Power System

Abstract

To provide a power supply system at low cost capable of preventing unnecessary influences to a system and an important load caused by resonance while satisfying an FRT (Fault Ride Through) requirement, and of achieving both an uninterruptible power supply function and a load leveling function using a common dispersion type power supply.SOLUTION: A power supply system comprises: a mechanical switch 2 that opens and closes a power line L1; and a capacitor 31 connected in parallel with the mechanical switch 2. When abnormalities of the commercial power system are detected, the dispersion type power supply 1 continues an operation in a state where the mechanical switch 2 is opened to make the dispersion type power supply 1 and the commercial power system 10 be connected with each other via the capacitor 31. The power supply system further comprises a resonance suppression circuit 8 connected in series or in parallel with the capacitor 31 to suppress resonance between the capacitor 31 and a reactor of the power line L1 or an important load 20.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, a power supply system that satisfies FRT requirements while simultaneously achieving both an uninterruptible power supply function and a load leveling function by using a common distributed power source has been proposed, as shown in Patent Document 1.

[0003] The power supply system of Patent Document 1 is configured by providing a semiconductor switch and an impedance element connected in parallel to the semiconductor switch between the commercial power system and the important load, and providing a distributed power supply on the side of the important load of the semiconductor switch. Also, a parallel-off switch is provided on the commercial power system side of the semiconductor switch. When an instantaneous voltage drop or frequency fluctuation occurs in the commercial power system, this power supply system opens the semiconductor switch to connect the commercial power system and the distributed power supply via the impedance element, and the distributed power supply continues to operate including reverse power flow (FRT operation). On the other hand, when a power outage occurs in the commercial power system, the system recognizes the instantaneous voltage drop for a certain period of time (for example, 2 seconds) and performs FRT operation, and then recognizes the power outage and further opens the parallel-off switch, allowing the distributed power supply to operate independently. In this way, the system is able to achieve both an uninterruptible power supply function and a load leveling function by using a common distributed power supply while satisfying the FRT requirements. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6338131 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-mentioned power supply system uses expensive semiconductor switches to switch the power lines on and off, which increases the cost of the system.

[0006] Therefore, in order to provide a low-cost power supply system that satisfies the FRT requirements and achieves both uninterruptible power supply and load leveling functions by using a common distributed power source, the inventors of the present application conducted intermediate studies during the development of the present invention on a system configuration in which a mechanical switch is provided on the power line that supplies power from the commercial power system to important loads and a capacitor is connected in parallel to this mechanical switch, as shown in FIG.

[0007] In such a system, when a momentary voltage drop or frequency fluctuation occurs, the mechanical switch is opened, and the distributed power source and the commercial power grid are connected via a capacitor. This makes it possible to substitute an inexpensive mechanical switch for an expensive semiconductor switch, and to provide a power supply system that satisfies the FRT requirements while simultaneously achieving uninterruptible power supply and load leveling functions using a common distributed power source at low cost, which seemed to solve the above-mentioned problems.

[0008] However, if a distributed power source is connected to the commercial power system via a capacitor when an instantaneous voltage drop or frequency fluctuation occurs in the commercial power system, there is a risk of resonance between the capacitor and the power line or the reactor of the important load. For this reason, if operation is continued during frequency fluctuation, it may have an unnecessary effect on the system and important loads if the resonant frequency coincides with harmonics present in the system or harmonics generated by the distributed power source.

[0009] Therefore, the present invention has been made to solve the above-mentioned problems at once, and its main objective is to provide a power supply system at low cost that satisfies the FRT requirements, prevents unnecessary effects on the grid and important loads due to resonance, and achieves both uninterruptible power supply function and load leveling function by using a common distributed power source. [Means for solving the problem]

[0010] That is, the power supply system of the present invention is a power supply system provided between a commercial power system and an important load, and supplies power to the important load, the power supply system comprising: a distributed power source connected to a power line for supplying power from the commercial power system to the important load; a mechanical switch provided on the power line closer to the commercial power system than the distributed power source and configured to open and close the power line; a capacitor connected in parallel to the mechanical switch on the power line; a system side voltage detection unit that detects a voltage on the commercial power system side of the mechanical switch; a system abnormality detection unit that detects an abnormality in the commercial power system from the detected voltage of the system side voltage detection unit; and a control unit that controls power supply to the important load, wherein when an abnormality in the commercial power system is detected by the system abnormality detection unit, the control unit opens the mechanical switch, and the distributed power source continues operation in a state in which the distributed power source and the commercial power system are connected via the capacitor, and the power supply system further comprises a resonance suppression circuit that is connected in series or in parallel to the capacitor and suppresses resonance between the capacitor and the power line or a reactor of the important load.

[0011] In a power supply system configured in this manner, similar to the system configuration shown in Figure 4 above, when an abnormality occurs in the commercial power grid, the mechanical switch is opened and the distributed power source and the commercial power grid are connected via a capacitor, so that expensive semiconductor switches can be substituted with inexpensive mechanical switches. This makes it possible to provide a power supply system at low cost that satisfies the FRT requirements imposed when an abnormality occurs in the commercial power grid while achieving both an uninterruptible power supply function and a load leveling function using a common distributed power source. Furthermore, since the system is equipped with a resonance suppression circuit that suppresses resonance between the capacitor and the power line or the reactor of the important load, even if the resonant frequency matches the harmonics present in the system or the harmonics generated by the distributed power source, it is possible to suppress resonance between the capacitor and the power line or the reactor of the important load, thereby preventing unnecessary effects on the system and important loads. In this way, according to the present invention, it is possible to provide a power supply system at low cost that satisfies the FRT requirements, prevents unnecessary effects on the grid and important loads due to resonance, and achieves both an uninterruptible power supply function and a load leveling function using a common distributed power source.

[0012] A specific embodiment of the resonance suppression circuit includes a resistor element connected in series to the capacitor, and a switching element connected in parallel to the resistor element.

[0013] In such a configuration, a possible control method for the mechanical switch and switching element is to open the mechanical switch and switching element simultaneously when an abnormality is detected in the commercial power system. In this case, however, if the opening of the mechanical switch is delayed compared to the switching element due to variations in the switch opening time, an arc may be generated between the contacts of the switching element, which may shorten the life of the contacts. Therefore, when the system abnormality detection unit detects an abnormality in the commercial power system, it is preferable that the control unit opens the mechanical switch and then opens the switching element. This makes it possible to reliably divert and limit the current to the capacitor when an abnormality occurs in the commercial power system.

[0014] It is preferable that the power supply system further includes a disconnection switch provided on the power line for cutting off power supply from the commercial power system to the important load, and an abnormality judgment unit for determining whether the abnormality detected by the system abnormality detection unit is a frequency fluctuation or a power outage, wherein when the abnormality judgment unit determines that the abnormality detected by the system abnormality detection unit is a frequency fluctuation, the control unit opens the switching element, and the distributed power source continues to operate with the capacitor and the resistance element connected, and when the abnormality judgment unit determines that the abnormality detected by the system abnormality detection unit is a power outage, the control unit opens the disconnection switch and disconnects the important load from the commercial power system. With this configuration, when the abnormality in the commercial power system is a frequency fluctuation, the commercial power system and the distributed power source are linked via the capacitor, and the distributed power source is operated in FRT operation while the capacitor and the resistive element are connected in series, thereby suppressing the above-mentioned resonance. On the other hand, if the abnormality in the commercial power grid is a power outage, the parallel-off switch can be opened to allow the distributed power sources to operate independently. This allows the FRT requirements to be met while also achieving uninterruptible power supply and load leveling functions using a common distributed power source.

[0015] In addition to the above, the FRT requirements also stipulate that when the voltage of the commercial power grid returns to a normal state (hereinafter referred to as power restoration) after a momentary voltage drop occurs, the output of the distributed power source must be restored to 80% within a minimum of 0.1 seconds after power restoration.

[0016] To meet this FRT requirement and restore the output of distributed power sources within 0.1 seconds, the mechanical switches must be precisely controlled; however, mechanical switches are unstable, with closing times ranging from approximately 60 milliseconds to several tens of milliseconds, making precise control difficult in practice.

[0017] Therefore, it is preferable that the power supply system of the present invention further includes a semiconductor switch connected in parallel to the mechanical switch and the capacitor in the power line, and a grid power restoration detection unit that detects the restoration of power to the commercial power system from the detection voltage of the grid side voltage detection unit, and during steady-state operation, the mechanical switch is turned on and the semiconductor switch is opened, and when the grid power restoration detection unit detects the restoration of power to the commercial power system, the control unit turns on the semiconductor switch, and the distributed power source and the commercial power system are connected via the semiconductor switch. With a power supply system configured in this manner, the semiconductor switch is turned on when power is restored to the commercial power grid, making it possible to restore the output of the distributed power source within 0.1 seconds of power restoration, thereby satisfying the FRT requirements imposed when power is restored. Moreover, by connecting the semiconductor switch in parallel with the mechanical switch, it is possible to use elements such as thyristors, which have a simple element structure, high voltage resistance, and large capacity but do not have self-extinguishing ability, as the semiconductor switch. Furthermore, since this semiconductor switch is only turned on and off when power is restored to the commercial power system, the number of times the semiconductor switch is used can be reduced by half compared to the conventional configuration, i.e., the configuration in which the semiconductor switch is turned on and off both when there is an abnormality in the commercial power system and when power is restored, and the life of the semiconductor switch and the system can be extended. These effects lead to reductions in the initial cost and running cost of the power supply system.

[0018] It is preferable that after the semiconductor switch is turned on by the control unit, the mechanical switch is turned on by the control unit, and then the semiconductor switch is opened by the control unit. This allows the semiconductor switch to be opened quickly after the output of the distributed power source is restored, further extending the lifespan of the semiconductor switch, leading to a longer lifespan and lower costs for the system.

[0019] In order to be able to meet even strict FRT requirements imposed when power is restored to a commercial power grid, it is preferable that the semiconductor switch be turned on within 0.1 seconds after the power restoration detection unit detects the restoration of power.

[0020] A specific embodiment of the semiconductor switch is an element that does not have a self-extinguishing ability, such as a thyristor. Effect of the Invention

[0021] According to the present invention configured in this manner, it is possible to provide a power supply system at low cost that satisfies the FRT requirements while preventing unnecessary effects on the grid and important loads due to resonance, and that achieves both an uninterruptible power supply function and a load leveling function by using a common distributed power source. [Brief description of the drawings]

[0022] [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 schematic diagram showing the configuration of a power supply system according to another embodiment. [Diagram 3] FIG. 13 is a schematic diagram showing the configuration of a power supply system according to another embodiment. [Figure 4] FIG. 1 is a schematic diagram showing a system configuration that was intermediately considered during the development of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] 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.

[0024] <Overall system configuration> As shown in FIG. 1 , the power supply system 100 of this embodiment is provided between a commercial power system 10 and important loads 20, and performs a function as an uninterruptible power supply system (uninterruptible power supply function) that supplies power to the important loads 20 in the event of an abnormality in the commercial power system 10, and a function as a distributed power supply system (load leveling function) that levels the load by providing forward and reverse power flows to the commercial power system 10.

[0025] Here, the commercial power system 10 is a power supply network of a power company (electric utility company) and includes a power plant, a power transmission system, and a power distribution system. The important loads 20 are loads that should stably supply power even during system abnormalities such as power outages and voltage drops, and although there is only one important load in FIG. 1, there may be multiple important loads.

[0026] Specifically, the power supply system 100 includes a distributed power source 1, an open / close switch 2 that connects a commercial power system 10 to the distributed power source 1 and an important load 20, a commutation circuit 3 connected in parallel to the open / close switch 2, a disconnection switch 4 for disconnecting the important load 20 from the commercial power system 10, a system side voltage detection unit 5 that detects the voltage on the commercial power system 10 side of the open / close switch 2, a system abnormality detection unit 6 that detects an abnormality in the commercial power system 10 from the detected voltage of the system side voltage detection unit 5, and a control unit 7 that controls power supply to the important load 20.

[0027] The distributed power source 1 is connected to a power line L1 for supplying power from a commercial power system 10 to a critical load 20. This distributed power source 1 is connected to the commercial power system 10, and is, for example, a DC power generation facility such as a solar power generation facility or a fuel cell, a power storage device (power storage device) such as a secondary battery (storage battery), a power generation facility such as a wind power generation facility or a micro gas turbine that rectifies the electrical energy output in AC to DC and then connects to the system using a power conversion device, or an AC power generation facility such as a synchronous generator or an induction generator.

[0028] The open / close switch 2 is provided on the power line L1 closer to the commercial power system 10 than the connection point of the distributed power source 1 to open and close the power line L1, and is specifically a mechanical switch (hereinafter also referred to as the mechanical switch 2). The mechanical switch 2 is driven to open and close for a predetermined contact opening time in response to a signal transmitted from the control unit 7.

[0029] The commutation circuit 3 is configured to allow a current to flow (commutate) when the mechanical switch 2 is opened, and limits this current. Specifically, the commutation circuit 3 is connected in parallel to the mechanical switch 2, and includes a capacitor 31 and a commutation element 32 connected in parallel to each other. Specifically, the capacitor 31 is, for example, a film capacitor, and the commutation element 32 is, for example, an element formed by combining a resistor and a reactor.

[0030] The capacitance of the capacitor 31 is determined so that when the mechanical switch 2 is opened, the current flowing through the mechanical switch 2 is instantly commutated to the commutation circuit 3 without generating an arc, and the mechanical switch 2 can be quickly cut off regardless of the zero point. In other words, the impedance of the capacitor 31 is smaller than the arc resistance of the mechanical switch 2.

[0031] To explain the capacitor 31 of this embodiment more specifically, the rated voltage of the commercial power system 10 is V, the time (also called the transient time) from when the opening (or opening) of the mechanical switch 2 is started until the amount of change in the voltage across the mechanical switch 2 stabilizes is T, and the breaking current (at maximum) that flows when the mechanical switch 2 is opened is i SW Capacitor 31 is configured so that capacitance C of capacitor 31 satisfies the following formula (1). Taking into account errors in each parameter, it is preferable to configure capacitor 31 so that it satisfies formula (1)' with a margin of error. C×(V / T)>i SW (1) C×(V / T)>1.3×i SW ...(1)'

[0032] The parallel-off switch 4 is provided on the power line L1 closer to the commercial power system 10 than the distributed power source 1, and is, for example, a mechanical switch. The parallel-off switch 4 is controlled and driven in response to a signal transmitted from the control unit .

[0033] The system-side voltage detection unit 5 detects the voltage on the power line L1 closer to the commercial power system 10 than the mechanical switch 2 via a voltage transformer. Specifically, the system-side voltage detection unit 5 is connected to the commercial power system 10 side of the parallel circuit made up of the mechanical switch 2 and the commutation circuit 3 via the voltage transformer.

[0034] The system abnormality detection unit 6 compares the detected voltage detected by the system side voltage detection unit 5 with a predetermined set value, and detects an instantaneous voltage drop when the detected voltage is equal to or lower than the set value. The system abnormality detection unit 6 also detects frequency fluctuations (frequency up (OF) and frequency down (UF)) from the detected voltage detected by the system side voltage detection unit 5. The frequency fluctuations are, for example, step up and ramp up / down. The system abnormality detection unit 6 also detects a power outage from the detected voltage detected by the system side voltage detection unit 5. In addition, the system abnormality detection unit 6 may detect at least one of a voltage up, a phase fluctuation, a voltage imbalance, a harmonic abnormality, and a flicker, in addition to an instantaneous voltage drop, a frequency fluctuation, and a power outage.

[0035] The control unit 7 controls operation / stop, opening / closing, etc. of each device included in the power supply system 100.

[0036] Thus, the power supply system 100 of this embodiment further includes a resonance suppression circuit 8 that is connected in series or in parallel to the capacitor 31 and suppresses resonance between the capacitor 31 and the power line L1 or the reactor of the important load 20.

[0037] The resonance suppression circuit 8 of the present embodiment is connected in series with the capacitor 31, and is disposed on the commercial power system 10 side of the mechanical switch 2, between the mechanical switch 2 and the parallel-off switch 4. However, the arrangement of the resonance suppression circuit 8 is not limited to this, and may be, for example, on the important load 20 side of the mechanical switch, or on the commercial power system 10 side of the parallel-off switch.

[0038] Specifically, the resonance suppression circuit 8 has a resistive element 81 serving as a damping element connected in series to the capacitor 31, and a switching element 82 connected in parallel to the resistive element 81.

[0039] <System operation explanation> Next, a specific operation of the control unit 7 will be described.

[0040] The control unit 7 of this embodiment is configured to take a plurality of control modes, including (1) a normal operation mode, (2) a momentary sag / frequency fluctuation mode, and (3) a power outage mode, in response to a signal from the system abnormality detection unit 6. Each control mode will be described below.

[0041] (1) Normal operation mode During normal operation when no system abnormality is detected by the system abnormality detection unit 6, the control unit 7 closes the mechanical switch 2 and the parallel-off switch 4. In this case, the distributed power source 1 and the important load 20 are connected to the commercial power system 10 via the mechanical switch 2. The commutation circuit 3 is connected in parallel to the mechanical switch 2, but since the impedance of the mechanical switch 2 is smaller than the impedance of the commutation circuit 3, power is exchanged between the commercial power system 10 and the distributed power source 1 and the important load 20 via the mechanical switch 2. With this configuration, peak shaving can be achieved by the reverse power flow by the distributed power source 1.

[0042] (2) Mode during instantaneous sag / frequency fluctuation At the time of an instantaneous voltage sag or frequency fluctuation detected by the system abnormality detection unit 6, the control unit 7 opens the mechanical switch 2. Then, with the commercial power system 10, the distributed power source 1, and the important load 20 connected via the commutation circuit 3, operation by the distributed power source 1 continues, and the important load 20 is charged and discharged so that the voltage and frequency of the important load 20 are stabilized, thereby adjusting the power flow balance. Here, the control unit 7 of this embodiment is configured to open the mechanical switch 2 as described above when the system abnormality detection unit 6 detects an abnormality in the commercial power system 10, and then open the switching element 82.

[0043] More specifically, the control unit 7 of this embodiment has a function as an abnormality determination unit 71 that determines whether the abnormality detected by the system abnormality detection unit 6 is a momentary sag / frequency fluctuation or a power outage. When the voltage detected by the system side voltage detection unit 5 satisfies a predetermined parallel-off condition, the abnormality determination unit 71 determines that the abnormality in the commercial power system 10 is a power outage, and determines that the abnormality in the commercial power system 10 is a momentary sag / frequency fluctuation until the parallel-off condition is satisfied. Here, the predetermined parallel-off condition is that the duration of a voltage drop in the system voltage (a state in which the detected voltage is equal to or lower than the set value) is equal to or greater than a predetermined value (a time longer than the duration of the momentary sag).

[0044] In this configuration, when the abnormality judgment unit 71 judges that the abnormality detected by the system abnormality detection unit 6 is a momentary sag or frequency fluctuation, the control unit 7 opens the switching element 82 and causes the distributed power source 1 to continue FRT operation with the capacitor 31 and the resistance element 81 connected.

[0045] (3) Power outage mode In the event of a power outage in which the abnormality determination unit 71 determines that the abnormality detected by the grid abnormality detection unit 6 is a power outage, the control unit 7 opens the parallel-off switch 4 and causes the distributed power source 1 to operate in an independent manner. Specifically, when the voltage detected by the grid side voltage detection unit 5 satisfies the above-mentioned predetermined parallel-off condition, that is, when the duration of the voltage drop of the grid voltage becomes equal to or longer than a predetermined value, the control unit 7 opens the parallel-off switch 4 and disconnects the important load 20 from the commercial power grid 10. When the parallel-off switch 4 is opened, the distributed power source 1 enters an independent operation mode and supplies power to the important load 20. In this way, the distributed power source 1 goes from a normal grid-connected operation to an FRT operation and then enters an independent operation. Note that when the parallel-off switch 4 is opened, the mechanical switch 2 has already been opened, so that the overcurrent caused by the opening of the parallel-off switch 4 is limited by the commutation circuit 3.

[0046] <Effects of this embodiment> With the power supply system 100 configured in this manner, when an abnormality occurs in the commercial power system 10, the mechanical switch 2 is opened and the distributed power source 1 and the commercial power system 10 are interconnected via the capacitor 31, so that it is possible to achieve both an uninterruptible power supply function and a load leveling function using the common distributed power source 1 while satisfying the FRT requirements imposed when an abnormality occurs in the commercial power system 10. Moreover, since the capacitor 31 is selected to have an impedance smaller than the arc resistance of the mechanical switch 2, it is possible to commutate and limit the current to the capacitor 31 without generating an arc when the mechanical switch 2 is opened, and it is possible to quickly shut off the mechanical switch 2 regardless of the zero point. Furthermore, since the system is provided with a resonance suppression circuit 8 that suppresses resonance between the capacitor 31 and the power line L1 or the reactor of the important load 20, even if the resonant frequency matches the harmonics present in the system or the harmonics generated by the distributed power source 1, resonance between the capacitor 31 and the power line L1 or the reactor of the important load 20 can be suppressed, and unnecessary effects on the system and the important load 20 can be prevented. In this way, according to the power supply system 100 of this embodiment, it is possible to provide a power supply system at low cost that satisfies the FRT requirements while preventing unnecessary effects on the grid and important loads 20 due to resonance, and that achieves both an uninterruptible power supply function and a load leveling function by using a common distributed power source 1.

[0047] Furthermore, when the system abnormality detection unit 6 detects an abnormality in the commercial power system 10, the control unit 7 opens the mechanical switch 2 and then opens the switching element 82. This makes it possible to reliably divert and limit the current to the capacitor 31 when an abnormality occurs in the commercial power system 10.

[0048] <Other Modified Embodiments> The present invention is not limited to the above-described embodiment.

[0049] For example, the resonance suppression circuit 8 may be connected in parallel to the capacitor 31 as shown in FIG. 2, or a plurality of resonance suppression circuits 8 may be provided, although not shown.

[0050] In addition, in the above embodiment, the resistive element 81 is used as a damping element, but the damping element may be a combination of the resistive element 81 and a reactor, which can be changed to any resonance point, such as an even harmonic.

[0051] Further, the commutation circuit 3 in the above embodiment includes the capacitor 31 and the commutation element 32 connected in parallel, but the commutation circuit 3 may include only the capacitor 31.

[0052] Incidentally, the FRT requirements stipulate that when the voltage of the commercial power grid 10 returns to a normal state (hereinafter referred to as power restoration) after a momentary voltage drop occurs, the output of the distributed power source 1 must be restored to 80% within a minimum of 0.1 seconds after power restoration.

[0053] In order to satisfy this FRT requirement and restore the output of the distributed power source 1 within 0.1 seconds, the mechanical switch 2 must be precisely controlled; however, the closing time of the mechanical switch 2 is unstable, with a range of approximately 60 milliseconds plus or minus several tens of milliseconds, making precise control difficult in practice.

[0054] Therefore, as shown in FIG. 3 , the power supply system 100 according to the present invention may further include a semiconductor switch X connected in parallel to the mechanical switch 2 and the capacitor 31 in the power line L1, and a grid power restoration detection unit 9 that detects the restoration of power to the commercial power grid 10 from the detection voltage of the grid side voltage detection unit 5. During normal operation, the mechanical switch 2 is closed and the semiconductor switch X is open. When the power restoration detection unit 9 detects the restoration of power to the commercial power grid 10, the control unit 7 may close the semiconductor switch X so that the distributed power source 1 and the commercial power grid 10 are connected via the semiconductor switch X.

[0055] More specifically, the semiconductor switch X operates faster than the mechanical switch 2 and is turned on within 0.1 seconds after the power recovery is detected by the power system recovery detection unit 9. Specifically, a thyristor or other element that does not have a self-extinguishing ability and can be turned on quickly may be used. Note that an IGBT may also be used as the semiconductor switch X.

[0056] It is preferable that after the semiconductor switch X is turned on by the control unit 7, the mechanical switch 2 is turned on by the control unit 7, and then the semiconductor switch X is opened by the control unit 7.

[0057] In a power supply system configured in this manner, the semiconductor switch X is turned on when power is restored to the commercial power grid 10, making it possible to restore the output of the distributed power source 1 within 0.1 seconds after power is restored, and also making it possible to satisfy the FRT requirements imposed at the time of power restoration. Moreover, a thyristor having a simpler element structure than an IGBT, high voltage resistance, and large capacity but no self-extinguishing ability is used as the semiconductor switch X, and this semiconductor switch X is turned on and off only when power is restored to the commercial power system 10, so that the number of times the semiconductor switch X is used can be reduced by half compared to a conventional configuration, i.e., a configuration in which an element having self-extinguishing ability such as an IGBT is used as the semiconductor switch X and the semiconductor switch X is turned on and off both when an abnormality occurs in the commercial power system 10 and when power is restored, and the life of the semiconductor switch 9 and the system can be extended. Such an effect leads to a reduction in the initial cost and running cost of the power supply system 100.

[0058] Furthermore, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0059] 100 Power Supply System 10...Commercial power system 20...Important load L1...power line 1...distributed power supply 2. Mechanical Switch 31 Capacitor 4. Parallel-off switch 5. Grid voltage detection section 6 System abnormality detection section 7 Control section 71...Abnormality judgment unit 8...Resonance suppression circuit

Claims

1. A power supply system provided between a commercial power system and a critical load, for supplying power to the critical load, comprising: A distributed power source connected to a power line for supplying power from the commercial power system to the critical load; a mechanical switch that is provided on the power line closer to the commercial power system than the distributed power source and that opens and closes the power line; a capacitor connected in parallel with the mechanical switch in the power line; a system-side voltage detection unit that detects a voltage on the commercial power system side of the mechanical switch; a system abnormality detection unit that detects an abnormality in the commercial power system from a voltage detected by the system side voltage detection unit; A control unit that controls power supply to the important load, when the system abnormality detection unit detects an abnormality in the commercial power system, the control unit opens the mechanical switch, and the distributed power source continues to operate in a state in which the distributed power source and the commercial power system are connected via the capacitor, The power supply system further comprises a resonance suppression circuit having a resistive element connected in series with the capacitor, suppressing resonance between the capacitor and the power line or a reactor of the significant load.

2. The resonance suppression circuit is 2. The power supply system according to claim 1, further comprising a switching element connected in parallel with said resistive element.

3. 3. The power supply system according to claim 2, wherein when the system abnormality detection unit detects an abnormality in the commercial power system, the control unit opens the mechanical switch and then opens the switching element.

4. a parallel-off switch provided on the power line and configured to cut off power supply from the commercial power system to the important load; An abnormality determination unit that determines whether the abnormality detected by the system abnormality detection unit is a frequency abnormality or a power outage, When the abnormality determination unit determines that the abnormality detected by the grid abnormality detection unit is a frequency abnormality, the control unit opens the switching element, and the distributed power source continues to operate in a state in which the capacitor and the resistance element are connected, 4. The power supply system according to claim 2, wherein when the abnormality determination unit determines that the abnormality detected by the system abnormality detection unit is a power outage, the control unit opens the parallel-off switch to disconnect the important load from the commercial power system.

5. a semiconductor switch connected in parallel to the mechanical switch and the capacitor in the power line; A system recovery detection unit detects a recovery of the commercial power system from a detection voltage of the system side voltage detection unit, During normal operation, the mechanical switch is turned on and the semiconductor switch is turned off.

5. The power supply system according to claim 1, wherein when the grid restoration detection unit detects restoration of power to the commercial power grid, the control unit turns on the semiconductor switch, and the distributed power source and the commercial power grid are connected via the semiconductor switch.

6. 6. The power supply system according to claim 5, wherein after the semiconductor switch is turned on by the control unit, the mechanical switch is turned on by the control unit, and thereafter, the semiconductor switch is opened by the control unit.

7. 7. The power supply system according to claim 5, wherein the semiconductor switch is turned on within 0.1 seconds after the power restoration detection unit detects the power restoration.

8. 8. The power supply system according to claim 5, wherein the semiconductor switch is an element that does not have a self-extinguishing capability.

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