JP6848700B2 - Grid interconnection device - Google Patents

Description

The present invention relates to a grid interconnection device that converts DC power of a power generation device such as a photovoltaic power generation device into AC power and interconnects it with a commercial power system to supply power to an indoor load.

The grid interconnection device is provided on a power conditioner having a DC AC conversion device for converting DC power into AC power, and a first electric wire and a second electric wire connecting the power conditioner and a commercial power system. It includes a first grid interconnection relay and a second grid interconnection relay. This grid interconnection device controls the relay for each grid interconnection to disconnect the commercial power system and the power generation device from the interconnection operation in which the commercial power system and the power generation device are interconnected, and to disconnect the commercial power system and the power generation device to generate the power generation device. Switch between self-sustaining operation that supplies power to indoor loads. The grid interconnection device controls each grid interconnection relay so as to disconnect the commercial power system and the power generation device in order to change from the interconnection operation to the independent operation when the commercial power system loses power.

By the way, there is a case where the contacts of the relay for grid interconnection are welded and a welding defect that cannot be opened occurs. In this case, the grid interconnection device also controls the relays for each grid interconnection so as to disconnect the commercial power system and the power generation device in order to change from the interconnection operation to the independent operation in the event of a power failure of the commercial power system. Nevertheless, in reality, the commercial power system and the power generation equipment have not been disconnected. Therefore, the grid interconnection device determines whether or not the contacts of the relays for each grid interconnection are welded in the event of a power failure of the commercial power system. In one example, the grid interconnection device is used for the first grid interconnection by operating the DC AC converter while the first grid interconnection relay is in the open state and the second grid interconnection relay is in the closed state. Determine if the relay contacts are welded. Further, in the grid interconnection device, when the first grid interconnection relay is in the closed state and the second grid interconnection relay is in the open state, the DC AC converter is operated to operate the second grid interconnection relay. It is determined whether or not the contacts are welded (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2011-135767

By the way, when the commercial power system has a power failure, if the commercial power system recovers power while the DC / AC converter is operating to determine the welding failure of each grid interconnection relay, the DC / AC converter and power generation The voltage of the DC bus that connects to the device may rise. As a result, the electronic components connected to the DC bus may break down.

An object of the present invention is to provide a grid interconnection device capable of enhancing safety.

The grid interconnection device that solves the above problems includes a DC AC converter that converts DC power into AC power and outputs it to the first and second electric wires connected to the commercial power system, and the first electric wire. For the first grid interconnection relay provided in, the second grid interconnection relay provided in the second electric wire, and the first grid interconnection relay in the first electric wire. Is connected to the DC / AC converter side, is connected to the DC / AC converter side with respect to the second grid interconnection relay in the second electric wire, and charges / discharges the power from the DC / AC converter. A charge / discharge unit, a DC / AC converter, a control unit for controlling the first grid interconnection relay, and a control unit for controlling the second grid interconnection relay are provided, and the control unit comprises the commercial power supply. When the system is out of power, the DC-AC converter is operated so as to charge the charge / discharge unit, and then the output side of the DC-AC converter is electrically insulated from the input side of the DC-AC converter. The operation of the DC / AC converter is stopped so that at least one of the first grid interconnection relay and the second grid interconnection relay is welded based on the discharge mode from the charging / discharging unit. Welding determination control is executed to determine whether or not this is done.

According to this configuration, in a state where the operation of the DC / AC converter is stopped, it is determined in order to determine whether or not at least one of the relays for interconnection of each system is welded by the discharge of the charge / discharge unit. Even if the commercial power system is restored during the period, the voltage rise of the DC bus to which the input side of the DC AC converter is connected can be suppressed. Therefore, since the occurrence of failure of the electronic component connected to the DC bus can be suppressed, the safety of the grid interconnection device can be enhanced.

In one form of the grid interconnection device, the charge / discharge unit includes a filter capacitor.
According to this configuration, the restoration work of the commercial power system can be safely performed by determining whether or not at least one of the relays for interconnection of each system is welded based on the discharge of the filter capacitor having a small capacity. Can be done.

In one form of the grid interconnection device, the voltage of the charge / discharge unit charged from the DC / AC conversion device is equal to or lower than the dangerous voltage.
According to this configuration, the restoration work of the commercial power system can be performed more safely.

In one form of the grid interconnection device, the portion between the DC AC converter and the first grid interconnection relay in the first wire and the DC AC converter in the second wire. It further has a first voltage detection unit connected to a portion between the second grid interconnection relay, and the first voltage detection unit is charged when the DC AC converter is stopped. The output voltage of the discharge unit can be detected, and the control unit can detect the output voltage after a predetermined time from the start of discharge of the charge / discharge unit based on the detection result of the first voltage detection unit in the welding determination control. It is determined whether or not any of the first grid interconnection relay and the second grid interconnection relay is welded.

When a closed circuit is formed between the DC / AC converter and the commercial power system via each grid interconnection relay, the voltage of the charge / discharge section drops rapidly when the charge / discharge section is discharged. On the other hand, if a closed circuit is not formed between the DC / AC converter and the commercial power system via the relays for interconnection of each system, the charge / discharge section becomes spontaneous discharge, so the voltage of the charge / discharge section becomes gentle. descend. As described above, the voltage of the charge / discharge unit after a predetermined time differs depending on whether or not a closed circuit is formed between the DC / AC converter and the commercial power system. From this point of view, it is easy to determine whether or not any of the relays for interconnection of each system is welded based on the voltage of the charging / discharging section after a predetermined time from the start of discharging of the charging / discharging section. it can.

In one form of the grid interconnection device, the control unit is based on the detection result of the first voltage detection unit during the period of charging the charge / discharge unit at the time of executing the welding determination control. It is determined whether or not both the grid interconnection relay 1 and the second grid interconnection relay are welded.

When at least one of the relays for interconnection of each system is opened, a closed circuit is not formed between the DC AC converter and the commercial power system. Therefore, the voltage detected by the first voltage detection unit rises due to the power output from the DC / AC converter. On the other hand, when both of the relays for interconnection of each system are welded, a closed circuit is formed between the DC / AC converter and the commercial power system. Therefore, since the charge / discharge unit discharges from the side where the charge / discharge unit is charged from the DC / AC converter, the voltage detected by the first voltage detection unit does not increase. From such a viewpoint, it can be easily determined whether or not both of the relays for interconnection of each system are welded based on the detection result of the first voltage detection unit during the period of charging the charging / discharging unit.

In one form of the grid interconnection device, a first current detection unit provided in a portion between the first grid interconnection relay and the commercial power system in the first electric wire, and the first current detection unit. The second electric wire further includes a second current detection unit provided in a portion between the second system interconnection relay and the commercial power system, and the control unit executes the welding determination control. Based on the detection result of the first current detection unit and the detection result of the second current detection unit when the current is sometimes discharged from the charging / discharging unit, the first grid interconnection relay and the second Determine if any of the grid interconnection relays are welded.

According to this configuration, it is possible to determine whether or not any of the grid interconnection relays is welded based on at least one of the voltage at the time of discharge of the charging / discharging unit and the current flowing through each grid interconnection relay. Therefore, for example, even if an abnormality occurs in the voltage detection unit, it can be determined whether or not any of the grid interconnection relays is welded based on the current flowing through the grid interconnection relays.

In one form of the grid interconnection device, the control unit detects the detection result of the first current detection unit and the second current detection when the charge / discharge unit discharges when the welding determination control is executed. Based on the detection result of the unit, it is determined whether or not both the first grid interconnection relay and the second grid interconnection relay are welded.

According to this configuration, it is possible to determine whether or not both of the relays for interconnection of each system are welded based on at least one of the voltage at the time of charging the charging / discharging unit and the current flowing through the relays for each system interconnection. Therefore, even if an abnormality occurs in the second voltage detection unit, it can be determined whether or not both of the grid interconnection relays are welded based on the current flowing through the grid interconnection relays.

According to the grid interconnection device of the present invention, safety can be enhanced.

Schematic configuration diagram of the power management system. A schematic of a part of a power management system. A flowchart showing a processing procedure of switching control executed by a control unit. The graph which shows the discharge mode of a filter capacitor. The flowchart which shows the processing procedure of the preparatory processing of welding judgment control at the time of a power failure of a commercial power system. The flowchart which shows the processing procedure of the stop time judgment processing of the welding judgment control at the time of the power failure of a commercial power system. The flowchart which shows the processing procedure of welding judgment control at the time of starting a power conditioner.

Hereinafter, one embodiment will be described with reference to the drawings.
As shown in FIG. 1, the power management system 1 includes a grid interconnection device 10 and a photovoltaic power generation device 2 connected to the grid interconnection device 10. The grid interconnection device 10 is connected to the commercial power system 3 via the first electric wire 11 and the second electric wire 12 which are AC buses. An AC load 4 is connected to the first electric wire 11 and the second electric wire 12 via a first system interconnection relay 13 and a second system interconnection relay 14, and a first independent system relay. The self-supporting load 5 is connected via the 15A and the second self-supporting system relay 15B. The AC load 4 is, for example, an indoor load, and examples thereof include lighting, a refrigerator, a washing machine, an air conditioner, and a microwave oven. The self-sustaining load 5 is a pre-selected load among the AC loads 4, and includes lighting, a refrigerator, and the like. The power management system 1 adjusts the power between the photovoltaic power generation device 2, the commercial power system 3, and the AC load 4 (self-sustaining load 5) by the grid interconnection device 10. In one example, the reverse power flow of the power generated by the photovoltaic power generation device 2 to the commercial power system 3 and the adjustment of the supply to the AC load 4 (self-sustaining load 5), and the AC load 4 (self-sustaining load) of the power of the commercial power system 3 are adjusted. Adjustment of supply to 5) can be mentioned. In addition to the photovoltaic power generation device 2, the power management system 1 can use a wind power generation device, a gas power generation device, a geothermal power generation device, or the like as a power generation device connected to the grid interconnection device 10.

The photovoltaic power generation device 2 has a photovoltaic power generation panel (not shown), and supplies the DC power generated by the photovoltaic power generation panel to the grid interconnection device 10. The photovoltaic power generation device 2 executes maximum power point tracking control for extracting current at an output voltage that maximizes the power output by the photovoltaic power generation panel.

The grid interconnection device 10 has an interconnection operation in which the photovoltaic power generation device 2 and the commercial power system 3 are interconnected, and the photovoltaic power generation device 2 and the commercial power system 3 are not interconnected in the grid, and the self-sustaining load 5 is applied. It is possible to switch between independent operation and operation by the photovoltaic power generation device 2 (power generation device). The grid interconnection device 10 includes a power conditioner 20, relays 13 and 14 for each grid interconnection, relays 15A and 15B for each independent system, and a control unit 30.

The power conditioner 20 is connected to the commercial power system 3 via the first electric wire 11 and the second electric wire 12. The first grid interconnection relay 13 is provided on the first electric wire 11. The second grid interconnection relay 14 is provided on the second electric wire 12. The first electric wire 11 is an electric wire portion 11a between the power conditioner 20 and the first grid interconnection relay 13, and an electric wire portion between the first grid interconnection relay 13 and the commercial power system 3. Includes 11b and. The second electric wire 12 includes an electric wire portion 12a between the power conditioner 20 and the second grid interconnection relay 14, and an electric wire portion 12b between the second grid interconnection relay 14 and the commercial power system 3. And include.

When the relays 13 and 14 for grid interconnection are closed, the power conditioner 20 and the commercial power grid 3 can be interconnected to the grid. When the relays 13 and 14 for grid interconnection are in the open state, the power conditioner 20 and the commercial power grid 3 are in a state in which grid interconnection is not possible, that is, in a disconnected state. The control unit 30 controls the operation of the power conditioner 20 and the relays 13 and 14 for interconnection of each system.

The power conditioner 20 converts the DC power generated by the photovoltaic power generation device 2 into AC power and outputs it to the commercial power system 3. The power conditioner 20 includes a PV converter 21, a DC AC converter 22 (inverter circuit), a first DC bus 23, a second DC bus 24, a smoothing capacitor 25, and a filter circuit 26. The PV converter 21 and the DC AC converter 22 are connected to each other by a first DC bus 23 and a second DC bus 24. The first end of the smoothing capacitor 25 is connected to the first DC bus 23, and the second end of the smoothing capacitor 25 is connected to the second DC bus 24. As the smoothing capacitor 25, for example, an aluminum electrolytic capacitor or a tantalum electrolytic capacitor is used.

The photovoltaic power generation device 2 is connected to the PV converter 21. The PV converter 21 outputs the photovoltaic power generation device 2, which changes depending on the sunshine conditions such as the season, the weather, and the time zone, to the first DC bus 23 by the maximum power point tracking control. An example of the set voltage output by the PV converter 21 to the first DC bus 23, that is, the voltage between the first DC bus 23 and the second DC bus 24 is 380V. The smoothing capacitor 25 smoothes the voltage output from the PV converter 21. The DC AC conversion device 22 converts the DC power of the first DC bus 23 into, for example, an AC power of 200 V in effective value and outputs it to the first electric wire 11 and the second electric wire 12. The filter circuit 26 is provided on the first electric wire 11 and the second electric wire 12. The filter circuit 26 removes the high-frequency component of the AC power output from the DC-AC converter 22 to make the output voltage of the DC-AC converter 22 into a sinusoidal waveform and outputs it to the commercial power system 3.

As shown in FIG. 2, the DC / AC converter 22 includes a first switching arm 22a and a second switching arm 22b connected in parallel with each other. The first switching arm 22a has a switching element MU1 on the upper stage side and a switching element ML1 on the lower stage side. The switching elements MU1 and ML1 are preferably field effect transistors, for example. In one example, the switching elements MU1 and ML1 are MOSFETs. The switching element MU1 on the upper stage side and the switching element ML1 on the lower stage side are connected in series with each other. More specifically, the drain terminal of the switching element MU1 is connected to the first DC bus 23, the source terminal of the switching element MU1 and the drain terminal of the switching element ML1 are connected to each other, and the source terminal of the switching element ML1 is the second. It is connected to the DC bus 24 of.

The second switching arm 22b has a switching element MU2 on the upper stage side and a switching element ML2 on the lower stage side. The switching elements MU2 and ML2 are preferably field effect transistors, for example. In one example, the switching elements MU2 and ML2 are MOSFETs. The switching element MU2 on the upper stage side and the switching element ML2 on the lower stage side are connected in series with each other. More specifically, the drain terminal of the switching element MU2 is connected to the first DC bus 23, the source terminal of the switching element MU2 and the drain terminal of the switching element ML2 are connected to each other, and the source terminal of the switching element ML2 is the second. It is connected to the DC bus 24. The switching elements MU1, ML1, MU2, and ML2 may be insulated gate bipolar transistors (IGBTs).

The filter circuit 26 has a first reactor 26a, a second reactor 26b, and a filter capacitor 26c. The first reactor 26a is provided in the electric wire portion 11a of the first electric wire 11, and the second reactor 26b is provided in the electric wire portion 12a of the second electric wire 12. The first end of the first reactor 26a is connected to the node between the switching element MU1 and the switching element ML1, and the second end of the first reactor 26a is connected to the first end of the filter capacitor 26c. There is. The first end of the second reactor 26b is connected to the node between the switching element MU2 and the switching element ML2, and the second end of the second reactor 26b is connected to the second end of the filter capacitor 26c. There is. As the filter capacitor 26c, for example, a film capacitor or a monolithic ceramic capacitor is used. The capacitance of the filter capacitor 26c is smaller than the capacitance of the smoothing capacitor 25, for example, several μF.

The grid interconnection device 10 further includes a first voltage detection unit 16, a second voltage detection unit 17, a first current detection unit 18, and a second current detection unit 19.
The first voltage detection unit 16 includes a portion (electric wire unit 11a) between the DC AC converter 22 in the first electric wire 11 and the relay 13 for grid interconnection in the first electric wire 11 and a DC AC in the second electric wire 12. It is connected to a portion (electric wire portion 12a) between the conversion device 22 and the second grid interconnection relay 14. More specifically, the first end of the first voltage detection unit 16 is the portion of the electric wire portion 11a to which the first end of the filter capacitor 26c is connected and the first end of the first grid interconnection relay 13. It is connected to the part between the parts. The second end of the first voltage detection unit 16 is between the portion of the electric wire portion 12a to which the second end of the filter capacitor 26c is connected and the first end of the second grid interconnection relay 14. It is connected to the part. The first end of the grid interconnection relays 13 and 14 is the end of the filter circuit 26 side with respect to the grid interconnection relays 13 and 14. The first voltage detection unit 16 detects the voltage between the electric wire unit 11a and the electric wire unit 12a (hereinafter, “voltage Vout”), and outputs the detection result to the control unit 30. When the DC / AC converter 22 is operating, the voltage Vout becomes the output voltage output by the DC / AC converter 22 via the filter circuit 26.

The second voltage detection unit 17 includes a portion (electric wire portion 11b) between the second end portion of the first grid interconnection relay 13 in the first electric wire 11 and the commercial power system 3 and a second electric wire. 12 is connected to a portion (electric wire portion 12b) between the second end portion of the second grid interconnection relay 14 and the commercial power system 3. The second voltage detection unit 17 detects the voltage between the electric wire unit 11b and the electric wire unit 12b (hereinafter, “voltage Vgrid”), and outputs the detection result to the control unit 30. The second end of the grid interconnection relays 13 and 14 is the end on the commercial power system 3 side with respect to the grid interconnection relays 13 and 14. The voltage Vgrid is the voltage between the terminals of the commercial power system 3 except during a power failure of the commercial power system 3.

The first current detection unit 18 is provided in a portion (electric wire portion 11b) between the second end portion of the first grid interconnection relay 13 and the commercial power system 3 in the first electric wire 11. The first current detection unit 18 detects the current flowing through the electric wire unit 11b and outputs the detection result to the control unit 30.

The second current detection unit 19 is provided in a portion (electric wire portion 12b) between the second end portion of the second grid interconnection relay 14 and the commercial power system 3 in the second electric wire 12. The second current detection unit 19 detects the current flowing through the electric wire unit 12b and outputs the detection result to the control unit 30.

The grid interconnection device 10 further includes a rectifier circuit 31, a smoothing capacitor 32, backflow prevention diodes 33 and 34, and a DC / DC converter 35, and supplies power from the photovoltaic power generation device 2 or the commercial power system 3 to the control unit 30. Supply.

The DC / DC converter 35 is connected to the commercial power system 3 via a rectifier circuit 31, a smoothing capacitor 32, a first electric wire 11, and a second electric wire 12. The input side terminal of the rectifier circuit 31 is connected to the first electric wire 11 (electric wire portion 11b) and the second electric wire 12 (electric wire portion 12b), and the output side terminal of the rectifier circuit 31 is connected to the smoothing capacitor 32. The rectifier circuit 31 rectifies the alternating current of the first electric wire 11 and the second electric wire 12 into a direct current. In one example, the rectifier circuit 31 is a bridge-type full-wave rectifier circuit composed of four diodes. The smoothing capacitor 32 is connected to the first DC bus 23 and the second DC bus 24, while being connected to the DC / DC converter 35. The smoothing capacitor 32 smoothes the voltage output from the rectifier circuit 31.

The input side of the DC / DC converter 35 is connected to the power conditioner 20 via the first DC bus 23 and the second DC bus 24. A backflow prevention diode 33 is connected to the first DC bus 23. The cathode of the backflow prevention diode 33 is connected to the DC / DC converter 35 (smoothing capacitor 32). A backflow prevention diode 34 is connected to the second DC bus 24. The anode of the backflow prevention diode 34 is connected to the DC / DC converter 35 (smoothing capacitor 32).

The output side of the DC / DC converter 35 is connected to the control unit 30. The DC / DC converter 35 lowers the output voltage from the photovoltaic power generation device 2 or the commercial power system 3 to a voltage suitable for the operation of the control unit 30 and outputs the output voltage to the control unit 30. The DC / DC converter 35 outputs electric power to the control unit 30 based on the electric power from the higher voltage of the photovoltaic power generation device 2 or the commercial electric power system 3.

The control unit 30 executes switching control for switching between interconnection operation and independent operation based on whether or not the commercial power system 3 has a power failure. The control unit 30 performs the interconnection operation when the commercial power system 3 does not have a power failure, and switches from the interconnection operation to the independent operation when the commercial power system 3 has a power failure. Then, when the commercial power system 3 recovers from a power failure, the control unit 30 switches from independent operation to interconnected operation. The control unit 30 controls the relays 13 and 14 for interconnection of each system so that the power conditioner 20 and the commercial power system 3 are disconnected when switching from the interconnection operation to the independent operation, and each independent system. The relays 15A and 15B are closed. The control unit 30 controls the relays 13 and 14 for interconnection of each system so that the power conditioner 20 and the commercial power system 3 are connected to each other when switching from the independent operation to the interconnection operation, and each independent system. The relays 15A and 15B are opened. Then, when the commercial power system 3 loses power, the control unit 30 causes welding failure in the first system interconnection relay 13 and the second system interconnection relay 14 before switching from the interconnection operation to the independent operation. Welding determination control for determining whether or not this is performed is executed.

A processing procedure for switching control by the control unit 30 will be described with reference to FIG. The switching control is repeatedly executed at predetermined time intervals.
The control unit 30 determines in step S11 whether or not the interconnection operation is in progress. When the control unit 30 determines that the interconnection operation is in progress (step S11: YES), the control unit 30 determines in step S12 whether or not the commercial power system 3 is out of power. The control unit 30 determines whether or not the commercial power system 3 is out of power based on, for example, communication from an electric power company or the like.

When the control unit 30 determines that the commercial power system 3 is not out of power (step S12: NO), that is, when it has not received a signal from the electric power company or the like that the commercial power system 3 is out of power, the control unit 30 once receives a signal. End the process. In this case, the interconnection operation is continued. On the other hand, when the control unit 30 determines that the commercial power system 3 is out of power (step S12: YES), that is, when it receives a signal from the electric power company or the like that the commercial power system 3 is out of power, the step. In S13, the power conditioner 20 and the commercial power system 3 are disconnected. Specifically, the control unit 30 controls each of the grid interconnection relays 13 and 14 from the closed state to the open state. Then, the control unit 30 executes the welding determination control in step S14.

The control unit 30 acquires the result of welding determination control, and in step S15, whether or not at least one of the contact of the first grid interconnection relay 13 and the contact of the second grid interconnection relay 14 is welded. Is determined. When the control unit 30 determines that at least one of the contacts of the first grid interconnection relay 13 and the contacts of the second grid interconnection relay 14 is welded (step S15: YES), step S16. In, switching to independent operation is prohibited, and the process is temporarily terminated. On the other hand, when the control unit 30 determines that both the contacts of the first grid interconnection relay 13 and the contacts of the second grid interconnection relay 14 are not welded (step S15: NO), step S17. Switch to independent operation.

Further, the control unit 30 determines in step S18 whether or not the commercial power system 3 is repowered when the interconnection operation is not in progress (step S11: NO), that is, in the case of the self-sustaining operation. The control unit 30 determines whether or not the commercial power system 3 has recovered power based on, for example, communication from a power company or the like.

When the commercial power system 3 is restored (step S18: YES), that is, when the control unit 30 receives a signal from the electric power company or the like that the commercial power system 3 is restored, the control unit 30 continues in step S19. Switch to system operation. On the other hand, when the commercial power system 3 has not been restored (step S18: NO), that is, when the control unit 30 has not received a signal from the electric power company or the like that the commercial power system 3 has been restored. The process ends once. In this case, the independent operation is continued.

Next, the detailed contents of the welding determination control will be described.
If one of the relays 13 and 14 for grid interconnection is in the open state, a closed circuit is not formed between the DC AC converter 22 and the commercial power system 3, so that the DC AC converter 22 is transferred to the commercial power system 3. No power is supplied. On the other hand, if both the relays 13 and 14 for grid interconnection are in the closed state, a closed circuit is formed between the DC AC converter 22 and the commercial power system 3, so that the DC AC converter 22 is commercially available. Power is supplied to the power system 3. That is, if one of the relays 13 and 14 for grid interconnection is controlled to be in the closed state and the other is controlled to be in the open state, if power is supplied from the DC AC converter 22 to the commercial power system 3. , It can be determined that the other contacts of the relays 13 and 14 for each grid interconnection are welded. Therefore, in the welding determination control, the control unit 30 controls the DC AC converter 22 after controlling the first grid interconnection relay 13 in the open state and the second grid interconnection relay 14 in the closed state. By monitoring whether or not a voltage appears in the second voltage detection unit 17 when driven, it is determined whether or not the contacts of the first grid interconnection relay 13 are welded. Further, when the control unit 30 drives the DC AC converter 22 after controlling the first grid interconnection relay 13 in the closed state and the second grid interconnection relay 14 in the open state, the second system interconnection relay 13 is in a closed state. By monitoring whether or not a voltage appears in the voltage detection unit 17, it is determined whether or not the contacts of the second grid interconnection relay 14 are welded.

By the way, if it is assumed that a voltage appears in the second voltage detection unit 17 when the DC / AC converter 22 is driven (hereinafter, “virtual grid interconnection device”), the DC / AC converter 22 is commercially available during operation. When the power system 3 recovers power, the voltage applied to the first DC bus 23 and the second DC bus 24 of the DC AC converter 22 may become higher than 380 V. As a result, in the virtual system interconnection device, the withstand voltage of the smoothing capacitor 25 connected to the first DC bus 23 and the second DC bus 24 may be higher, and the smoothing capacitor 25 may fail. As described above, the first grid interconnection relay 13 is in the open state and the second grid interconnection relay 14 is in the closed state, and the first grid interconnection relay 13 is in the closed state and the second grid. In two patterns in which the interconnection relay 14 is in the open state, the virtual grid interconnection device supplies power from the DC AC converter 22 toward the commercial power system 3. For this reason, in the virtual grid interconnection device, the DC AC converter 22 often operates in order to determine the welding failure of the relays 13 and 14 for each grid interconnection, and therefore, it is commercially available during the operation of the DC AC converter 22. There is a high possibility that the power system 3 will be restored.

Therefore, the inventor of the present application stops the operation of the DC AC converter 22 when supplying power to the commercial power system 3 for the two patterns of opening and closing of the relays 13 and 14 for each system interconnection. I focused on doing. As a means for stopping the operation of the DC / AC converter 22, the inventor of the present application supplies electric power to the relays 13 and 14 for grid interconnection from the charge / discharge unit that stores the electric power from the DC / AC converter 22. I thought. As a result, when the commercial power system 3 has a power failure, the DC / AC converter 22 supplies power to the charge / discharge unit, and the charge / discharge unit supplies power to the relays 13 and 14 for each system interconnection. The operation of the DC / AC converter 22 can be stopped while determining whether or not the contacts of the system relays 13 and 14 are welded.

In addition, the inventor of the present application pays attention to the use of the filter capacitor 26c as the charge / discharge unit, and when the commercial power system 3 has a power failure, the DC AC converter 22 and the commercial power system 3 are connected to the relay 13 for each system interconnection. It was found that the discharge mode of the filter capacitor 26c differs depending on whether or not a closed circuit is formed via 14. More specifically, when the DC / AC converter 22 and the commercial power system 3 form a closed circuit due to the closed state of the respective grid interconnection relays 13 and 14, when the discharge of the filter capacitor 26c is started. , A large discharge current flows from the filter capacitor 26c to the commercial power system 3 side. The filter capacitor 26c was originally provided to filter out high-frequency noise superimposed on the AC voltage waveform output during the operation of the DC-AC converter 22, and its capacitance value is about several tens of pF to several μF. Since it is very small and the amount of charge that can be stored is small, the time required for charging and discharging can be very short. As a result, as shown by the alternate long and short dash line in FIG. 4, when the discharge of the filter capacitor 26c is started at time t1, the voltage (voltage Vout) of the filter capacitor 26c drops sharply. On the other hand, when at least one of the relays 13 and 14 for grid interconnection does not form a closed circuit between the DC AC converter 22 and the commercial power system 3 due to the open state, the filter capacitor 26c is spontaneously discharged. As a result, as shown by the solid line in FIG. 4, when the discharge of the filter capacitor 26c is started at time t1, the voltage (voltage Vout) of the filter capacitor 26c gradually decreases.

If the discharge mode of the filter capacitor 26c can be grasped in this way, the DC AC converter 22 and the commercial power system 3 form a closed circuit from the discharge mode of the filter capacitor 26c via the relays 13 and 14 for each system interconnection. It can be determined whether or not it is. That is, even if one of the relays 13 and 14 for interconnection of each system is controlled to be in the open state, if the DC AC converter 22 and the commercial power system 3 form a closed circuit, the relays 13 for interconnection of each system, It can be determined that one of the contacts of 14 is welded. Therefore, the control unit 30 uses the filter capacitor 26c as the charge / discharge unit in the welding determination control, and the first grid interconnection relay 13 and the second grid interconnection relay 14 based on the discharge mode of the filter capacitor 26c. It is determined whether or not a welding defect has occurred in the capacitor.

With reference to FIGS. 5 and 6, welding determination control at the time of a power failure of the commercial power system 3 will be described.
The welding determination control includes the preparatory process shown in FIG. 5 and the power failure determination process shown in FIG. The preparatory process is mainly a process in which the DC / AC converter 22 operates to charge the filter capacitor 26c. The power failure determination process is a process performed after the preparatory process, and is one of the first grid interconnection relay 13 and the second grid interconnection relay 14 by monitoring the discharge mode of the charged filter capacitor 26c. This is a process for determining whether or not a welding defect has occurred in the capacitor.

As shown in FIG. 5, the control unit 30 charges the filter capacitor 26c from the DC / AC converter 22 in step S21. In one example, the control unit 30 sets a preset duty for the switching element MU1 on the upper stage side of the first switching arm 22a and the switching element ML2 on the lower stage side of the second switching arm 22b in the DC AC converter 22 of FIG. The switching element ML1 on the lower stage side of the first switching arm 22a and the switching element MU2 on the upper stage side of the second switching arm 22b are turned off by the ratio. The control unit 30 sets the duty ratios of the switching element MU1 and the switching element ML2 so that the voltage of the filter capacitor 26c becomes a predetermined voltage. Here, the predetermined voltage is equal to or lower than the dangerous voltage. An example of a dangerous voltage is a voltage exceeding DC60V in the IEC60950-1 standard. Further, the predetermined voltage is preferably equal to or lower than the safety voltage. The safe voltage is a voltage that does not pose a danger to the human body, and is, for example, DC50V. In this embodiment, the predetermined voltage is DC40V.

Next, the control unit 30 determines in step S22 whether or not the charging of the filter capacitor 26c is completed. When the charging of the filter capacitor 26c is completed, the voltage of the filter capacitor 26c (the output voltage of the filter capacitor 26c) is within the voltage range. The voltage range is a predetermined voltage range including the above-mentioned predetermined voltage, and is preset by a test or the like. The voltage range of this embodiment is DC35V or more and DC40V or less. Here, it is determined whether or not the charging of the filter capacitor 26c is completed based on the detection result of the first voltage detection unit 16. The reason is as follows. That is, if one of the relays 13 and 14 for grid interconnection is in the open state, a closed circuit is not formed between the DC AC converter 22 and the commercial power system 3, so that the first voltage detection unit 16 Detects DC40V, and the second voltage detection unit 17 detects about 0V. In this case, the electric power from the DC / AC converter 22 is charged into the filter capacitor 26c. On the other hand, when both the contacts of the relays 13 and 14 for grid interconnection are welded together, a closed circuit is formed between the DC AC converter 22 and the commercial power system 3, so that the DC AC converter 22 is installed. Even if DC40V is applied to the first electric wire 11, both the first voltage detection unit 16 and the second voltage detection unit 17 detect about 0V. In this case, the power from the DC / AC converter 22 is discharged toward the commercial power system 3 side from the side supplied to charge the filter capacitor 26c, so that the first voltage detection unit 16 and the second voltage detection unit 16 and the second The detection voltage of the voltage detection unit 17 of the above does not increase at all. On the other hand, when the relays 13 and 14 for each grid interconnection are normally opened, the first voltage detection is performed because a closed circuit is not formed between the DC AC converter 22 and the commercial power grid 3. The unit 16 detects DC40V, and the second voltage detection unit 17 detects about 0V. In this way, both the detection result of the second voltage detection unit 17 when at least one of the grid interconnection relays 13 and 14 is open and the contacts of the grid interconnection relays 13 and 14 are welded together. Since the detection result of the second voltage detection unit 17 is substantially equal to that of the second voltage detection unit 17, it is not possible to determine whether or not the charging of the filter capacitor 26c is completed only from the detection result of the second voltage detection unit 17. On the other hand, the detection result of the first voltage detection unit 16 when at least one of the relays 13 and 14 for each grid is open and the contacts of the relays 13 and 14 for each grid are welded together. The detection results of the first voltage detection unit 16 are different from each other. Therefore, it can be determined whether or not the charging of the filter capacitor 26c is completed based on the detection result of the first voltage detection unit 16.

When the charging of the filter capacitor 26c is not completed (step S22: NO), that is, when the voltage of the filter capacitor 26c falls below the voltage range, the control unit 30 determines after the charging of the filter capacitor 26c is started in step S23. Determine if time has passed. The predetermined time is the time from the start of charging of the filter capacitor 26c until the predetermined voltage (DC40V in this embodiment) is reached, and is set in advance by a calculation formula, an experiment, or the like. In one example, the predetermined time is 10 μs.

When the control unit 30 determines that a predetermined time has not elapsed since the charging of the filter capacitor 26c was started (step S23: NO), the control unit 30 returns to the determination in step S22. On the other hand, when the control unit 30 determines that a predetermined time has elapsed since the charging of the filter capacitor 26c was started (step S23: YES), in step S24, both the contacts of the relays 13 and 14 for grid interconnection are connected. Judge that it is welded.

Then, when the control unit 30 determines that the contacts of the relays 13 and 14 for interconnection of each system are welded, the control unit 30 stops the operation of the DC / AC converter 22 in step S25. That is, the control unit 30 maintains all of the switching elements MU1, ML1, MU2, and ML2 of the DC / AC converter 22 in the off state. In this case, since the filter capacitor 26c cannot be charged, and the control unit 30 shifts to the switching control step S15 (see FIG. 3). In this case, since the control unit 30 determines affirmatively in step S15, the control unit 30 shifts to step S16 and prohibits switching to independent operation.

Further, when the control unit 30 determines that the charging of the filter capacitor 26c is completed (step S22: YES), that is, when both the contacts of the relays 13 and 14 for each system interconnection are not welded, the step. In S26, the operation of the DC / AC converter 22 is stopped in the same manner as in step S25, and in step S27, the process shifts to the stop determination process.

In the stop time determination process shown in FIG. 6, the control unit 30 controls so that the first grid interconnection relay 13 is in the closed state in step S31, and whether or not the stop state welding condition is satisfied in step S32. To judge. As a welding condition at the time of stop, the voltage (voltage Vout) of the filter capacitor 26c when a predetermined time elapses from the start of discharging the filter capacitor 26c is less than the threshold value VX. An example of the predetermined time is 200 μs. Further, the filter capacitor 26c starts discharging when the power supply from the DC / AC converter 22 to the filter capacitor 26c is stopped in step S26 of the preparatory process shown in FIG. The threshold value VX is a lower limit value of the voltage after a lapse of a predetermined time after the filter capacitor 26c starts spontaneous discharge, and is preset by a test or the like. An example of the threshold VX is DC35V. That is, as shown in FIG. 4, if the voltage (voltage Vout) of the filter capacitor 26c after the elapse of a predetermined time (time t2) from the discharge start (time t1) of the filter capacitor 26c is less than the threshold value VX, the control unit 30 It is determined that the filter capacitor 26c is discharged due to a cause other than natural discharge, and satisfies the welding determination condition. On the other hand, if the voltage (voltage Vout) of the filter capacitor 26c after a lapse of a predetermined time (time t2) from the discharge start (time t1) of the filter capacitor 26c is equal to or higher than the threshold value VX, the control unit 30 naturally uses the filter capacitor 26c. It is determined that the welding determination condition is not satisfied, assuming that only the discharge is performed.

When the control unit 30 determines that the stop welding condition is satisfied (step S32: YES), the control unit 30 determines that one of the contacts of the relays 13 and 14 for interconnection of each system is welded in step S33. In this case, the contacts of the second grid interconnection relay 14 are welded. Then, the control unit 30 controls the first grid interconnection relay 13 to be in the open state in step S34, and then ends the process. In this case, the control unit 30 ends the welding determination control and proceeds to step S15 of the switching control of FIG. Then, in order to make an affirmative determination in step S15, the control unit 30 shifts to step S16 and prohibits switching to independent operation.

When the control unit 30 determines that the stop welding condition is not satisfied (step S32: NO), the control unit 30 controls the first grid interconnection relay 13 to be in the open state in step S35, and then in step S36, the first step is performed. The system interconnection relay 14 of 2 is controlled so as to be in a closed state. Then, the control unit 30 determines in step S37 whether or not the stop welding condition is satisfied.

When the control unit 30 determines that the stop welding condition is satisfied (step S37: YES), the control unit 30 determines that one of the contacts of the relays 13 and 14 for interconnection of each system is welded in step S38. In this case, the contacts of the first grid interconnection relay 13 are welded. Then, the control unit 30 controls the second grid interconnection relay 14 so as to be in the open state in step S39, and then ends the process. Then, the control unit 30 ends the welding determination control, and proceeds to step S15 of the switching control of FIG. In this case, since the control unit 30 determines affirmatively in step S15, the control unit 30 shifts to step S16 and prohibits switching to independent operation.

On the other hand, when the control unit 30 determines that the stop welding condition is not satisfied (step S37: NO), the control unit 30 determines in step S40 that the contacts of the relays 13 and 14 for each system interconnection are not welded, and in step S39. And then end the process. In this case, the control unit 30 shifts to step S15 of the switching control of FIG. Then, in order to make a negative determination in step S15, the control unit 30 shifts to step S17 and switches to independent operation.

Further, the control unit 30 executes the welding determination control not only at the time of power failure of the commercial power system 3 but also at the time of starting the power conditioner 20, for example. When the power conditioner 20 is activated, for example, when the control unit 30 receives the activation signal of the power conditioner 20, both the relays 13 and 14 for interconnection to each system are in the open state before executing the welding determination control. It is controlled so as to be. The power conditioner 20 outputs a start signal to the control unit 30 when, for example, the power button provided on the power conditioner 20 is turned on by the user.

In the welding determination control at the time of starting the power conditioner 20, since the commercial power system 3 is not out of power, the AC power of the commercial power system 3 is supplied to the relays 13 and 14 for each system interconnection. Since the power management system 1 is a single-phase three-wire system, an effective value of 200 V is applied from the commercial power system 3 to the relays 13 and 14 for each system interconnection. That is, the voltage Vgrid (effective value) is about 200V. Here, when both the grid interconnection relays 13 and 14 are closed, the voltage Vout (effective value) on the power conditioner 20 side of the grid interconnection relays 13 and 14 is 200V. Further, when at least one of the relays 13 and 14 for interconnection of each system is opened, the voltage Vout becomes 0V. Therefore, the control unit 30 is based on the combination of the closed state and the open state of the relays 13 and 14 for each system interconnection and the voltage Vout on the power conditioner 20 side of the relays 13 and 14 for each system interconnection. It is possible to determine whether or not the contacts of the relays 13 and 14 for interconnection of each system are welded. As described above, in the welding determination control at the time of starting the power conditioner 20, unlike the welding determination control at the time of power failure of the commercial power system 3, the power conditioner 20 is supplied from the commercial power system 3 to the relays 13 and 14 for interconnection of each system. Based on the electric power, it can be determined whether or not the contacts of the relays 13 and 14 for grid interconnection are welded.

With reference to FIG. 7, the welding determination control at the time of starting the power conditioner 20 will be described.
The control unit 30 determines in step S51 whether or not the start-up welding condition is satisfied. As a start-up welding condition, the voltage Vout (effective value) on the power conditioner 20 side of the relays 13 and 14 for each system interconnection is equal to or higher than the threshold value VY. The threshold value VY is a value for determining that the relays 13 and 14 for interconnection of each system are in the closed state, and is set in advance by a test or the like. An example of the threshold value VY is 100V.

When the control unit 30 determines that the start-up welding condition is satisfied (step S51: YES), that is, when the voltage Vout is equal to or higher than the threshold value VY, at least one of the contacts of the relays 13 and 14 for grid interconnection in step S52. Is determined to be welded, and the welding determination control is terminated. In this case, the control unit 30 prohibits switching to independent operation. If an affirmative decision is made in step S51, both contacts of the relays 13 and 14 for interconnection of each system are welded.

When the control unit 30 determines that the start-up welding condition is not satisfied (step S51: NO), that is, when the voltage Vout is less than the threshold value VY, the first grid interconnection relay 13 is closed in step S53. In step S54, it is determined whether or not the start-up welding condition is satisfied.

When the control unit 30 determines that the start-up welding condition is satisfied (step S54: YES), the control unit 30 determines in step S55 that at least one of the contacts of the relays 13 and 14 for interconnection of each system is welded, and the step In S56, the first grid interconnection relay 13 is controlled to be in the open state, and the welding determination control is terminated. In this case, the control unit 30 prohibits switching to independent operation. If an affirmative decision is made in step S54, the contacts of the second grid interconnection relay 14 are welded.

When the control unit 30 determines that the start-up welding condition is not satisfied (step S54: NO), the control unit 30 controls the first grid interconnection relay 13 to be in the open state in step S57, and then in step S58, the first step is performed. The system interconnection relay 14 of 2 is controlled so as to be in a closed state. Then, the control unit 30 determines in step S59 whether or not the start-up welding condition is satisfied.

When the control unit 30 determines that the start-up welding condition is satisfied (step S59: YES), the control unit 30 determines in step S60 that at least one of the contacts of the relays 13 and 14 for interconnection of each system is welded, and the step In S61, the second grid interconnection relay 14 is controlled to be in the open state, and the welding determination control is terminated. In this case, the control unit 30 prohibits switching to independent operation. If an affirmative decision is made in step S59, the contacts of the first grid interconnection relay 13 are welded. On the other hand, when the control unit 30 determines that the start-up welding condition is not satisfied (step S59: NO), the control unit 30 determines in step S62 that the contacts of the relays 13 and 14 for each grid are not welded together, and steps. Move to S61. In this case, the control unit 30 does not prohibit switching to independent operation.

The operation of this embodiment will be described.
The processing time of the stop determination process in the welding determination control is about 1 second, and the output of the DC / AC converter 22 is several kW. Therefore, assuming that power is supplied from the DC AC converter 22 to the relays 13 and 14 for interconnection of each system to execute welding determination control in the event of a power failure in the commercial power system 3, the DC AC converter 22 is normally used. When operated by the PWM control of the above, the power output from the DC / AC converter 22 is large. Therefore, if at least one of the contacts of the relays 13 and 14 for interconnection of each system is welded, the power flowing in the reverse direction increases.

On the other hand, in the present embodiment, power is supplied from the filter capacitor 26c having a small capacity to the relays 13 and 14 for grid interconnection. Since the capacitance of the filter capacitor 26c is several tens of pF to several μF, the power discharged by the filter capacitor 26c is much smaller than the power output by the DC / AC converter 22. Therefore, when at least one of the contacts of the relays 13 and 14 for interconnection of each system is welded, the power flowing back is reduced. Therefore, the safety when performing the restoration work of the commercial power system 3 is enhanced.

As described above, the following effects can be obtained according to the present embodiment.
(1) After the DC / AC converter 22 operates to charge the charge / discharge section (filter capacitor 26c) and the DC / AC converter 22 stops operating, each system is discharged by the charge / discharge section (filter capacitor 26c). It is determined whether or not any of the interconnection relays 13 and 14 is welded. Therefore, even if the commercial power system 3 recovers power during the period of welding determination of the relays 13 and 14 for each system interconnection, the voltage of each DC bus 23 and 24 connected to the DC AC converter 22 rises. Can be suppressed. Therefore, since the occurrence of failure of the electronic components connected to the DC buses 23 and 24 can be suppressed, the safety of the grid interconnection device 10 can be enhanced.
In addition, in the welding determination control, the filter capacitor 26c spontaneously discharges when a closed circuit is not formed between the DC AC converter 22 and the commercial power system 3 via the relays 13 and 14 for interconnection of each system. Therefore, when the first grid interconnection relay 13 is in the closed state and the second grid interconnection relay 14 is in the open state, the determination of welding defects of the respective grid interconnection relays 13 and 14 and the first The DC / AC converter 22 filters the determination of welding defects of the relays 13 and 14 for grid interconnection when the relay 13 for grid interconnection of 1 is in the open state and the relay 14 for grid interconnection is in the closed state. It can be executed only with the electric power once charged to the capacitor 26c. Further, when at least one of the relays 13 and 14 for grid interconnection is poorly welded, the filter capacitor 26c is discharged to the commercial power system 3 and the control is terminated. As described above, since the welding determination control can be executed only by the electric power once charged from the DC AC converter 22 to the filter capacitor 26c, the possibility that the commercial power system 3 is restored while the DC AC converter 22 is operating is reduced. .. Therefore, the safety of the grid interconnection device 10 can be further enhanced.

(2) In the welding determination control, it is determined whether or not any of the grid interconnection relays 13 and 14 is welded based on the discharge from the filter capacitor 26c to the grid interconnection relays 13 and 14. Since the discharge of the filter capacitor 26c having a small capacity is used in this way, the safety of the worker who performs the restoration work of the commercial power system 3 is improved. In addition, since a dedicated charge / discharge unit for welding determination control becomes unnecessary, the grid interconnection device 10 can be simplified and downsized.

(3) Since the voltage of the filter capacitor 26c is equal to or lower than the dangerous voltage, the restoration work of the commercial power system 3 can be safely performed. Further, when the voltage of the filter capacitor 26c is equal to or lower than the safe voltage, the restoration work of the commercial power system 3 can be performed more safely.

(4) When a closed circuit is formed between the DC AC converter 22 and the commercial power system 3 via the relays 13 and 14 for interconnection of each system, the filter capacitor 26c is discharged when the filter capacitor 26c is discharged. The voltage drops rapidly. On the other hand, if a closed circuit is not formed between the DC AC converter 22 and the commercial power system 3 via the relays 13 and 14 for interconnection of each system, the filter capacitor 26c becomes a natural discharge, so that the filter capacitor 26c The voltage of is gradually reduced. As described above, the voltage of the filter capacitor 26c after a predetermined time from the start of discharging the filter capacitor 26c differs depending on whether or not a closed circuit is formed between the DC AC converter 22 and the commercial power system 3. From this point of view, it is easy to determine whether or not any of the relays 13 and 14 for interconnection of each system is welded based on the output voltage Vout after a predetermined time from the start of discharge of the filter capacitor 26c. Can be judged.

(5) The probability that the commercial power system 3 will be restored with the passage of time after the power failure of the commercial power system 3 increases. If the welding determination is made for each combination of the closed state and the open state of the relays 13 and 14 for interconnection of each system while the DC / AC converter 22 is operating, the determination takes time. Therefore, there is a high possibility that the commercial power system 3 will recover power while the DC / AC converter 22 is operating.

On the other hand, in the present embodiment, when the commercial power system 3 loses power, the DC / AC converter 22 charges the filter capacitor 26c and stops after charging. That is, the DC / AC converter 22 is operated only when the probability that the commercial power system 3 recovers power is low. Therefore, the possibility that the commercial power system 3 is restored when the DC / AC converter 22 is operating is reduced, and the safety of the system interconnection device 10 is enhanced.

(6) In the welding determination control, the control unit 30 changes the first grid interconnection relay 13 to the closed state, changes the first grid interconnection relay 13 to the open state, and changes the second grid interconnection relay 13 to the open state. The interconnection relay 14 is changed to the closed state. By operating the relays 13 and 14 for grid interconnection in this way, it is possible to prevent the relays 13 and 14 for grid interconnection from being closed at the same time. Therefore, since the normal relays 13 and 14 for grid interconnection are closed at the same time, it is possible to avoid an erroneous determination that any of the relays 13 and 14 for grid interconnection is welded.

(Modification example)
The description of the above embodiment is an example of possible embodiments of the grid interconnection device of the present invention, and is not intended to limit the embodiments. The grid interconnection device of the present invention may take, for example, a modification of the above embodiment shown below and a combination of at least two modifications that do not contradict each other.

-In the welding determination control of FIG. 7 of the above embodiment, a determination as to whether or not the start-up welding condition is satisfied may be inserted between steps S57 and S58.
-In the power failure determination process of the above embodiment, a determination as to whether or not the power failure welding condition is satisfied may be inserted between steps S35 and S36.

The control unit 30 of the above embodiment determines whether or not the filter capacitor 26c has been charged within a predetermined time, and instead of determining whether or not the filter capacitor 26c has been charged, the first voltage during the period in which the DC / AC converter 22 charges the filter capacitor 26c. Based on the detection result of the detection unit 16, it may be determined whether or not both the first grid interconnection relay 13 and the second grid interconnection relay 14 are welded. Specifically, when the voltage Vout, which is the voltage detected by the first voltage detection unit 16, is less than a predetermined voltage, the control unit 30 relays the first system interconnection 13 and the second system interconnection. It is determined that both of the relays 14 are welded. Further, when the voltage Vout detected by the second voltage detection unit 17 is equal to or higher than a predetermined voltage, the control unit 30 of the first grid interconnection relay 13 and the second grid interconnection relay 14 It is determined that both are not welded. An example of a predetermined voltage is DC35V. According to this configuration, are both the relays 13 and 14 for interconnection of each system welded based on the detection result of the first voltage detection unit 16 during the period of charging the filter capacitor 26c from the DC AC converter 22? Whether or not it can be easily determined.

-In the preparatory process of the above embodiment, the charging welding condition is set to be that the charging of the filter capacitor 26c is not completed even after a lapse of a predetermined time from the start of charging the filter capacitor 26c, but the welding condition at the time of charging is limited to this. Absent. For example, the welding conditions during charging may be changed as any of the following (A1) to (A6).
(A1) As for the welding condition during charging, both the current detected by the first current detection unit 18 and the current detected by the second current detection unit 19 are equal to or higher than the threshold value AX. The threshold value AX is preset by a test or the like. An example of the threshold AX is 2A.
(A2) The welding condition at the time of charging is that the voltage Vgrid, which is the voltage detected by the second voltage detection unit 17, is DC35V or more during the period in which the filter capacitor 26c is charged from the DC AC converter 22.
(A3) The charging welding condition is that both the charging welding conditions (A1) and (A2) are satisfied.
(A4) The charging welding condition satisfies both the charging welding condition of the above embodiment and the charging welding condition of (A1).
The charging welding condition (A5) satisfies both the charging welding condition of the above embodiment and the charging welding condition of (A2).
(A6) The charging welding condition of the above embodiment is to satisfy all of the charging welding condition of the above embodiment, the charging welding condition of (A1), and the charging welding condition of (A2).
When any of the above (A1), (A4), and (A6) is used as the welding condition at the time of charging, at least one of the voltage at the time of charging the filter capacitor 26c and the current flowing through the relays 13 and 14 for interconnection of each system. It is possible to determine whether or not any of the relays 13 and 14 for interconnection of each system is welded based on the above. Therefore, for example, even if an abnormality occurs in at least one of the voltage detection units 16 and 17, both of the grid interconnection relays 13 and 14 are welded based on the current flowing through the grid interconnection relays 13 and 14. It can be determined whether or not it is done. In particular, when (A4) and (A6) are used as the welding conditions during charging, one of the relays 13 and 14 for each grid interconnection is based on both the voltage and the current to the relays 13 and 14 for each grid interconnection. The reliability of this determination is enhanced because it is determined whether or not the metal is welded, that is, the determination is performed by double-checking the voltage and the current.

-In the stop determination process of the above embodiment, the welding conditions at the time of power failure may be changed as any of the following (B1) to (B6).
(B1) As for the welding condition at the time of power failure, both the current value detected by the first current detection unit 18 and the current value detected by the second current detection unit 19 are equal to or higher than the threshold value AX. The threshold value AX is preset by a test or the like. An example of the threshold AX is 2A.
(B2) The welding condition at the time of power failure is that the voltage Vgrid, which is the voltage detected by the second voltage detection unit 17, is equal to or higher than the threshold value VX in the period from the start of discharging the filter capacitor 26c to the elapse of a predetermined time.
(B3) The power failure welding condition is to satisfy both the above (B1) and the above (B2) power failure welding conditions.
(B4) The power failure welding condition is to satisfy both the power failure welding condition of the above embodiment and the power failure welding condition of (B1).
(B5) The power failure welding condition is to satisfy both the power failure welding condition of the above embodiment and the power failure welding condition of (B2).
(B6) The power failure welding condition is to satisfy all of the power failure welding condition of the above embodiment, the power failure welding condition of (B1), and the power failure welding condition of (B2).
When any of the above (B1), (B4), and (B6) is used as the welding condition at the time of power failure, at least one of the voltage at the time of discharging the filter capacitor 26c and the current flowing through the relays 13 and 14 for each grid interconnection. It is possible to determine whether or not any of the relays 13 and 14 for interconnection of each system is welded based on the above. Therefore, for example, even if an abnormality occurs in at least one of the voltage detection units 16 and 17, any of the grid interconnection relays 13 and 14 will be based on the current flowing through the grid interconnection relays 13 and 14. It can be determined whether or not it is welded. In particular, when (B4) and (B6) are used as the welding conditions at the time of stopping, any one of the relays 13 and 14 for each grid interconnection is based on both the voltage and the current to the relays 13 and 14 for each grid interconnection. The reliability of this determination is enhanced because it is determined whether or not the metal is welded, that is, the determination is performed by double-checking the voltage and the current.

The welding condition at the time of power failure of the above embodiment is not limited to the voltage at which the voltage after a predetermined time has elapsed from the start of discharge of the filter capacitor 26c is equal to or higher than the threshold value VX, but is not limited to this, as described in (C1) and (C2) below. You may change it. It should be noted that the power failure welding conditions of the above embodiments (B4) to (B6) can be replaced with the power failure welding conditions of (C1) and (C2).
(C1) The welding condition at the time of power failure is that the time from the start of discharging the filter capacitor 26c until the voltage of the filter capacitor 26c becomes the threshold value VX or less is a predetermined time or less. That is, the control unit 30 has the first grid interconnection relay 13 and the second grid interconnection based on the time from the start of discharging the filter capacitor 26c until the voltage of the filter capacitor 26c becomes equal to or lower than the threshold value VX. It is determined whether or not any of the relays 14 is welded.
(C2) Under the welding condition at the time of power failure, the voltage drop rate when the filter capacitor 26c is discharged is equal to or higher than the threshold value SX. That is, in the control unit 30, whether either the first grid interconnection relay 13 or the second grid interconnection relay 14 is welded based on the voltage drop rate when the filter capacitor 26c is discharged. Judge whether or not. The threshold value SX is a value for determining whether or not the filter capacitor 26c is spontaneously discharged, and is preset by a test or the like.

(Additional note)
Next, the technical idea that can be grasped from the above-described embodiment and each of the above-described modifications will be described.
(Appendix 1)
For DC AC conversion device that converts DC power to AC power and outputs it to the first and second electric wires connected to the commercial power system, and for the first system interconnection provided in the first electric wire. The relay, the second grid interconnection relay provided on the second electric wire, and the first grid interconnection relay on the first electric wire are connected to the DC AC converter side with respect to the first grid interconnection relay. A filter capacitor that is connected to the DC / AC converter side of the second electric wire to the relay for grid interconnection and removes noise from the output from the DC / AC converter, and the DC / AC converter. A control unit for controlling the first grid interconnection relay and the second grid interconnection relay is provided, and the control unit includes the filter capacitor when the commercial power system is out of power. The DC / AC converter is operated so as to charge, and at least one of the first grid interconnection relay and the second grid interconnection relay is welded based on the discharge mode of the filter capacitor. A grid interconnection device that determines whether or not a current system is used, and executes welding determination control.

The issues corresponding to the above notes are as follows.
The grid interconnection device determines whether or not the first grid interconnection relay and the second grid interconnection relay are welded before changing from grid operation to independent operation in the event of a power failure of a commercial power system. Execute judgment control. This ensures the safety of workers who perform restoration work on the commercial power system. On the other hand, it is desired that the safety of the workers who perform the restoration work of the commercial power system is higher.
From the above, the problem with this grid interconnection device is to further enhance the safety of the restoration work of the commercial power system.

3 ... Commercial power system, 10 ... System interconnection device, 11 ... First electric wire, 11a ... Electric wire part, 11b ... Electric wire part, 12 ... Second electric wire, 12a ... Electric wire part, 12b ... Electric wire part, 13 ... No. 1 grid interconnection relay, 14 ... second grid interconnection relay, 16 ... first voltage detector, 18 ... first current detector, 19 ... second current detector, 22 ... DC AC Conversion device, 26c ... Filter capacitor (charging / discharging section), 30 ... Control section.

Claims (7)

A DC-AC converter that converts DC power to AC power and outputs it to the first and second wires connected to the commercial power system.
The first system interconnection relay provided on the first electric wire and
A second grid interconnection relay provided on the second electric wire and
The first electric wire is connected to the DC AC converter side with respect to the first grid interconnection relay, and the second electric wire is connected to the DC AC converter to the second grid interconnection relay. A charge / discharge unit that is connected to the device side and charges / discharges power from the DC / AC converter.
A control unit that controls the DC / AC converter, the first grid interconnection relay, and the second grid interconnection relay.
With
When the commercial power system is out of power, the control unit operates the DC AC conversion device so as to charge the charge / discharge unit, and then sets the output side of the DC AC conversion device to the DC AC conversion device. The operation of the DC / AC converter is stopped so as to be electrically insulated from the input side of the above, and the first grid interconnection relay and the second grid interconnection are based on the discharge mode from the charging / discharging unit. A grid interconnection device that executes welding determination control to determine whether or not at least one of the relays for welding is welded. The grid interconnection device according to claim 1, wherein the charging / discharging unit includes a filter capacitor. The grid interconnection device according to claim 1 or 2, wherein the voltage of the charge / discharge unit charged from the DC / AC converter device is equal to or less than a dangerous voltage. A portion between the DC AC converter and the first grid interconnection relay in the first electric wire, and the DC AC converter and the second grid interconnection relay in the second electric wire. It further has a first voltage detector connected to the intervening part,
The first voltage detection unit can detect the output voltage of the charge / discharge unit when the DC / AC converter is stopped.
In the welding determination control, the control unit uses the output voltage after a predetermined time from the start of discharge of the charge / discharge unit based on the detection result of the first voltage detection unit to obtain the first grid interconnection relay and The grid interconnection device according to any one of claims 1 to 3, which determines whether or not any of the second grid interconnection relays is welded. The control unit performs the first grid interconnection relay and the second system based on the detection result of the first voltage detection unit during the period of charging the charge / discharge unit at the time of executing the welding determination control. The grid interconnection device according to claim 4, wherein it is determined whether or not both of the grid interconnection relays of the above are welded. A first current detection unit provided in a portion between the first grid interconnection relay in the first electric wire and the commercial power system, and the second grid interconnection in the second electric wire. It further has a second current detector provided in the portion between the relay and the commercial power system.
The control unit is based on the detection result of the first current detection unit and the detection result of the second current detection unit when the charge / discharge unit is discharged at the time of executing the welding determination control. The grid interconnection device according to claim 4 or 5, wherein it is determined whether or not any of the grid interconnection relay and the second grid interconnection relay is welded. The control unit is based on the detection result of the first current detection unit and the detection result of the second current detection unit when the charge / discharge unit is discharged at the time of executing the welding determination control. The grid interconnection device according to claim 6, wherein it is determined whether or not both the grid interconnection relay and the second grid interconnection relay are welded together.

Images