Uninterruptible Power Supply System

Abstract

To provide an inexpensive electric power system which can perform a compensation operation in the case of abnormality of an electric power system and prevent drop in voltage quality of a compensation object load in the case of the compensation operation.SOLUTION: An uninterruptible power supply system 100 of a continuous commercial power supply system which supplies power to a load from a dispersion type power source 1 connected to a power line L1 for supplying power to the load 30 from a power system 10 includes: a mechanical switch 2 which opens or closes the power line; a commutation circuit 3 connected in parallel to the mechanical switch; a system abnormal detection part 5 which detects voltage abnormality of the power system; a switching control part 6 which outputs an open command to the mechanical switch when detecting the voltage abnormality by the system abnormal detection part; an opening start detection part 7 which detects opening timing at which the mechanical switch starts an opening operation after outputting the open command; and a dispersion type power supply control part 8 for starting power supply from the dispersion type power source to the load based on the opening timing detected by the opening start detection part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an uninterruptible power supply system that uses a continuous commercial power supply system. [Background technology]

[0002] As shown in Patent Document 1, an uninterruptible power supply system using a continuous commercial power supply method includes a circuit breaker that cuts off the power supply from the power grid to a compensated load (hereinafter simply referred to as a load), and a distributed power source such as a storage battery connected to the load side of the circuit breaker.

[0003] When the power grid is operating normally, this uninterruptible power supply system supplies power to the load from the power grid via a circuit breaker, while operating the distributed power sources in grid-connected mode. Meanwhile, when a power grid abnormality occurs, the circuit breaker is opened to cut off the power supply from the power grid to the load, and the operating mode of the distributed power sources is switched from current control to voltage control to operate independently. This allows for reliable, uninterruptible power supply to the load even during a power grid abnormality. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3402886 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the uninterruptible power supply system described above uses semiconductor switches such as IGBTs as circuit breakers, which allows for high-speed switching operations, but the current loss caused by the on-resistance of the elements is not small. Also, in high-voltage environments such as high voltage and extra-high voltage, it is necessary to connect multiple expensive semiconductor switches in series, which increases costs and complicates the control circuit.

[0006] In recent years, the use of mechanical switches instead of semiconductor switches as circuit breakers has been considered as a way to build uninterruptible power systems with low current loss and low cost. However, when using mechanical switches as circuit breakers, variations in the time between issuing an opening command and the actual start of the opening operation occur due to factors such as the roughness of the contacts and the deterioration of the grease. Therefore, when using mechanical switches as circuit breakers, it is necessary to take into account variations in the time until the opening operation begins by waiting a sufficient amount of time (a time when the mechanical switch is considered to have opened reliably) after issuing an opening command to the mechanical switch before power is supplied to the load from the distributed power source. This raises concerns about delays in the load's recovery to normal voltage. Conversely, if the distributed power source begins supplying power before the mechanical switch has completely opened after issuing an opening command, a short-circuit current will flow from the distributed power source to the power grid, damaging the contacts of the mechanical switch. Another problem is the application of overvoltage to the compensated load.

[0007] The present invention has been made to solve the above problems at once, and its main object is to provide an inexpensive power system that can perform compensation operation when an abnormality occurs in the power grid and can prevent a decrease in the voltage quality of the load to be compensated during the compensation operation. [Means for solving the problem]

[0008] That is, the uninterruptible power supply system of the present invention is a continuous commercial power supply system that supplies power to a load from a power system when the power system is normal, cuts off the power supply to the load from the power system when an abnormality occurs in the power system, and supplies power to the load from a distributed power source connected to a power line that supplies power from the power system to the load, and is characterized by comprising: a mechanical switch that is provided on the power line closer to the power system than the distributed power source and opens and closes the power line; a commutation circuit that is connected in parallel to the mechanical switch on the power line; a system abnormality detection unit that detects a voltage abnormality in the power system based on the voltage on the power system side of the mechanical switch; a switching control unit that outputs an open command to the mechanical switch when a voltage abnormality is detected by the system abnormality detection unit; an opening start detection unit that detects the opening timing at which the mechanical switch starts an opening operation after outputting the opening command; and a distributed power supply control unit that starts the supply of power from the distributed power source to the load based on the opening timing detected by the opening start detection unit.

[0009] Such an uninterruptible power supply system uses an inexpensive mechanical switch as a circuit breaker, and when a power grid abnormality is detected, the mechanical switch opens and the distributed power source starts supplying power to the load, thereby enabling power to be supplied to the load to be compensated even during a grid abnormality. Here, after an opening command is output to the mechanical switch, the timing at which the mechanical switch actually starts its opening operation is detected. Therefore, even if there is variation in the timing at which the mechanical switch opens, the power supply from the distributed power source to the load can be started at the appropriate timing without excessively delaying or advancing, thereby preventing a deterioration in the voltage quality of the load to be compensated. This makes it possible to provide an inexpensive power system that can perform compensation operation in the event of a power grid abnormality and prevent a deterioration in the voltage quality of the load to be compensated during compensation operation.

[0010] As a specific aspect of the distributed power supply control unit, it is preferable that the distributed power supply control unit is configured to start outputting the distributed power supply to the load after a predetermined first delay time set in accordance with the opening characteristics of the mechanical switch has elapsed after the opening timing has been detected. This first delay time is a value determined by the opening characteristics, and is the time it takes for the contact voltage to reach the maximum contact voltage Vp determined by the rated voltage of the circuit after the mechanical switch starts to open. For example, if the rated voltage of the circuit is 6.6 kV, the maximum contact voltage Vp is 5.93 kV (= 6.6 kV × √2 / √3 × 1.1).

[0011] Furthermore, it is preferable that the uninterruptible power supply system is configured so that the distributed power supply control unit starts supplying power from the distributed power supply to the load at the earlier of either the first delay time elapsed after the open timing is detected, or the second delay time longer than the first delay time elapsed after the voltage abnormality is detected. In this way, even if, for example, the current (commutation current) flowing in the commutation circuit when the mechanical switch is opened is very small or no commutation current flows and the opening start detection unit cannot detect the opening timing, it is possible to start supplying power from the distributed power source to the load a predetermined time after a voltage abnormality on the system side is detected, and compensation operation can be performed reliably.

[0012] Specific examples of the opening start detection unit include one that detects the opening timing based on the value of the current flowing through the commutation circuit, and one that detects the opening timing based on the voltage value between contacts of the mechanical switch. [Effects of the Invention]

[0013] According to the present invention configured in this manner, it is possible to provide an inexpensive power system that can perform compensation operation when an abnormality occurs in the power system and can prevent a decrease in the voltage quality of the load to be compensated during the compensation operation. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing the configuration of an uninterruptible power supply system according to an embodiment of the present invention; [Figure 2] 10 is a diagram showing the relationship between the inter-electrode withstand voltage characteristics, the first delay time, and the second delay time with respect to the operating time of the mechanical switch. [Figure 3] A diagram showing the principle of how LC resonant current flows in a commutation circuit when a three-phase short circuit occurs in a power system. [Figure 4] An example of a simulation showing the time variation of the applied load voltage, etc. when the start of output to the distributed power source is sufficiently delayed to take into account variations in the opening time of the mechanical switch in response to a three-phase short circuit in the grid. [Figure 5] This is a simulation example showing the time variation of the applied load voltage, etc. when output to a distributed power source is started at the earliest timing allowed for the opening time of a mechanical switch in response to a three-phase short circuit in the grid. [Figure 6] A simulation example showing the time changes in the applied load voltage, etc. when output to a distributed power source is started earlier than the mechanical switch opens in response to a three-phase short circuit in the grid. [Figure 7] This is a simulation example showing the time variation of the applied load voltage, etc. when output to a distributed power source is started at the earliest timing allowed for the opening time of a mechanical switch in response to a two-phase short circuit in the grid. [Figure 8] A simulation example showing the time variation of the load applied voltage, etc. when output to the distributed power source is started after the second delay time has elapsed after an abnormality in the power grid is detected during a grid-open power outage. [Figure 9] FIG. 10 is a schematic diagram showing the configuration of an uninterruptible power supply system according to another embodiment. [Figure 10] FIG. 10 is a schematic diagram showing the configuration of an uninterruptible power supply system according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] An uninterruptible power supply system 100 according to an embodiment of the present invention will be described below with reference to the drawings.

[0016] 1, an uninterruptible power supply system 100 of this embodiment is of a continuous commercial power supply type that is installed between a power grid 10 and a load 30. This uninterruptible power supply system 100 supplies power from the power grid 10 to the load 30 when the power grid 10 is normal, and cuts off the power supply from the power grid 10 to the load 30 when a voltage abnormality occurs due to a system short-circuit accident (a two-phase short-circuit accident or a three-phase short-circuit accident) in the power grid 10, and supplies power from a distributed power source 1 to the load 30.

[0017] Specifically, the uninterruptible power supply system 100 includes a distributed power source 1, an open / close switch 2 that connects a power system 10 to the distributed power source 1 and a load 30, a commutation circuit 3 connected in parallel to the open / close switch 2, disconnection switches 4a and 4b that are respectively provided on the power system 10 side and the load 30 side of the open / close switch 2, a system abnormality detection unit 5 that detects voltage abnormalities in the power system 10, a open / close control unit 6 that controls the open / close states of the open / close switch 2 and the disconnection switches 4a and 4b, an opening start detection unit 7, and a distributed power source control unit 8 that controls power supply by the distributed power source 1.

[0018] The distributed power source 1 is connected to a power line L1 for supplying power from a power grid 10 to a load 30. This distributed power source 1 is interconnected to the power grid 10 and includes, for example, a DC power generation facility 11 such as a solar power generation facility or a fuel cell, a power storage device (power storage device) 12 such as a secondary battery (storage battery), a power generation facility (not shown) that rectifies AC electrical energy output from a wind power generation facility or a micro gas turbine into DC and connects the DC energy to the grid using a power conversion device, or an AC power generation facility 13 such as a synchronous generator or an induction generator. The DC power generation facility 11 and the power storage device (power storage device) 12 are each equipped with a power conversion device (not shown).

[0019] The open / close switch 2 is provided on the power line L1 closer to the power system 10 than the connection point of the distributed power source 1 to open or 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 configured to be driven to open or close in response to a command signal output from the open / close control unit 6.

[0020] The commutation circuit 3 limits the current that flows into (commutates) when the mechanical switch 2 is opened. Specifically, the commutation circuit 3 includes a capacitor 31 connected in parallel to the mechanical switch 2. Specific examples of the capacitor 31 include a film capacitor. The capacitance C of the capacitor 31 in this embodiment is determined so that when the mechanical switch 2 is opened, the current flowing through the mechanical switch 2 is commutated to the commutation circuit 3 instantly without generating an arc, and the mechanical switch 2 can be quickly turned off regardless of the zero point.

[0021] The parallel-off switches 4a and 4b are provided on the power line L1 closer to the power system 10 and closer to the load 30 than the distributed generation 1 (here, closer to the mechanical switch 2), and are, for example, mechanical switches. The parallel-off switches 4a and 4b are controlled to be opened or closed by a switching control unit 6.

[0022] The system abnormality detection unit 5 detects a voltage abnormality in the power system 10 based on the voltage on the power line L1 closer to the power system 10 than the mechanical switch 2. Specifically, the system abnormality detection unit 5 is connected via a voltage transformer to the power system 10 side of the parallel circuit consisting of the mechanical switch 2 and the commutation circuit 3, and constantly detects the voltage on the power line L1 closer to the power system 10 than the mechanical switch 2. The system abnormality detection unit 5 compares the detected voltage with a predetermined set value and detects an instantaneous voltage drop if the detected voltage is equal to or lower than the set value. The system abnormality detection unit 5 also detects frequency fluctuations (frequency upswing (OF) and frequency downswing (UF)) from the detected voltage. The frequency fluctuations include, for example, step upswings and ramp upswings / downswings. In addition to instantaneous voltage drops, frequency fluctuations, and power outages, the system abnormality detection unit 5 may also detect at least one of voltage upswings, phase fluctuations, voltage imbalances, harmonic abnormalities, and flicker.

[0023] The switching control unit 6 outputs command signals (open command signal, close command signal) to the mechanical switch 2 and the parallel-off switches 4a, 4b to control their open / closed states. Specifically, the switching control unit 6 is configured to output an open command signal to the mechanical switch 2 when the system abnormality detection unit 5 detects a voltage abnormality (detects an instantaneous voltage drop).

[0024] The opening start detection unit 7 detects the timing (also called opening timing or opening time) when the mechanical switch 2 actually starts the opening operation (contact opening operation) after the opening command is output by the switching control unit 6. Specifically, this opening start detection unit 7 is connected to the commutation circuit 3 via an instrument current transformer, and is configured to constantly measure the values ​​of the three-phase currents flowing through the commutation circuit 3 and detect the opening timing of the mechanical switch 2 based on the current values.

[0025] More specifically, the opening start detection unit 7 compares the detected current values ​​for the three phases with a predetermined set value, and when the detected current value for any of the three phases exceeds the set value, detects the start of the opening operation of the mechanical switch 2. In other words, the opening start detection unit 7 regards the timing (or time) when the detected current value for any of the three phases exceeds the set value as the timing (or time) when the opening operation of the mechanical switch 2 starts. This set value is preferably set small enough to be unaffected by noise.

[0026] The distributed power supply control unit 8 controls the power supply from the distributed power supply 1 based on the opening timing of the mechanical switch 2 detected by the opening start detection unit 7. Specifically, the distributed power supply control unit 8 is configured to start the supply of power from the distributed power supply 1 to the load 30 a predetermined first delay time after the opening timing of the mechanical switch 2 is detected. This first delay time is a value determined by the opening contact characteristics, and as shown in FIG. 2, it is the time from when the mechanical switch 2 starts opening until the contact voltage reaches the maximum contact voltage Vp determined by the rated voltage of the circuit (commutation circuit 3, etc.). For example, if the rated voltage of the circuit is 6.6 kV, the maximum contact voltage Vp is 5.93 kV (= 6.6 kV × √2 / √3 × 1.1).

[0027] Furthermore, the distributed power supply control unit 8 of this embodiment is configured to start the supply of power from the distributed power supply 1 to the load 30 even when a predetermined second delay time has elapsed since the system abnormality detection unit 5 detected a voltage abnormality in the power grid 10. Specifically, the distributed power supply control unit 8 starts the supply of power from the distributed power supply 1 to the load 30 when a predetermined first delay time has elapsed since the opening timing of the mechanical switch 2 was detected, or when a predetermined second delay time has elapsed since the voltage abnormality in the power grid 10 was detected, whichever comes first. This second delay time is sufficiently longer than the first delay time. Specifically, as shown in FIG. 2 , this second delay time is the sum of the predetermined first delay time and the estimated time (estimated opening time) from the output of an opening command to the mechanical switch 2 to the start of the actual opening operation. This estimated opening time is a maximum value that takes into account variations in the opening timing of the mechanical switch 2. Note that in the example shown in FIG. 2 , the opening operation starts when the estimated opening time has elapsed since the output of an opening command to the mechanical switch 2.

[0028] The uninterruptible power supply system 100 of this embodiment configured as described above is configured to take multiple control modes including (1) a normal mode and (2) an abnormal mode by controlling the operation / stop, opening / closing, etc. of each device according to the voltage value on the power system 10 side in the power line L1 and the current value flowing through the commutation circuit 3. Each control mode will be described below.

[0029] (1) Normal mode When the system abnormality detection unit 5 has not detected a system abnormality (i.e., when the power system 10 is normal), the switching control unit 6 closes the mechanical switch 2 and the parallel-off switches 4a and 4b. In this case, the power system 10 supplies AC power to the load 30 via the mechanical switch 2. Although the commutation circuit 3 is connected in parallel to the mechanical switch 2, the impedance of the mechanical switch 2 is smaller than the impedance of the commutation circuit 3, so power is exchanged between the power system 10 and the load 30 via the mechanical switch 2. Note that in this normal mode, the distributed power source 1 only charges the power storage device 12 and does not supply power to the load 30.

[0030] (2) Abnormal mode When a short circuit or other fault occurs in the power grid 10 and the grid fault detector 5 detects a grid fault such as an instantaneous voltage drop, the switching controller 6 outputs an opening command to the mechanical switch 2. After the opening command is output, the current value in the commutation circuit 3 exceeds a predetermined set value, and the opening start detector 7 detects the start timing of the opening operation of the mechanical switch 2. After the first delay time has elapsed, the distributed power source controller 8 sends an output signal to the distributed power source 1 to start supplying power to the load 30. At this time, the power grid 10 and the distributed power source 1 are connected via the commutation circuit 3, but the current flowing from the power grid 10 to the distributed power source 1 is limited by the capacitor 31 of the commutation circuit 3, so almost no power flow occurs. In this state, the switching controller 6 opens the parallel-off switches 4a and 4b, completely disconnecting the power grid 10 from the load 30.

[0031] In this abnormality mode, the opening start detector 7 detects the current value flowing through the commutation circuit 3 and can detect the timing to open the mechanical switch 2 not only during a two-phase short-circuit fault in the power grid 10 but also during a three-phase short-circuit fault. As shown in FIG. 3 , a filter capacitor connected in parallel to the output circuit of the AC / DC converter of the power storage device 12 is connected to the power line L1 closer to the load 30 than the mechanical switch 2, and a transformer is connected in series to the power grid 10. The capacitance C of the filter capacitor, the leakage inductance L of the transformer, and the short-circuit point form an LC resonant circuit, generating a resonant current whose initial values ​​are the capacitor voltage (i.e., energy due to charging charges) and the transformer leakage inductance current (magnetic energy) when a three-phase short circuit occurs. If power is being supplied from the power grid 10 to the load 30 at this time, at least one of the initial values ​​of each element is not zero. As a result, when a three-phase short circuit fault occurs, a resonant current flows through the commutation circuit 3, and the open start detection unit 7 can detect the open state (non-short circuit state) between the poles of the mechanical switch 2 by detecting the resonant current.

[0032] During an open power outage in the power grid 10, the above-mentioned LC resonant circuit is not generated, so no current flows through the commutation circuit 3, and the opening start detection unit 7 cannot detect the opening timing of the mechanical switch 2. In such a case, the distributed power supply control unit 8 sends an output signal to the distributed power supply 1 to start supplying power to the load 30 after the second delay time has elapsed after the system abnormality detection unit 5 has detected an abnormality in the power grid 10 (or after an opening command has been output to the mechanical switch 2).

[0033] Next, the time variation of the voltage applied to the load during the compensation operation of various types of uninterruptible power supply systems will be shown by simulation.

[0034] Figure 4 is a simulation example showing the time variation of the applied load voltage, etc. when the start of output to the distributed power source is sufficiently delayed to account for variations in the opening time of the mechanical switch in response to a three-phase short circuit in the grid. In other words, this simulation does not detect the opening timing of the mechanical switch, but instead detects a drop in grid voltage and then starts output to the distributed power source after a time sufficiently longer than the opening time of the mechanical switch has passed. As can be seen from Figure 4, this simulation confirmed that there is a significant delay in the recovery of the healthy voltage of the load after the mechanical switch is opened.

[0035] 5 is a simulation example showing the time variation of the load applied voltage, etc., when output to the distributed power sources is initiated at the earliest timing allowed for the opening time of the mechanical switch in response to a three-phase short circuit in the grid. That is, this simulation uses the same method as the uninterruptible power supply system 100 of the present embodiment described above, in which the opening timing of the mechanical switch in response to a three-phase short circuit in the grid is detected and output to the distributed power sources is initiated based on this timing. As can be seen from FIG. 5, in this example, it was confirmed that the compensated load voltage can be restored to normal more quickly than in the example of FIG. 4.

[0036] Figure 6 is a simulation example showing the time variation of the applied voltage to the load, etc. when output to the distributed power supply starts earlier than the opening of the mechanical switch in response to a three-phase short circuit in the grid. As can be seen from this figure, if the distributed power supply system starts output too early, an overcurrent (short-circuit current) flows in the mechanical switch, an overvoltage occurs between the poles of the mechanical switch, and an overvoltage is applied to the load to be compensated.

[0037] 7 is a simulation example showing the time variation of the load applied voltage, etc., when output to the distributed power sources is started at the earliest timing allowed for the opening time of the mechanical switch in response to a grid two-phase short circuit. That is, this simulation uses the same method as the uninterruptible power supply system 100 of this embodiment described above, in which the opening timing of the mechanical switch in response to a grid two-phase short circuit is detected and output to the distributed power sources is started based on this timing. As can be seen from FIG. 7, it was confirmed that the method used by the uninterruptible power supply system 100 of this embodiment can quickly restore the compensated load voltage to normal even in the event of a grid two-phase short circuit.

[0038] Figure 8 is a simulation example showing the time changes in the load applied voltage, etc., when output to the distributed power sources is initiated after the second delay time has elapsed following the detection of an abnormality in the power grid during a grid-open power outage. In other words, this example shows that no commutation current flows through the commutation circuit 3, and the open-circuit start detector 7 is unable to detect the opening timing. This figure shows that even in this example, the compensated load voltage can be restored to normal after a certain time has elapsed since the grid voltage dropped. Compared to the examples in Figures 5 and 7, it takes longer for the compensated load voltage to be restored to normal, but it also shows that the worst-case scenario of no output command being issued to the distributed power sources 1 and no voltage being applied to the compensated load can be prevented.

[0039] <Effects of this embodiment> The uninterruptible power supply system 100 of this embodiment configured as described above uses an inexpensive mechanical switch 2 as a circuit breaker, and when an abnormality is detected in the power grid 10, the mechanical switch 2 is opened and the supply of power from the distributed power source 1 to the load 30 is started, so that power can be supplied to the compensated load even during a grid abnormality. Here, after an opening command is output to the mechanical switch 2, the opening start detection unit 7 detects the timing at which the mechanical switch 2 actually starts its opening operation. Therefore, even if there is variation in the opening timing of the mechanical switch 2, the supply of power from the distributed power source 1 to the load 30 can be started at an appropriate timing without being excessively early or late, and a deterioration in the voltage quality of the load 30 can be prevented.

[0040] Furthermore, the uninterruptible power supply system is configured so that the distributed power supply control unit 8 starts supplying power from the distributed power supply 1 to the load 30 either when a first delay time has elapsed since the opening timing is detected, or when a predetermined second delay time longer than the first delay time has elapsed since a voltage abnormality is detected, whichever is earlier.Therefore, even if, for example, the current flowing through the commutation circuit 3 is very small when the mechanical switch 2 is opened and the opening start detection unit 7 cannot detect the opening timing, it is possible to start supplying power from the distributed power supply 1 to the load 30 a predetermined time after a voltage abnormality on the power grid 10 side is detected, and compensation operation can be performed reliably.

[0041] <Other Modified Embodiments> The present invention is not limited to the above-described embodiment.

[0042] For example, an uninterruptible power supply system 100 according to another embodiment may include a self-discharge circuit 9 connected in parallel to the mechanical switch 2 and the commutation circuit 3, as shown in FIG. 9 . In this way, after current-limiting interruption by the mechanical switch 2 and the commutation circuit 3, the charge remaining in the capacitor 31 of the commutation circuit 3 can be discharged by the self-discharge circuit 9. The self-discharge circuit 9 may include, for example, a resistor element 91 and an open / close switch 92 connected in series to the mechanical switch 2 and the commutation circuit 3. In this case, the open / close switch 92 included in the self-discharge circuit 9 is turned on only when the mechanical switch 2 is open. The self-discharge circuit 9 does not have to include the open / close switch 92. In this case, the resistance value of the self-discharge circuit 9 is configured to be at least greater than the current-carrying resistance of the mechanical switch 2.

[0043] In the uninterruptible power supply system 100 of the above embodiment, the opening start detection unit 7 is configured to constantly measure the three-phase current values ​​flowing through the commutation circuit 3 via a current transformer and detect the opening timing of the mechanical switch 2 based on the current values, but this is not limiting. As shown in Fig. 10, the uninterruptible power supply system 100 of another embodiment may be connected via a voltage transformer in a power line L2 connected in parallel to the mechanical switch 2 and the commutation circuit 3, constantly measure the three-phase inter-contact voltages of the mechanical switch 2, and detect the opening timing of the mechanical switch 2 based on the inter-contact voltage values.

[0044] Although the parallel-off switches 4a and 4b are provided on both the power system 10 side and the load 30 side of the mechanical switch 2 in the power line L1, this is not limitative and they may be provided on only one side.

[0045] Furthermore, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0046] 100 Power Supply System 10...Electric power system 30 Load L1...power line 1...distributed power supply 2. Mechanical Switch 3. Commutation Circuit 31 Capacitor 4a Parallel-off switch 4b Parallel-off switch 5. System abnormality detection section 6. Opening and closing control section 7 Open start detection section 8. Distributed power supply control unit

Claims

1. An uninterruptible power supply system of a continuous commercial power supply type that supplies power to a load from a power system when the power system is normal, cuts off the power supply from the power system to the load when an abnormality occurs in the power system, and supplies power to the load from a distributed power source connected to a power line for supplying power from the power system to the load, a mechanical switch that is provided on the power line closer to the power grid than the distributed power source and that opens and closes the power line; a commutation circuit connected in parallel to the mechanical switch in the power line; a system abnormality detection unit that detects a voltage abnormality in the power system based on a voltage on the power system side of the mechanical switch; a switching control unit that outputs an opening command to the mechanical switch when a voltage abnormality is detected by the system abnormality detection unit; an opening start detection unit that detects an opening timing, which is a timing at which the mechanical switch actually starts an opening operation after the opening command is output; a distributed power supply control unit that starts the supply of power from the distributed power supply to the load based on the opening timing detected by the opening start detection unit.

2. 2. The uninterruptible power supply system according to claim 1, wherein the distributed power supply control unit starts outputting the distributed power supply to the load after a predetermined first delay time set in accordance with the opening characteristics of the mechanical switch has elapsed since the opening timing was detected.

3. The distributed power supply control unit When the first delay time has elapsed since the release timing was detected, or 3. The uninterruptible power supply system according to claim 2, wherein the supply of power from the distributed power source to the load is started at either the earlier of when the voltage abnormality is detected or when a predetermined second delay time longer than the first delay time has elapsed.

4. 3. The uninterruptible power supply system according to claim 1, wherein the opening start detection unit detects the opening timing based on a value of a current flowing through the commutation circuit.

5. 3. The uninterruptible power supply system according to claim 1, wherein the opening start detection unit detects the opening timing based on a voltage value between contacts of the mechanical switch.

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