JP2015032601A - Photovoltaic power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photovoltaic power generation system that can eliminate or reduce blind spots where it is difficult to detect ground fault, while grounding is performed as a measure against Potential Induced Degradation (PID).SOLUTION: A photovoltaic power generation system 100 according to an aspect of the present invention comprises: a solar cell array 300 that uses one or more solar cell modules for generating power using sunlight; a load device 400 that consumes or converts the electric power generated by the solar cell array 300 while insulated from the solar cell array 300 and the ground; a ground wire 40 that grounds the anode or cathode of the solar cell array 300; a switch device 44 arranged to allow for elimination of effects of grounding by the ground wire 40 on a ground potential of a power generation part; and a ground fault detection part 36 that detects ground fault of the solar cell array 300 by controlling the ground potential of the solar cell array 300 at two or more different types of potentials, while the effects of the grounding by the ground wire 40 on the ground potential of the solar cell array 300 are eliminated by the switch device 44.

Description

  The present invention relates to a photovoltaic power generation system, for example, a photovoltaic power generation system in which a PID (Potential Induced Degradation) measure is taken.

  In a photovoltaic power generation system that generates power using sunlight, generally, a plurality of solar cell modules are connected in series and in parallel, and the generated power that has become a large voltage and a large current is a power conditioner or the like. Are supplied to a commercial power system and the like. In the photovoltaic power generation system, a plurality of solar cell modules are connected in series to form a solar cell string. A plurality of solar cell strings are connected in parallel to form a solar cell array.

  Recently, as the voltage generated by the photovoltaic power generation system becomes higher, the performance of the photovoltaic power generation system deteriorates due to the influence of the ground voltage and the power generation amount decreases in such a photovoltaic power generation system. It has become.

  FIG. 9 is a conceptual diagram for explaining an example of the PID phenomenon. In FIG. 9, one solar cell string 502 is shown as an example in the solar cell array of the photovoltaic power generation system. FIG. 9A shows an example in which a p-type semiconductor is used for the bulk of the solar cell. When the potential in the middle of the solar cell string 502 connected to the load device 510 becomes a ground potential, the performance may be deteriorated at a negative potential rather than the ground potential. On the other hand, FIG. 9B shows an example in which an n-type semiconductor is used for the bulk of the solar cell. When the potential in the middle of the solar cell string 502 connected to the load device 510 becomes a ground potential, the performance may be deteriorated at a positive potential rather than the ground potential.

  FIG. 10 is a conceptual diagram for explaining an example of a countermeasure method for the PID phenomenon. As a countermeasure method against the PID phenomenon, it has been considered to take a countermeasure on the solar cell module and the cell itself, but as a reliable technique, it is considered to ground the negative electrode or the positive electrode of the photovoltaic power generation system. ing. FIG. 10A shows an example where a p-type semiconductor is used for the bulk of the solar cell. In such a case, the negative electrode side of the solar cell string 502 is grounded in a state where the solar power generation system is constructed in a system insulated from a commercial power system or the like. As a result, the entire solar cell string 502 can be prevented from having a negative potential with respect to the ground potential. Such measures can avoid the PID phenomenon. FIG. 10B shows an example in which an n-type semiconductor is used for the bulk of the solar cell. In such a case, the positive electrode side of the solar cell string 502 is grounded in a state where the solar power generation system is constructed in a system insulated from a commercial power system or the like. Thereby, it can prevent that the solar cell string 502 whole becomes a positive electric potential rather than the electric potential of the earth. Such measures can avoid the PID phenomenon.

  However, new problems arise from grounding the system. That is when a ground fault occurs in the system. If there is an insulation failure in the solar cell array, a ground fault may occur where the electric circuit comes into contact with the outside in an unintended manner. For example, when a person or an object touches a poorly insulated part, or when a poorly insulated part comes into contact with a metal mount or the like. If a ground fault occurs even at one location in the system, the potential of the ground fault location becomes the ground potential, so a closed loop circuit is formed between the ground location for PID countermeasures and the ground fault location, and a large current is externally supplied. May lead to a major accident.

JP2013-033825A

  FIG. 11 is a conceptual diagram for explaining an example of a ground fault countermeasure for a photovoltaic power generation system in which a PID countermeasure is taken. FIG. 11 shows a case where the negative electrode side of the solar cell string 502 is grounded. FIG. 11 shows a configuration in which an ammeter or / and a fuse are arranged at the grounding location 530 for PID countermeasures for ground fault countermeasures. In such a configuration, as shown in FIG. 11, for example, when a ground fault occurs in the middle of the solar cell string 502 or on the positive electrode side, a closed loop circuit is formed between the grounding point 530 for PID countermeasures and the ground fault point 600. As a result, a large current flows to the outside. Therefore, such a current is monitored with an ammeter or / and a fuse, and when a current exceeding a threshold value flows, the photovoltaic power generation system can be urgently stopped as a ground fault. However, such a configuration creates a blind spot for ground fault detection as described below.

  FIG. 12 is a conceptual diagram for explaining an example of a blind spot for detecting a ground fault in a photovoltaic power generation system in which a PID countermeasure is taken. As shown in FIG. 12, for example, when a first ground fault occurs on the negative electrode side of the solar cell string 502, no potential difference is generated between the ground location 530 and the ground fault location 602 for PID countermeasures. Therefore, it is difficult to detect such a first ground fault with an ammeter or / and a fuse arranged at the grounding location 530 for PID countermeasures. Therefore, the solar power generation system continues normal operation. In this state, for example, when a second ground fault occurs in the middle of the solar cell string 502 or on the positive electrode side, the ground fault location 602 of the first ground fault accident and the ground fault location 600 of the second ground fault accident. When the insulation resistance at the first ground fault point is smaller than the resistance value of the ground wire for PID countermeasures, a large current flows to the outside. However, since the ground location 530 for PID countermeasures is located outside the closed loop circuit, the ammeter or / and the fuse disposed at the ground location 530 for PID countermeasures cannot detect such a second ground fault. Have difficulty. As a result, it will lead to a big accident that a large current flows outside without detecting a ground fault. As described above, the configuration shown in FIG. 12 forms a blind spot (detection dead zone) where ground fault detection is difficult.

  Therefore, the present invention has an object to provide a photovoltaic power generation system capable of overcoming the above-described problems and eliminating a blind spot where ground fault detection is difficult while grounding for PID countermeasures is performed. .

The photovoltaic power generation system of one embodiment of the present invention is
A power generation unit configured using one or more solar cell modules that generate power using sunlight; and
A load device that consumes or converts the power generated by the power generation unit while being insulated from the power generation unit side or the ground; and
A grounding portion for grounding the negative electrode or the positive electrode of the power generation unit;
An exclusion unit arranged to be able to eliminate the influence on the ground potential of the power generation unit caused by the grounding by the grounding unit;
In the state where the influence on the ground potential of the power generation unit caused by the grounding by the grounding unit is excluded by the exclusion unit, the ground potential of the power generation unit is detected by controlling the ground potential of the power generation unit to two or more different potentials. A ground fault detector;
It is provided with.

A photovoltaic power generation system according to another aspect of the present invention is provided.
A power generation unit configured using one or more solar cell modules that generate power using sunlight; and
A load device that consumes or converts the power generated by the power generation unit while being insulated from the power generation unit side or the ground; and
A grounding portion for grounding the negative electrode or the positive electrode of the power generation unit;
An exclusion unit arranged to be able to eliminate the influence on the ground potential of the power generation unit caused by the grounding by the grounding unit;
A current monitoring unit that is disposed on the grounding unit and monitors a current flowing through the grounding unit to detect a ground fault of the power generation unit;
In a state where the influence on the ground potential of the power generation unit caused by the grounding by the grounding unit is excluded by the exclusion unit, the ground potential of the power generation unit is controlled to a ground potential different from that when grounded by the grounding unit to control the ground of the power generation unit. A ground fault detector for detecting a fault,
It is provided with.

Further, as the exclusion unit, a switch for separating the grounding unit from the negative electrode or the positive electrode of the power generation unit is used,
It is preferable that the ground fault detection unit is arranged so that it can be disconnected from the photovoltaic power generation system and connected to the photovoltaic power generation system, and is configured to be connected to the photovoltaic power generation system when detecting a ground fault of the power generation unit. is there.

Further, as the power generation unit, a solar cell array in which a plurality of solar cell strings in which a plurality of solar cell modules are connected in series is connected in parallel is used.
The ground fault detection unit is preferably configured to perform ground fault detection in units of solar cell arrays in a state where the grounding unit is separated from the negative electrode or the positive electrode of the power generation unit by the exclusion unit.

Alternatively, as the power generation unit, a solar cell array in which a plurality of solar cell strings in which a plurality of solar cell modules are connected in series is connected in parallel is used.
The exclusion unit has a plurality of switches for individually separating the grounding unit from the plurality of solar cell strings,
The ground fault detection unit is preferably configured to detect ground faults in units of solar cell strings and to detect ground faults of solar cell strings separated by any of a plurality of switches.

  According to one aspect of the present invention, a blind spot where it is difficult to detect a ground fault can be eliminated or reduced while grounding for PID countermeasures is performed.

1 is a configuration diagram showing a configuration of a photovoltaic power generation system in Embodiment 1. FIG. It is a block diagram which shows the structure of the solar energy power generation system in Embodiment 2. FIG. 10 is a configuration diagram showing a configuration of a photovoltaic power generation system in a third embodiment. It is a block diagram which shows the structure of the solar energy power generation system in Embodiment 4. FIG. 10 is a configuration diagram showing a configuration of a photovoltaic power generation system in a fifth embodiment. FIG. 10 is a configuration diagram showing a configuration of a solar power generation system in a sixth embodiment. FIG. 10 is a configuration diagram illustrating a configuration of a solar power generation system in a seventh embodiment. It is a figure for demonstrating the switch operation | movement in the case of performing the ground fault detection of the photovoltaic power generation system in Embodiment 7. FIG. It is a conceptual diagram for demonstrating an example of a PID phenomenon. It is a conceptual diagram for demonstrating an example of the countermeasure method to a PID phenomenon. It is a conceptual diagram for demonstrating an example of the ground fault countermeasure of the solar power generation system in which the PID countermeasure was taken. It is a conceptual diagram for demonstrating an example of the blind spot of the ground fault detection of the photovoltaic power generation system with which the PID countermeasure was taken.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram showing the configuration of the photovoltaic power generation system in the first embodiment. In FIG. 1A, a solar power generation system 100 is a system that generates power using solar energy. The solar power generation system 100 includes a solar cell array 300 (an example of a power generation unit) and a load device 400. A solar cell string 12 (an example of a power generation unit) is configured by a plurality of solar cell modules 10a to 10e (an example of a power generation unit) electrically connected in series. Each solar cell module 10 is a module that uses sunlight to convert solar energy into electrical energy and output it as DC power. The solar cell array 300 includes a plurality of solar cell strings 12a to 12c arranged in parallel. The plurality of solar cell strings 12a to 12c are electrically connected in parallel inside the solar cell array 300. In the example of Fig.1 (a), although each solar cell string 12 is comprised by five solar cell modules 10a-e connected in series, it does not restrict to this. The number in series may be two, three, four, or six or more. What is necessary is just to set suitably. Similarly, although the solar cell array 300 is comprised by the three solar cell strings 12a-c connected in parallel, it is not restricted to this. The number in parallel may be one, two, or four or more. What is necessary is just to set suitably. Thus, the power generation unit is configured using one or more solar cell modules that generate power using sunlight.

  In the solar cell array 300, the positive electrode (+) and the negative electrode (-) of each solar cell string 12a-c are connected to the solar cell strings 12a-c from the system or connected to the system, respectively. Is connected. In the example of FIG. 1A, one end of the switch device 102a is connected to the negative electrode wiring of the solar cell string 12a, and one end of the switch device 102b is connected to the positive electrode wiring. Further, a backflow prevention diode 20a is connected to the other side of both ends of the switch device 102b. Similarly, one end of the switch device 102c is connected to the negative electrode wiring of the solar cell string 12b, and one end of the switch device 102d is connected to the positive electrode wiring. Further, a backflow prevention diode 20b is connected to the other side of both ends of the switch device 102d. Similarly, one end of the switch device 102e is connected to the negative electrode wiring of the solar cell string 12c, and one end of the switch device 102f is connected to the positive electrode wiring. A backflow prevention diode 20c is connected to the other side of both ends of the switch device 102f. Each backflow prevention diode 20a-c is arrange | positioned so that the direction through which the electric current supplied from the respectively corresponding solar cell string 12a-c may flow may become a forward direction. The number of switch devices 102 that can be arranged on both poles of the solar cell string 12 is arranged. Each switch device 102 is preferably a switch capable of automatically controlling the opening / closing operation electrically. In this case, when a ground fault is detected in the solar cell, it may be a mechanical switch that allows the system to be disconnected and stopped in string units, but it is more preferable to use a semiconductor switch or the like, for example. It is. For example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is preferably used.

  Further, in the example of FIG. 1A, the backflow prevention diode 20 is disposed only on the positive electrode side of each solar cell string 12, but this is not restrictive. The backflow prevention diode 20 may be disposed only on the negative electrode side of each solar cell string 12. Or the backflow prevention diode 20 may be arrange | positioned at both the positive electrode of each solar cell string 12, and the negative electrode, respectively. In any case, each backflow prevention diode 20 is arranged such that the direction in which the current supplied from the corresponding solar cell string 12 flows is the forward direction.

In the example of FIG. 1A, each solar cell string 12a-c is connected in parallel on the other side of the switch device 102, one of which is connected to the negative electrode of the corresponding solar cell string 12, and one of which corresponds to the solar cell. The other side of the backflow prevention diode 20 connected to the positive side of the string 12 is connected in parallel. Thereby, the several solar cell string 12a-c is connected in parallel, and the solar cell array 300 is comprised.
A fuse can be used instead of the backflow prevention diode. In this case, although a reverse current cannot be prevented completely, a solar cell array capable of preventing an excessive reverse current can be configured.

  The negative electrode wiring (negative electrode bus) of the solar cell array 300 is connected to a switch 402 such as a circuit breaker or disconnector, and the positive electrode wiring (positive electrode bus) is connected to a switch 404 such as a circuit breaker or disconnector. The switches 402 and 404 are connected to the load device 400, respectively. As described above, the positive electrode (+) side of the solar cell array 300 is connected to the load device 400 via the switch 404, and the negative electrode (−) side is connected to the load device 400 via the switch 402. The load device 400 has an insulating transformer inside or on the output side thereof, and prevents the solar cell array from being electrically connected to the ground on the load side. Examples of the load device 400 include a power conditioner. The DC power supplied from the solar cell array 300 to the load device 400 is converted into, for example, three-phase AC power in the load device 400 and supplied to, for example, a commercial power system. As described above, the load device 400 consumes or converts the power generated by the solar cell array 300 while being insulated from the solar cell array 300 (power generation unit) side or the ground.

  Further, a ground wire 40 (an example of a grounding portion) branched from the negative electrode wiring (negative electrode bus) of the solar cell array 300 is grounded for PID (Potential Induced Degradation) measures. In the example of Fig.1 (a), the case where a p-type semiconductor is used for the bulk of a solar cell, or the solar cell using a transparent conductive film is shown as an example. Therefore, the negative electrode wiring is grounded. Needless to say, when an n-type semiconductor is used for the bulk of the solar cell, the positive electrode wiring (positive electrode bus) is grounded. In addition, a switch device 44 (an example of an exclusion unit) that disconnects or connects the ground location 41 and the photovoltaic power generation system 100 is disposed in the middle of the ground wire 40. The switch device 44 uses a switch capable of automatically controlling the opening / closing operation electrically. Although a mechanical switch may be used, it is more preferable to use, for example, a semiconductor switch. For example, it is preferable to use a MOSFET.

  Further, in the middle of the ground line 40, a current monitoring unit 42 that can monitor the current flowing through the ground line 40 is disposed. In other words, the current monitoring unit 42 is disposed between the negative electrode of the solar cell array 300 (the positive electrode when an n-type semiconductor is used for the bulk of the solar cell) and the ground location 41 by the ground wire 40. As the current monitoring unit 42, for example, an ammeter connected in series to the ground line 40 and / or a fuse is preferably used. Alternatively, the current may be monitored by providing a separate resistor (not shown) in the middle of the ground line 40 as the current monitoring unit 42 and monitoring the voltage at both ends thereof.

  In the first embodiment, a ground fault detection device 36 (an example of the ground fault detection unit or the first ground fault detection unit) is further arranged. In the example of FIG. 1A, the wiring branched from the negative electrode wiring (negative electrode bus) of the solar cell array 300 is connected to the ground fault detection device 36 via the switch device 33. Similarly, the wiring branched from the positive electrode wiring (positive electrode bus) of the solar cell array 300 is connected to the ground fault detection device 36 via the switch device 31. In this way, the switch devices 31 and 33 that connect the ground fault detection device 36 to the solar power generation system 100 from the solar power generation system 100 are arranged. The switch devices 31 and 33 use switches capable of automatically controlling the opening / closing operation electrically. Although a mechanical switch may be used, it is more preferable to use, for example, a semiconductor switch. For example, it is preferable to use a MOSFET. As described above, the ground fault detection unit 36 is arranged to be disconnected from the solar power generation system 100 and connectable to the solar power generation system 100.

  The solar power generation system 100 as described above is operated as follows. Each switch device 102, switch device 44, and switches 402 and 404 driven by control from a control system (not shown) are all in an ON state (closed), and switch devices 31 and 33 are in an OFF state (open). Normal operation is performed. That is, during normal operation, the negative electrode of the photovoltaic power generation system 100 is grounded. Thereby, the negative electrode of each solar cell string 12a-c can be controlled to a ground potential, and a PID phenomenon can be avoided. Then, the current monitoring unit 42 (second ground fault detection unit) detects the ground fault of the solar cell array 300 during the normal operation of the solar power generation system 100. The current monitoring unit 42 is disposed on the ground line 40 as described above, and monitors the current flowing through the ground line 40 to detect a ground fault in the power generation unit. As described with reference to FIG. 11, during such normal operation, for example, when a ground fault occurs in the middle of one of the solar battery strings 12 or on the positive electrode side, between the grounding location 41 for PID countermeasures and the ground fault location. As a result, a closed loop circuit is formed, and a large current flows to the outside. Therefore, the current is monitored by the current monitoring unit 42 as a measurement value based on such current, and by monitoring whether a current determined to be dangerous is flowing, a current that is equal to or greater than a threshold before a large current flows to the outside. When the control signal flows, the control system (not shown) can determine that there is a ground fault and can stop the photovoltaic power generation system 100 in an emergency. However, in this configuration, as described above, a blind spot portion (detection dead zone) for ground fault detection is generated.

Therefore, in the first embodiment, the ground fault detection device 36 periodically performs ground fault detection. For example, the ground fault is detected every time the photovoltaic power generation system 100 is started or periodically during operation. The ground fault detection unit 36 is connected to the negative electrode of the solar cell array 300 (when an n-type semiconductor is used for the bulk of the solar cell) by a switch device 44 (an example of an exclusion unit) that is driven by control from a control system (not shown). In the state separated from the positive electrode), ground fault detection is performed in units of 300 solar cell arrays. In this way, the switch device 44 is arranged so as to eliminate the influence on the potential of the negative electrode of the solar cell array 300 (positive electrode when an n-type semiconductor is used for the bulk of the solar cell) caused by grounding by the ground wire 40. The In other words, the switch device 44 is disposed so as to be able to eliminate the influence on the ground potential of the power generation unit caused by the grounding by the grounding wire 40. Then, the ground fault detection device 36 detects the ground fault of the solar cell array 300 in a state where the influence on the negative electrode potential of the solar cell array 300 caused by the grounding by the ground wire 40 is eliminated by the switch device 44. In other words, the ground fault detection device 36 changes the ground potential of the power generation unit to two or more different potentials in a state where the influence on the ground potential of the power generation unit caused by the grounding by the ground line 40 is eliminated by the switch device 44. Control to detect a ground fault of the power generation unit. The switch devices 31 and 33 driven by control from a control system (not shown) are turned on (closed). As described above, the ground fault detection unit 36 is connected to the solar power generation system 100 when detecting the ground fault of the solar cell array 300.
Further, the switches 402 and 404 may be turned off (open), and in this case, the influence from the load device 400 can be eliminated.

  FIG. 1B shows the negative electrode wiring of the solar cell array 300 (“negative electrode bus” connecting the negative electrode of the solar cell array 300 and the negative electrode of the load device 400) and the positive electrode wiring (positive electrode of the solar cell array 300 and the load device). An example of a ground fault detection device connected to both of the “positive buses” connecting the 400 positive electrodes is shown. A changeover switch 80, a resistor 84, and a voltage monitoring unit 86 are disposed in the ground fault detection device 36. One of the resistors 84 is connected to the changeover switch 80 and the other is grounded. Further, the voltage monitoring unit 86 monitors the potential difference (voltage) at both ends of the resistor 84. As the voltage monitoring unit 86, for example, a voltmeter electrically connected in parallel with the resistor 84 can be used. Further, the other of the changeover switch 80, one of which is connected to the resistor 84, has a wiring branched from the negative electrode wiring (negative electrode bus) of the solar cell array 300 and a wiring branched from the positive electrode wiring (positive electrode bus) of the solar cell array 300. And are connected to be switchable. When detecting a ground fault, the changeover switch 80 connects the resistor 84 to, for example, the negative electrode wiring (negative electrode bus) side of the solar cell array 300. In this state, the voltage monitoring unit 86 measures the voltage V <b> 1 across the resistor 84. Next, the resistor 84 is connected to the positive electrode wiring (positive electrode bus) side of the solar cell array 300, for example. In this state, the voltage monitoring unit 86 measures the voltage V <b> 2 applied across the resistor 84. When at least one of the voltages V2 of the voltage V1 exceeds a preset threshold value, it is determined that there is a ground fault by a control system (not shown). And the solar power generation system 100 can be stopped urgently. In the example (A) of the ground fault detection device shown in FIG. 1B, it is possible to detect such a ground fault even when a ground fault accident (insulation failure or the like) occurs in any part of the solar cell array 300. In other words, when a ground fault occurs on the positive electrode side of any of the solar cell strings 12, a potential difference is generated with the negative electrode wiring (negative electrode bus) of the solar cell array 300, so that the ground fault can be determined based on the voltage V1. Conversely, as in the first ground fault of FIG. 12, when a ground fault occurs on the negative electrode side of any of the solar cell strings 12, there is a potential difference between the positive electrode wiring (positive electrode bus) of the solar cell array 300. Therefore, the ground fault can be determined by the voltage V2. When a ground fault occurs in the middle of any of the solar battery strings 12, a ground fault can be determined based on the voltage V1 and the voltage V2. In this manner, in the ground fault detection device shown in FIG. 1B, the switch device 44 is opened to eliminate the influence of the ground wire 40 for PID countermeasures, and then connected to the solar cell array 300 (switch The devices 31 and 31 are closed), and the grounding position of the solar cell array 300 is switched between the positive electrode wiring and the negative electrode wiring by switching the changeover switch 80, and the ground potential of the solar cell array 300 is controlled to two different potentials, The voltage V1 and V2 at both ends of the resistor 84 are monitored to determine the ground fault. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and a blind spot location for ground fault detection by the current monitoring unit 42 during normal operation can be eliminated. Therefore, when using the ground fault detection apparatus shown in FIG. 1B, the current monitoring unit 42 may be omitted.

  FIG. 1C shows another example of the ground fault detection device connected to both the negative electrode wiring (negative electrode bus) and the positive electrode wiring (positive electrode bus) of the solar cell array 300. In the ground fault detection device 36, two resistors 83a and 83b, a resistor 84, and a voltage monitoring unit 86 are arranged. For the resistors 83a and 83b, for example, resistors having the same resistance value may be used. One end of the resistor 83a is connected to a wiring branched from the negative electrode wiring (negative electrode bus) of the solar cell array 300. One of the resistors 83b is connected to a wiring branched from the positive electrode wiring (positive electrode bus) of the solar cell array 300. The other of the resistors 83 a and 83 b is connected to one of the resistors 84. The other end of the resistor 84 is grounded. In other words, the middle point obtained by dividing the voltage (potential difference) between the two electrodes of the solar cell array 300 by the resistors 83 a and 83 b is connected to the ground via the resistor 84. In this state, the voltage monitoring unit 86 monitors the voltage at both ends of the resistor 84. As the voltage monitoring unit 86, for example, a voltmeter electrically connected in parallel with the resistor 84 can be used. In this state, the voltage monitoring unit 86 measures the voltage V applied across the resistor 84. When the voltage V exceeds a preset threshold value, a control system (not shown) determines that there is a ground fault. And the solar power generation system 100 can be stopped urgently. In the example (B) of the ground fault detection device shown in FIG. 1C, if a ground fault occurs at the intermediate potential position of any of the solar battery strings 12, it is difficult to determine the ground fault. When a ground fault occurs, the current monitoring unit 42 described above can determine the ground fault during normal operation. That is, when monitoring is performed by the ground fault detection device shown in FIG. 1C, the ground potential of the solar cell array 300 is controlled to a potential different from that when the current monitoring unit 42 performs monitoring, and the solar cell array 300 is controlled. Perform ground fault detection. In other words, the ground fault detection device 36 is configured when the ground potential of the power generation unit is grounded by the ground line 40 in a state where the influence on the ground potential of the power generation unit caused by grounding by the ground line 40 is eliminated by the switch device 44. The ground potential of the power generation unit is detected by controlling to a ground potential different from the above. Therefore, even if a ground fault occurs in any part of the solar cell array 300, the ground fault is reliably detected by either the current monitoring unit 42 or the ground fault detection device. Therefore, it becomes possible to detect a ground fault at the stage when the first ground fault accident (first ground fault accident) occurs, and it is possible to eliminate the blind spot of ground fault detection by the current monitoring unit 42 during normal operation.

  As described above, according to the first embodiment, it is possible to eliminate a blind spot where it is difficult to detect a ground fault while grounding for PID countermeasures is performed.

Embodiment 2. FIG.
FIG. 2 is a configuration diagram showing the configuration of the photovoltaic power generation system according to the second embodiment. 2A, the photovoltaic power generation system 100 according to the second embodiment is similar to that shown in FIG. 1A except that the ground fault detection device 36 is connected only from the positive electrode wiring (positive electrode bus) of the solar cell array 300. It is the same. The contents other than those described in particular are the same as those in the first embodiment.

The photovoltaic power generation system 100 according to Embodiment 2 is operated as follows. The switch device 102, the switch device 44, and the switches 402 and 404 that are driven by control from a control system (not shown) are all in the ON (closed) state, and the switch device 31 is in the OFF (open) state. Is done. That is, during normal operation, the negative electrode of the photovoltaic power generation system 100 is grounded. Thereby, the negative electrode of each solar cell string 12a-c can be controlled to ground potential, and a PID phenomenon can be avoided. Then, the current monitoring unit 42 (second ground fault detection unit) detects the ground fault of the solar cell array 300 during the normal operation of the solar power generation system 100. As described with reference to FIG. 11, during such normal operation, for example, when a ground fault occurs in the middle of one of the solar battery strings 12 or on the positive electrode side, between the grounding location 41 for PID countermeasures and the ground fault location. Thus, a closed loop circuit is formed, and a large current flows to the outside.
Therefore, by monitoring the current with the current monitoring unit 42 and monitoring whether or not the current determined to be dangerous flows, when a current greater than the threshold flows before the large current flows to the outside, A control system (not shown) can determine that there is a ground fault and can stop the photovoltaic power generation system 100 urgently. However, such a configuration causes a blind spot for ground fault detection as described above.

  Thus, in the second embodiment, the ground fault detection device 36 periodically performs ground fault detection. For example, the ground fault is detected every time the photovoltaic power generation system 100 is started or periodically during operation. The ground fault detection unit 36 is connected to the negative electrode of the solar cell array 300 (when an n-type semiconductor is used for the bulk of the solar cell) by a switch device 44 (an example of an exclusion unit) that is driven by control from a control system (not shown). In the state separated from the positive electrode), ground fault detection is performed in units of 300 solar cell arrays. The switch device 31 driven by control from a control system (not shown) is turned on (closed). The ground fault detection unit 36 is connected to the solar power generation system 100 when detecting a ground fault of the solar cell array 300. Further, in order to eliminate the influence from the load device 400, the switches 402 and 404 are turned OFF (open).

  FIG. 2B shows an example of the ground fault detection device connected only from the positive electrode wiring (positive electrode bus) of the solar cell array 300. A resistor 84 and a voltage monitoring unit 86 are disposed in the ground fault detection device 36. One of the resistors 84 is connected to a wiring branched from the positive electrode wiring (positive electrode bus) of the solar cell array 300, and the other is grounded. The voltage monitoring unit 86 monitors the voltage at both ends of the resistor 84. In this state, the voltage monitoring unit 86 measures the voltage V applied across the resistor 84. When the voltage V exceeds a preset threshold value, a control system (not shown) determines that there is a ground fault. And the solar power generation system 100 can be stopped urgently. In the example (C) of the ground fault detection device shown in FIG. 2 (b), if a ground fault occurs on the positive electrode side of any of the solar battery strings 12, it is difficult to determine the ground fault. When a fault has occurred, a ground fault can be determined during normal operation by the current monitoring unit 42 described above. That is, when monitoring is performed by the ground fault detection device shown in FIG. 2B, the ground potential of the solar cell array 300 is different from that when the current monitoring unit 42 performs monitoring. Even if a ground fault occurs, the ground fault is reliably detected by either the current monitoring unit 42 or the ground fault detection device. In other words, the ground fault detection device 36 is configured when the ground potential of the power generation unit is grounded by the ground line 40 in a state where the influence on the ground potential of the power generation unit caused by grounding by the ground line 40 is eliminated by the switch device 44. The ground potential of the power generation unit is detected by controlling to a ground potential different from the above. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and a blind spot location for ground fault detection by the current monitoring unit 42 during normal operation can be eliminated.

  FIG. 2C shows another example of the ground fault detection device connected only from the positive electrode wiring (positive electrode bus) of the solar cell array 300. In the ground fault detection device 36, a changeover switch 81, a DC power source 85, a resistor 84, and a voltage monitoring unit 86 are arranged. One of the resistors 84 is connected to the changeover switch 81 and the negative electrode of the DC power supply 85, and the other is grounded. Further, the voltage monitoring unit 86 monitors the voltage at both ends of the resistor 84. One of the changeover switches 81 is connected to a wiring branched from the positive electrode wiring (positive electrode bus) of the solar cell array 300, and the other is connected so that the resistor 84 and the positive electrode of the DC power supply 85 can be switched. The DC power supply 85 applies a voltage so that, for example, the ground potential of the negative electrode of the solar cell array 300 becomes almost zero when the positive electrode of the solar cell array 300 is connected to the ground via the DC power supply 85 and the resistor 84. It is preferable. When detecting a ground fault, the changeover switch 81 connects the resistor 84 to, for example, the positive electrode wiring (positive electrode bus) side of the solar cell array 300 without using the DC power supply 85. In this state, the voltage monitoring unit 86 measures the voltage V <b> 1 across the resistor 84. Next, the resistor 84 is connected to the positive electrode wiring (positive electrode bus) side of the solar cell array 300 via the DC power source 85, for example. In this state, the voltage monitoring unit 86 measures the voltage V <b> 2 applied across the resistor 84. When at least one of the voltages V2 of the voltage V1 exceeds a preset threshold value, it is determined that there is a ground fault by a control system (not shown). And the solar power generation system 100 can be stopped urgently. In the example (D) of the ground fault detection device shown in FIG. 2 (c), it is possible to detect such a ground fault even when a ground fault accident (insulation failure or the like) occurs in any part of the solar cell array 300. In other words, when a ground fault occurs on the positive electrode side of any of the solar cell strings 12, a potential difference is generated between both ends of the resistor 84 by the DC power supply 85, and therefore the ground fault can be determined based on the voltage V2. Conversely, as in the first ground fault of FIG. 12, when a ground fault occurs on the negative electrode side of any of the solar cell strings 12, there is a potential difference between the positive electrode wiring (positive electrode bus) of the solar cell array 300. Therefore, the ground fault can be determined by the voltage V1. When a ground fault occurs in the middle of any of the solar battery strings 12, a ground fault can be determined based on the voltage V1 and the voltage V2. Thus, according to the ground fault detection apparatus shown in FIG. 2C, the ground fault is detected by controlling the ground potential of the solar cell array 300 to two different potentials. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and a blind spot location for ground fault detection by the current monitoring unit 42 during normal operation can be eliminated. Therefore, when using the ground fault detection apparatus shown in FIG. 2C, the current monitoring unit 42 may be omitted.

  FIG. 2D shows another example of the ground fault detection device connected only from the positive electrode wiring (positive electrode bus) of the solar cell array 300. An AC power supply 87, a resistor 84, and a voltage monitoring unit 86 are disposed in the ground fault detection device 36. One of the resistors 84 is connected to the wiring branched from the positive electrode wiring (positive electrode bus) of the solar cell array 300 via the AC power supply 87, and the other is grounded. The voltage monitoring unit 86 monitors the voltage at both ends of the resistor 84. In this state, the voltage monitoring unit 86 measures the voltage V in phase with the AC power supply 87 applied to both ends of the resistor 84 in synchronization with the phase of the AC power supply 87. When the voltage V exceeds a preset threshold for the phase, a control system (not shown) determines that a ground fault has occurred. And the solar power generation system 100 can be stopped urgently. In the example (E) of the ground fault detection device shown in FIG. 2D, a potential difference occurs between both ends of the resistor 84 even if a ground fault (insulation failure or the like) occurs in any part of the solar cell array 300. Such a ground fault can be detected. As described above, according to the ground fault detection device shown in FIG. 2D, the ground fault is detected by controlling the ground potential of the solar cell array 300 to two or more different potentials by the AC power source 87. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and a blind spot location for ground fault detection by the current monitoring unit 42 during normal operation can be eliminated. Therefore, when the ground fault detection apparatus shown in FIG. 2D is used, the current monitoring unit 42 may be omitted.

  FIG. 2E shows another example of the ground fault detection device connected only from the positive electrode wiring (positive electrode bus) of the solar cell array 300. A DC power supply 89, a resistor 84, and a voltage monitoring unit 86 are disposed in the ground fault detection device 36. One end of the resistor 84 is connected to the positive electrode of the DC power supply 89, and is connected to a wiring branched from the positive electrode wiring (positive electrode bus) of the solar cell array 300 via the DC power supply 89. The other end of the resistor 84 is grounded. The DC power supply 89 applies a voltage so that the ground potential of the positive electrode of the solar cell array 300 becomes negative. The voltage monitoring unit 86 monitors the voltage at both ends of the resistor 84. In this state, the voltage monitoring unit 86 measures the voltage V applied across the resistor 84. When the voltage V exceeds a preset threshold value, a control system (not shown) determines that there is a ground fault. And the solar power generation system 100 can be stopped urgently. In the example (H) of the ground fault detection device shown in FIG. 2 (e), a potential difference occurs between both ends of the resistor 84 even if a ground fault (insulation failure or the like) occurs in any part of the solar cell array 300. Such a ground fault can be detected. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and a blind spot location for ground fault detection by the current monitoring unit 42 during normal operation can be eliminated.

  As described above, according to the second embodiment, it is possible to eliminate or further reduce a blind spot where it is difficult to detect a ground fault while performing grounding for PID countermeasures.

Embodiment 3 FIG.
FIG. 3 is a configuration diagram illustrating the configuration of the photovoltaic power generation system according to the third embodiment. 3A, the photovoltaic power generation system 100 according to Embodiment 3 is similar to that shown in FIG. 1A except that the ground fault detection device 36 is connected only from the negative electrode wiring (negative electrode bus) of the solar cell array 300. It is the same. The contents other than those described in particular are the same as those in the first embodiment.

  The photovoltaic power generation system 100 according to Embodiment 3 is operated as follows. The switch device 102, the switch device 44, and the switches 402 and 404 that are driven by control from a control system (not shown) are all in an ON (closed) state, and the switch device 33 is in an OFF (open) state. Is done. That is, during normal operation, the negative electrode of the photovoltaic power generation system 100 is grounded. Thereby, the negative electrode of each solar cell string 12a-c can be controlled to ground potential, and a PID phenomenon can be avoided. Then, the current monitoring unit 42 (second ground fault detection unit) detects the ground fault of the solar cell array 300 during the normal operation of the solar power generation system 100. As described with reference to FIG. 11, during such normal operation, for example, when a ground fault occurs in the middle of one of the solar battery strings 12 or on the positive electrode side, between the grounding location 41 for PID countermeasures and the ground fault location. Thus, a closed loop circuit is formed, and a large current flows to the outside. Therefore, by monitoring the current with the current monitoring unit 42 and monitoring whether or not the current determined to be dangerous flows, when a current greater than the threshold flows before the large current flows to the outside, A control system (not shown) can determine that there is a ground fault and can stop the photovoltaic power generation system 100 urgently. However, in such a configuration, as described above, a blind spot portion for ground fault detection is generated.

Therefore, in the third embodiment, the ground fault detection device 36 periodically performs ground fault detection. For example, the ground fault is detected every time the photovoltaic power generation system 100 is started or periodically during operation. The ground fault detection unit 36 is connected to the negative electrode of the solar cell array 300 (when an n-type semiconductor is used for the bulk of the solar cell) by a switch device 44 (an example of an exclusion unit) that is driven by control from a control system (not shown). In the state separated from the positive electrode), ground fault detection is performed in units of 300 solar cell arrays. The switch device 33 driven by control from a control system (not shown) is turned on (closed). The ground fault detection unit 36 is connected to the solar power generation system 100 when detecting a ground fault of the solar cell array 300.
Further, the switches 402 and 404 may be turned off (open). In this case, the influence from the load device 400 can be eliminated.

  FIG. 3B shows an example of a ground fault detection device connected only from the negative electrode wiring (negative electrode bus) of the solar cell array 300. A DC power supply 90, a resistor 84, and a voltage monitoring unit 86 are disposed in the ground fault detection device 36. One end of the resistor 84 is connected to the positive electrode of the DC power supply 90, and is connected to a wiring branched from the negative electrode wiring (negative electrode bus) of the solar cell array 300 via the DC power supply 90. The other end of the resistor 84 is grounded. The DC power supply 90 applies a voltage so that the ground potential of the positive electrode of the solar cell array 300 is almost zero. The voltage monitoring unit 86 monitors the voltage at both ends of the resistor 84. In this state, the voltage monitoring unit 86 measures the voltage V applied across the resistor 84. When the voltage V exceeds a preset threshold value, a control system (not shown) determines that there is a ground fault. And the solar power generation system 100 can be stopped urgently. In the example (F) of the ground fault detection device shown in FIG. 3 (b), when a ground fault occurs on the positive electrode side of any of the solar battery strings 12, it becomes difficult to determine the ground fault. When a fault has occurred, a ground fault can be determined during normal operation by the current monitoring unit 42 described above. That is, when monitoring is performed by the ground fault detection device shown in FIG. 3B, the ground potential of the solar cell array 300 (power generation unit) is different from that when the current monitoring unit 42 performs monitoring. No matter where the ground fault occurs, the ground fault is reliably detected by monitoring either the current monitoring unit 42 or the ground fault detection device. In other words, the ground fault detection device 36 is configured when the ground potential of the power generation unit is grounded by the ground line 40 in a state where the influence on the ground potential of the power generation unit caused by grounding by the ground line 40 is eliminated by the switch device 44. The ground potential of the power generation unit is detected by controlling to a ground potential different from the above. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and a blind spot location for ground fault detection by the current monitoring unit 42 during normal operation can be eliminated.

  FIG. 3C shows another example of the ground fault detection device connected only from the negative electrode wiring (negative electrode bus) of the solar cell array 300. In the ground fault detection device 36, a changeover switch 81, a DC power supply 91, a resistor 84, and a voltage monitoring unit 86 are arranged. One of the resistors 84 is connected to the changeover switch 81 and the positive electrode of the DC power supply 91, and the other is grounded. Further, the voltage monitoring unit 86 monitors the voltage at both ends of the resistor 84. One of the changeover switches 81 is connected to a wiring branched from the negative electrode wiring (negative electrode bus) of the solar cell array 300, and the other is connected so that the resistor 84 and the negative electrode of the DC power supply 91 can be switched. The DC power supply 91 applies a voltage so that, for example, the ground potential of the positive electrode of the solar cell array 300 becomes almost zero when the negative electrode of the solar cell array 300 is connected to the ground via the DC power supply 91 and the resistor 84. It is preferable. When detecting a ground fault, the changeover switch 81 connects the resistor 84 to the negative electrode wiring (negative electrode bus) side of the solar cell array 300 without using the DC power supply 91, for example. In this state, the voltage monitoring unit 86 measures the voltage V <b> 1 across the resistor 84. Next, the resistor 84 is connected to the negative electrode wiring (negative electrode bus) side of the solar cell array 300 via the DC power supply 85, for example. In this state, the voltage monitoring unit 86 measures the voltage V <b> 2 applied across the resistor 84. When at least one of the voltages V2 of the voltage V1 exceeds a preset threshold value, it is determined that there is a ground fault by a control system (not shown). And the solar power generation system 100 can be stopped urgently. As described above, in the example (G) of the ground fault detection device shown in FIG. 3C, even if a ground fault (insulation failure or the like) occurs in any part of the solar cell array 300, there is a potential difference across the resistor 84. As a result, such a ground fault can be detected.

  FIG. 3 (d) shows another example of the ground fault detection device connected only from the negative electrode wiring (negative electrode bus) of the solar cell array 300. An AC power supply 87, a resistor 84, and a voltage monitoring unit 86 are disposed in the ground fault detection device 36. One of the resistors 84 is connected to the wiring branched from the negative electrode wiring (negative electrode bus) of the solar cell array 300 via the AC power supply 87, and the other is grounded. The voltage monitoring unit 86 monitors the voltage at both ends of the resistor 84. In this state, the voltage monitoring unit 86 measures the voltage V in phase with the AC power supply 87 applied to both ends of the resistor 84 in synchronization with the phase of the AC power supply 87. When the voltage V exceeds a preset threshold for the phase, a control system (not shown) determines that a ground fault has occurred. And the solar power generation system 100 can be stopped urgently. In the example (E) of the ground fault detection device shown in FIG. 3D, a potential difference occurs between both ends of the resistor 84 even if a ground fault (insulation failure or the like) occurs in any part of the solar cell array 300. Such a ground fault can be detected. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and a blind spot location for ground fault detection by the current monitoring unit 42 during normal operation can be eliminated.

  FIG. 3E shows another example of the ground fault detection device connected only from the negative electrode wiring (negative electrode bus) of the solar cell array 300. In the ground fault detection device 36, a DC power source 92, a resistor 84, and a voltage monitoring unit 86 are arranged. One end of the resistor 84 is connected to the negative electrode of the DC power supply 92, and is connected to a wiring branched from the negative electrode wiring (negative electrode bus) of the solar cell array 300 via the DC power supply 92. The other end of the resistor 84 is grounded. The DC power source 92 applies a voltage so that the ground potential of the negative electrode of the solar cell array 300 is positive. The voltage monitoring unit 86 monitors the voltage at both ends of the resistor 84. In this state, the voltage monitoring unit 86 measures the voltage V applied across the resistor 84. When the voltage V exceeds a preset threshold value, a control system (not shown) determines that there is a ground fault. And the solar power generation system 100 can be stopped urgently. In the example (I) of the ground fault detection device shown in FIG. 3 (e), a potential difference occurs between both ends of the resistor 84 even when a ground fault (insulation failure or the like) occurs in any part of the solar cell array 300. Such a ground fault can be detected. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and a blind spot location for ground fault detection by the current monitoring unit 42 during normal operation can be eliminated.

  In the above-described example, the case where the ground fault detection is performed in units of the solar cell array 300 is shown, but the present invention is not limited to this. For example, the ground fault detection may be performed in units of 12 solar cell strings. In such a case, after the two switch devices 102 connected to the detection target solar cell string 12 are turned off (open), the two switch devices 31 and 33 of the detection target solar cell string 12 are turned on (closed). In addition, each of the two switch devices 102 of the remaining solar cell string 12 is turned on (closed), and the two switch devices 31 and 33 of the remaining solar cell string 12 are turned off (open). What is necessary is just to perform the ground fault detection of the content. Thereby, ground fault detection can be performed about the solar cell string 12 to be detected while each solar cell string 12 other than the solar cell string 12 to be detected is normally operated.

  As described above, according to the third embodiment, it is possible to eliminate or further reduce a blind spot where it is difficult to detect a ground fault while performing grounding for PID countermeasures.

Embodiment 4 FIG.
In each of the above-described embodiments, a configuration has been described in which the current flowing through the ground line 40 for PID countermeasures is monitored, and ground fault detection is possible during normal operation except for the blind spot location for ground fault detection. However, it is not necessary to monitor the current flowing through the ground line 40 from the viewpoint of measures against PID. Therefore, in the fourth embodiment, a configuration in which ground fault detection is performed without monitoring the current flowing through the PID countermeasure ground line 40 will be described. The contents other than those described in particular are the same as those in the first embodiment.

  FIG. 4 is a configuration diagram illustrating the configuration of the photovoltaic power generation system according to the fourth embodiment. In FIG. 4A, instead of connecting the ground fault detection device 36 with a wiring branched from both the negative electrode wiring (negative electrode bus) and the positive electrode wiring (positive electrode bus) of the solar cell array 300, for each solar cell string 12. , A point that is connected by a line branched from both the negative electrode line and the positive electrode line of the solar cell string 12, a point that the switch device 44 is not connected to the ground line 40, and a current that monitors the current flowing through the ground line 40 Except for the point that the monitoring unit 42 is omitted, it is the same as FIG. And the negative electrode wiring connected to the ground fault detection apparatus 36 is branched from between the negative electrode of solar cell string 12a-c and switch apparatus 102a, c, e. The positive electrode wiring connected to the ground fault detection device 36 is branched from between the positive electrode of the solar cell strings 12a to 12c and the switch devices 102b, e, and f.

  Specifically, in FIG. 4A, the wiring branched from the negative electrode wiring that connects the negative electrode of the solar cell string 12a and the switch device 102a is connected to the ground fault detection device 36 via the switch device 33a. Moreover, the wiring branched from the positive electrode wiring which connects the positive electrode of the solar cell string 12a and the switch apparatus 102b is connected to the ground fault detection apparatus 36 via the switch apparatus 31a. Similarly, the wiring branched from the negative electrode wiring which connects the negative electrode of the solar cell string 12b and the switch apparatus 102c is connected to the ground fault detection apparatus 36 via the switch apparatus 33b. Moreover, the wiring branched from the positive electrode wiring which connects the positive electrode of the solar cell string 12b and the switch apparatus 102d is connected to the ground fault detection apparatus 36 via the switch apparatus 31b. Similarly, the wiring branched from the negative electrode wiring which connects the negative electrode of the solar cell string 12c and the switch apparatus 102e is connected to the ground fault detection apparatus 36 via the switch apparatus 33c. Moreover, the wiring branched from the positive electrode wiring which connects the positive electrode of the solar cell string 12c and the switch apparatus 102f is connected to the ground fault detection apparatus 36 via the switch apparatus 31c. The connection from each solar cell string 12 to the ground fault detection device 36 is connected in parallel as shown in FIG.

  Further, a ground wire 40 (an example of a grounding portion) branched from the negative electrode wiring (negative electrode bus) of the solar cell array 300 is grounded for PID (Potential Induced Degradation) measures. In the example of Fig.4 (a), the case where a p-type semiconductor is used for the bulk of a solar cell, or the solar cell using a transparent conductive film is shown as an example. Therefore, the negative electrode wiring is grounded. Needless to say, when an n-type semiconductor is used for the bulk of the solar cell, the positive electrode wiring (positive electrode bus) is grounded.

  The solar power generation system 100 as described above is operated as follows. Each switch device 102 and the switches 402 and 404 driven by control from a control system (not shown) are all in an ON (closed) state, and each switch device 31 and 33 is in an OFF (open) state, and normal operation is performed. Done. That is, during normal operation, the negative electrode of the photovoltaic power generation system 100 is grounded. Thereby, the negative electrode of each solar cell string 12a-c can be controlled to ground potential, and a PID phenomenon can be avoided. However, in the fourth embodiment, the ground fault detection is not performed in units of the solar cell array 300 during the normal operation of the photovoltaic power generation system 100. In the fourth embodiment, ground fault detection is performed in units of 12 solar cell strings. In such a case, after the two switch devices 102 of the detection target solar cell string 12 are turned off (opened), the two switch devices 31 and 33 of the detection target solar cell string 12 are turned on (closed). The ground fault detection may be performed in a state where each of the two switch devices 102 of the remaining solar cell strings 12 is left ON (closed). Thereby, ground fault detection can be performed about the solar cell string 12 to be detected while each solar cell string 12 other than the solar cell string 12 to be detected is normally operated.

  Therefore, in the fourth embodiment, for each solar cell string 12, the ground fault detection is periodically performed by the ground fault detection device 36. For example, the ground fault is detected every time the photovoltaic power generation system 100 is started or periodically during operation. The ground fault detection unit 36 is driven by control from a control system (not shown), and the ground line 40 is detected by the positive and negative switch devices 102 (an example of an exclusion unit) of the solar cell string 12 to be detected. The ground fault is detected in units of the solar cell string 12 in a state of being disconnected from the negative electrode of the battery string 12 (positive electrode when an n-type semiconductor is used for the bulk of the solar cell). As described above, the plurality of switch devices 102a to 102f individually disconnect the ground wire 40 (ground portion) from the plurality of solar cell strings 12a to 12c. As described above, the switch device 102 on the negative electrode side of the solar cell string 12 to be detected is the negative electrode of the solar cell string 12 to be detected caused by the grounding by the ground wire 40 (when an n-type semiconductor is used for the bulk of the solar cell). Are arranged so as to eliminate the influence on the potential of the positive electrode). And the ground fault detection apparatus 36 is the state of the solar cell string 12 of detection object in the state by which the influence on the electric potential of the negative electrode of the solar cell string 12 of detection object produced by the earthing | grounding by the ground wire 40 was excluded by the switch apparatus 102. Detect a ground fault. Moreover, the detection target solar cell string 12 is disconnected from the system by turning off (opening) the two switch devices 102 of the detection target solar cell string 12. The switch devices 31 and 33 that are connected to the positive and negative electrodes of the solar cell string 12 to be detected and are driven by control from a control system (not shown) are turned on (closed). As described above, the ground fault detection unit 36 is connected to the solar power generation system 100 when detecting a ground fault of the solar cell string 12 to be detected. The two switch devices 102 connected to the positive and negative electrodes other than the detection target solar cell string 12 and driven by control from a control system (not shown) are turned on (closed) and driven by control from a control system (not shown). The switch devices 31 and 33 are OFF (open). The switches 402 and 404 are turned on (closed).

  FIG. 4B shows an example of a ground fault detection device connected to both the negative electrode wiring and the positive electrode wiring of the solar cell string 12 to be detected. The configuration of the ground fault detection device 36 is the same as that shown in FIG. When detecting the ground fault, the changeover switch 80 connects the resistor 84 to, for example, the negative electrode wiring side of the solar cell string 12 to be detected. In this state, the voltage monitoring unit 86 measures the voltage V <b> 1 across the resistor 84. Next, the resistor 84 is connected to the positive electrode wiring side of the solar cell string 12 to be detected, for example. In this state, the voltage monitoring unit 86 measures the voltage V <b> 2 applied across the resistor 84. If at least one of the voltages V2 of the voltage V1 exceeds a preset threshold, it is determined that there is a ground fault by a control system (not shown). And the solar power generation system 100 can be stopped urgently. In the example (A) of the ground fault detection device shown in FIG. 4B, it is possible to detect such a ground fault even if a ground fault accident (insulation failure or the like) occurs in any part of the solar cell string 12 to be detected. Become. In other words, when a ground fault occurs on the positive electrode side of the solar cell string 12 to be detected, a potential difference is generated with the negative electrode wiring of the solar cell string 12 to be detected, so that the ground fault can be determined based on the voltage V1. Conversely, as in the first ground fault of FIG. 12, when a ground fault occurs on the negative electrode side of the detection target solar cell string 12, there is a potential difference with the positive electrode wiring of the detection target solar cell string 12. Therefore, the ground fault can be determined by the voltage V2. When a ground fault occurs in the middle of the solar cell string 12 to be detected, a ground fault can be determined based on the voltage V1 and the voltage V2. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and the blind spot location for ground fault detection can be eliminated.

  As described above, according to the fourth embodiment, it is possible to eliminate a blind spot where it is difficult to detect a ground fault while performing grounding for PID countermeasures.

Embodiment 5 FIG.
FIG. 5 is a configuration diagram showing the configuration of the photovoltaic power generation system in the fifth embodiment. 5A, the photovoltaic power generation system 100 according to the fifth embodiment is the same as FIG. 4A except that the ground fault detection device 36 is connected only from the positive electrode wiring of each solar cell string 12. In FIG. is there. Further, the contents other than those specifically described are the same as those in the fourth embodiment.

  The photovoltaic power generation system 100 according to Embodiment 5 is operated as follows. Each switch device 102 driven by control from a control system (not shown) and the switches 402 and 404 are both in an ON (closed) state, and each switch device 31 is in an OFF (open) state, and a normal operation is performed. . That is, during normal operation, the negative electrode of the photovoltaic power generation system 100 is grounded. Thereby, the negative electrode of each solar cell string 12a-c can be controlled to ground potential, and a PID phenomenon can be avoided. However, in Embodiment 5, during the normal operation of the solar power generation system 100, the ground fault detection is not performed in units of the solar cell array 300. In the fifth embodiment, ground fault detection is performed in units of 12 solar cell strings.

  In the fifth embodiment, ground fault detection is periodically performed by the ground fault detection device 36. For example, the ground fault is detected every time the photovoltaic power generation system 100 is started or periodically during operation. The ground fault detection unit 36 is driven by control from a control system (not shown), and the ground line 40 of the detection target solar cell string 12 is detected by the bipolar switch device 102 (an example of an exclusion unit) of the detection target solar cell string 12. Ground fault detection is performed in units of 12 solar cell strings in a state separated from the negative electrode (positive electrode when an n-type semiconductor is used for the bulk of the solar cell). The switch device 31 of the solar cell string 12 to be detected that is driven by control from a control system (not shown) is set to ON (closed). The ground fault detection unit 36 is connected to the solar power generation system 100 when detecting a ground fault of the solar cell string 12 to be detected.

  FIG. 5B shows another example of the ground fault detection device connected only from the positive electrode wiring of the solar cell string 12 to be detected. The configuration of the ground fault detection device 36 is the same as that shown in FIG. When detecting a ground fault, the changeover switch 81 connects the resistor 84 to, for example, the positive electrode wiring (positive electrode bus) side of the solar cell array 300 without using the DC power supply 85. In this state, the voltage monitoring unit 86 measures the voltage V <b> 1 across the resistor 84. Next, the resistor 84 is connected to the positive electrode wiring side of the solar cell string 12 to be detected via the DC power source 85, for example. In this state, the voltage monitoring unit 86 measures the voltage V <b> 2 applied across the resistor 84. When at least one of the voltages V2 of the voltage V1 exceeds a preset threshold value, it is determined that there is a ground fault by a control system (not shown). Then, the detection target solar cell string 12 or the photovoltaic power generation system 100 can be urgently stopped. In the example (D) of the ground fault detection device shown in FIG. 5B, it is possible to detect such a ground fault even if a ground fault accident (insulation failure or the like) occurs at any location of the solar cell string 12 to be detected. Become. In other words, when a ground fault occurs on the positive electrode side of the solar cell string 12 to be detected, a potential difference is generated between both ends of the resistor 84 by the DC power supply 85, so that the ground fault can be determined by the voltage V2. Conversely, as in the first ground fault of FIG. 12, when a ground fault occurs on the negative electrode side of the detection target solar cell string 12, there is a potential difference with the positive electrode wiring of the detection target solar cell string 12. Therefore, the ground fault can be determined by the voltage V1. When a ground fault occurs in the middle of the solar cell string 12 to be detected, a ground fault can be determined based on the voltage V1 and the voltage V2. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and the blind spot location for ground fault detection can be eliminated.

  FIG. 5 (d) shows another example of the ground fault detection device connected only from the positive electrode wiring of the solar cell string 12 to be detected. The configuration of the ground fault detection device 36 is the same as that shown in FIG. In this state, the voltage monitoring unit 86 measures the voltage V in phase with the AC power supply 87 applied to both ends of the resistor 84 in synchronization with the phase of the AC power supply 87. When the voltage V exceeds a preset threshold for the phase, a control system (not shown) determines that a ground fault has occurred. Then, the detection target solar cell string 12 or the photovoltaic power generation system 100 can be urgently stopped. In the example (E) of the ground fault detection device shown in FIG. 5D, even when a ground fault (insulation failure or the like) occurs in any part of the solar cell string 12 to be detected, there is a potential difference between both ends of the resistor 84. As a result, such a ground fault can be detected. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and a blind spot location for ground fault detection by the current monitoring unit 42 during normal operation can be eliminated.

  FIG. 5 (e) shows another example of the ground fault detection device connected only from the positive electrode wiring (positive electrode bus) of the solar cell array 300. The configuration of the ground fault detection device is the same as that shown in FIG. In this state, the voltage monitoring unit 86 measures the voltage V applied across the resistor 84. When the voltage V exceeds a preset threshold value, a control system (not shown) determines that there is a ground fault. Then, the detection target solar cell string 12 or the photovoltaic power generation system 100 can be urgently stopped. In the example (H) of the ground fault detection device shown in FIG. 5 (e), a potential difference occurs between both ends of the resistor 84 even when a ground fault (insulation failure or the like) occurs in any part of the solar cell array 300. Such a ground fault can be detected. Therefore, it becomes possible to detect a ground fault at the stage when the first ground fault accident (first ground fault accident) occurs, and it is possible to eliminate the blind spot of ground fault detection by the current monitoring unit 42 during normal operation.

  As described above, according to the fifth embodiment, it is possible to eliminate a blind spot where it is difficult to detect a ground fault while performing grounding for PID countermeasures.

Embodiment 6 FIG.
FIG. 6 is a configuration diagram illustrating the configuration of the photovoltaic power generation system according to the sixth embodiment. 6 (a), the photovoltaic power generation system 100 according to Embodiment 6 is the same as FIG. 4 (a) except that the ground fault detection device 36 is connected only from the positive electrode wiring of each solar cell string 12. is there. Further, the contents other than those specifically described are the same as those in the fourth embodiment.

  The photovoltaic power generation system 100 according to Embodiment 6 is operated as follows. Each switch device 102 driven by control from a control system (not shown) and the switches 402 and 404 are both in an ON (closed) state, and each switch device 33 is in an OFF (open) state, and a normal operation is performed. . That is, during normal operation, the negative electrode of the photovoltaic power generation system 100 is grounded. Thereby, the negative electrode of each solar cell string 12a-c can be controlled to ground potential, and a PID phenomenon can be avoided. However, in the sixth embodiment, the ground fault detection is not performed for each solar cell array 300 during the normal operation of the photovoltaic power generation system 100. In the sixth embodiment, ground fault detection is performed in units of 12 solar cell strings.

  In the sixth embodiment, the ground fault detection device 36 periodically performs ground fault detection. For example, the ground fault is detected every time the photovoltaic power generation system 100 is started or periodically during operation. The ground fault detection unit 36 is driven by control from a control system (not shown), and the ground line 40 of the detection target solar cell string 12 is detected by the bipolar switch device 102 (an example of an exclusion unit) of the detection target solar cell string 12. Ground fault detection is performed in units of 12 solar cell strings in a state separated from the negative electrode (positive electrode when an n-type semiconductor is used for the bulk of the solar cell). The switch device 33 of the solar cell string 12 to be detected that is driven by control from a control system (not shown) is set to ON (closed). The ground fault detection unit 36 is connected to the solar power generation system 100 when detecting a ground fault of the solar cell string 12 to be detected.

  FIG. 6B shows an example of a ground fault detection device connected only from the negative electrode wiring of the solar cell string 12 to be detected. The configuration of the ground fault detection device 36 is the same as that shown in FIG. When detecting a ground fault, the changeover switch 81 connects the resistor 84 to the negative electrode wiring side of the solar cell string 12 to be detected without using the DC power supply 91, for example. In this state, the voltage monitoring unit 86 measures the voltage V <b> 1 across the resistor 84. Next, the resistor 84 is connected to the negative electrode wiring side of the solar cell string 12 to be detected via the DC power source 85, for example. In this state, the voltage monitoring unit 86 measures the voltage V <b> 2 applied across the resistor 84. When at least one of the voltages V2 of the voltage V1 exceeds a preset threshold value, it is determined that there is a ground fault by a control system (not shown). Then, the detection target solar cell string 12 or the solar power generation system 100 can be urgently stopped. In the example (G) of the ground fault detection device shown in FIG. 6B, even if a ground fault (insulation failure or the like) occurs in any part of the solar cell string 12 to be detected, there is a potential difference between both ends of the resistor 84. As a result, such a ground fault can be detected. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and the blind spot location for ground fault detection can be eliminated.

  FIG. 6C shows another example of the ground fault detection device connected only from the negative electrode wiring of the solar cell string 12 to be detected. The configuration of the ground fault detection device 36 is the same as that shown in FIG. In this state, the voltage monitoring unit 86 measures the voltage V in phase with the AC power supply 87 applied to both ends of the resistor 84 in synchronization with the phase of the AC power supply 87. When the voltage V exceeds a preset threshold for the phase, a control system (not shown) determines that a ground fault has occurred. Then, the detection target solar cell string 12 or the solar power generation system 100 can be urgently stopped. In the example (E) of the ground fault detection device shown in FIG. 3D, even when a ground fault (insulation failure or the like) occurs at any location of the solar cell string 12 to be detected, a potential difference is present at both ends of the resistor 84. As a result, such a ground fault can be detected. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and the blind spot location for ground fault detection can be eliminated.

  FIG. 6 (d) shows another example of the ground fault detection device connected only from the negative electrode wiring of the solar cell string 12 to be detected. The configuration of the ground fault detection device 36 is the same as that shown in FIG. In this state, the voltage monitoring unit 86 measures the voltage V applied across the resistor 84. When the voltage V exceeds a preset threshold value, a control system (not shown) determines that there is a ground fault. Then, the detection target solar cell string 12 or the solar power generation system 100 can be urgently stopped. In the example (I) of the ground fault detection device shown in FIG. 6D, even when a ground fault (insulation failure or the like) occurs at any location of the solar cell string 12 to be detected, there is a potential difference between both ends of the resistor 84. As a result, such a ground fault can be detected. Therefore, ground fault detection becomes possible at the stage when the first ground fault accident (first ground fault accident) occurs, and the blind spot location for ground fault detection can be eliminated.

  As described above, according to the sixth embodiment, it is possible to eliminate a blind spot where it is difficult to detect a ground fault while performing grounding for PID countermeasures.

Embodiment 7 FIG.
In each of the above-described embodiments, the ground wire 40 is branched from the negative electrode bus of the solar cell array 300 (a positive bus when an n-type semiconductor is used for the bulk of the solar cell) and is grounded. It is not a thing. In the seventh embodiment, a configuration in which the ground line 40 is branched and grounded from the negative electrode (positive electrode when an n-type semiconductor is used for the bulk of the solar cell) for each solar cell string 12 will be described. Hereinafter, the contents other than those specifically described are the same as those of the fourth embodiment.

  FIG. 7 is a configuration diagram showing the configuration of the photovoltaic power generation system in the seventh embodiment. In FIG. 7A, instead of branching the ground wire 40 from the negative electrode bus of the solar cell array 300 and grounding, the ground wires 40a to 40c are branched and ground from the negative electrode wiring of the solar cell strings 12a to 12c, respectively. Except for the point that the diodes 46a to 46c for backflow prevention are connected in the middle of the ground lines 40a to 40c and the point that the switch devices 48a to 48f are provided for the solar cell strings 12a to 12c, respectively. Same as (a). As shown in FIG. 7B, the diodes 46 a to 46 c are connected with the direction from the ground (ground) toward the negative electrode of the solar cell strings 12 a to 12 c as the forward direction. When the diode is installed in the reverse direction, the negative electrode of the solar cell string 12 has a lower potential than the ground, and PID may not be prevented. Each diode 46a-c arrange | positions the switch apparatus 48a, c, e between the connection points of the ground line 40a-c corresponding to the negative electrode of the solar cell string 12a-c. Further, the switch devices 48b, e, f are arranged between the positive electrodes of the solar cell strings 12a-c and the corresponding switch devices 102b, e, f. And the negative electrode wiring connected to the ground fault detection device 36 is branched from between the negative electrode of the solar cell strings 12a to 12c and the switch devices 48a, c, e. The positive electrode wiring connected to the ground fault detection device 36 is branched from between the positive electrode of the solar cell strings 12a to 12c and the switch devices 48b, e, and f. The switch device 48 uses a switch that can automatically control the opening / closing operation electrically. Although a mechanical switch may be used, it is more preferable to use, for example, a semiconductor switch. For example, it is preferable to use a MOSFET.

  The solar power generation system 100 as described above is operated as follows. Each switch device 102, each switch device 48, and switches 402 and 404 driven by control from a control system (not shown) are all in an ON (closed) state, and each switch device 31 and 33 is in an OFF (open) state. Then, normal operation is performed. That is, during the normal operation, the negative electrodes of the solar cell strings 12a to 12c are grounded. Thereby, the negative electrode of each solar cell string 12a-c can be controlled to ground potential, and a PID phenomenon can be avoided. However, in the seventh embodiment, during the normal operation of the photovoltaic power generation system 100, the ground fault detection is not performed in units of the solar cell array 300. In the seventh embodiment, ground fault detection is performed in units of 12 solar cell strings.

  FIG. 8 is a diagram for explaining a switch operation when performing ground fault detection in the photovoltaic power generation system according to the seventh embodiment. When the ground fault detection is performed in units of the solar cell string 12, after the two switch devices 48 of the solar cell string 12 to be detected are turned off (opened) from the state illustrated in FIG. The two switch devices 31 and 33 of the string 12 are turned on (closed). What is necessary is just to perform a ground fault detection in this state. Thereby, ground fault detection can be performed about the solar cell string 12 to be detected while each solar cell string 12 other than the solar cell string 12 to be detected is normally operated.

  In the seventh embodiment, for each solar cell string 12, the ground fault detection is periodically performed by the ground fault detection device 36. For example, the ground fault is detected every time the photovoltaic power generation system 100 is started or periodically during operation. The ground fault detection unit 36 is driven by control from a control system (not shown), and the positive and negative switch devices 48 (for example, the switch devices 48a and 48b) of the solar cell string 12 to be detected (for example, the solar cell string 12a) ( In the state where the ground wire 40 (for example, the ground wire 40a) is separated from the negative electrode of the solar cell string 12 to be detected (positive electrode when an n-type semiconductor is used for the bulk of the solar cell) by the example of the exclusion unit, Ground fault detection is performed in units of 12 solar cell strings. As described above, the plurality of switch devices 48a to 48f individually disconnect the ground lines 40a to 40c (ground portions) from the plurality of solar cell strings 12a to 12c. As described above, the switch device 48 on the negative electrode side of the solar cell string 12 to be detected is provided with the negative electrode of the solar cell string 12 to be detected caused by grounding by the ground wire 40 (when an n-type semiconductor is used for the bulk of the solar cell). Are arranged so as to eliminate the influence on the potential of the positive electrode). The ground fault detection device 36 is configured so that the influence of the detection target solar cell string 12 caused by the grounding by the ground line 40 on the negative electrode potential is eliminated by the switch device 48 in the detection target solar cell string 12. Detect a ground fault. Moreover, the detection target solar cell string 12 is disconnected from the system by turning off (opening) the two switch devices 48 of the detection target solar cell string 12. The switch devices 31 and 33 that are connected to the positive and negative electrodes of the solar cell string 12 to be detected and are driven by control from a control system (not shown) are turned on (closed). As described above, the ground fault detection unit 36 is connected to the solar power generation system 100 when detecting a ground fault of the solar cell string 12 to be detected. The two switch devices 48 connected to the positive and negative electrodes other than the detection target solar cell string 12 and driven by control from a control system (not shown) are turned on (closed) and driven by control from a control system (not shown). The switch devices 31 and 33 are OFF (open). Each switch device 102 and switches 402 and 404 are turned ON (closed).

  The internal configuration of the ground fault detection device 36 and the ground fault detection method may be the same as those described in FIG.

  As described above, according to the seventh embodiment, it is possible to eliminate a blind spot where it is difficult to detect a ground fault while performing grounding for PID countermeasures.

  In the seventh embodiment, an example is shown in which both the positive electrode and the negative electrode of each solar cell string 12 are connected to the ground fault detection device 36. However, one of the positive electrode or the negative electrode of each solar cell string 12 is connected to the ground fault detection device 36. It may be configured to connect to. The internal configuration of the ground fault detection device 36 and the ground fault detection method when the positive electrode of each solar cell string 12 is connected to the ground fault detection device 36 are the same as those described in FIGS. 5 (b) to 5 (d). The same is OK. The internal configuration of the ground fault detection device 36 and the ground fault detection method when the negative electrode of each solar cell string 12 is connected to the ground fault detection device 36 are the same as those described in FIGS. 6 (b) to 6 (d). The same is OK.

  The embodiments have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. The failure detection method described above is an example, and is not limited to the failure detection method described above. Other fault detection methods such as ground faults may be used.

  In addition, although descriptions are omitted for parts and the like that are not directly required for the description of the present invention, such as a device configuration and a control method, a required device configuration and a control method can be appropriately selected and used.

  In addition, all photovoltaic power generation systems that include the elements of the present invention and that can be appropriately modified by those skilled in the art are included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Solar cell module 12,502 Solar cell string 20,46 Diode 31,33,44,48,102 Switch apparatus 36 Detection part 40 Ground line 41,530 Ground location 42 Current monitoring part 80, 81 Changeover switch 83, 84 Resistance 85 , 89, 90, 91 DC power supply 86 Voltage monitoring unit 87 AC power supply 100 Photovoltaic power generation system 300 Solar cell array 400, 510 Load device 402, 404 Switch 500 Photovoltaic power generation system 600, 602 Ground fault location

Claims (5)

A power generation unit configured using one or more solar cell modules that generate power using sunlight; and
A load device that consumes or converts the power generated by the power generation unit while being insulated from the power generation unit side or the ground,
A grounding portion for grounding the negative electrode or the positive electrode of the power generation unit;
An exclusion unit arranged to be able to eliminate the influence on the ground potential of the power generation unit caused by the grounding by the grounding unit;
The ground potential of the power generation unit is controlled by controlling the ground potential of the power generation unit to two or more different potentials in a state where the influence on the ground potential of the power generation unit caused by the grounding by the grounding unit is excluded by the exclusion unit. A ground fault detector for detecting a fault,
A photovoltaic power generation system characterized by comprising: A power generation unit configured using one or more solar cell modules that generate power using sunlight; and
A load device that consumes or converts the power generated by the power generation unit while being insulated from the power generation unit side or the ground,
A grounding portion for grounding the negative electrode or the positive electrode of the power generation unit;
An exclusion unit arranged to be able to eliminate the influence on the ground potential of the power generation unit caused by the grounding by the grounding unit;
A current monitoring unit disposed on the grounding unit and monitoring a current flowing through the grounding unit to detect a ground fault of the power generation unit;
In the state where the influence on the ground potential of the power generation unit caused by the grounding by the grounding unit is eliminated by the exclusion unit, the ground potential of the power generation unit is controlled to a ground potential different from that when grounded by the grounding unit. A ground fault detection unit for detecting a ground fault of the power generation unit;
A photovoltaic power generation system characterized by comprising: As the exclusion unit, a switch for separating the grounding unit from the negative electrode or the positive electrode of the power generation unit is used,
The ground fault detection unit is arranged to be disconnected from the solar power generation system and connectable to the solar power generation system, and is connected to the solar power generation system when detecting a ground fault of the power generation unit. The photovoltaic power generation system according to claim 1 or 2. As the power generation unit, a solar cell array in which a plurality of solar cell strings in which a plurality of solar cell modules are connected in series is connected in parallel is used,
3. The ground fault detection unit performs ground fault detection in units of the solar cell array in a state where the grounding unit is separated from a negative electrode or a positive electrode of the power generation unit by the exclusion unit. The described solar power generation system. As the power generation unit, a solar cell array in which a plurality of solar cell strings in which a plurality of solar cell modules are connected in series is connected in parallel is used,
The exclusion unit has a plurality of switches for individually separating the grounding unit from the plurality of solar cell strings,
The said ground fault detection part performs a ground fault detection in a solar cell string unit, and performs the ground fault detection of the solar cell string cut | disconnected by either of these switches. Solar power system.

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