SOLAR POWER GENERATION SYSTEM

A solar power generation system includes a string, an inverter, and a plurality of shut-off devices. The string includes a plurality of solar cell module groups. The plurality of shut-off devices are configured to cut off a connection between the plurality of solar cell module groups. The plurality of solar cell module groups include a first group, a second group connected to the first group, and a third group connected to the second group. The plurality of shut-off devices includes a first open-close unit connected to the second group, a semiconductor switching device connected in series to the first open-close unit, and a power supply unit connected to the second group and configured to generate power to drive the first open-close unit. The semiconductor switching device enters an OFF state when an amount of power generated by second group is smaller than a predetermined threshold.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2022-121832, filed Jul. 29, 2022. The contents of that application are incorporated by reference in their entirety.

FIELD

The present invention relates to a solar power generation system.

BACKGROUND

In the United States, to protect firefighters from electric shock in an emergency such as a fire, the introduction into a solar power generation system of a so-called rapid shutdown function for immediately stopping the power generation by a solar power generation system in an emergency is mandated by National Electrical Code (NEC). For example, Published Japanese Translation No. 2012-511299 of the PCT International Publication discloses a solar power generation system in which the output of power from solar cell modules to an inverter is stopped according to the operating state of the inverter.

SUMMARY

In a solar power generation system, in order to further improve the safety of firefighters in the event of a fire, for example, a shut-off device having the rapid shutdown function is preferably installed for each solar cell module. However, providing a shut-off device for each solar cell module increases the installation cost of the shut-off devices.

Further, the shut-off device of a solar power generation system uses a switching device for opening and closing a mechanical contact such as a relay as a switching device for cutting off an electric circuit in the solar power generation system. The power for driving the switching device is supplied from the solar cell modules of the solar power generation system. That is, the power generated by the solar cell modules is used for driving an external device (for example, an inverter) and driving the switching device. In this case, if the amount of power generated by the solar cell modules drops for some reason and the power required to drive the switching device is no longer supplied to the switching device, a phenomenon in which if an attempt is made to close the contact of the switching device with the power from the solar cell modules (i.e., to turn the switching device into an ON state), the contact is opened immediately (i.e., the switching device is turned into an OFF state), and this sequence of closing and opening is repeated. Further, when the amount of power generated by the solar cell modules becomes unstable, the switching device may be repeatedly switched between the ON state and the OFF state. The occurrence of this phenomenon makes the operation of the solar power generation system unstable, thereby hindering the operation of the solar power generation system.

An object of the present invention is to provide a solar power generation system that decreases the installation cost of shut-off devices and improves stability of the solar power generation system.

A solar power generation system according to one aspect of the claimed invention includes a string, an inverter, and a plurality of shut-off devices. The string includes a plurality of solar cell module groups connected in series with each other. Each of the plurality of solar cell module groups includes one or more solar cell modules connected in series. The inverter is connected to the string for converting DC power output from the solar cell modules to AC power. The plurality shut-off devices are configured to cut off a connection between the plurality of solar cell module groups in response to a control signal from the inverter. Each of the plurality of solar cell module groups has an open-circuit voltage equal to or less than a predetermined open-circuit voltage. The plurality of solar cell module groups include a first group, a second group connected to the first group, and a third group connected to the second group. The plurality of solar cell modules include a first shut-off device. The first shut-off device includes a first open-close unit, a first semiconductor switching device, and first power supply unit. The first open-close unit is connected to an anode-side terminal of the second group. The first semiconductor switching device is connected in series between the anode-side terminal of the second group and the first open-close unit. The first power supply unit is configured to generate power to drive the first open-close unit. The first power supply unit has an anode-side terminal connected between the anode-side terminal of the second group and the first semiconductor switching device, and a cathode-side terminal connected to a cathode-side terminal of the second group. The first semiconductor switching device is configured to enter an OFF state in a case where an amount of power generated by the second group is smaller than a predetermined threshold.

In this solar power generation system, since each of the plurality of solar cell module groups has an open-circuit voltage equal to or less than a predetermined open-circuit voltage, a highly safe solar power generation system can be provided. Further, the first semiconductor switching device is turned into an OFF state when the amount of power generated by the second group is smaller than a predetermined threshold. Thus, when the amount of power generated by the second group is small, an electric path from the second group to the inverter is cut off, and the second group can supply power only to the first power supply unit. That is, when the amount of power generated by the second group is small, the power generated by the second group is used only to drive the first open-close unit. As a result, the first open-close unit can be maintained in the closed state (ON state) even if the amount of power generated by the second group is small or unstable. As a result, the solar power generation system operates stably.

The first shut-off device may include a first bypass device. The first bypass device may include one end connected to the cathode-side terminal of the second group, and another end connected between the first open-close unit and the first semiconductor switching device. In this case, even if the amount of power generated by the second group decreases, the power generated by another solar cell module group can be transferred to the inverter via the first bypass device.

The first semiconductor switching device may be a MOSFET device or an IGBT device. These devices can reduce the power required to turn the semiconductor switching device into an ON state or an OFF state.

The first shut-off device may include a second open-close unit connected to the cathode-side terminal of the second group. In this case, a plurality of electric circuits can be opened and closed by the first shut-off device.

The second open-close unit may be driven by the power supplied from the first power supply unit. In this case, the second open-close unit can be maintained in the closed state (ON state) even if the amount of power generated by the second group is small or unstable.

The second open-close unit may be driven by the power supplied from the first power supply unit. In this case, for example, when a defect such as a contact failure occurs in the third open-close unit, it is possible to continue to use the fourth open-close unit that is operating normally.

At least one of the first group, the second group, and the third group of the plurality of solar cell module groups may include the plurality of solar cell modules connected in series. In this case, the plurality of solar cell modules can be collectively cut off by the first shut-off device.

The plurality of solar cell module groups may further include a fourth group connected to the third group and a fifth group connected to the fourth group. The plurality shut-off device may include a second shut-off device, a third open-close unit, a second semiconductor switching device, and a second power supply unit. The third open-close unit may be connected to an anode-side terminal of the fourth group. The second semiconductor switching device may be connected in series between the anode-side terminal of the fourth group and the third open-close unit. The second power supply unit may be configured to generate power to drive the third open-close unit. The second power supply unit may have an anode-side terminal connected between the anode-side terminal of the fourth group and the second semiconductor switching device, and a cathode-side terminal connected to a cathode-side terminal of the fourth group. The second semiconductor switching device may be configured to enter an OFF state in a case where an amount of power generated by the fourth group is smaller than a predetermined threshold. In this case, when the amount of power generated by the fourth group is small, the power generated by the fourth group is used only to drive the third open-close unit. As long as the power generated by the fourth group is supplied only to drive the third open-close unit, the third open-close unit can be maintained in the closed state (ON state) even if the power generated by the fourth group is small or unstable.

The second shut-off device may include a second bypass device. The second bypass device may include one end connected to the cathode-side terminal of the fourth group, and another end connected between the third open-close unit and the second semiconductor switching device. In this case, even if the amount of power generated by the fourth group decreases, the power generated by another solar cell module group can be transferred to the inverter via the second bypass device.

The second semiconductor switching device may be a MOSFET device or an IGBT device. These devices can reduce the power required to turn the second semiconductor switching device into an ON state or an OFF state.

The second shut-off device may include a fourth open-close unit connected to the cathode-side terminal of the fourth group. In this case, a plurality of electric circuits can be opened and closed by the second shut-off device.

The fourth open-close unit may be driven by the power supplied from the second power supply unit. In this case, the fourth open-close unit can be maintained in the closed state (ON state) even if the amount of power generated by the fourth group is small or unstable.

The second shut-off device may be configured to control the opening and closing of the third open-close unit and the fourth open-close unit independently of each other. In this case, for example, when a defect such as a contact failure occurs in the third open-close unit, it is possible to continue to use the fourth open-close unit that is operating normally.

The predetermined open-circuit voltage may be 165 V. In this case, a safer solar power generation system can be provided.

The inverter may output the control signal to the plurality of shut-off devices by power line communication. In this case, when the plurality of shut-off devices are disposed in an existing solar power generation system, additional wiring for ensuring the communication between the inverter and the plurality of shut-off device can be omitted, which reduces the installation cost of the plurality of shut-off device.

The inverter may output the control signal to the plurality of shut-off devices by wireless communication. In this case, the control signal can be output to the plurality of shut-off devices by remote control.

DETAILED DESCRIPTION

FIG.1is a block diagram schematically showing a configuration of a solar power generation system1in accordance with the claimed invention. The solar power generation system1includes a string2, an inverter3, and a plurality of shut-off devices4.

The string2includes a plurality of solar cell module groups connected in series with each other. Each of the plurality of solar cell module groups includes one or more solar cell modules6connected in series. That is, the string2includes a plurality of (for example,18in the present embodiment) solar cell modules6connected in series with each other. The plurality of solar cell module groups in the present embodiment are composed of six solar cell module groups6A to6F. Note that the solar power generation system1may include a solar cell array in which a plurality of strings2are connected in parallel.

Each of the plurality of solar cell module groups6A to6F has an open-circuit voltage equal to or less than a predetermined open-circuit voltage. The predetermined open-circuit voltage may, for example, be 165V. That is, modules in the solar cell module groups in the string2are grouped so that the open-circuit voltage for each group is 165 V or less. The open-circuit voltage of each of the solar cell modules6is, for example, 50V. Hereinafter, the solar cell module groups6A to6F may be referred to as groups6A to6F. The groups6A to6F in this embodiment are examples of the first group to the sixth group.

Each of the groups6A to6F includes three solar cell modules6connected in series with each other. Therefore, the open-circuit voltage of each of the groups6A to6F is 150V.

The groups6A to6F are arranged in alphabetical order from the group6A to the group6F and are connected in series with each other. Each of the groups6A to6F includes an anode-side terminal and a cathode-side terminal. The anode-side terminal in each of the groups6A to6F corresponds to the anode-side terminal of the solar cell modules6closest to the anode of the inverter3among the plurality of solar cell modules6in the groups6A to6F. The cathode-side terminal in each of the groups6A to6F corresponds to the cathode-side terminal of the solar cell modules6farthest from the anode of the inverter3among the plurality of solar cell modules6in the groups6A to6F.

The anode-side terminal of the group6A corresponds to the anode-side terminal of the solar cell module closest to the group6B among the solar cell modules6in the group6A and is connected to the cathode-side terminal of the group6B. The cathode-side terminal of the group6A corresponds to the cathode-side terminal of the solar cell module farther from the group6B among the solar cell modules6in the group6A and is connected to the cathode-side terminal of the inverter3.

The anode-side terminal of the group6B corresponds to the anode-side terminal of the solar cell module closest to the group6C among the solar cell modules6in the group6B and is connected to the cathode-side terminal of the group6C. The cathode-side terminal of the group6B corresponds to the cathode-side terminal of the solar cell module closest to the group6A among the solar cell modules6in the group6B and is connected to the anode-side terminal of the group6A.

The anode-side terminal of the group6C is connected to the cathode-side terminal of the group6D. The cathode-side terminal of the group6C is connected to the anode-side terminal of the group6B. The anode-side terminal of the group6D is connected to the cathode-side terminal of the group6E. The cathode-side terminal of the group6D is connected to the anode-side terminal of the group6C. The anode-side terminal of the group6E is connected to the cathode-side terminal of the group6F. The cathode-side terminal of the group6E is connected to the anode-side terminal of the group6D. The anode-side terminal of the group6F is connected to the cathode-side terminal of the inverter3. The cathode-side terminal of the group6F is connected to the anode-side terminal of the group6E.

The solar cell modules6receive sunlight to generate power, and they output the generated power to the inverter3. The inverter3is connected to the string2via a power line. The inverter3converts the DC power from the solar cell modules6in the string2into AC power. The inverter3is connected to a power system7and supplies the AC power to the commercial power system and load devices.

Specifically, the inverter3includes a DC/DC converter3a, a DC/AC inverter3b, and a control unit3c. The DC/DC converter3aconverts the voltage of the power output from the solar cell modules6into a predetermined voltage and inputs it to the DC/AC inverter3b. The DC/AC inverter3bconverts, via the DC/DC converter3a, the DC power output from the solar cell modules6into AC power. The control unit3cincludes a CPU and memory and controls the DC/DC converter3aand the DC/AC inverter3b. The control unit3coutputs a control signal to the plurality of shut-off devices4by power line communication.

The plurality of shut-off devices4are connected to electric paths connecting the groups6A to6F. The plurality of shut-off devices4cut off the connection between the groups6A to6F in response to the control signal from the inverter3. The plurality of shut-off devices4include shut-off devices4ato4c. The shut-off device4ain the present embodiment is an example of the first shut-off device, and the shut-off device4bis an example of the second shut-off device.

The shut-off device4ais connected to an electric path8aconnecting the group6A and the group6B and an electric path8bconnecting the group6B and the group6C. The shut-off device4acuts off the connection between the group6A and the group6B and the connection between the group6B and the group6C in response to the control signal from the inverter3. Specifically, the shut-off device4acuts off the electric paths8aand8bby cutting off the voltage output from the solar cell modules6of the group6B in response to the control signal from the inverter3. As a result, the connection between the group6A and the group6B and the connection between the group6B and the group6C are cut off.

The shut-off device4ais driven by the electric power generated by the solar cell modules6of the group6B. The shut-off device4ais externally attached, for example, to the solar cell modules6of the group6B.

FIG.2is a block diagram schematically showing a configuration of the shut-off device4a. The shut-off device4aincludes a power supply unit41, a signal-receiving unit42, a control unit43, a relay44, a bypass circuit45, a semiconductor switching device47, and a bypass device48.

The power supply unit41is a regulator connected in parallel to the group6B. Specifically, the power supply unit41has an anode-side terminal connected to the anode-side terminal of the group6B and a cathode-side terminal connected to the cathode-side terminal of the group6B.

FIG.3is a circuit diagram schematically showing a configuration of the power supply unit41. The power supply unit41includes input terminals21aand21b, output terminals22aand22b, a line filter23, capacitors24and25, a booster circuit26, a switching device27, a control circuit28, a transformer29, a diode30, and a DC/DC converter31, and a feedback circuit32.

The power supply unit41uses the power generated by the solar cell modules6as a power source to generate drive power to drive the shut-off device4s. Here, only the power generated by the solar cell modules6of the group6B is used to generate the drive power to drive the shut-off device4a.

The signal-receiving unit42receives the control signal from the control unit3cof the inverter3and outputs the received control signal to the control unit43. Specifically, the signal-receiving unit42receives the control signal from the control unit3cof the inverter3via a signal detection unit46that detects the control signal from the control unit3cof the inverter3.

The control unit43includes a CPU and memory. The control unit43controls the electric current flowing through the coil in the relay44based on the signals output from the signal-receiving unit42and controls the opening and closing of the contacts of the relay44. The relay44is, for example, a mechanical relay, and is able to open and close a high-voltage direct current.

The relay44includes a first open-close unit44aand a second open-close unit44b. The first open-close unit44ais connected to the anode-side terminal of the group6B. The first open-close unit44ais disposed in the electric path8band opens and closes the connection between the group6B and the group6C. The second open-close unit44bis connected to the cathode-side terminal of the group6B. The second open-close unit44bis disposed in the electric path8aand opens and closes the connection between the group6A and the group6B. Hereinafter, the first open-close unit44aand the second open-close unit44bmay be referred to as open-close units44aand44b.

While the drive power is not supplied from the power supply unit41, the open-close units44aand44bare in an open state all the time. Accordingly, while the shut-off device4ais not driven, the connection between the group6A and the group6B and the connection between the group6B and the group6C are in a cutoff state.

The bypass circuit45is a circuit for the signal-receiving unit42to receive the control signal from the control unit3cin a state where the connection between the groups6A to6F is cut off. In a state where the connection between the group6A and the group6B and the connection between the group6B and the group6C are cut off, the signal-receiving unit42is able to receive the control signal from the control unit3cvia the bypass circuit45.

The semiconductor switching device47is connected in series with the first open-close unit44ain the electric path8b. Specifically, the semiconductor switching device47is connected at one end to the anode-side terminal of group6A. The other end of the semiconductor switching device47is connected to the first open-close unit44a. The semiconductor switching device47is, for example, a MOSFET device or an Insulated Gate Bipolar Transistor (IGBT) device.

The semiconductor switching device47is connected to the control unit43. The control unit43controls switching between the ON state and the OFF state of the semiconductor switching device47. Here, the “ON state” means that one end and the other end of the semiconductor switching device47are in a conductive state. The “OFF state” means that one end and the other end of the semiconductor switching device47are in a non-conducting state.

When the semiconductor switching device47is a MOSFET device or an IGBT device, the control unit43is connected to a gate terminal of the semiconductor switching device47. The control unit43can turn the semiconductor switching device47into an ON state or an OFF state by outputting a predetermined voltage signal to the gate terminal. When a voltage signal is output to the gate terminal to turn the MOSFET device or the IGBT device into the ON state or the OFF state, almost no current flows through the gate terminal. Thus, the MOSFET device or the IGBT device as the semiconductor switching device47can reduce the power required to turn the semiconductor switching device47into the ON state or the OFF state.

In the shut-off device4a, when the semiconductor switching device47is turned OFF, the anode-side terminal of the group6B and the group6C are cut off. Even if the semiconductor switching device47is turned OFF, however, the power supply unit41is not cut off from the group6B. That is, in a case where the semiconductor switching device47is in the OFF state, the power generated by the group6B is supplied to the power supply unit41but not to the inverter3.

The control unit43turns the semiconductor switching device47into an OFF state in a case where the amount of power generated by the group6B is smaller than a predetermined threshold. Thus, when the amount of power generated by the group6B is smaller than the predetermined threshold, the power of the group6B is supplied only to the shut-off device4a(the power supply unit41). With this configuration, when the amount of power generated by the group6B is small, the power from the group6B can be used only to drive the open-close units44aand44b. When the power from the group6B is supplied only to the open-close units44aand44b, even if the amount of power generated by the group6B is small or unstable, the open-close units44aand44bcan be maintained in the closed state (ON state). As a result, the solar power generation system1operates stably. The above threshold can be set, for example, as the amount of power with which the open-close units44aand44boperate stably even if the power of the group6B is supplied to both of the power supply unit41and the inverter3.

Since the shut-off device4aincludes the semiconductor switching device47, the open-close units44aand44bare maintained in the closed state (ON state) even if there occurs an abnormality in the amount of power generated by the group6B. Thus, the open-close units44aand44bare less likely to open and close while a high voltage is applied to the open-close units44aand44b. As such, the open-close units44aand44bare not required to have a large voltage-handling capacity and can be inexpensive.

The bypass device48is connected in parallel to the group6B. Specifically, the bypass device48is connected at one end between the cathode-side terminal of group6B and the second open-close unit44b. The other end of the bypass device48is connected between the first open-close unit44aand the semiconductor switching device47. The bypass device48is, for example, a diode having an anode connected to the cathode side of group6B and a cathode connected between the first open-close unit44aand the semiconductor switching device47.

When the solar cell modules of the group6B are shaded at sunrise or sunset, sometimes sufficient power cannot be output from the group6B due to an abnormality such as a sudden power drop or abnormal heat generation in the group6B. At that time, the bypass device48forms an electric path that “bypasses” the group6B and transfers the power generated by the other solar cell module groups. Specifically, in a case where the amount of power generated by the group6B is insufficient, the semiconductor switching device47is turned OFF, and the open-close units44aand44benter the closed state, the bypass device48forms a path through which the power generated by the other solar cell module groups is transferred to the inverter3.

When the group6B cannot output sufficient power, the bypass device48is able to immediately form an electric path that bypasses the group6B in which an abnormality has occurred, based on its own electrical characteristics without any command of an external signal.

Note that, the connection of the two terminals of the bypass device48can be positioned as desired, as long as the group6B where the shut-off device4ais connected is bypassed and also at least one of the terminals of the bypass device48is connected to the group6B without connection to the first open-close unit44aor the second open-close unit44b. For example, the anode of the bypass device48may be connected to the electric path connecting the anode-side terminal of the group6A and the second open-close unit44b, and the cathode of the bypass device48may be connected to the electric path connecting the anode-side terminal of the group6B and the first open-close unit44a.

The shut-off device4bhas the same configuration as the shut-off device4aexcept that the connected electric path is different from the shut-off device4a. The shut-off device4bis connected to an electric path8cconnecting the group6C and the group6D and an electric path8dconnecting the group6D and the group6E. The shut-off device4bcuts off the connection between the group6C and the group6D and the connection between the group6C and the group6E in response to the control signal from the inverter3.

The shut-off device4bis driven by the electric power generated by the solar cell modules6of the group6D. The shut-off device4bis externally attached, for example, to the solar cell modules6of the group6D.

As shown inFIG.4, the shut-off device4bincludes a power supply unit51, a signal-receiving unit52, a control unit53, a relay54, a bypass circuit55, a signal detection unit56, a semiconductor switching device57, and a bypass device58. The relay54includes a first open-close unit54a(an example of a third open-close unit) and a second open-close unit54b(an example of a fourth open-close unit). Since each configuration of the shut-off device4bis the same as each configuration of the shut-off device4a, it will be briefly described.

The power supply unit51uses the power generated by the solar cell modules6as a power source to generate drive power to drive the shut-off device4b. Here, only the power generated by the solar cell modules6of the group6D is used to generate the drive power to drive the shut-off device4b.

The signal-receiving unit52receives the control signal from the control unit3cof the inverter3and outputs the received control signal to the control unit53.

The control unit53controls the opening and closing of the contacts of the relay54. The first open-close unit54aof the relay54is connected to the anode-side terminal of the group6D. The first open-close unit54ais disposed in the electric path8dand opens and closes the connection between the group6D and the group6E. The second open-close unit54bis connected to the cathode-side terminal of the group6D. The second open-close unit54bis disposed in the electric path8cand opens and closes the connection between the group6C and the group6D.

The semiconductor switching device57is connected in series with the first open-close unit54ain the electric path8d. The semiconductor switching device57is, for example, a MOSFET device or an IGBT device.

The control unit53turns the semiconductor switching device57into an OFF state in a case where the amount of power generated by the group6D is smaller than a predetermined threshold. The above threshold can be set, for example, as the amount of power with which the first open-close unit54aand second open-close unit54boperate stably even if the power of the group6D is supplied to both of the power supply unit51and the inverter3.

The bypass device58is connected in parallel to the group6D. The bypass device48is connected at one end between the cathode-side terminal of group6D and the second open-close unit54b. The other end of the bypass device58is connected between the first open-close unit54aand the semiconductor switching device57. The bypass device58is, for example, a diode having an anode connected to the cathode side of group6D and a cathode connected between the first open-close unit54aand the semiconductor switching device57.

The shut-off device4chas the same configuration as the shut-off device4aexcept that the connected electric path is different from the shut-off device4aand shut-off device4b. That is, the shut-off device4cincludes a power supply unit, a signal-receiving unit, a control unit, a relay64including a first open-close unit64aand a second open-close unit64b, a bypass circuit, a signal detection unit, a semiconductor switching device, and a bypass device. Since each configuration of the shut-off device4cis the same as each configuration of the shut-off device4a, the description thereof will be omitted.

The shut-off device4cis connected to an electric path8econnecting the group6E and the group6F and an electric path8fconnecting the group6F and the inverter3. The shut-off device4ccuts off the connection between the group6E and the group6F and the connection between the group6F and the inverter3in response to the control signal from the inverter3.

Next, the operation modes of the plurality of shut-off devices4will be described with reference toFIG.5, mainly by taking the operation of the shut-off device4aas an example. The operation modes of the plurality of shut-off devices4includes three operation modes of a start mode, an active mode, and a safety mode. The safety mode includes a normal shut-off mode and an emergency safety shut-off mode. Thus, the plurality of shut-off devices4operate in four operation modes: a start mode, an active mode, a normal shut-off mode, and an emergency safety shut-off mode.

The start mode is a mode for when sunlight starts to hit the solar cell modules6. At this time, the solar cell modules6receive sunlight and generate power. Then, the shut-off device4ais driven by the drive power generated by the power supply unit41using the power generated by the solar cell modules6. When the shut-off device4ais driven and the control unit43receives the control signal from the control unit3cof the inverter3via the signal-receiving unit42, the control unit43closes the open-close units44aand44bof the relay44.

Similarly, the shut-off device4bis driven by the drive power generated by the power supply unit51of the shut-off device4busing the power generated by the solar cell modules6. When the shut-off device4bis driven and the control unit53receives the control signal from the control unit3cof the inverter3via the signal-receiving unit52, the control unit53turns the first open-close unit54aand the second open-close unit54bof the relay54into a closed state. The shut-off device4coperates in the same manner as the shut-off device4a. Consequently, the groups6A to6F are connected to the string2via the plurality of shut-off devices4(shut-off devices4ato4c), and the power generated by the solar cell modules6is output to the inverter3.

In the start mode (particularly at sunrise), the amount of power generated by the solar cell module groups is small. Thus, in the start mode, for example, if the power from the solar cell modules6of the group6B is used to drive the open-close units44aand44band also to be supplied to the inverter3, it might happen that sufficient power is not provided to drive the open-close units44aand44b, and thereby even if the open-close units44aand44battempt to shift from the open state (OFF state) to the closed state (ON state), they immediately return to the open state (OFF state), and this attempt-and-return action may be repeated.

Thus, in the start mode, when the amount of power generated by the group6B is smaller than a predetermined threshold, the control unit43turns the semiconductor switching device47into an OFF state. With this configuration, the power from the group6B is used only to drive the open-close units44aand44b, and thereby the open-close units44aand44bcan be maintained in the closed state (ON state) even if the amount of power generated by the group6B is small.

After that, when the amount of power generated by the group6B exceeds the predetermined threshold, the control unit43turns the semiconductor switching device47into an ON state. With this configuration, after the amount of power generated by the group6B increases sufficiently, it becomes possible to use the power generated by the group6B to drive the open-close units44aand44band to supply the inverter3.

The active mode is a state in which the solar cell modules6receive sunlight during the daytime to generate power, and it is substantially the same as the start mode. Thus, in the active mode, the groups6A to6F are in connection with each other via the plurality of shut-off devices4(shut-off device4ato4c), and the power generated by the solar cell modules6is output to the inverter3.

In the active mode, when the amount of power generated by the group6B is smaller than a predetermined threshold due, for example, to the influence of the weather or an abnormality of the solar cell module, the control unit43turns the semiconductor switching device47into an OFF state. As a result, the electric power from the group6B can be used only to drive the open-close units44aand44bso that the open-close units44aand44bcan be maintained in the closed state (ON state) even if the amount of power generated by the group6B is small.

In the start mode and the active mode, when the amount of power generated by the group6D is smaller than a predetermined threshold, the control unit53of the shut-off device4bturns the semiconductor switching device57into an OFF state. Similarly, when the amount of power generated by the group6F is smaller than a predetermined threshold, the control unit of the shut-off device4cturns the semiconductor switching device67into an OFF state.

The normal shut-off mode is a mode when the solar cell modules6are not exposed to sunlight at night or due to the influence of bad weather such as rain or a mode when the power generation of the solar cell modules6is unstable. In the normal shut-off mode, when there is no power from the solar cell modules6in the normal shutdown mode, no control signal is output from the control unit3cof the inverter3, and the first open-close unit and the second open-close unit of the shut-off devices4ato4care all in the open state.

In the normal shut-off mode, when the power generation by the solar cell modules6is unstable due to the unstable weather or the like, the control signal is output from the control unit3cof the inverter3. For example, when the amount of power generated by the group6B is unstable and does not become smaller than the predetermined threshold, the open-close units44aand44bof the relay44are turned into the ON/OFF state depending on the power supplied from the solar cell modules6of the group6B.

The emergency safety shut-off mode is a mode in which the electric paths8ato8fare cut off so that the power supply from the solar cell modules6to the inverter3is stopped during the start mode or the active mode. In the present embodiment, as shown inFIG.1, when an operation switch35is connected to the inverter3and the operation switch35is operated during the start mode or the active mode of the plurality of shut-off devices4, the operation mode of the plurality of shut-off devices4is switched to the emergency safety shut-off mode.

Specifically, when the operation switch35is operated, the control unit3cstops the output of the control signal. When the signal detection unit46detects the stop of the control signal of a fixed cycle, the open-close units44aand44bof the relay44are turned open via the signal-receiving unit42and the control unit43. At this point in time, the control unit43turns the semiconductor switching device47into an OFF state, and then turns the open-close units44aand44bof the relay44into the open state. As a result, the connection between the group6A and the group6B and the connection between the group6B and the group6C are cut off, and the output of power from the solar cell modules6to the inverter3is stopped.

Similarly, when the shut-off device4bdetects the stop of the control signal of a fixed cycle, the shut-off device4bcontrols the open-close units54aand54bof the relay54in the open state. As a result, the connection between the group6C and the group6D and the connection between the group6D and the group6E are cut off. Similarly, when the shut-off device4cdetects the stop of the control signal of a fixed cycle, the shut-off device4bcontrols the open-close units64aand64bof the relay64in the open state. As a result, the connection between the group6C and the group6D and the connection between the group6D and the group6E are cut off. As a result, all the groups6A to6F are separated from each other, so that the open-circuit voltage of the string2is divided into 165V or less.

In the solar power generation system1of the above configuration, since the plurality of solar cell module groups6A to6F each have an open-circuit voltage of165, a highly safe solar power generation system can be provided. Further, the semiconductor switching device47is turned into an OFF state when the amount of power generated by the group6B is smaller than a predetermined threshold. Thus, when the amount of power generated by the group6B is small, the electric path from the group6B to the inverter3is cut off, and the group6B can supply power only to the power supply unit41. That is, when the amount of power generated by the group6B is small, the power generated by the group6B is used only to drive the open-close units44aand44b. As a result, the open-close units44aand44bcan be maintained in the closed state (ON state) even if the amount of power generated by the group6B is small or unstable. As a result, the solar power generation system1operates stably. The open-close units54aand54bof the shut-off device4band the open-close units64aand64bof the shut-off device4ccan also obtain the same effects as the open-close units44aand44bof the shut-off device4a.

One embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment, and various modifications are possible as long as the modifications are within the scope of the appended claims.

The number of groups of the plurality of solar cell module groups and the number of solar cell modules included in each group are not limited to the above embodiment. The string2may be divided into a plurality of solar cell module groups as long as each group has an open-circuit voltage of 165 V or less. Similarly, in the above embodiment, the plurality of shut-off devices4include three shut-off devices4ato4c, but the number in the plurality of shut-off devices4is not limited to the number used in the described embodiment.

As briefly shown inFIG.6, the plurality of shut-off devices4may be disposed so that the open-circuit voltage of the string2is divided into 165V or less in a cut-off state. InFIG.6, the plurality of shut-off devices4include four shut-off devices4ato4d. Further, each of the groups6A,6C,6E, and6G includes three solar cell modules6connected in series with each other, and each of the groups6B,6D,6F, and6H includes one solar cell module6. Therefore, the open-circuit voltage of the groups6A,6C,6E,6G is 150V, and the open-circuit voltage of the groups6B,6D,6F,6H is 50V. Alternatively, at least one group among the plurality of solar cell module groups may include two solar cell modules6.

As shown briefly inFIG.7, the plurality of shut-off devices4may be disposed in each of the plurality of solar cell module groups. In this case, it is preferable that each of the plurality of solar cell module groups includes the plurality of solar cell modules6.

In the embodiment described above, the relay44of the shut-off device4ahas two contacts of the first open-close unit44aand the second open-close unit44b, but as shown briefly inFIG.8, the relay44may be two relays having a single contact. That is, the shut-off device4amay be configured to independently control the opening and closing of the first open-close unit44aand the second open-close unit44b. Similarly, the shut-off device4bmay be configured to be able to independently control the first open-close unit54aand the second open-close unit54b. Similarly, the shut-off device4cmay be configured to be able to independently control the first open-close unit64aand the second open-close unit64b.

In the above-described embodiment, the control signal is output to the plurality of shut-off devices4by power line communication, but the control signal may be output to the plurality of shut-off devices4by wireless communication such as Wi-Fi®. Alternatively, the inverter3and the plurality of shut-off devices4may be configured to be in communication with each other by wireless communication.

The first control signal may be stopped in modes other than the emergency safety shut-off mode or as a part of the normal shut-off mode (i.e., “NO” in “POWER GENERATION” inFIG.5), and the output of the control signal may be output in the emergency safety shut-off mode or as a part of the normal shut-off mode. In this case, the plurality of shut-off devices4may open the open-close units of the relay when the control signal from the inverter is received and may close the open-close units of the relay while not receiving the control signal.

REFERENCE NUMERALS

1Solar power generation system2String3Inverter4Plurality of shut-off device4aShut-off device (example of first shut-off device)6Solar cell module41Power supply unit (example of power supply unit)44aFirst open-close unit44bSecond open-close unit47Semiconductor switching device (example of first semiconductor switching device)48Bypass device (example of power supply unit)