Power converter and power storage system

Abstract

To more securely inhibit a current sensor required for a power converter from being mounted unfavourably.SOLUTION: A power converter provided between a user's DC power supply and a commercial power system comprises: a first cable way end connected to the commercial power system; a second cable way end connected to a distribution board provided at the user; a power conversion unit that is connected to the DC power supply and performs power conversion between DC and AC; a changeover unit that is connected to the first cable way end, the second cable way end, and a third cable way end, as which an AC side cable way end of the power conversion unit is taken, and changes over an electrification route so that electrification is performed between cable way ends selected from the three cable way ends depending on whether the power conversion unit is to perform system interconnection operation or autonomous operation; and a current sensor for inverse load flow detection, the current sensor provided on the downstream side of the first cable way end, where the commercial power system's side is taken as the upstream side.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] Power generated by renewable energy such as solar power generation is generally converted to AC power via a power conversion device called a power conditioner, and the power conversion device can be interconnected with a commercial power system. In recent years, hybrid-type power storage systems that use storage batteries in combination with such solar power generation systems are becoming more widespread. A grid-connected power conditioner with an independent operation function is capable of operating independently and supplying power to a consumer's load during a power outage in the commercial power system. Conventionally, during independent operation, only an independent output of single-phase two-wire 100V was provided, but a so-called "full-load compatible" power conditioner has also been proposed that can supply power to all loads of a consumer's 200V and 100V by providing an independent output of single-phase three-wire (see, for example, Patent Document 1).

[0003] The current path to the consumer's distribution board is different between grid-connected operation and stand-alone operation. Therefore, a current path switching circuit is used. Switching from grid-connected operation to stand-alone operation, or vice versa, may be performed manually, but it is more convenient to do it automatically (see, for example, Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-239625 A [Patent Document 2] JP 2014-212655 A [Patent Document 3] JP 2001-238464 A Summary of the Invention [Problem to be solved by the invention]

[0005] The electricity generated by photovoltaic power generation can be sold as reverse power flow to the commercial power grid. On the other hand, when installing a storage battery, it is currently prohibited to use the discharged power of the storage battery as a reverse power flow. Therefore, in order to prevent reverse power flow from the storage battery, a current transformer (CT) is required as a current sensor to detect reverse power flow, and a reverse power relay (RPR) is required to suppress reverse power flow based on the detected current.

[0006] The above-mentioned CT is installed on the primary side of the contract breaker (main breaker) in the consumer's distribution board. The CT is a split type that is attached by clamping and gripping the insulated electric wires, and is provided as an accessory for power conditioners. When carrying out electrical work at the consumer's premises, the contractor attaches a CT to each of two of the single-phase three-wire voltage lines on the primary side of the contract breaker. When attaching the CT, it is essential that it is securely tightened until it clicks into place and that it is installed in the correct direction.

[0007] However, in reality, human error can occur, causing the CT scanner to be improperly attached or fall off after being attached. An object of the present disclosure is to more reliably prevent improper installation of a current sensor required for a power conversion device. [Means for solving the problem]

[0008] The present disclosure includes the following inventions, however, the present invention is defined by the claims.

[0009] The power conversion device of the present disclosure is a power conversion device provided between a DC power source of a consumer and a commercial power system, A first electric circuit end portion connected to the commercial power system; A second circuit end portion connected to a distribution board provided at the consumer facility; a power conversion unit connected to the DC power source and performing power conversion between DC and AC; a switching unit that is connected to three electric circuit ends, i.e., the first electric circuit end, the second electric circuit end, and the third electric circuit end, where the AC side electric circuit end of the power conversion unit is defined as a third electric circuit end, and that switches a current path so that current is conducted between electric circuit ends selected from the three electric circuit ends depending on whether the power conversion unit performs a grid-connected operation or an independent operation; When the commercial power system is regarded as an upstream side, the power conversion device further includes a current sensor for detecting reverse power flow, the current sensor being provided downstream of the first electric path end portion.

[0010] The power storage system includes the power conversion device and is provided with a solar power generation panel and a storage battery as the DC power source. Effect of the Invention

[0011] According to the present disclosure, improper installation of a current sensor required for a power conversion device can be more reliably prevented. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is an example of a single-line connection diagram of a conventional power storage system shown as a reference example for comparison with the present disclosure. [Diagram 2] FIG. 2 is an example of a single-line diagram including a power storage system based on the basic concept of the present disclosure. [Diagram 3] FIG. 3 is a circuit diagram showing a first example of a power conversion device according to the present disclosure. [Figure 4] FIG. 4 is a circuit diagram showing a second example of a power conversion device according to the present disclosure. [Diagram 5] FIG. 5 is a flowchart repeatedly executed by the control unit of the power conversion unit in FIG. 3 and FIG. [Figure 6] FIG. 6 is a flowchart repeatedly executed by the control unit of the switching unit in FIGS. [Figure 7] FIG. 7 is a flowchart repeatedly executed by the control unit of the power conversion unit in FIG. 3 and FIG. [Figure 8]FIG. 8 is a partial circuit diagram showing how the switching unit shown in FIG. 3 changes relay operation depending on the situation. [Figure 9] FIG. 9 is a partial circuit diagram showing how the switching unit shown in FIG. 4 changes relay operation depending on the situation. [Figure 10] FIG. 10 is a diagram showing an image of the arrangement of the electricity storage system and its peripheral devices at a consumer facility according to the first example. [Figure 11] FIG. 11 is a diagram showing an image of the arrangement of the power storage system and its peripheral devices at a consumer facility according to the second example. [Figure 12] FIG. 12 is a first example of a connection diagram in which an electricity storage system including a power conversion device basically similar to that shown in FIG. 4 is unitized. [Figure 13] FIG. 13 is a connection diagram showing a state in which the power conversion unit is removed from the state shown in FIG. [Figure 14] FIG. 14 is a second example of a connection diagram in which an electricity storage system including a power conversion device basically similar to that shown in FIG. 4 is unitized. [Figure 15] FIG. 15 is a connection diagram showing a state in which the power conversion unit is removed from the state shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] [Description of the embodiments of the present disclosure] The gist of the present disclosure includes at least the following.

[0014] (1) This is a power conversion device provided between a consumer's DC power source and a commercial power system, comprising: a first electric circuit end connected to the commercial power system; a second electric circuit end connected to a distribution board provided at the consumer's premises; a power conversion unit connected to the DC power source and performing power conversion between DC and AC; a switching unit connected to three electric circuit end portions, i.e., the first electric circuit end portion, the second electric circuit end portion, and the third electric circuit end portion, where the AC side electric circuit end portion of the power conversion unit is defined as a third electric circuit end portion, and switching the current path so that current is passed between an electric circuit end portion selected from the three electric circuit end portions depending on whether the power conversion unit performs grid-connected operation or independent operation; and a current sensor for detecting reverse power flow provided downstream of the first electric circuit end portion when the commercial power system is defined as the upstream side.

[0015] Such a power conversion device is interposed in the middle of the AC circuit connecting the commercial power system and the distribution board, and the distribution board always receives power through the power conversion device. Since the power conversion device is equipped with a switching unit, by connecting the first circuit end to the commercial power system and the second circuit end to the distribution board, the connection of the AC circuit that can realize multiple types of current paths is completed. Since the current sensor is also downstream of the first circuit end, it can be pre-installed as a part of the power conversion device. Therefore, it is possible to more reliably suppress installation errors of the current sensor required for the power conversion device. In this way, the connection form of the power conversion device is simplified and the connection work is made easier. In addition, the overall cost is lower than when the switching unit is installed separately and independently.

[0016] (2) The power conversion device of (1) may have a configuration and function including a first control unit that controls the power conversion unit, and a second control unit that is provided in the switching unit and operates to connect or disconnect the first electric circuit end portion and the second electric circuit end portion to each other, and the first control unit and the second control unit may be capable of communicating with each other.

[0017] In such a configuration, for example, the first control unit can send a signal indicating whether or not to permit operation to the second control unit, and the second control unit can send a signal indicating the state of operation to the first control unit. This allows both the operation of the switching unit in accordance with the operating state of the power conversion unit and the independent operation of the switching unit that does not depend on the power conversion unit. For example, when the power conversion unit is stopped due to a failure, the first control unit sends an operation permission signal (a signal that does not prohibit operation) to the second control unit, and the first electric circuit end and the second electric circuit end can be connected to each other. This makes it possible to secure a current path that supplies power from the commercial power system to the distribution board. Also, when the first electric circuit end and the second electric circuit end are connected to each other, a signal indicating that state is sent from the second control unit to the first control unit, and the power conversion unit cannot operate independently. When the first electric circuit end and the second electric circuit end are disconnected from each other, a signal indicating that state is sent from the second control unit to the first control unit, and the power conversion unit can operate independently. When the power conversion unit is in independent operation, the first control unit sends an operation disallowance signal to the second control unit, and the first electric circuit end portion and the second electric circuit end portion cannot be connected to each other.

[0018] (3) In the power conversion device of (2), the three electric circuit ends are compatible with a single-phase three-wire system and include an output switch provided in an electric circuit between the first electric circuit end and the third electric circuit end, a connection switch provided between the output switch and the first electric circuit end and configured to connect or disconnect the commercial power system and the distribution board, an independent output electric circuit that leads the electric circuit between the output switch and the connection switch to the second electric circuit end, and a neutral wire grounding switch provided between a neutral wire of the independent output electric circuit and a ground potential, and the first control unit and the second control unit are (i) during grid-connected operation, the output switch and the connection switch are closed and the neutral grounding switch is open; (ii) when an abnormality is detected in the commercial power system, the output switch is opened, the connection switch is closed, and the neutral grounding switch is opened; (iii) If the abnormality is a system abnormality other than a power outage, return to the state of (i) above. If the abnormality is a power outage and transition to independent operation is to be made, open the output switch and the connection switch, then close the neutral grounding switch and then close the output switch; (iv) When returning from isolated operation to grid-connected operation, the output switch, the connection switch, and the neutral grounding switch may be opened, and then the output switch and the connection switch may be closed.

[0019] In this case, the two switches, the output switch and the connection switch, can switch the current path between grid-tied operation and independent operation. If an abnormality is detected in the commercial power grid, the system detects isolated operation in state (ii), and if the system abnormality is other than a power outage, it returns to state (i). If there is a power outage, the system performs independent operation. When transitioning to independent operation, the output switch and the connection switch are opened, which acts as a sort of buffer to prevent neutral grounding in the commercial power grid and neutral grounding in the power conversion device from occurring at the same time.

[0020] (4) In any one of the power converters described above in (1) to (3), the switching unit is preferably provided inside a housing of the power converter. In this case, the switching unit is physically a part of the power conversion device, so that the worker does not need to be aware of the switching unit when installing the power conversion device, making the installation work easier.

[0021] (5) In the power conversion device according to any one of (1) to (4), for example, the current sensor includes a CT or a board-mounted current sensor. In this case, there is no need to use a split CT that clamps the electric wire, and it is possible to use a ring-shaped CT through which the electric wire passes, or a current sensor that is pre-mounted on the board. This makes it possible to prevent the falling off that can occur with split CTs. Also, by eliminating the restriction of the split type, options are expanded and lower-cost current sensors can be used.

[0022] (6) In the power conversion device of (4) or (5), the power conversion unit and the switching unit may each be unitized, physically separable from each other, and electrically connected using a connector, and the power conversion unit may be detachable from the housing of the power conversion device. In this case, if the power conversion unit breaks down, it is possible to remove only the power conversion unit for repair. Even after removal, the ends of the electric wires are protected by the connector, so it is safe.

[0023] (7) In the power conversion device of (6), the connection switch may be provided in a unit of the switching unit, and when the power conversion unit is removed from the housing, the second control unit may close the connection switch. In this case, by closing the connection switch with the power conversion unit removed from the housing, it is possible to ensure a current path for supplying power from the commercial power system to the distribution board. Therefore, even with the power conversion unit removed, it is possible to ensure power supply to consumers.

[0024] (8) In the power conversion device of (6) above, a switch may be provided in a unit of the switching section, and the DC power source may be connected to the switch. In this case, when the power conversion unit is removed, the end of the electric wire from the DC power source can be stored inside the switching unit. If the switch inside the unit is opened, the electric circuit from the DC power source can be safely disconnected when the power conversion unit is attached or detached.

[0025] (9) The power storage system may include any one of the power conversion devices (1) to (8) described above, and may include a solar panel and a storage battery as the DC power source. By configuring such an electricity storage system, it is possible to simplify external connections on the AC circuit side of the electricity storage system.

[0026] (Additional Note) Note that the configuration excluding a part of (1) above may be combined with the configuration (2). Such a power conversion device can be expressed as follows. A power conversion device is provided between a consumer's DC power source and a commercial power system, comprising: a first electric circuit end connected to the commercial power system; a second electric circuit end connected to a distribution board provided at the consumer's facility; a power conversion unit connected to the DC power source and performing power conversion between DC and AC; and a switching unit connected to three electric circuit end portions, i.e., the first electric circuit end portion, the second electric circuit end portion, and the third electric circuit end portion, where the AC side electric circuit end portion of the power conversion unit is defined as a third electric circuit end portion, and switching the current path so that current flows between an electric circuit end portion selected from the three electric circuit end portions depending on whether the power conversion unit performs grid-connected operation or independent operation. The power conversion device has a first control unit that controls the power conversion unit, and a second control unit that is provided in the switching unit and operates to connect or disconnect the first electric circuit end portion and the second electric circuit end portion to each other, and the first control unit and the second control unit are capable of communicating with each other.

[0027] In addition, the configuration excluding a part of (1), a part of (2), and the configuration (3) may be combined. Such a power conversion device can be expressed as follows. A power conversion device is provided between a consumer's DC power source and a commercial power system, comprising: a first electric circuit end connected to the commercial power system; a second electric circuit end connected to a distribution board provided at the consumer's facility; a power conversion unit connected to the DC power source and performing power conversion between DC and AC; and a switching unit connected to three electric circuit end portions, i.e., the first electric circuit end portion, the second electric circuit end portion, and the third electric circuit end portion, where the AC side electric circuit end portion of the power conversion unit is defined as a third electric circuit end portion, and switching the current path so that current flows between an electric circuit end portion selected from the three electric circuit end portions depending on whether the power conversion unit performs grid-connected operation or independent operation. The power conversion device has a first control unit that controls the power conversion unit, and a second control unit that is provided in the switching unit and operates to connect or disconnect the first electric circuit end portion and the second electric circuit end portion to each other. The three electric circuit ends correspond to a single-phase three-wire system, and include an output switch provided in an electric circuit between the first electric circuit end and the third electric circuit end, a connection switch provided between the output switch and the first electric circuit end and configured to connect or disconnect the commercial power system and the distribution board, an independent output electric circuit that leads the electric circuit between the output switch and the connection switch to the second electric circuit end, and a neutral wire grounding switch provided between the neutral wire of the independent output electric circuit and ground potential, and the first control unit and the second control unit are: (i) during grid-connected operation, the output switch and the connection switch are closed and the neutral grounding switch is open; (ii) when an abnormality is detected in the commercial power system, the output switch is opened, the connection switch is closed, and the neutral grounding switch is opened; (iii) If the abnormality is a system abnormality other than a power outage, return to the state of (i) above. If the abnormality is a power outage and transition to independent operation is to be made, open the output switch and the connection switch, then close the neutral grounding switch and then close the output switch; (iv) When returning from isolated operation to grid-connected operation, the output switch, the connection switch, and the neutral grounding switch are opened, and then the output switch and the connection switch are closed.

[0028] [Details of the embodiment of the present disclosure] 《Reference example》 First, FIG. 1 is an example of a single-wire connection diagram of a conventional energy storage system shown as a reference example for comparison with the present disclosure. In FIG. 1, a power feeder is drawn from a single-phase three-wire commercial power system to a general load distribution board 70 in a consumer's house via a watt-hour meter 53 and an outdoor switch 54. A contract breaker (main breaker) 701 is provided in the general load distribution board 70. A split-type CT 702 is attached as a current sensor to detect reverse power on the primary side of the contract breaker 701 in the general load distribution board 70. Two CTs 702 are attached in total to the voltage lines (U line, W line) of the single-phase three-wire (U line, O line, W line). The CT 702 is an accessory of the energy storage system 100. In the distribution board 70, for example, earth leakage circuit breakers 703 and 704 and a child breaker (a group of multiple breakers according to indoor wiring) 705 are also provided.

[0029] The power storage system 100 is usually installed outdoors of a consumer's house. The power storage system 100 includes an interconnection output electric circuit for interconnecting with a commercial power system, and an independent output electric circuit for providing an independent output during a power outage in the commercial power system. The interconnection output electric circuit is connected to the secondary side of a ground fault circuit interrupter 703. The independent operation output is provided to a specific load distribution board 80 to which a load to which it is not desired to stop supplying power even during a power outage is connected. A changeover switch 801 is provided in the specific load distribution board 80 to select whether to receive power from the general load distribution board 70 or from the independent output of the power storage system 100. A child breaker (a group of breakers corresponding to specific loads) 802 is provided via this changeover switch 801.

[0030] <<Basic Concept of the Present Disclosure>> FIG. 2 is an example of a single-line connection diagram including the power storage system 10 based on the basic concept of the present disclosure. In FIG. 2, a power feeder is drawn from a single-phase three-wire commercial power system to a distribution board 60 in a consumer's house via a watt-hour meter 53 and an outdoor switch 54. A contract breaker (main breaker) 601 is provided in the distribution board 60. In addition, for example, a ground fault circuit interrupter 604 and a child breaker (a group of multiple breakers according to indoor wiring) 605 are provided in the distribution board 60. Unlike FIG. 1, a CT of the power storage system is not provided in the distribution board 60. The CT is provided inside the power storage system 10. Also, the output electric circuit of the power storage system 10 is not divided into a grid-connected operation and an independent operation. And, power is always supplied to a load via the power storage system 10.

[0031] <<Power conversion device circuit configuration example 1>> FIG. 3 is a circuit diagram showing a first example of a power conversion device of the present disclosure. In FIG. 3, the power conversion device 1 includes a power conversion unit 2 and a switching unit 3. The power conversion unit 2 includes a control unit 20, for example, four boost circuits 21a, 21b, 21c, and 21d, a bidirectional DC / DC converter 22, a DC bus 23, an intermediate capacitor 24, an inverter 25, AC reactors 26u, 26o, and 26w, and AC side capacitors 27, 28, and 29, which are connected as shown in the figure. The AC reactors 26u, 26o, and 26w are provided on all three lines of the single-phase three-wire system. The AC side capacitor 27 is connected between the U line and the W line, the AC side capacitor 28 is connected between the U line and the O line, and the AC side capacitor 29 is connected between the W line and the O line.

[0032] The boost circuits 21a, 21b, 21c, and 21d receive the power generated by the corresponding photovoltaic power generation panels PV_a, PV_b, PV_c, and PV_d, respectively. The boost circuits 21a, 21b, 21c, and 21d output DC power at a boosted voltage to a common DC bus 23. The bidirectional DC / DC converter 22 is connected to a storage battery B. When the storage battery B is discharging, the bidirectional DC / DC converter 22 outputs DC power at a boosted voltage to the DC bus 23. The bidirectional DC / DC converter 22 can also step down the voltage of the DC bus 23 to charge the storage battery B.

[0033] The voltage of the DC bus 23 is smoothed by the intermediate capacitor 24 and input to the inverter 25. The inverter 25 is configured with six IGBTs (Insulated Gate Bipolar Transistors) to form a three-leg full bridge circuit compatible with single-phase three-wire. Note that MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors) may be used instead of the IGBTs. The AC side output of the inverter 25 is smoothed by AC reactors 26u, 26o, and 26w and AC side capacitors 27, 28, and 29, and the AC voltage and current of the single-phase three-wire are output to the U line, O line, and W line. This AC side electric circuit end of the single-phase three-wire is referred to as a third electric circuit end T3.

[0034] The switching unit 3 includes a control unit 30, a grid-connection relay 31, an independent relay 32, a connection relay 33, a neutral grounding relay 34, and current sensors 37 and 38, which are connected as shown in the figure. The three wires of the grid-connection relay 31 are led to a first electric circuit end T1. The three wires of the independent relay 32 are led to a second electric circuit end T2. Note that the grid-connection relay 31, the independent relay 32, the connection relay 33, and the neutral grounding relay 34 are not limited to contact relays, but may be semiconductor switches or other controllable switches. They are collectively referred to as a grid-connection switch, an independent switch, a connection switch, and a neutral grounding switch.

[0035] The dotted lines in FIG. 3 represent signal lines for control or measurement. The inverter 25 is PWM (Pulse Width Modulation) controlled by the control unit 20. Although the signal lines are not shown, the boost circuits 21a, 21b, 21c, and 21d and the bidirectional DC / DC converter 22 are also controlled by the control unit 20. The control unit 20 also controls the opening and closing of the interconnection relay 31, the independent relay 32, and the neutral grounding relay 34. The current sensors 37 and 38 detect the currents flowing through the U line and the W line, and send detection signals to the control unit 20. Based on this, the control unit 20 suppresses the discharge power of the storage battery B from being provided to the commercial power system as reverse power (reverse power flow). In reality, current sensors or voltage sensors are provided at various points in the power conversion unit 2 and the switching unit 3, and the control units 20 and 30 execute control based on the detection outputs of these sensors, but these sensors are not shown here. The control unit 30 mainly controls the opening and closing of the connection relay 33.

[0036] A first electric circuit end T1 of the switching unit 3 is connected to a single-phase three-wire (U, O, W) on the low-voltage side of a transformer 52 of a commercial power system 51 via a watt-hour meter 53. A second electric circuit end T2 of the switching unit 3 is connected to a distribution board 60. A general load 61 and a specific load 62 in a consumer are connected to the distribution board 60.

[0037] When the commercial power system 51 is normal, the power conversion unit 2 performs grid-connected operation to supply power to the distribution board 60 via single-phase three-wire, and surplus power from the solar power generation can also be sold as reverse flow power. When the commercial power system 51 experiences a power outage, the power conversion unit 2 operates in an independent manner, so that a single-phase three-wire independent output can be supplied to the distribution board 60. When there is a surplus in the independent output, the distribution board 60 may supply power to both the general load 61 and the specific load 62, or may supply power only to the specific load 62. How the interconnection relay 31, the independent relay 32, the connection relay 33, and the neutral wire grounding relay 34 are opened and closed during grid-connected operation and independent operation will be described later.

[0038] The control units 20 and 30 each include, for example, a computer, which executes software (computer program) to realize the necessary control functions. The software is stored in a storage device (not shown) of the control units 20 and 30. The control units 20 and 30 also have a function that allows them to communicate with each other. The control units 20 and 30 may be implemented using, for example, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array) in addition to a CPU (Central Processing Unit).

[0039] The independent relay 32 and the connection relay 33 in the switching unit 3 must not be closed at the same time, but the independent relay 32 is under the control of the control unit 20, and the connection relay 33 is under the control of the control unit 30. Thus, the control unit 20 sends a signal to the control unit 30 as to whether or not the connection relay 33 is permitted to be closed. The control unit 30 sends a status signal (closed: on, open: off) indicating the open / closed state of the connection relay 33 to the control unit 20. The control power supply voltage for the control units 20 and 30 can be generated based on the system voltage applied to the first electric circuit end T1, or can be generated from the voltage output by the storage battery B. The switching unit 3 operates in conjunction with the power conversion unit 2, and can also operate independently when the power conversion unit 2 is stopped.

[0040] <<Power conversion device circuit configuration example 2>> Fig. 4 is a circuit diagram showing a second example of a power conversion device of the present disclosure. In Fig. 4, a power conversion device 1 includes a power conversion unit 2 and a switching unit 3. The difference from the first example (Fig. 3) is the internal circuit of the switching unit 3, and the connection circuits outside the power conversion unit 2 and the power conversion device 1 are the same as those in the first example, so a description thereof will be omitted.

[0041] 4, the switching unit 3 includes a control unit 30, an output relay 35, a connection relay 36, a neutral grounding relay 34, and current sensors 37 and 38, which are connected as shown in the figure. The three wires of the output relay 35 and the connection relay 36 are led to a first electric circuit end T1. The three wires of the output relay 35 are led to a second electric circuit end T2 through an independent output electric circuit Po.

[0042] When the commercial power system 51 is normal, the power conversion unit 2 performs grid-connected operation to supply power to the distribution board 60 via single-phase three-wire, and surplus power from the solar power generation can also be sold as reverse flow power. When the commercial power system 51 experiences a power outage, the power conversion unit 2 operates in an independent manner, so that a single-phase three-wire independent output can be supplied to the distribution board 60. When there is a surplus in the independent output, the distribution board 60 may supply power to both the general load 61 and the specific load 62, or may supply power only to the specific load 62. How the output relay 35, the connection relay 36, and the neutral wire grounding relay 34 are opened and closed during grid-connected operation and during independent operation will be described later.

[0043] The control units 20 and 30 each include, for example, a computer, and the computer executes software (computer program) to realize the necessary control functions. The software is stored in a storage device (not shown) of the control units 20 and 30. The control units 20 and 30 can also communicate with each other.

[0044] If the connection relay 36 and the neutral grounding relay 34 in the switching unit 3 are simultaneously closed, there will be two grounds, and leakage current may flow. Therefore, the connection relay 36 and the neutral grounding relay 34 must not be simultaneously closed, but the connection relay 36 is under the control of the control unit 30, and the neutral grounding relay 34 is under the control of the control unit 20. Therefore, the control unit 20 sends a signal to the control unit 30 as to whether or not the connection relay 36 is permitted to be closed. The control unit 30 sends a status signal (closed: on, open: off) indicating the open / closed state of the connection relay 36 to the control unit 20. The control power supply voltage for the control units 20 and 30 can be generated based on the system voltage applied to the first electric circuit end T1, or can be generated from the voltage output by the storage battery B. The switching unit 3 operates in conjunction with the power conversion unit 2, and can also operate independently when the power conversion unit 2 is stopped.

[0045] <Features common to power conversion device circuit configuration examples 1 and 2> The power conversion device 1 shown in Figures 3 and 4 can be expressed as follows. These are power conversion devices 1 provided between DC power sources of consumers (photovoltaic power generation panels PV_a, PV_b, PV_c, and PV_d, and storage battery B) and a commercial power grid 51. The power conversion device 1 includes a first electric circuit end T1 connected to a commercial power system 51, a second electric circuit end T2 connected to a distribution board 60 installed at a consumer's premises, a power conversion unit 2 connected to a DC power source and performing power conversion between DC and AC, a switching unit 3 connected to three electric circuit end portions, i.e., the first electric circuit end portion T1, the second electric circuit end portion T2, and the third electric circuit end portion T3, assuming that the AC side electric circuit end portion of the power conversion unit 2 is the third electric circuit end portion T3, and switching the current path so that current is passed between the electric circuit end portions selected from the three electric circuit end portions depending on whether the system is in grid-connected operation or independent operation, and current sensors (CTs) 37, 38 for detecting reverse power flow, which are provided downstream of the first electric circuit end portion T1 when the commercial power system 51 is considered to be the upstream side.

[0046] Such a power conversion device 1 is interposed in the middle of an AC electric circuit connecting a commercial power system 51 and a distribution board 60, and the distribution board 60 always receives power through the power conversion device 1. Since the power conversion device 1 includes a switching unit 3, by connecting the first electric circuit end T1 to an electric circuit on the commercial power system 51 side and connecting the second electric circuit end T2 to the distribution board 60, the connection of an AC electric circuit that can realize a plurality of types of current paths is completed. The current sensors (CTs 37, 38) are also located downstream of the first electric circuit end T1, and can be mounted in advance as a part of the power conversion device 1. Therefore, improper installation of the current sensor required for the power conversion device 1 can be more reliably suppressed. In this way, the connection form of the power conversion device 1 is simplified, and the connection work is facilitated. Also, the overall cost is lower than when the switching unit 3 is installed separately and independently.

[0047] In addition, the power conversion unit 2 has a first control unit (control unit 20) that controls the power conversion unit 2, and the switching unit 3 has a second control unit (control unit 30) that operates to connect or disconnect the first electric circuit end T1 and the second electric circuit end T2 to each other, and the first control unit and the second control unit are capable of communicating with each other.

[0048] Example of a flow chart Fig. 5 is a flowchart repeatedly executed by the control unit 20 in Fig. 3 and Fig. 4. The control unit 20 first judges whether the commercial power system is normal or not (step S51). If normal, the control unit 20 sets the closing permission signals of the connection relays 33, 36 to "permitted" (step S52). If not normal in step S51, the control unit 20 sets the closing permission signals of the connection relays 33, 36 to "not permitted" (step S53).

[0049] Fig. 6 is a flowchart repeatedly executed by the control unit 30 in Fig. 3 and Fig. 4. The control unit 30 first checks the relay closing permission signal from the control unit 20 (step S61). If the closing of the connection relays 33, 36 is "permitted", the control unit 30 closes the connection relays 33, 36 and notifies the control unit 20 that the status is on (closed) (step S63). If the closing of the connection relays 33, 36 is "not permitted", the control unit 30 opens the connection relays 33, 36 and notifies the control unit 20 that the status is off (open) (step S64).

[0050] Fig. 7 is a flowchart repeatedly executed by the control unit 20 in Fig. 3 and Fig. 4. The control unit 20 first checks the status signal from the control unit 30 (step S71). If the control unit 20 checks in step S72 that the statuses of the connection relays 33 and 36 are off (open circuit), the control unit 20 starts independent operation (step S73). If the control unit 20 checks in step S72 that the statuses of the connection relays 33 and 36 are on (closed circuit), the control unit 20 does not perform independent operation (step S74).

[0051] As described above, in a configuration in which the power conversion unit 2 and the switching unit 3 have a first control unit (control unit 20) and a second control unit (control unit 30), respectively, the first control unit can send a signal indicating whether or not to allow operation to the second control unit, and the second control unit can send a signal indicating the operation state to the first control unit. This allows both the operation of the switching unit 3 in accordance with the operating state of the power conversion unit 2 and the independent operation of the switching unit that does not depend on the power conversion unit 2.

[0052] For example, when the power conversion unit 2 is stopped due to a failure, the first control unit sends an operation permission signal (signal not prohibiting operation) to the second control unit, and the first electric circuit end T1 and the second electric circuit end T2 can be connected to each other. This makes it possible to secure an electric current path for supplying power from the commercial power system 51 to the distribution board 60. Also, when the first electric circuit end T1 and the second electric circuit end T2 are connected to each other, a signal representing that state is sent from the second control unit to the first control unit, and the power conversion unit 2 cannot perform an independent operation. When the first electric circuit end T1 and the second electric circuit end T2 are disconnected from each other, a signal representing that state is sent from the second control unit to the first control unit, and the power conversion unit 2 can perform an independent operation. When the power conversion unit 2 is in an independent operation, the first control unit sends an operation prohibition signal to the second control unit, and the first electric circuit end T1 and the second electric circuit end T2 cannot be connected to each other.

[0053] <<Operation of the switching unit in FIG. 3>> FIG. 8 is a partial circuit diagram showing how the switching unit 3 shown in FIG. 3 changes the relay operation depending on the situation.

[0054] (1) Shutdown (Figure 8 (a)) As shown in (a) of Fig. 8, when the operation of the power conversion unit 2 is stopped, the interconnection relay 31 is disconnected from the system (open circuit), and the self-standing relay 32 and the neutral grounding relay 34 are also open circuit. The connection relay 33 is closed circuit. The power conversion unit 2 is gate blocked. Power is supplied to the distribution board 60 from the watt-hour meter 53 via the connection relay 33. (2) Preparation for grid-connected operation (Figure 8(b)) 8(b), as a transitional preparation step for grid-connected operation, the grid-connection relay 31 is closed from the state of (a). The other relays are in the same state as in (a).

[0055] (3) Grid-connected operation (Figure 8(c)) Here, as shown in FIG. 8(c), when the power conversion unit 2 starts operating, the system enters grid-connected operation. (4) System abnormality (Figure 8 (a)) When an abnormality occurs in the commercial power grid, the power conversion unit 2 blocks the gate and opens the interconnection relay 31, returning to the state of (a) and quickly detecting whether or not the grid has entered an islanding state due to a power outage. If the grid abnormality is a short-term disturbance in the grid, etc., and it is quickly detected that the grid is normal again, the system does not prepare for isolated operation ((6) below) but attempts to resume grid-connected operation ((9) below). A short-term disturbance is when a grid overvoltage, grid undervoltage, frequency rise, frequency abnormality, etc. is detected for a short period of time. The same applies when the islanding detection function works quickly and it turns out that the grid was not in islanding operation. On the other hand, if the grid abnormality continues, the system does not return to grid-connected operation and takes the following action.

[0056] (5) System abnormality (Figure 8 (d)) If the power grid abnormality, such as a power outage, continues, the power conversion unit 2 is in a gate blocked state, and all of the relays (31, 32, 33, 34) are in an open state. (6) Preparation for autonomous operation (Figure 8 (e)) After the occurrence of a system abnormality, in preparation for isolated operation, as shown in FIG. 8(e), the interconnection relay 31 and the connection relay 33 are opened, while the isolated relay 32 and the neutral grounding relay 34 are closed. (7) Autonomous operation (Figure 8 (f)) After the preparation for the independent operation is completed, the power conversion unit 2 is operated to perform the independent operation, as shown in (f) of Fig. 8. Power is supplied to the distribution board 60 through a single-phase three-wire.

[0057] (8) Power recovery detection (Figure 8 (d)) When restoration of power to the commercial power grid (system normality) is detected during independent operation, after waiting for a certain period of time, as shown in (d) of FIG. 8, the power conversion unit 2 goes into a gate-blocked state and all relays (31, 32, 33, 34) are opened. (9) Preparation for grid-connected operation (Figure 8(b)) Thereafter, as a transitional preparation stage for grid-connected operation, the grid-connection relay 31 and the connection relay 33 are closed, resulting in the state shown in FIG. 8(b). After that, the power conversion unit 2 resumes operation, resulting in the state shown in FIG. 8(c).

[0058] <<Operation of the switching unit in FIG. 4>> FIG. 9 is a partial circuit diagram showing how the switching unit 3 shown in FIG. 4 changes the relay operation depending on the situation.

[0059] (1) Operation shutdown (Figure 9 (a)) As shown in (a) of Fig. 9, when the operation of the power conversion unit 2 is stopped, the output relay 35 is disconnected from the system (open circuit), and the neutral grounding relay 34 is also open circuit. The connection relay 36 is closed circuit. The power conversion unit 2 is gate blocked. Power is supplied to the distribution board 60 from the watt-hour meter 53 via the connection relay 36. (2) Preparation for grid-connected operation (Figure 9(b)) 9(b), as a transitional preparation step for grid-connected operation, the output relay 35 is closed from the state of (a). The other relays are in the same state as in (a).

[0060] (3) Grid-connected operation (Figure 9(c)) Here, as shown in FIG. 9(c), when the power conversion unit 2 starts operating, the system enters grid-connected operation. (4) System abnormality (Figure 9(a)) If an abnormality occurs in the commercial power grid, the power conversion unit 2 blocks the gate and opens the output relay 35, returning to the state of (a) and quickly detecting whether or not the grid has entered an islanding state due to a power outage. If the grid abnormality is a short-term grid disturbance, etc., and it is quickly detected that the grid is normal again, the system does not prepare for isolated operation ((6) below) but attempts to resume grid-connected operation ((9) below). A short-term disturbance is when a grid overvoltage, grid undervoltage, frequency rise, frequency abnormality, etc. is detected for a short period of time. The same applies when the islanding detection function works quickly and it turns out that the grid is not in islanding operation. On the other hand, if the grid abnormality continues, the system does not return to grid-connected operation and takes the following action.

[0061] (5) System abnormality (Figure 9 (d)) If the power grid abnormality, such as a power outage, continues, the power conversion unit 2 is in a gate blocked state, and all of the relays (34, 35, 36) are in an open state. (6) Preparation for autonomous operation (Figure 9 (e)) After the occurrence of a system abnormality, in preparation for isolated operation, as shown in FIG. 9(e), the connection relay 36 is opened and the output relay 35 and the neutral grounding relay 34 are closed. (7) Autonomous operation (Figure 9(f)) After the preparation for the independent operation is completed, the power conversion unit 2 is operated to perform the independent operation, as shown in (f) of Fig. 9. Power is supplied to the distribution board 60 through a single-phase three-wire.

[0062] (8) Power recovery detection (Figure 9 (d)) If restoration of power to the commercial power grid (system normal) is detected during isolated operation, after waiting for a certain period of time, as shown in (d) of FIG. 9, the power conversion unit 2 goes into a gate blocked state and all relays (34, 35, 36) are opened. (9) Preparation for grid-connected operation (Figure 9(b)) Thereafter, as a transitional preparation stage for grid-connected operation, the output relay 35 and the connection relay 36 are closed, resulting in the state shown in FIG. 9(b). After that, the power conversion unit 2 resumes operation, resulting in the state shown in FIG. 9(c).

[0063] In this way, the switching unit 3 in Fig. 4 has one less relay than the switching unit 3 in Fig. 3, but the current path can be switched between grid-connected operation and independent operation by two relays, the output relay 35 and the connection relay 36. When switching from grid-connected operation to independent operation, the so-called one-cushion buffer operation shown in (5) above can prevent the neutral grounding in the commercial power system and the neutral grounding in the power conversion device from occurring at the same time.

[0064] <First example of storage system layout> Next, an example of the arrangement of a power storage system including the above-mentioned power conversion device 1 at a consumer facility will be described. Fig. 10 is a diagram showing an image of the arrangement of a power storage system 10 and its peripheral devices at a consumer facility 200 according to a first example. The power storage system 10 incorporates a power conversion unit 2, a switching unit 3, and current sensors 37, 38 in a housing 10c. The first electric circuit end T1 is connected to a commercial power system 51 via a watt-hour meter 53. The second electric circuit end T2 is connected to a distribution board 60. The power conversion unit 2 and the switching unit 3 are connected to each other via a third electric circuit end T3.

[0065] Since the switching unit 3 is provided inside the housing 10c, the switching unit 3 becomes physically a part of the power conversion device 1. Therefore, when installing the power conversion device 1, the worker does not need to be aware of the switching unit 3, and the installation work becomes easier. In addition, the current sensors 37 and 38 can be CTs or board-mounted current sensors. Even in the case of CTs, it is not necessary to use a split-type CT that clamps the electric wire, and a ring-shaped CT through which the electric wire passes or a current sensor that is mounted on a board in advance can be used. Therefore, it is possible to prevent the split-type CT from falling off. In addition, the elimination of the restriction of the split type expands the options, and a lower-cost current sensor can be used.

[0066] The power storage system 10 is typically installed outdoors along the outer wall of the consumer premises 200 due to its size and weight that make it difficult to install indoors. The photovoltaic power generation panels PV_a, PV_b, PV_c, and PV_d are installed on the roof of the consumer premises 200. The power meter 53 is installed on the outer wall of the consumer premises 200 or on a pole or the like within the premises. The distribution board 60 is installed indoors of the consumer premises 200. The router 41 is connected to the power conversion unit 2 via the switching unit 3. The router 41 is capable of communicating with a server, a smartphone, or the like via the Internet.

[0067] <Second example of storage system layout> Fig. 11 is a diagram showing an image of the arrangement of the power storage system 10 and its peripheral devices at a consumer 200 according to the second example. The difference from Fig. 10 is that a remote control 42 is installed between the router 41 and the switching unit 3. The remote control 42 can control and monitor the operation of the power conversion device 1.

[0068] <<Unitization of Energy Storage System: Example 1>> FIG. 12 is a first example of a connection diagram in which a power storage system 10 including a device basically similar to the power conversion device 1 shown in FIG. 4 is unitized. However, the location of the relay is different from that in FIG. 4. In addition, this is an example that specifically shows other devices necessary for actual wiring. A power conversion unit 2, a switching unit 3, and a storage battery B are built into a housing 10c of the power storage system 10. The power conversion unit 2 houses a boost circuit 21, a bidirectional DC / DC converter 22, an inverter 25, an output relay 35, and a control unit 30, and is one unit. The switching unit 3 includes a connection relay 36, a first electric circuit end T1, a second electric circuit end T2, switches 301 and 302, and a remote control board 39.

[0069] The photovoltaic power generation panels PV_a, PV_b, PV_c, and PV_d are connected to the switch 301. The first electric circuit end T1 is connected to the commercial power system 51 via the watt-hour meter 53. The second electric circuit end T2 is connected to the distribution board 60. The remote control board 39 is connected to the router 41 via a communication line of a LAN (Local Area Network). The remote control board 39 corresponds to the control unit 30 in FIG. 4, and is connected to the control unit 30 of the power conversion unit 2 by a DC 12V control power line and a communication line. An earth wire E is drawn from the distribution board 60 to the switching unit 3 and the power conversion unit 2 via the second electric circuit end T2. The storage battery B is connected to the power conversion unit 2 via the switching unit 3 by a power line (solid line) and a CAN communication line (dotted line).

[0070] Connectors C1, C2, C3, C4, C5, and C6 are used to connect the power conversion unit 2 and the switching unit 3, except for the earth wire E. The use of connectors C1, C2, C3, C4, C5, and C6 makes it easy to attach and detach. If a failure occurs in the power conversion unit 2, it may be difficult to repair it on-site, and it may be necessary to take it back to a factory or the like. Even in such a case, the inconvenience of being unable to use electricity at the consumer's house must be avoided. Therefore, the switches 301 and 302 are opened, and the connectors C1, C2, C3, C4, C5, and C6 are separated. Only the earth wire E is disconnected because a connector connection is not permitted.

[0071] 13 is a connection diagram showing a state in which the power conversion unit 2 is removed. In this state, the photovoltaic power generation panels PV_a, PV_b, PV_c, and PV_d and the storage battery B cannot be used, but the power supply from the commercial power system 51 to the distribution board 60 is ensured by closing the connection relay 36. Therefore, the consumer can use the power even after the power conversion unit 2 is taken home.

[0072] As described above, according to the configuration shown in Fig. 12, the power conversion unit 2 and the switching unit 3 are each unitized, physically separable from each other, electrically connected using the connectors C1 to C6, and the power conversion unit 2 is detachable from the housing 10c. If the power conversion unit 2 breaks down, it is possible to remove only the power conversion unit 2 for repair. Even after removal, the ends of the electric wires are protected by the connectors C1 to C6, so that it is safe. Note that by providing the female side of the connectors C1 to C6 in the unit of the switching unit 3, it is possible to prevent the charging unit (live wire unit) from being exposed.

[0073] Furthermore, the connection relay 36 is provided in the unit of the switching unit 3, and the remote control board can close the connection relay 36 when the power conversion unit 2 is removed from the housing 10c (FIG. 13). This makes it possible to ensure a current path for supplying power from the commercial power system 51 to the distribution board 60. Therefore, even when the power conversion unit 2 is removed, power supply to the consumer can be ensured.

[0074] Furthermore, switches 301 and 302 are provided in the unit of the switching unit 3, and the photovoltaic power generation panels PV_a, PV_b, PV_c, and PV_d are connected to the switch 301. Therefore, when the unit of the power conversion unit 2 is removed, the ends of the electric wires from the photovoltaic power generation panels PV_a, PV_b, PV_c, and PV_d can be stored in the unit of the switching unit 3. If the switch 301 in the unit is opened, the electric circuits from the photovoltaic power generation panels PV_a, PV_b, PV_c, and PV_d can be safely disconnected when the unit of the power conversion unit 2 is attached or detached.

[0075] <<Unitization of Energy Storage System: Example 2>> FIG. 14 is a second example of a connection diagram in which a power storage system 10 including a device basically similar to the power conversion device 1 shown in FIG. 4 is unitized. However, the location of the relay is different from that in FIG. 4. In addition, this is an example that specifically shows other devices necessary for actual wiring. The power conversion unit 2, the switching unit 3, and the storage battery B are built into the housing 10c of the power storage system 10. The power conversion unit 2 houses the boost circuit 21, the bidirectional DC / DC converter 22, the inverter 25, the output relay 35, the connection relay 36, the control unit 30, and the remote control board 39, and is one unit. The switching unit 3 includes a first electric circuit end T1, a second electric circuit end T2, and a switch 301.

[0076] The photovoltaic power generation panels PV_a, PV_b, PV_c, and PV_d are connected to the switch 301. The first electric circuit end T1 is connected to the commercial power system 51 via the watt-hour meter 53. The second electric circuit end T2 is connected to the distribution board 60. The remote control board 39 is connected to the router 41 via a LAN communication line. The remote control board 39 corresponds to the control unit 30 in FIG. 4, and is connected to the control unit 30 of the power conversion unit 2 via a DC 12V control power line and a communication line. An earth wire E is drawn from the distribution board 60 to the switching unit 3 and the power conversion unit 2 via the second electric circuit end T2. The storage battery B is connected to the power conversion unit 2 via the switching unit 3, a power line (solid line) and a CAN communication line (dotted line).

[0077] Connectors C11, C12, C13, C14, C15, and C16 are used to connect the power conversion unit 2 and the switching unit 3, except for the earth wire E. The connectors C11, C12, C13, C14, C15, and C16 make it easy to attach and detach. If a failure occurs in the power conversion unit 2, it may be difficult to repair it on-site, and it may be necessary to take it back to a factory or the like. Even in such a case, the inconvenience of being unable to use electricity at the consumer's house must be avoided. Therefore, the switch 301 is opened, and the connectors C11, C12, C13, C14, C15, and C16 are separated. Only the earth wire E is disconnected because a connector connection is not permitted.

[0078] 15 is a connection diagram showing a state in which the power conversion unit 2 has been removed in this manner. In this state, the photovoltaic power generation panels PV_a, PV_b, PV_c, and PV_d and the storage battery B cannot be used, but by connecting the connectors C12 and C13 to each other, the power supply from the commercial power system 51 to the distribution board 60 is ensured. Therefore, the consumer can use the power even after the power conversion unit 2 is taken home.

[0079] 《Addendum》 In addition, at least a portion of all of the above disclosures may be combined with each other in any desired manner. The present invention is intended to cover all modifications within the scope of the claims, including those equivalent thereto, and is not ... [Explanation of symbols]

[0080] 1 Power conversion device 2 Power conversion section 3 Switching section 10 Energy Storage System 10c Case 20 Control section 21, 21a, 21b, 21c, 21d Boost circuit 22 Bidirectional DC / DC converter 23 DC Bus 24 Intermediate Capacitor 25 Inverter 26u, 26o, 26w AC reactor 27, 28, 29 AC side capacitor 30 Control section 31 Grid-connected relay 32 Independent Relay 33 Connection Relay 34 Neutral earth relay 35 Output Relay 36 Connection Relay 37,38 Current Sensors 39 Remote control board 41 Router 42 Remote Control 51 Commercial power system 52 Transformer 53 Electric energy meter 54 Outdoor switch 60 Distribution Board 61,62 Load 70 General load distribution board 80 Specific load distribution board 100 Energy Storage System 200 Consumer 301,302 Switchgear 601 Contract Breaker 604 Earth leakage circuit breaker 605 Child Breaker 701 Contract Breaker 702 CT 703,704 Earth leakage circuit breaker 705 Child Breaker 801 Changeover switch 802 Child Breaker B. Storage battery C1, C2, C3, C4, C5, C6 Connectors C11, C12, C13, C14, C15, C16 Connectors E Earth wire Po independent output circuit PV_a, PV_b, PV_c, PV_d Photovoltaic panels T1 1st circuit end T2 2nd circuit end The third circuit end of T3

Claims

1. A power conversion device provided between a DC power source and a commercial power system, A first electric circuit end portion connected to the commercial power system; A second circuit end portion connected to a distribution board provided at a consumer home; a power conversion unit connected to the DC power source and performing power conversion between DC and AC; a switching unit that is connected to three electric circuit ends, i.e., the first electric circuit end, the second electric circuit end, and the third electric circuit end, when the AC side electric circuit end of the power conversion unit is a third electric circuit end corresponding to a single-phase three-wire system, and that switches a current path so that current is conducted between electric circuit ends selected from the three electric circuit ends depending on whether the power conversion unit performs a grid-connected operation or an independent operation; a current sensor for detecting reverse power flow provided downstream of the first electric path end when the commercial electric power system is defined as an upstream side; an independent output electric path that is derived by switching the switching unit and that causes current to flow between the second electric path end portion and the third electric path end portion; a neutral line grounding switch provided between the neutral line of the independent output electric circuit and a ground potential; Equipped with Power conversion equipment.

2. an output switch provided in an electric path between the first electric path end and the third electric path end; A connection switch is provided between the output switch and the first electric circuit end portion, and connects or disconnects the commercial power system and the distribution board to each other. The power conversion device according to claim 1 , wherein the independent output electric path leads an electric path between the output switch and the connection switch to the second electric path end portion.

3. Further comprising an independent switch provided in an electric path between the second electric path end and the third electric path end, The power conversion device according to claim 1 , wherein the neutral conductor grounding switch is provided between the neutral conductor in the electric path between the independent switch and the second electric path end and the ground potential.

4. The power conversion device according to claim 1 , wherein the switching unit is provided inside a housing of the power conversion device.

5. The power conversion device according to claim 1 , wherein the current sensor includes a CT or a board-mounted current sensor.

6. 6. The power conversion device according to claim 4 or claim 5, wherein the power conversion unit and the switching unit are each unitized, physically separable from each other, and electrically connected using a connector, and the power conversion unit is detachable from a housing of the power conversion device.

7. The power conversion device according to claim 6 , wherein a switch is provided in a unit of the switching section, and the DC power source is connected to the switch.

8. 8. A power storage system comprising the power conversion device according to claim 1, and comprising a solar power generation panel and a storage battery as the DC power source.

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