Bidirectional Power System

Abstract

To provide an inexpensive bidirectional type power supply system that can perform compensation operation when a commercial power system is abnormal and also can prevent voltage quality of a compensation object load from deteriorating in the compensation operation.SOLUTION: A bidirectional type power supply system 100 comprises: a distributed power supply 1 which is connected to an electric power line L1 for supplying electric power from a commercial power system 10 to a compensation object load 30; a mechanical switch 2 which opens and closes the electric power line L1; a commutating capacitor 31 which is connected in parallel to the mechanical switch; a system abnormality detection part 5 which detects voltage abnormality on the commercial power system side with respect to the mechanical switch; an opening / closing control part 6 which outputs an open command to the mechanical switch when voltage abnormality is detected; an opening start detection part 7 which detects opening timing when the mechanical switch starts opening after the output of the open command; and a distributed-power-supply control part 8 which performs current control on the distributed power supply before the opening timing is detected, and switches from the current control to voltage control that are each to be performed on the distributed power supply once the opening timing is detected.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a bidirectional power supply system that is provided between a commercial power system and a load to be compensated and performs interconnected operation including supplying power to the load to be compensated and flowing reverse power to the commercial power system. [Background technology]

[0002] Conventionally, as shown in Patent Document 1, a distributed power supply facility connected to a grid has been considered to include a circuit breaker that cuts off the power supply from the commercial power grid to the load, and a distributed power supply such as a storage battery connected to the load side of the circuit breaker.

[0003] When the commercial power grid is operating normally, this distributed power generation facility supplies power to the load from the commercial power grid via a circuit breaker, while operating the distributed power source in a grid-connected manner. Meanwhile, when an abnormality occurs in the commercial power grid, the circuit breaker opens, cutting off the power supply from the commercial power grid to the load, and the operating mode of the distributed power source switches from current control to voltage control, allowing for stand-alone operation. This ensures uninterrupted and reliable power supply to the load even during an abnormality in the commercial power grid. [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 distributed power generation equipment 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 inexpensive bidirectional power systems with low current loss. 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, which raises concerns about delays in the load's recovery to normal voltage. Conversely, if the distributed power supply begins supplying power to the load before the mechanical switch has completely opened after issuing an opening command, a short-circuit current will flow from the distributed power supply to the commercial power grid, damaging the mechanical switch contacts. Another problem is the application of overvoltage to the load.

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

[0008] That is, the bidirectional power supply system of the present invention is a bidirectional power supply system that is provided between a commercial power system and a load to be compensated, and performs interconnected operation including supplying power to the load to be compensated and flowing reverse power to the commercial power system, and is characterized by comprising: a distributed power source connected to a power line for supplying power from the commercial power system to the load to be compensated; a mechanical switch that is provided on the commercial power system side of the distributed power source and opens and closes the power line; a commutation capacitor connected in parallel to the mechanical switch; a system abnormality detection unit that detects a voltage abnormality on the commercial power system side of the mechanical switch; a switching control unit that outputs an opening command to the mechanical switch when the voltage abnormality is detected; 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 current controls the distributed power source before detecting the opening timing, and switches the distributed power source from current control to voltage control when the opening timing is detected.

[0009] This bidirectional power supply system uses an inexpensive mechanical switch as a circuit breaker, and when an abnormality in the commercial power grid is detected, the mechanical switch opens and the distributed power source starts supplying power to the compensated load, allowing power to be supplied to the compensated load even during a grid abnormality. 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 compensated load can be started at the appropriate time without excessively delaying or advancing, preventing a degradation in voltage quality to the compensated load. This makes it possible to provide an inexpensive bidirectional power system that can perform compensation operation when an abnormality in the commercial power grid occurs and prevent a degradation in voltage quality to the compensated load during compensation operation.

[0010] As a specific aspect of the distributed power source control unit, it is preferable that the distributed power source control unit starts voltage control of the distributed power sources after a predetermined first delay time set in accordance with the opening characteristics of the mechanical switch has elapsed since the opening timing is detected. Specifically, the distributed power source control unit stops current control of the distributed power sources between the detection of the opening timing and the elapse of the predetermined first delay time set in accordance with the opening characteristics of the mechanical switch, and starts voltage control of the distributed power sources after the elapse of the first delay time.

[0011] 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).

[0012] Furthermore, it is preferable that the distributed power source control unit starts voltage control of the distributed power source at the earlier of either when the first delay time has elapsed since the open timing was detected, or when a predetermined second delay time longer than the first delay time has elapsed since the voltage abnormality was detected.

[0013] With this configuration, even if, for example, the current (commutation current) flowing through the commutation capacitor 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 to be compensated a predetermined time after a voltage abnormality on the grid side is detected, and the compensation operation can be performed reliably.

[0014] Specific embodiments of the opening start detection unit include one that detects the opening timing based on the value of the current flowing through the commutation capacitor, and one that detects the opening timing based on the voltage value between contacts of the mechanical switch.

[0015] Furthermore, the bidirectional power supply system of the present invention preferably further comprises a discharge resistor connected in parallel to the mechanical switch for discharging the commutation capacitor. [Effects of the Invention]

[0016] According to the present invention configured as described above, it is possible to provide an inexpensive bidirectional power supply system that can perform compensation operation when an abnormality occurs in the commercial power grid and can prevent a decrease in the voltage quality of the load to be compensated during the compensation operation. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing the configuration of a bidirectional 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 characteristic, the first delay time, and the second delay time with respect to the operating time of the mechanical switch. FIG. [Figure 3] FIG. 1 is a diagram illustrating the principle of how an LC resonant current flows through a commutation circuit when a three-phase short circuit occurs in a commercial power system. [Figure 4] 10 is a simulation example showing the time variation of the applied voltage to the load to be compensated, etc., when the start of output to the distributed power source is sufficiently delayed in consideration of 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 changes in the load applied voltage, etc. when output to a distributed power source (constant voltage control) 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] This is a simulation example showing the time changes in the load applied voltage, etc. when output to a distributed power source (constant voltage control) is started at a timing earlier than the opening of a mechanical switch in response to a three-phase short circuit in the grid. [Figure 7] This is a simulation example showing the time changes in the load applied voltage, etc. when output to a distributed power source (constant voltage control) 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 system. [Figure 8]This is a simulation example showing the time changes in the load applied voltage, etc. when output to the distributed power source (constant voltage control) is started after the second delay time has elapsed after an abnormality is detected in the commercial power system during a grid-open power outage. [Figure 9] FIG. 10 is a schematic diagram showing the configuration of a bidirectional power supply system according to another embodiment. [Figure 10] FIG. 10 is a schematic diagram showing the configuration of a bidirectional power supply system according to another embodiment. [Figure 11] FIG. 10 is a schematic diagram showing the configuration of a bidirectional power supply system according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] A bidirectional power supply system 100 according to an embodiment of the present invention will be described below with reference to the drawings.

[0019] <Configuration of bidirectional power supply system 100> 1, the bidirectional power supply system 100 of this embodiment is installed between a commercial power system 10 and a load 30 to be compensated, and performs interconnected operation including power supply to the load 30 to be compensated and reverse power flow to the commercial power system 10. Specifically, the bidirectional power supply system 100 is installed between the commercial power system 10 and the load 30 to be compensated, and performs a function as an uninterruptible power supply system that supplies power to the load 30 to be compensated in the event of an abnormality in the commercial power system 10 (uninterruptible power supply function), and a function as a distributed power supply system that levels the load by providing forward and reverse power flows to the commercial power system 10 (load leveling function).

[0020] Here, the commercial power system 10 is a power supply network of an electric power company (electric utility), and includes a power plant, a power transmission system, and a power distribution system. The compensated load 30 is a load to which a stable supply of power should be provided even during a system abnormality such as a power outage or a voltage drop. Although there is only one compensated load 30 in FIG. 1, there may be multiple compensated loads.

[0021] Specifically, as shown in FIG. 1 , the bidirectional power supply system 100 includes a distributed power supply 1, an open / close switch 2 that connects the distributed power supply 1 to a commercial power system 10 and a load to be compensated 30, a commutation circuit 3 connected in parallel to the open / close switch 2, parallel-off switches 4a and 4b that are provided on the commercial power system 10 side and the load to be compensated 30 side of the open / close switch 2, a system abnormality detection unit 5 that detects voltage abnormalities in the commercial power system 10, a open / close control unit 6 that controls the open / close states of the open / close switch 2 and the parallel-off switches 4a and 4b, an opening start detection unit 7, and a distributed power supply control unit 8 that controls power supply by the distributed power supply 1.

[0022] The distributed power source 1 is connected to a power line L1 for supplying power from a commercial power system 10 to a load 30 to be compensated. This distributed power source 1 is interconnected to the commercial power system 10 and includes, 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 (not shown) that rectifies AC electrical energy output from a wind power generation facility or a micro gas turbine into DC and then interconnects the power system using a power conversion device, or an AC power generation facility such as a synchronous generator or an induction generator. The DC power generation facility and the power storage device (power storage device) are equipped with a power conversion device (not shown).

[0023] 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 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.

[0024] 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 commutation capacitor 31 connected in parallel to the mechanical switch 2. Specific examples of the commutation capacitor 31 include a film capacitor. The capacitance C of the commutation 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.

[0025] The parallel-off switches 4a and 4b are provided on the power line L1 closer to the power grid 10 and closer to the load to be compensated 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.

[0026] The system abnormality detection unit 5 detects a voltage abnormality in the commercial power system 10 based on the voltage on the power line L1 closer to the commercial power system 10 than the mechanical switch 2. Specifically, the system abnormality detection unit 5 is connected via a potential transformer to the commercial power system 10 side of the parallel circuit made up of the mechanical switch 2 and the commutation circuit 3, and constantly detects the voltage on the power line L1 closer to the commercial power system 10 than the mechanical switch 2.

[0027] The system abnormality detection unit 5 then compares the detected voltage with a predetermined set value, and if the detected voltage is less than the set value (UV set value), detects an instantaneous voltage drop, and if the detected voltage exceeds the set value (OV set value), detects a voltage rise.

[0028] The system abnormality detection unit 5 can also detect frequency fluctuations (frequency up (OF) and frequency down (UF)) from the detected voltage. The frequency fluctuations are, for example, step ups and ramp ups and downs. In addition to instantaneous voltage drops, power outages, and voltage rises, the system abnormality detection unit 5 may also detect at least one of phase fluctuations, voltage imbalances, harmonic abnormalities, and flicker.

[0029] 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 (either detected voltage < undervoltage (UV) set value, or detected voltage > overvoltage (OV) set value). The switching control unit 6 is also configured to output a close command signal to the mechanical switch 2 when it detects either detected voltage ≥ UV set value, or detected voltage ≤ OV set value.

[0030] 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.

[0031] 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 (|detected current|≧set value), it 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 mechanical switch 2 starts the opening operation. This set value is preferably set small enough to be unaffected by noise.

[0032] The distributed power supply control unit 8 controls the power supply from the distributed power source 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 current-control (CC control) the distributed power source 1 before detecting the opening timing, and switch the distributed power source 1 from current control to voltage control after a predetermined first delay time has elapsed since the opening timing of the mechanical switch 2 was detected. In this embodiment, the distributed power supply control unit 8 stops the current control (CC control) of the distributed power source 1 before the first delay time has elapsed, and starts voltage control (CVCF control) of the distributed power source 1 after the first delay time has elapsed. Here, the current control of the distributed power source 1 is output control (CC control) that controls the current to be constant based on the voltage received from the commercial power grid 10. Furthermore, the voltage control of the distributed power source 1 is output control (CVCF control) in which the distributed power source 1 itself operates as a voltage source, maintaining a constant output voltage and a constant output frequency. Furthermore, the distributed power supply control unit 8 is configured to switch the distributed power supply 1 from voltage control (CVCF control) to current control (CC control) when the switching control unit 6 outputs a closing command signal to the mechanical switch 2.

[0033] 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 (commutation circuit 3, etc.) after the mechanical switch 2 starts to open, as shown in Figure 2. 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).

[0034] Furthermore, the distributed power supply control unit 8 of this embodiment is configured to switch the distributed power supply 1 from current control (CC control) to voltage control (CVCF control) when a predetermined second delay time has elapsed since the system abnormality detection unit 5 detected a voltage abnormality in the commercial power system 10. Specifically, the distributed power supply control unit 8 switches the distributed power supply 1 from current control (CC control) to voltage control (CVCF control) 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 commercial power system 10 was detected, whichever comes first.

[0035] This second delay time is sufficiently longer than the first delay time. Specifically, as shown in Fig. 2, this second delay time is the time obtained by adding the predetermined first delay time to 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 the variability that occurs in the opening timing of the mechanical switch 2. 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.

[0036] <Operation of the bidirectional power supply system 100> The bidirectional 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 commercial power system 10 side of the power line L1 and the current value flowing through the commutation circuit 3. Each control mode will be described below.

[0037] (1) Normal mode When the system abnormality detection unit 5 has not detected a system abnormality (i.e., when the commercial 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 commercial power system 10 supplies AC power to the compensated load 30 via the mechanical switch 2. The commutation circuit 3 is connected in parallel to the mechanical switch 2, but because 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 compensated load 30 on the side of the mechanical switch 2. Note that in this normal mode, the distributed power source 1 is current controlled (CC controlled) and performs interconnected operation including charging and discharging, and includes a reverse power flow state during discharging operation.

[0038] (2) Abnormal mode When a short circuit or other fault occurs in the commercial power grid 10 and the grid fault detector 5 detects a grid fault such as a momentary voltage drop, the switching controller 6 outputs an opening command to the mechanical switch 2. After the opening command is output, the current value of the commutation circuit 3 exceeds a predetermined setpoint, 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 switch from current control (CC control) to voltage control (CVCF control). However, this switchover also involves the distributed power source controller 8 stopping current control (CC control) early after detecting the start timing of the opening operation of the mechanical switch 2. As a result, the distributed power source 1 becomes a voltage source and supplies power to the compensated load 30. At this time, the commercial power grid 10 and the distributed power source 1 are connected via the commutation circuit 3. Reverse power flow is limited by the current limiting function of the commutation capacitor 31, but interconnected operation is maintained to satisfy the FRT (Fault Ride Through) requirement. If the system abnormality continues, the switching control unit 6 opens the parallel-off switches 4 a and 4 b, and the load to be compensated 30 and the distributed generation 1 are completely isolated from the commercial power system 10 .

[0039] 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 commercial 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 energy storage device is connected to the power line L1 closer to the compensated load 30 than the mechanical switch 2, and a transformer is connected in series to the commercial power grid 10. An LC resonant circuit is formed by the capacitance C of the filter capacitor, the leakage inductance L of the transformer, and the short-circuit point, and a resonant current is generated with the capacitor voltage (i.e., energy due to charging) and the transformer leakage inductance current (magnetic energy) as initial values ​​when a three-phase short circuit occurs. At this time, if power is being supplied from the commercial power grid 10 to the compensated load 30, 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.

[0040] During an open power outage in the commercial power grid 10, the above-mentioned LC resonant circuit is not generated, so no current flows through the commutation circuit 3, and the open 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 transmits an output signal to the distributed power supply 1 to start supplying power to the compensated load 30 after the second delay time has elapsed after the system abnormality detection unit 5 detects an abnormality in the commercial power grid 10 (or after an open command is output to the mechanical switch 2).

[0041] <Simulation results> Next, the time variation of the voltage applied to the load during the compensation operation of various aspects of the bidirectional power supply system will be shown by simulation.

[0042] 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 compensated load after the mechanical switch opens.

[0043] 5 is a simulation example showing the time variation of the applied load voltage, etc., when output to the distributed power source is started at the earliest timing allowed for the opening time of the mechanical switch in response to a three-phase short circuit on the grid. That is, this simulation uses the same method as the bidirectional 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 on the grid is detected and output to the distributed power source is started based on this timing. As can be seen from FIG. 5, it was confirmed that the compensated load voltage can be restored to normal more quickly in this example compared to the example in FIG. 4.

[0044] Figure 6 is a simulation example showing the time variation of the voltage applied to the load when output to the distributed power source is started 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 bidirectional 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.

[0045] 7 is a simulation example showing the time variation of the applied load voltage, etc., when output to the distributed power source 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 bidirectional 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 source is started based on this timing. As can be seen from FIG. 7, it was confirmed that the method used by the bidirectional 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.

[0046] 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 detection of an abnormality in the commercial 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 after the grid voltage drops. 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.

[0047] <Effects of this embodiment> The bidirectional 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 commercial power grid 10, the mechanical switch 2 is opened and the supply of power from the distributed power source 1 to the compensated load 30 is started, so that power can be supplied to the compensated load 30 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 compensated load 30 can be started at an appropriate timing without being excessively early or late, and a deterioration in the voltage quality of the compensated load 30 can be prevented.

[0048] Furthermore, in the bidirectional power supply system 100 of this embodiment, the distributed power supply control unit 8 is configured to switch the distributed power supply 1 from current control (CC control) to voltage control (CVCF control) 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 the voltage abnormality is detected, whichever is earlier.Therefore, even if, for example, the current flowing through the commutation circuit 3 when the mechanical switch 2 is opened is very small and the opening start detection unit 7 cannot detect the opening timing, the distributed power supply 1 can be switched from current control (CC control) to voltage control (CVCF control) after a predetermined time has elapsed since the voltage abnormality on the commercial power grid 10 side was detected, and compensation operation can be performed reliably.

[0049] <Other Modified Embodiments> The present invention is not limited to the above-described embodiment.

[0050] For example, as shown in FIG. 9 , a bidirectional 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. 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 discharge resistor 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 closed 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 discharge resistor 91 is configured to be at least greater than the current-carrying resistance of the mechanical switch 2.

[0051] Furthermore, in the bidirectional 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 an instrument 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 bidirectional power supply system 100 of another embodiment may be configured to be connected via an instrument transformer in a power line L2 connected in parallel to the mechanical switch 2 and the commutation circuit 3, to constantly measure the three-phase inter-pole voltages of the mechanical switch 2, and to detect the opening timing of the mechanical switch 2 based on the inter-pole voltage values.

[0052] 11, the distributed power supply control unit 8 may be configured to switch the distributed power supply 1 from current control (CC control) to voltage control (CVCF control) when a predetermined first delay time has elapsed since the opening timing of the mechanical switch 2 was detected, without considering the second delay time. However, this switching includes the distributed power supply control unit 8 stopping the current control (CC control) early after detecting the start timing of the opening operation of the mechanical switch 2.

[0053] Although the parallel-off switches 4a and 4b are provided on both the commercial power system 10 side and the compensation target 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.

[0054] 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]

[0055] 100···Two-way power supply system 10...Commercial power system 30 Compensated load L1...power line 1...distributed power supply 2. Mechanical Switch 31 Commutation 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 91...discharge resistor

Claims

1. A bidirectional power supply system that is provided between a commercial power system and a load to be compensated and performs interconnected operation including power supply to the load to be compensated and reverse power flow to the commercial power system, a distributed power source connected to a power line for supplying power from the commercial power system to the load to be compensated; a mechanical switch that is provided closer to the commercial power grid than the distributed power source and that opens and closes the power line; a commutation capacitor connected in parallel to the mechanical switch; a system abnormality detection unit that detects a voltage abnormality on the commercial power system side of the mechanical switch; an opening / closing control unit that outputs an opening command to the mechanical switch when the voltage abnormality is detected; an opening start detection unit that detects an opening timing at which the mechanical switch starts an opening operation after the opening command is output; a distributed power supply control unit that controls the current of the distributed power supply before detecting the opening timing, and switches the distributed power supply from current control to voltage control when the opening timing is detected.

2. 2. The bidirectional power supply system according to claim 1, wherein the distributed power supply control unit starts voltage control of the distributed power supplies after a predetermined first delay time set in accordance with an opening characteristic of the mechanical switch has elapsed after the opening timing is detected.

3. The distributed power supply control unit When the first delay time has elapsed since the opening timing was detected, or 3. The bidirectional power supply system according to claim 2, wherein the voltage control of the distributed power sources is started either at an earlier point in time after the voltage abnormality is detected or when a predetermined second delay time longer than the first delay time has elapsed.

4. 3. The bidirectional 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 capacitor.

5. 3. The bidirectional 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.

6. 6. The bidirectional power supply system according to claim 1, further comprising a discharge resistor connected in parallel with the mechanical switch for discharging the commutation capacitor.

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