Power conversion device, solar power generation system, and power storage system

Abstract

To provide a power conversion device that can detect and respond appropriately to a ground fault with a simple configuration.SOLUTION: A power conversion device, which includes first, second, and third terminals connected to a DC power supply, an AC power supply, and a load, respectively, comprises: power converter having an AC-side terminal and a DC-side terminal connected to the first terminal; an interconnect line between the AC-side terminal and the second terminal; a first relay and a second relay interposed between the AC-side terminal and second terminal of the interconnect line; a branch interconnect line connected to the third terminal, branching from the interconnect line between the first relay and the second relay; a zero-phase current transformer arranged on the interconnect line between the AC-side terminal and the third terminal or on the branch interconnect line; and a grounding relay connected to the interconnect line between the AC-side terminal and the zero-phase current transformer or to the branch interconnect line. The power conversion device further includes an output stop unit for stopping an output of the power conversion device responding to the occurrence of a ground fault detected by the zero-phase current transformer, when the first relay is ON and the second relay is OFF.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion device, a solar power generation system, and a power storage system. [Background technology]

[0002] Power conversion devices that are connected to a DC power source such as a solar panel or a storage battery and operate in conjunction with the power grid are known. These power conversion devices can switch between grid-connected operation, in which they operate in conjunction with the grid, and stand-alone operation, in which they convert power from the DC power source into AC current and supply it to a load when the grid experiences a power outage.

[0003] During stand-alone operation, the power conversion device supplies power to the load without going through the grid distribution panel, so it is necessary to provide a mechanism to detect ground faults and, if a ground fault occurs, cut off the power supply to the load.

[0004] One proposal for solving these problems is disclosed in Patent Document 1. The technology disclosed in Patent Document 1 aims to reduce stress on the switching device and load when the grid recovers from a power outage and switches the power supply from the power converter to the grid. To this end, the invention disclosed in Patent Document 1 divides the output of the power converter into a grid terminal and a load terminal, and connects a parallel-off relay and an isolation relay to each terminal. Furthermore, a ground fault circuit interrupter is provided between the switching device, which switches the power supply to the load between the grid and the power converter, and the isolation relay of the power converter. During a power outage, the parallel-off relay is turned off, and the isolation relay is turned on after a predetermined time has elapsed. During power recovery, the isolation relay is turned off a predetermined time after the start of power restoration, and the parallel-off relay is turned on after another predetermined time has elapsed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-131423 Summary of the Invention [Problem to be solved by the invention]

[0006] The invention disclosed in Patent Document 1 has the effect of reducing stress on the switching device and the load. In addition, since a ground fault circuit interrupter is provided, if a ground fault occurs between the power converter's self-sustaining relay and the switching device, it can detect this and cut off the power supply from the power converter to the load.

[0007] However, in the invention disclosed in Patent Document 1, the connection line connecting the power converter and the switch must be provided separately from the connection line connecting the power converter and the grid, which creates the problem of a complex configuration of the power converter. Furthermore, there is also the problem of the overall circuit size becoming larger, as a switch is required external to the power converter in addition to the stand-alone relay.

[0008] An object of this disclosure is to provide a power conversion device, a solar power generation system, and a power storage system that can detect a ground fault and take appropriate action with a simple configuration. [Means for solving the problem]

[0009] A power conversion device according to a first aspect of the present disclosure is a power conversion device including: a power converter having a first terminal connected to a DC power source, a second terminal connected to an AC power source, and a third terminal connected to a load, the power converter having an AC side terminal and a DC side terminal connected to the first terminal; a connecting line connecting the AC side terminal and the second terminal; a first relay and a second relay arranged in series between the AC side terminal and the second terminal of the connecting line; a branch connecting line branching from the connecting line between the first relay and the second relay and connected to the third terminal; a zero-phase-sequence current transformer arranged in the connecting line between the AC side terminal and the third terminal or in the branch connecting line; and a grounding relay connected between the connecting line between the AC side terminal and the zero-phase-sequence current transformer or in the branch connecting line and ground potential, and further including an output stopping unit for stopping output of the power conversion device in response to the zero-phase-sequence current transformer detecting that a ground fault has occurred on the load side when the first relay is on and the second relay is off.

[0010] A solar power generation system according to a second aspect of the present disclosure includes the above-described power conversion device and a solar power generation panel connected to a first terminal of the power conversion device.

[0011] A power storage system according to a third aspect of the present disclosure includes the above power conversion device and a storage battery connected to a first terminal of the power conversion device.

[0012] A power storage system according to a fourth aspect of the present disclosure includes the above-described power conversion device, a storage battery connected to a first terminal of the power conversion device, and a solar power generation panel connected to a fourth terminal of the power conversion device. [Effects of the Invention]

[0013] As described above, according to this disclosure, it is possible to provide a power conversion device, a solar power generation system, and a power storage system that can detect a ground fault and take appropriate action with a simple configuration. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a circuit block diagram showing the circuit configuration of a power storage system according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a block diagram of the DC (Direct Current)-DC converter shown in FIG. [Figure 3] FIG. 3 is a block diagram of the earth leakage circuit breaker shown in FIG. [Figure 4] FIG. 4 is a block diagram showing a circuit configuration of a power storage system according to the second embodiment of the present disclosure. [Figure 5] FIG. 5 is a block diagram showing a circuit configuration of a solar power generation system according to the third embodiment of the present disclosure. [Figure 6] FIG. 6 is a block diagram showing a circuit configuration of a solar power generation system according to the fourth embodiment of the present disclosure. [Figure 7] FIG. 7 is a block diagram showing a circuit configuration of a solar power generation system according to the fifth embodiment of the present disclosure. [Figure 8] FIG. 8 is a block diagram showing a circuit configuration of a solar power generation system according to the sixth embodiment of the present disclosure. [Figure 9] FIG. 9 is a flowchart representing a control structure of a computer program executed by the output stopping unit shown in FIG. [Figure 10] FIG. 10 is a block diagram showing a hardware configuration of an MCU (Micro Controller Unit) that realizes the output stopping unit shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Description of the embodiments of the present disclosure] In the following description and drawings, the same parts are denoted by the same reference numerals. Therefore, detailed description thereof will not be repeated. Note that any part of the following embodiments may be combined.

[0016] (1) A power conversion device according to a first aspect of this disclosure includes: a power converter having a first terminal connected to a DC power source, a second terminal connected to an AC power source, and a third terminal connected to a load, the power converter having an AC side terminal and a DC side terminal connected to the first terminal; a connecting line connecting the AC side terminal and the second terminal; a first relay and a second relay arranged in series between the AC side terminal and the second terminal of the connecting line; a branch connecting line branching from the connecting line between the first relay and the second relay and connected to the third terminal; a zero-phase-sequence current transformer arranged in the connecting line between the AC side terminal and the third terminal or in the branch connecting line; and a grounding relay connected between the connecting line between the AC side terminal and the zero-phase-sequence current transformer or in the branch connecting line and ground potential, and further includes an output stopping unit for stopping the output of the power conversion device in response to the zero-phase-sequence current transformer detecting that a ground fault has occurred on the load side when the first relay is on and the second relay is off.

[0017] The power converter is connected to an AC power source from the second terminal via a connecting wire. This connecting wire branches and connects to the third terminal, which is then connected to the load. When the first relay is on and the second relay is off, that is, when the power converter is operating independently, if a ground fault occurs in the connecting wire between the third terminal and the load, the zero-phase current transformer detects the occurrence of the ground fault and the output stopping unit stops the output of the power converter. By providing the power converter with a zero-phase current transformer and output stopping unit, the occurrence of a ground fault can be detected and the output of the power converter is cut off. There is no need to provide a circuit for detecting ground faults outside the power converter. A ground fault can be detected and appropriately addressed with a simple circuit consisting of a zero-phase current transformer and output stopping unit.

[0018] (2) In the above (1), the output stopping unit may include a disconnector provided at any position on the connection line or the branch connection line between the AC side terminal and the third terminal, and a disconnection control unit that operates the disconnector in response to the output of the zero-phase current transformer indicating the occurrence of a ground fault.

[0019] With a simple configuration consisting of a disconnector and a disconnection control unit, it is possible to appropriately respond to a ground fault by stopping the output of the power conversion device when a ground fault occurs.

[0020] (3) In the above (2), the output stopping unit and the zero-phase current transformer may be housed in the same housing to form a ground fault circuit interrupter.

[0021] By arranging an earth leakage breaker that conforms to the specifications of the power conversion device at an appropriate location on the power conversion device, it is possible to appropriately respond to a ground fault using a simple configuration.

[0022] (4) In the above (1), the output stopping unit may include a conversion stopping unit that stops the power conversion operation of the power converter in response to the output of the zero-phase-sequence current transformer indicating the occurrence of a ground fault.

[0023] In response to the output of the zero-phase current transformer indicating the occurrence of a ground fault, the power conversion operation of the power converter is stopped rather than immediately shutting off the output to the outside of the power conversion device, which reduces stress on peripheral circuits compared to when the output of the power conversion device is immediately shut off while the power converter is operating.

[0024] (5) In the above (4), the output stopping unit may further include a relay control unit that turns off the first relay in response to the power converter being stopped.

[0025] The power converter's power conversion operation is first stopped, and then the first relay is turned off. As a result, the output of the power converter is shut off, and the output to the outside of the power conversion device is also shut off. This reduces stress on peripheral circuits compared to when the output of the power conversion device is immediately shut off while the power converter is operating.

[0026] (6) In any one of (1) to (5) above, the power conversion device may further include an output filter provided in the connection line between the AC side terminal and the first relay, and the zero-phase current transformer may be provided in the connection line between the first relay and the third terminal and the branch connection line.

[0027] Even if a zero-phase current transformer is provided between the first relay and the third terminal, a ground fault occurring on the load side can be detected.

[0028] (7) In the above (6), the grounding relay may be provided between the first relay and the zero-phase current transformer.

[0029] By providing a grounding relay between the first relay and the zero-phase current transformer, the zero-phase current transformer can appropriately detect a ground fault that occurs on the load side.

[0030] (8) In the above (6), the grounding relay may be provided between the output filter and the first relay.

[0031] By providing a grounding relay between the output filter and the first relay, the zero-phase current transformer can properly detect a ground fault that occurs on the load side.

[0032] (9) In any one of the above (6) to (8), the zero-phase-sequence current transformer may be provided in the branch connection line.

[0033] Even if the zero-phase-sequence current transformer is provided on the branch connection line, the zero-phase-sequence current transformer can detect a ground fault that occurs on the load side.

[0034] (10) In any one of the above (6) to (8), the zero-phase current transformer may be provided on the connecting line.

[0035] Even if a zero-phase current transformer is installed in the connecting line between the first relay and the third terminal and a grounding relay is installed between the first relay and the zero-phase current transformer or between the output filter and the first relay, the zero-phase current transformer can detect a ground fault that occurs on the load side.

[0036] (11) In any one of (1) to (5) above, the power conversion device may further include an output filter provided in a connecting line between the AC side terminal and the first relay, and the zero-phase-sequence current transformer may be provided in the connecting line between the output filter and the first relay.

[0037] Even if the zero-phase-sequence current transformer is provided on the connection line between the output filter and the first relay, the zero-phase-sequence current transformer can detect a ground fault that occurs on the load side.

[0038] (12) In any one of the above (1) to (11), the power conversion device may further include a first DC-DC converter connected between the first terminal and the DC side terminal.

[0039] This configuration makes it possible to convert DC power from a DC power source into an appropriate voltage and input it to the power converter, and to supply power from the DC power source to a load during stand-alone operation of the power conversion device.

[0040] (13) In the above (12), the power conversion device may further have a fourth terminal and further include a second DC-DC converter connected between the fourth terminal and the DC side terminal.

[0041] This configuration makes it possible to convert DC power from two or more types of DC power sources into appropriate voltages and input them into the power converter, allowing power from the DC power sources to be supplied to the load with high reliability when the power conversion device is operating independently.

[0042] (14) A solar power generation system according to a second aspect of the present disclosure includes the power conversion device according to (12) above, and a solar power generation panel connected to a first terminal of the power conversion device.

[0043] This configuration allows DC power from the solar panels to be converted to an appropriate voltage and input to the power converter, allowing the solar power generation system to appropriately supply power generated by the solar panels to the load when the power converter is operating independently.

[0044] (15) A power storage system according to a third aspect of the present disclosure includes the power conversion device according to (12) above, and a storage battery connected to a first terminal of the power conversion device.

[0045] This configuration makes it possible to convert DC power from the storage battery into an appropriate voltage and input it into the power converter, and this storage system can appropriately supply power obtained from the storage battery to the load when the power conversion device is operating independently.

[0046] (16) A fourth aspect of the present disclosure provides a power storage system including the power conversion device described in (13) above, a storage battery connected to a first terminal of the power conversion device, and a solar panel connected to a fourth terminal of the power conversion device.

[0047] This configuration allows DC power from both the solar panel and the storage battery to be converted to appropriate voltages and input to the power converter. As a result, this energy storage system can appropriately supply power obtained from the solar panel and the storage battery to the load when the power conversion device is operating independently.

[0048] [Details of the embodiments of the present disclosure] Specific examples of a power conversion device, a solar power generation system, and a power storage system according to embodiments of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0049] A. First embodiment a.Configuration 1, a solar power generation system 50 according to a first embodiment of the present disclosure includes a storage battery 62, a plurality of PV (Photovoltaic) panels 64, 66, 68, and 70, and a power conversion device 60 having a power storage terminal unit 90 connected to the storage battery 62, a PV terminal unit 92 connected to the PV panels 64, 66, 68, and 70, a grid terminal unit 94, and an independent terminal unit 96. Note that a configuration without the storage battery 62 is also possible, in which case the inverter 122 does not need to have a bidirectional power conversion function. There is no need to have multiple PV panels 64, and one PV panel is sufficient. Furthermore, if the solar power generation system 50 includes the storage battery 62, the PV panel 64 may not be present.

[0050] A distribution board 72 for the system is connected to the system terminal section 94. A distribution board 78 for the load is connected to the self-standing terminal section 96. The distribution board 72 is connected to the system 76 via the watt-hour meter 74. Loads 80, 82, etc. are connected to the distribution board 78. A ground fault circuit interrupter is provided in the distribution board 72. A ground fault circuit interrupter is also provided in the distribution board 78. However, the ground fault circuit interrupter of the distribution board 78 cannot detect a ground fault that occurs in the connection line 140 that connects the self-standing terminal section 96 and the distribution board 78.

[0051] The power conversion device 60 includes a DC-DC conversion unit 110 connected to the storage battery 62 via the storage terminal unit 90, DC-DC conversion units 112, 114, 116, and 118 connected to the PV panels 64 and 66, and the PV panels 68 and 70 via the PV terminal unit 92, respectively, and an inverter 122 having a DC terminal unit 120 and an AC terminal unit 124 connected to the DC-DC conversion units 110, 112, 114, 116, and 118, and performing bidirectional conversion between DC power and single-phase three-wire AC power.

[0052] The power conversion device 60 further includes a single-phase three-wire connection line 132 connecting the AC terminal unit 124 of the inverter 122 and the grid terminal unit 94, and an interconnection relay 128 and a grid-load connection relay 134 that are provided in series between the AC terminal unit 124 of the inverter 122 and the grid terminal unit 94. The power conversion device 60 further includes an output filter 126 that is provided between the AC terminal unit 124 of the inverter 122 and the interconnection relay 128, and a branch connection line 136 that branches off from the connection line 132 between the interconnection relay 128 and the grid-load connection relay 134 and is connected to the electricity storage terminal unit 90.

[0053] The power conversion device 60 further includes a ground fault circuit interrupter 130 provided between the interconnection relay 128 and the branch point of the connection line 132 to the branch connection line 136, and a grounding relay 138 for grounding the neutral line of the connection line 132 between the interconnection relay 128 and the ground fault circuit interrupter 130 during stand-alone operation.

[0054] 2, for example, DC-DC conversion unit 110 includes an input filter 170 and a converter 172 that performs bidirectional DC voltage conversion. DC-DC conversion units 112, 114, 116, and 118 shown in Fig. 1 also have a similar configuration. However, they differ in that the voltage conversion by these DC-DC conversion units 112, 114, 116, and 118 is unidirectional, from each PV panel to inverter 122.

[0055] The configuration of the earth leakage circuit breaker 130 is well known, but will be described with reference to Fig. 3. The earth leakage circuit breaker 130 includes a housing 210, and, all housed in the same housing 210, a zero-phase-sequence current transformer 200 through which three of the connecting wires 132 pass, a disconnecting switch 202 for disconnecting the connecting wires 132, and a ground fault relay 204 for operating the disconnecting switch 202 in response to the output of the zero-phase-sequence current transformer 200 indicating the occurrence of a ground fault.

[0056] b.Operation When the photovoltaic power generation system 50 operates in grid-connected mode, both the grid-load connection relay 134 and the grid-connection relay 128 are turned on. As a result, it becomes possible to supply power from the grid 76 to the load 80, etc., charge the storage battery 62 with power from the grid 76, supply power from the storage battery 62 and the PV panel 64, etc. to the load 80, etc., and sell power from the PV panel 64, etc. to the grid 76. Of course, to achieve this, the power conversion device 60 needs to be appropriately controlled, but the details of this are not relevant to this disclosure and will not be described in detail here.

[0057] When a ground fault occurs at either the branch connection line 136 or the connection line 140, the zero-phase-sequence current transformer 200 detects the difference in the current flowing through the connection line 132. The ground fault relay 204 determines whether or not a ground fault has occurred based on the output of the zero-phase-sequence current transformer 200. When it is determined that a ground fault has occurred, the ground fault relay 204 activates the disconnector 202. As a result, the supply of power from the power conversion device 60 is cut off.

[0058] 1, earth leakage breaker 130 is provided between interconnection relay 128 and the branch position of branch connection line 136 from connection line 132. With this arrangement, even if a ground fault occurs in connection line 140 between self-supporting terminal unit 96 and distribution board 78, earth leakage breaker 130 can detect it and cut off the power supply from power conversion device 60 to distribution board 78. Of course, if a ground fault occurs in connection line 132, the power supply from power conversion device 60 is similarly cut off.

[0059] In addition, when a ground fault occurs between the system 76 and the system-load connection relay 134, or between the distribution board 78 and the load 80, the ground fault is detected by the earth leakage breaker in the distribution board 72 and the earth leakage breaker in the distribution board 78, respectively, and the power supply is cut off.

[0060] As described above, in this embodiment, by providing the earth leakage breaker 130 and the grounding relay 138 in the positions shown in Fig. 1, a ground fault that occurs between the self-sustaining terminal unit 96 and the distribution board 78 can be detected with a simple configuration and the power supply from the power conversion device 60 can be cut off. There is no need to provide any additional circuit, and there is no need to separate the output of the inverter 122 into one for the system and one for the load. Any earth leakage breaker 130 may be used as long as it complies with the specifications and standards of the solar power generation system 50.

[0061] As a result, it is possible to provide a power conversion device, a solar power generation system, and a power storage system that can detect a ground fault and take appropriate action with a simple configuration.

[0062] B. Second embodiment Fig. 4 shows a block diagram of a solar power generation system 250 according to a second embodiment of the present disclosure. The solar power generation system 250 shown in Fig. 4 differs from the solar power generation system 50 shown in Fig. 1 in that it includes a power conversion device 260 instead of the power conversion device 60 shown in Fig. 1.

[0063] 4 has almost the same configuration as the power conversion device 60, but differs from the power conversion device 60 in the position of the earth leakage breaker 130. That is, in the power conversion device 260, the earth leakage breaker 130 is provided on the branch connection line 136, not on the connection line 132. The grounding relay 138 is provided on the connection line 132, as in FIG. 1.

[0064] When the earth leakage breaker 130 is provided in this manner, it is possible to detect and appropriately deal with a ground fault occurring in the connection line 140, just like in the first embodiment. Also, just like in the first embodiment, the circuit configuration can be simple.

[0065] C. Third embodiment Fig. 5 shows a block diagram of a solar power generation system 300 according to a third embodiment of the present disclosure. The solar power generation system 300 shown in Fig. 5 differs from the solar power generation system 50 shown in Fig. 1 in that the solar power generation system 300 includes a power conversion device 310 instead of the power conversion device 60 shown in Fig. 1.

[0066] 5 has almost the same configuration as the power conversion device 60. However, in the power conversion device 310, the positions of the earth leakage breaker 130 and the grounding relay 138 are different from those of the power conversion device 60. Specifically, the earth leakage breaker 130 is provided between the branch portion of the connection line 132 and the branch connection line 136 and the self-supporting terminal unit 96, and the grounding relay 138 is provided between the branch portion of the connection line 132 and the branch connection line 136 and the earth leakage breaker 130.

[0067] Even if the earth leakage breaker 130 and the grounding relay 138 are arranged as shown in FIG. 5, the same effects as those of the first embodiment can be obtained.

[0068] D. Fourth embodiment Fig. 6 shows a block diagram of a solar power generation system 350 according to a fourth embodiment of the present disclosure. The solar power generation system 350 differs from the solar power generation system 50 shown in Fig. 1 in that the solar power generation system 350 includes a power conversion device 360 ​​instead of the power conversion device 60 shown in Fig. 1.

[0069] 6 has almost the same configuration as the power conversion device 60, but the positions of the earth leakage circuit breaker 130 and the grounding relay 138 are different from those of the power conversion device 60. Specifically, in the power conversion device 360, the earth leakage circuit breaker 130 is provided between the branch point of the connection line 132 and the branch connection line 136 and the self-sustaining terminal unit 96, and the grounding relay 138 is provided in the connection line 132 between the output filter 126 and the grid-connection relay 128.

[0070] During the stand-alone operation, the interconnection relay 128 is closed. Therefore, even if the earth leakage breaker 130 and the grounding relay 138 are arranged as shown in Fig. 6, the same effects as those of the first embodiment can be obtained.

[0071] E. Fifth embodiment Fig. 7 shows a block diagram of a solar power generation system 400 according to a fifth embodiment of the present disclosure. The solar power generation system 400 differs from the solar power generation system 50 shown in Fig. 1 in that the solar power generation system 400 includes a power conversion device 410 instead of the power conversion device 60 shown in Fig. 1.

[0072] 7 has almost the same configuration as the power conversion apparatus 60. However, in the power conversion apparatus 410, the positions of the earth leakage circuit breaker 130 and the grounding relay 138 are different from those in the power conversion apparatus 60. Specifically, in the power conversion apparatus 410, the earth leakage circuit breaker 130 is provided on the connection line 132 between the output filter 126 and the grid-connection relay 128, and the grounding relay 138 is provided on the connection line 132 between the output filter 126 and the earth leakage circuit breaker 130.

[0073] The interconnection relay 128 is closed during the independent operation of the photovoltaic power generation system 400. Therefore, even if the earth leakage breaker 130 and the grounding relay 138 are arranged as shown in Fig. 7, the same effects as in the first embodiment can be obtained.

[0074] F. Sixth embodiment a.Configuration Fig. 8 shows a block diagram of a solar power generation system 450 according to a fifth embodiment of the present disclosure. The solar power generation system 450 differs from the solar power generation system 50 shown in Fig. 1 in that the solar power generation system 450 includes a power conversion device 460 instead of the power conversion device 60 of Fig. 1.

[0075] The power conversion device 460 has a similar configuration to the power conversion device 60 shown in Fig. 1. However, the power conversion device 460 differs from the power conversion device 60 shown in Fig. 1 in that it includes a zero-phase-sequence current transformer 470, instead of the earth leakage breaker 130 shown in Fig. 1, that is provided between the self-standing terminal unit 96 and the branch point of the connection line 132 and the branch connection line 136, that it includes a detection circuit 472 that detects the occurrence of a ground fault in the connection line 140 based on the output of the zero-phase-sequence current transformer 470 and outputs a detection signal, and that it includes an output stopping unit 474 that, in response to the detection signal from the detection circuit 472, first controls the inverter 122 to stop the output of the inverter 122, and then turns off the grid-connection relay 128 to stop the output of the power conversion device 460.

[0076] The output stopping unit 474 includes a conversion stopping unit 480 that stops the power conversion process by the inverter 122 by stopping switching by each semiconductor switch included in the inverter 122 in response to a detection signal from the detection circuit 472, and a relay control unit 482 that performs processing to turn off the grid-connected relay 128 in response to the inverter 122 stopping the power conversion process as controlled by the conversion stopping unit 480.

[0077] As will be described later, the output stopping unit 474 is actually realized by an MCU including an MPU (Micro-Processing Unit) and a program executed by the MPU.

[0078] 9 shows a simplified control structure of the program executed by the MPU to realize the output stopping unit 474. This program is executed repeatedly at predetermined time intervals. The values ​​of the variables updated during each execution are retained in memory even after the program is executed, and the next process is executed based on those values ​​during the next execution.

[0079] Referring to FIG. 9, this program includes, after starting execution, step 500 for first reading the input of the ground fault detection signal which is the output from detection circuit 472, step 502 for branching the control flow depending on whether the ground fault detection signal is off or not, and step 504 for continuing normal control processing other than the processing for stopping inverter 122 and terminating execution of this program when the determination in step 502 is negative.

[0080] This program further includes step 506, which determines whether or not inverter 122 has completely stopped when the determination in step 502 is negative, and branches the flow of control according to the result of the determination, and step 508, which outputs a stop instruction signal to inverter 122 or performs processing to maintain the output in response to the determination in step 506 that inverter 122 has not yet completely stopped, and terminates execution of this program.

[0081] This program further includes step 510, in response to a determination in step 506 that the inverter 122 has completely stopped, for determining whether the grid-connection relay 128 has been disconnected and branching the control flow in accordance with the determination result, step 512, in response to a determination in step 510 that the grid-connection relay 128 has not been disconnected, for outputting a relay control signal instructing the grid-connection relay 128 to be disconnected and terminating execution of this program, and step 514, in response to a determination in step 510 that the grid-connection relay 128 has been disconnected, for performing processing to stop the entire power conversion device 460 and terminating execution of this program. Execution of step 514 also stops the operation of the output stopping unit 474, and execution of this program also terminates.

[0082] 10 is a block diagram of MCU 550 that realizes output halting unit 474. Referring to FIG. 10, this MCU includes an MPU 602 including an arithmetic unit, a high-speed bus 600 to which MPU 602 is connected, an SRAM (Static Random Access Memory) 604 connected to high-speed bus 600, a flash memory 606 connected to high-speed bus 600, and a ROM (Read-Only Memory) 608 connected to high-speed bus 600. Data necessary for executing a program and the like are held in SRAM 604. A program 626, the control structure of which is shown in FIG. 9, is stored in flash memory 606 to realize the functions realized by output halting unit 474. A boot-up program for MPU 602 and the like are stored in ROM 608.

[0083] The MCU further includes a low-speed bus 610 connected to the high-speed bus 600 via a bridge 612, and a serial I / F (Interface) 614, an ADC (Analog-to-Digital Converter) 616, a timer / counter 618, a clock generator 620, a power supply control unit 622, and a general-purpose I / F 624, all of which are connected to the low-speed bus 610. In this embodiment, the ground fault detection signal from the detection circuit 472 is digitized and processed by the ADC 616, but it may also be digitized in the detection circuit 472.

[0084] The operation of the MCU 550 and MPU 602 is well known, and what is meaningful in the embodiment is the function of the programs they execute. Therefore, the operation of the MCU itself will not be described here.

[0085] b.Operation The photovoltaic power generation system 450 according to the sixth embodiment operates as follows. Below, only the operation of the photovoltaic power generation system 450 during stand-alone operation of the photovoltaic power generation system 450 will be described. During stand-alone operation, the grid-load connection relay 134 is open, and the grid-connection relay 128 is closed. When no ground fault occurs, the zero-phase-sequence current transformer 470 does not output a signal indicating ground fault detection. Therefore, the detection circuit 472 does not output a ground fault detection signal, and the inverter 122 converts DC power from the storage battery 62 or the PV panel 64, etc., into AC power and provides it to the load.

[0086] When a ground fault occurs in the connection line 140, the zero-phase current transformer 470 outputs a current indicating that the total current of the single-phase three wires has exceeded a threshold due to the ground fault. The detection circuit 472 detects that the output current of the zero-phase current transformer 470 has exceeded the threshold, and provides a ground fault detection signal to the output stop unit 474.

[0087] The output stopping unit 474 operates as follows. Referring to FIG. 9 , the MCU 550 repeatedly executes steps 500, 502, and 504 until it receives a ground fault detection signal. When the MCU 550 receives the ground fault detection signal, the determination in step 502 is NO. The determination in the subsequent step 506 is NO immediately after receiving the ground fault detection signal. Therefore, the MCU 550 outputs a stop instruction signal to the inverter 122. In response to this stop instruction signal, the control circuit in the inverter 122 starts a process to stop the inverter 122. At this time, if all the semiconductor switch elements in the inverter 122 were locked simultaneously, an electrical load would be placed on each component in the power conversion device 460. Therefore, instead of locking all the semiconductor switch elements simultaneously, the inverter 122 gradually reduces the output of the inverter 122, for example, by gradually reducing the output current, until all the semiconductor switch elements are finally locked. Naturally, it takes some time for this stop process to be completed.

[0088] 9 repeatedly, the determination in step 506 remains negative for a certain period of time. When the inverter 122 completely stops outputting, the determination in step 506 becomes positive, and control proceeds to step 510.

[0089] When control first proceeds to step 510, the interconnection relay 128 is closed. Therefore, the determination at step 510 is negative, and at step 512, a relay control signal for turning off the interconnection relay 128 is output to the interconnection relay 128.

[0090] The next time this program is executed, the determination in step 502 will be negative and the determination in step 506 will be positive. Therefore, the above processing is repeated until the determination in step 510 becomes positive. When the determination in step 510 becomes positive, control proceeds to step 514. In step 514, the entire power conversion device 460 is shut down, and execution of this program also comes to a complete end.

[0091] As described above, according to this embodiment, rather than immediately shutting off the output of the power conversion device by an earth leakage breaker, the various components of the power conversion device 460 operate cooperatively using the output of the zero-phase current transformer to stop the output of the power conversion device 460. That is, when a ground fault is detected, the operation of the inverter 122 is first gradually stopped, and after its output has disappeared, the output of the inverter 122 is completely shut off by the grid-connection relay 128. This reduces the possibility of excessive load being applied to the various components of the power conversion device 460 and the loads 80 and 82 that receive power from the power conversion device 460. Although the circuit scale is somewhat larger than when an earth leakage breaker is used, the cooperative processing makes it possible to appropriately respond to a ground fault.

[0092] Although this disclosure has been described above based on multiple embodiments, this disclosure is not limited to the above embodiments. Various other modifications are possible. For example, in the example shown in FIG. 8 , the zero-phase-sequence current transformer 470 is provided in the branch connection line 136, and the grounding relay 138 is provided between the interconnection relay 128 and the branch point of the connection line 132 and the branch connection line 136. However, the location of the zero-phase-sequence current transformer 470 is not limited thereto. For example, the zero-phase-sequence current transformer 470 and the grounding relay 138 may be located at the positions of the earth leakage breaker 130 and the grounding relay 138 shown in FIGS. 1 , 5 , 6 , and 7 , respectively.

[0093] 8, the grid-connection relay 128 is disconnected after the output of the inverter 122 has completely stopped. However, this disclosure is not limited to such an embodiment. The grid-connection relay 128 may be disconnected when the output of the inverter 122 falls below a certain threshold.

[0094] In this specification, the systems in the above embodiments are referred to as photovoltaic power generation systems because they all include PV panels. However, they also all include storage batteries. Therefore, the systems in the above embodiments can also be referred to as power storage systems. Therefore, the names of each system may be any name that reflects its actual nature.

[0095] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is not defined by the detailed description of the disclosure, but by the claims of the appended claims, and is intended to include all modifications within the scope and meaning equivalent to the wording of the claims. [Explanation of symbols]

[0096] 50, 250, 300, 350, 400, 450 Solar power generation system 60, 260, 310, 360, 410, 460 Power conversion equipment 62 Storage battery 64, 66, 68, 70 PV panels 72, 78 Distribution board 74 Energy meter 76 lines 80, 82 Load 90 Storage terminal part 92 PV terminal section 94 System terminal section 96 Stand-alone terminal section 110, 112, 114, 116, 118 DC-DC conversion unit 120 DC terminal section 122 Inverter 124 AC terminal section 126 Output Filter 128 Interconnection Relay 130 Earth leakage breaker 132, 140 connecting wires 134 System and Load Connection Relay 136 Branch Connection Line 138 Grounding relay 170 Input Filter 172 Converter 200, 470 zero phase current transformer 202 Disconnector 204 Earth fault relay 210 cabinet 472 Detection Circuit 474 Output Stop Unit 480 Conversion stop 482 Relay control section 550 MCU 600 Express Bus 602 MPU 604 SRAM 606 Flash Memory 608 ROM 610 Slow Bus 612 Bridge 614 Serial I / F 616 ADC 618 Timer Counter 620 Clock Generator 622 Power supply control unit 624 General-purpose I / F 626 Program

Claims

1. a first terminal connected to a DC power supply, a second terminal connected to an AC power supply, and a third terminal connected to a load; a power converter having an AC side terminal and a DC side terminal connected to the first terminal; a connection line connecting the AC side terminal and the second terminal; a first relay and a second relay provided in series between the AC side terminal and the second terminal of the connection line; a branch connection line branching from the connection line between the first relay and the second relay and connected to the third terminal; a zero-phase-sequence current transformer provided on the connection line or the branch connection line between the AC side terminal and the third terminal; a grounding relay connected between the connection line between the AC side terminal and the zero-phase current transformer or the branch connection line and a ground potential, the power conversion device switches between grid-connected operation and stand-alone operation using the first relay and the second relay; The power conversion device further includes an output stopping unit that stops the output of the power conversion device in response to the zero-phase current transformer detecting that a ground fault has occurred on the load side during the autonomous operation in which the first relay and the grounding relay are on and the second relay is off.

2. The output stopping unit a disconnector provided at any position of the connection line or the branch connection line between the AC side terminal and the third terminal; 2. The power conversion apparatus according to claim 1, further comprising: a disconnection control unit that operates the disconnector in response to an output of the zero-phase-sequence current transformer indicating the occurrence of a ground fault.

3. The power conversion device according to claim 2 , wherein the output stopping unit and the zero-phase current transformer are housed in the same housing and constitute an earth leakage breaker.

4. The power conversion device according to claim 1 , wherein the output stopping unit includes a conversion stopping unit that stops a power conversion operation by the power converter in response to an output of the zero-phase-sequence current transformer indicating the occurrence of a ground fault.

5. The power conversion device according to claim 4 , wherein the output stopping unit further includes a relay control unit that turns off the first relay in response to the power converter being stopped.

6. further including an output filter provided on the connection line between the AC side terminal and the first relay, 6. The power conversion device according to claim 1, wherein the zero-phase-sequence current transformer is provided on the connection line or the branch connection line between the first relay and the third terminal.

7. The power conversion device according to claim 6, wherein the grounding relay is provided between the first relay and the zero-phase current transformer.

8. The power conversion device according to claim 6 , wherein the grounding relay is provided between the output filter and the first relay.

9. The power conversion device according to claim 6 , wherein the zero-phase-sequence current transformer is provided on the branch connection line.

10. The power conversion device according to claim 6 , wherein the zero-phase-sequence current transformer is provided on the connection line.

11. further including an output filter provided on the connection line between the AC side terminal and the first relay, The power conversion device according to claim 1 , wherein the zero-phase-sequence current transformer is provided on the connection line between the output filter and the first relay.

12. The power conversion device according to any one of claims 1 to 5, further comprising a first DC-DC converter connected between the first terminal and the DC side terminal.

13. the power converter further has a fourth terminal; The power conversion device according to claim 12, further comprising a second DC-DC converter connected between the fourth terminal and the DC side terminal.

14. The power conversion device according to claim 12; a solar power generation panel connected to the first terminal of the power conversion device.

15. The power conversion device according to claim 12; a storage battery connected to the first terminal of the power conversion device.

16. The power conversion device according to claim 13; a storage battery connected to the first terminal of the power conversion device; a solar power generation panel connected to the fourth terminal of the power conversion device.

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