a switch open signal to open the open / close switch 3 to the drive circuit, and opens the open / close switch 3. Then, when the current value (current value flowing through the open / close switch 3) acquired from the switch current measurement unit 5 becomes 0 A, the control unit 7 determines that the opening of the open / close switch 3 is complete. Then, the control unit 7 calculates a power command value based on the difference between a target value (for example, a target value) of the load voltage and the system voltage, and controls the power converter 6 to output the calculated power command value.

[0023] Then, the control unit 7 controls the open / close switch 3 and the power converter 6 to close the open / close switch 3 when the system voltage is restored. Specifically, the control unit 7 determines whether power has been restored to the power system 10 based on the system voltage measured by the system voltage measurement unit 4. The restoration of power to the power system 10 means that the system voltage remains equal to the rated voltage for a certain period of time. When the control unit 7 determines that power has been restored to the power system 10, it closes the open / close switch 3 and gates the power converter 6. Specifically, the control unit 7 closes the open / close switch 3 to electrically connect the power system 10 and the load 20, and stops the power converter 6 to reduce the current output by the power converter 6 to zero.

[0024] Here, the results of a simulation using a power supply system for comparison in the conventional example and the results of a simulation using the power supply system 100 in this embodiment are shown. As the power supply system for comparison, a power supply system 100 in this embodiment was used that does not include the reactor element 9 that is connected in parallel to the open / close switch 3 and in series to the AC filter 8. In addition, each simulation was started from a normal state in which the open / close switch 3 is closed, an abnormality was generated in the system voltage, the open / close switch 3 was opened, and the power converter 6 was driven to perform voltage compensation control, and then the system voltage was restored and the open / close switch 3 was turned on again.

[0025] 2 and 3, in a conventional power supply system not including the reactor element 9, a surge current occurs due to a steep recovery voltage when the system voltage is restored, causing a load overvoltage. It can also be seen that the current flowing through the AC filter (filter C current) increases rapidly, and the slope of the capacitor charge is steep.

[0026] In contrast, in the power supply system 100 of this embodiment, as shown in Figures 4 and 5, it is understood that the surge current accompanying the recovery voltage can be suppressed at the timing when the system voltage is restored, and the occurrence of load overvoltage can be suppressed. It can also be confirmed that the slope of the capacitor charge in the AC filter 8 becomes gentler, and the sudden increase in the load voltage can be suppressed.

[0027] The power supply system 100 of this embodiment configured as described above includes the reactor element 9 connected in parallel to the open / close switch 3 and in series to the AC filter 8. Therefore, when power is restored to the power grid 10, the surge current associated with the steep recovery voltage can be absorbed by the reactor element 9, thereby making it possible to suppress the load overvoltage that occurs when the grid voltage is restored.

[0028] The present invention is not limited to the above-described embodiment.

[0029] For example, in the above embodiment, the power supply system 100 is configured to include the switch current measuring unit 5, but may be configured not to include the switch current measuring unit 5. For example, the power supply system 100 may cause the switch current to converge to 0 A or to intersect with 0 A.

[0030] 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]

[0031] 100 Power Supply System 10...Electric power system 20 Load 3 Open / Close Switch 4. System voltage measurement section 5 Switch current measurement section 6 Power Converter 7 Control section 8. AC Filter 9. Reactor element L...Power line

Claims

1. an open / close switch that opens and closes a power line for supplying power from the power system to the load; a power converter connected to the power line in parallel with the open / close switch, converting DC power into AC power and supplying the AC power to the load; an AC filter provided between the power converter and the power line so as to be in parallel with the open / close switch; A reactor element connected in parallel to the open / close switch and in series to the AC filter; A control unit that controls the open / close switch and the power converter, The control unit: When an abnormality occurs in the power system, the open / close switch is opened, and the power converter is driven to perform compensation control for compensating for a voltage drop in the load; The power supply system closes the open / close switch and stops the power converter when power is restored to the power grid.

2. The power converter is provided in parallel with the on-off switch via an injection transformer, 2. The power supply system according to claim 1, wherein the AC filter is provided between the injection transformer and the power line.

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