JP2000023370A - Solar light power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar light power generation system which has constant detection level for a grounding in a DC cableway and thereby can prevent erroneous detection of a ground. SOLUTION: A distributed power supply equipment 2 converts a DC voltage from a solar battery 1 to specified AC voltage and then supplies power to a load 4 in linkage with a commercial power system 3. A DC cableway for connecting the solar battery 1, and the distributed power supply 2 is passed through a through-hole 12 formed in a detection core 11 of a zero-phase current transformer 10. A ground detection circuit 9 detects the ground current in a DC cableway 21 from the output of a secondary winding wound around the detection core 11. When the ground detection circuit 9 detects a ground, a control circuit 8 stops the generation of power by the distributed power supply 2, based on the detection signal of the ground detection circuit 9. After that, when the distributed power supply 2 restarts power generation, a demagnetizing circuit 15 causes damped oscillating current to flow into the DC cableway 21 and passing through the through-hole 12 of the detection core 11 to eliminate the residual magnetism of the detection core 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic power generation system that uses a solar cell as a power source and converts a DC voltage of the solar cell into an AC voltage and supplies the AC voltage.

[0002]

2. Description of the Related Art Conventionally, a distributed power supply having a small capacity of about several kW using a DC power supply composed of a solar cell is provided, and a distributed power supply is connected to a commercial power system to supply power to a load. A power generation system has been provided (for example,
285015).

As shown in FIG. 5, a conventional photovoltaic power generation system arranges a large number of solar cells to form a panel.
Solar cell 1 that directly converts solar energy into DC voltage
And a distributed power supply that converts the DC power of the solar cell 1 into AC power, and that is connected to the commercial power system 3 via the disconnecting switch 14 and supplies power to the load 4 such as various home appliances connected to the distribution line. 2 is provided.

In the distributed power supply 2, the booster circuit 5 boosts the output voltage of the solar cell 1 to a predetermined DC voltage, and the inverter circuit 6 converts the DC voltage of the booster circuit 5 into an AC voltage. The output voltage of the circuit 6 is converted into a substantially sinusoidal AC voltage, and the load 4
To supply. The distributed power supply 2 includes a control circuit 8 for controlling the output voltages of the booster circuit 5 and the inverter circuit 6 and on / off of the parallel-off switch 14, a ground fault detection circuit 9 for detecting a ground fault of the DC power line 21. Is provided, and a ground fault detection circuit 9 is provided.
When the control circuit 8 detects a ground fault in the DC circuit 21, the control circuit 8 stops the outputs of the booster circuit 5 and the inverter circuit 6 based on the detection signal of the ground fault detection circuit 9 and turns off the paralleling switch 14.

Here, the ground fault detecting circuit 9 is a current sensor in which a direct current path 21 connecting the solar cell 1 and the boosting circuit 5 is inserted into a through hole 12 of a detecting core 11 formed of a magnetic material. The ground fault of the DC electric circuit 21 is detected from the output of the zero-phase current transformer 10. For example, the DC circuit 21 on the negative electrode side
When the ground fault occurs, the solar cell 1 → the booster circuit 5 → the switching element 61 (or 62) of the inverter circuit 6 → the inductor L1 (or L2) of the filter circuit 7 → the disconnecting switch 14 →
A ground fault current Ir flows through a route from the commercial power system 3 → ground fault resistance Rg → solar cell 1 (indicated by solid and broken arrows in FIG. 5), and a current flowing through the DC power path 21 on the positive side and a DC current on the negative side Since a difference is generated between the current flowing through the electric circuit 21 and the ground fault current Ir, an output corresponding to the current difference is generated in a secondary winding (not shown) wound around the detection core 11. I do.
Thus, the ground fault detection circuit 9 compares the magnitude relationship between the output of the zero-phase current transformer 10 and a predetermined judgment value. When the output of the zero-phase current transformer 10 becomes larger than the judgment value, the DC power line 21 And outputs a detection signal to the control circuit 8.

[0006]

In the photovoltaic power generation system having the above configuration, the ground fault detection circuit 9 detects the ground fault current Ir having a relatively small current value flowing due to the deterioration of the insulation performance of the DC circuit 21 or the like. , So that it can generate a detection signal,
The judgment value of the ground fault detection circuit 9 is set to a small value.
However, the DC line 21 is grounded due to an accident or the like, and the ground line current Ir having a relatively large current value is supplied to the DC line 21.
Flows, the detection core 11 of the zero-phase current transformer 10 is magnetized, and residual magnetism remains in the detection core 11, so that the zero-phase current transformer 1
There is a problem that the output of 0 is offset and the detection level when the ground fault detection circuit 9 detects the ground fault fluctuates.
There is a possibility that the ground fault detection circuit 9 malfunctions.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a photovoltaic power generation system which eliminates a malfunction of a ground fault detection circuit for detecting a ground fault in a DC circuit. It is in.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a power conversion means for converting a DC voltage of a solar cell into a predetermined AC voltage, and the power conversion means is provided via a parallel disconnect switch. In a photovoltaic power generation system that includes a distributed power supply that supplies power to a load in connection with a commercial power system, the distributed power supply includes a current sensor in which a DC power path is inserted into a through hole of a detection core made of a magnetic material, and a detection sensor. A ground-fault detection circuit that detects a ground-fault current flowing in the DC circuit from the output of the winding wound on the core, a control circuit that opens the disconnecting switch when the ground-fault detection circuit detects the ground-fault current, And a degaussing circuit for degaussing the detection core when the control circuit turns on the disconnection switch at least after the detection of the ground fault current. Current flows and the detection core arrives. Even if this happens, the degaussing circuit degauss the detection core when the disconnection switch is turned on again after the detection of the ground fault current, so that the residual magnetism of the detection core can be demagnetized, and the detection level of the ground fault detection circuit is kept constant Can be kept.

According to a second aspect of the present invention, in the first aspect, the degaussing circuit is connected via a capacitor to a capacitor charged by an output voltage of the solar cell and to a direct current path inserted into a through hole of the detection core. A first inductor, and discharging the electric charge accumulated in the capacitor to the DC circuit via the first inductor, thereby causing an attenuated oscillating current to flow in the DC circuit to demagnetize the detection core. The residual magnetism of the detection core can be demagnetized by passing an attenuated oscillating current through the direct current path inserted into the through hole of the detection core.

According to a third aspect of the present invention, in the first aspect of the present invention, the degaussing circuit is characterized in that a damped oscillating current for degaussing the detection core flows through a winding wound around the detection core.
By passing the damped oscillating current through the winding wound around the detection core, the remanence of the detection core can be demagnetized.

According to a fourth aspect of the present invention, in the second aspect of the present invention, the power conversion means includes a booster circuit for boosting the DC voltage of the solar cell to a predetermined voltage value, and the booster circuit is connected between the DC output terminals of the solar cell. And a second inductor connected to
Series circuit of a switching element, a diode having an anode connected to a connection point of the second inductor and the second switching element, and a smoothing second element connected between both ends of the second switching element via the diode. And a second inductor, wherein the second inductor also serves as a first inductor for flowing a damped oscillating current, and wherein the second inductor constituting the booster circuit is used for flowing a damped oscillating current. Since the same inductor is used,
The number of components can be reduced, and the size of the distributed power supply can be reduced.

[0012]

Embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) As shown in FIG. 1, a solar power generation system according to the present embodiment includes a solar cell 1 that arranges a large number of solar cell panels into a panel shape, and directly converts solar energy into a DC voltage. The DC power of the battery 1 is converted into AC power, and the distributed power supply 2 is connected to the commercial power system 3 via the disconnecting switch 14 and supplies power to the load 4 such as various home appliances connected to the distribution line. Be composed.

The distributed power supply 2 is constructed by connecting a booster circuit 5 for boosting the output voltage of the solar cell 1 to a predetermined DC voltage and four IGBTs 61 to 64 as first switching elements in a bridge manner. Output voltage of IGBT 61 to
An inverter circuit 6 for converting to an AC voltage by switching at 64; a filter circuit 7 comprising inductors L1 and L2 and capacitors C1 and C2 for smoothing the output voltage of the inverter circuit 6 and outputting a substantially sinusoidal AC voltage; , A control circuit 8 composed of, for example, a one-chip microcomputer for controlling the outputs of the booster circuit 5 and the inverter circuit 6, and the solar cell 1 and the booster circuit 5 in the through hole 12 of the detection core 11 made of a magnetic material. A ground fault in the DC circuit 21 is detected from an output of a zero-phase current transformer 10 as a current sensor in which a DC circuit 21 connecting the DC circuit 21 is inserted and a secondary winding (not shown) wound around the detection core 11. And a parallel-off switch 14 that turns on and off according to the output signal of the control circuit 8 and turns on and off the power supply from the distributed power supply 2 to the load 4. It is made. Here, the booster circuit 5
And the inverter circuit 6 constitute a power conversion means. Although not shown, a manual return type breaker is provided between the inverter circuit 6 and the commercial power system 3 separately from the disconnecting switch 14 for system protection, and a single-phase three-wire commercial power system is provided. A main switch and a branch switch are provided between the load 3 and the load 4 to protect the load 4.

The booster circuit 5 has a series circuit of a second inductor 51 connected between output terminals of the solar cell 1 and an IGBT 52 as a second switching element, and an anode connected to a connection point between the second inductor 51 and the IGBT 52. A connected diode 53 and a second capacitor 54 connected between both ends of the IGBT 52 via the diode 53
And a diode 55 connected antiparallel to the IGBT 52.

The inverter circuit 6 includes IGBTs 61 and 63
And the series circuit of IGBTs 62 and 64
IGBTs 61 to 6
4 are connected in reverse-parallel with diodes 65 to 68, respectively. The DC voltage of the booster circuit 5 is converted into an AC voltage by switching the DC voltage of the booster circuit 5 using these four IGBTs 61 to 64. And output. I
The connection point between the GBTs 62 and 64 and the connection point between the IGBTs 61 and 63 are respectively connected to the inductor L of the filter circuit 7.
1, L2, is connected to a contact on the voltage line side of the disconnecting switch 14, and a capacitor C1 of the filter circuit 7 is provided between the contact on the voltage line side of the disconnecting switch 14 and the contact on the ground line side. C2
The output waveform of the inverter circuit 6 is smoothed by the filter circuit 7 to become a substantially sinusoidal waveform, and is supplied to the load 4 via the disconnecting switch 14.

The output voltage of the solar cell 1 constantly changes in accordance with the amount of solar radiation, for example, from 0V to 300V. The control circuit 8 monitors the output voltage of the solar cell 1, and when the output voltage of the solar cell 1 is lower than 150 V, for example, at night or when the amount of light is insufficient, the disconnection switch 14 is turned off and the distributed power source 2 is commercialized. Disconnect from power system 3. On the other hand, when the output voltage of the solar cell 1 is, for example, 150 V or more, the booster circuit 5 switches the output voltage of the solar cell 1 by the IGBT 52 so that the output voltage of the solar cell 1 is approximately equal to the effective voltage of the commercial power supply. A DC voltage equivalent to four times (for example, 1
In the case of the 00V single-phase three-wire system, the voltage is boosted to 140 × 2 = 280V) and output to the inverter circuit 6. Where IG
The BT 52 is turned on / off by a control signal input from the control circuit 8 to a control electrode (gate). The control circuit 8 detects the output voltage of the booster circuit 5 by detecting means (not shown).
The output of the booster circuit 5 is controlled to be substantially constant by changing the on-duty of T52.

The control circuit 8 outputs control signals to the control electrodes (gates) of the IGBTs 61 to 64, respectively, converts the DC voltage of the booster circuit 5 into a substantially sinusoidal AC voltage, and outputs the converted voltage to the commercial power system 3. . As shown in FIGS. 2A to 2C, in the control circuit 8, the magnitude of a triangular-wave-shaped reference oscillation signal Vs as a reference and a sine-wave-shaped command signal Ve having a lower frequency than the reference oscillation signal Vs is determined. Compare the relationship, and
The pulse signal S1 in which the signal level is high only during the period when the voltage value of the reference oscillation signal Vs is higher than the voltage value of e, and the signal only during the period when the voltage value of the reference oscillation signal Vs is lower than the voltage value of the command signal Ve A pulse signal S2 having a high level is generated.

Thus, the control circuit 8 includes the IGBTs 61 to 64 connected diagonally in the bridge-connected IGBTs.
A pulse signal S1 is output to 61 and 64, and a pulse signal S2 is output to the remaining IGBTs 62 and 63, so that a pair of IGBTs 61 and 64 and another pair of IGBTs 62 and 6 are output.
3 are alternately turned on and off to convert the DC voltage of the booster circuit 5 into an AC voltage. Here, the control circuit 8 outputs the pulse signal S
By performing PWM control by modulating the pulse widths of S1 and S2, the ON period of the pair of IGBTs 61 and 64 and the ON period of the other pair of IGBTs 62 and 63 are changed to control the output of the inverter circuit 6. . The control circuit 8 controls the output of the inverter circuit 6 so that the phase of the output voltage of the filter circuit 7 substantially matches the voltage phase of the commercial power system 3.

In the distributed power supply 2, when the ground fault detection circuit 9 detects a ground fault in the DC power line 21, the control circuit 8 outputs the outputs of the booster circuit 5 and the inverter circuit 6 based on the detection signal of the ground fault detection circuit 9. Is stopped, and the disconnection switch 14
Is turned off, and the interconnection of the distributed power supply 2 is stopped. For example, when the negative electrode side of the DC circuit 21 is grounded, the solar cell 1 → the booster circuit 5 → the IGBT 61 (or 62) → the inductor L1 (or L2) → the disconnect switch 14 → the commercial power system 3 → the ground fault resistance R
g → a ground fault current Ir flows along the path of the solar cell 1 (indicated by solid and broken arrows in FIG. 1), and the DC power path 21 on the positive electrode side
A difference is generated between the current flowing through the detection core 11 and the current flowing through the DC power path 21 on the negative side, and an output corresponding to the difference in the current is wound around the detection core 11. Occurs on lines. Thus, the ground fault detection circuit 9 is connected to the zero-phase current transformer 10.
Is compared with a predetermined judgment value, and when the output of the zero-phase current transformer 10 becomes larger than the judgment value, the DC circuit 2
It is determined that the first ground fault has occurred, and a ground fault detection signal is output to the control circuit 8. When the ground fault detection circuit 9 detects a ground fault, the control circuit 8 stops the output of the booster circuit 5 and the inverter circuit 6 based on the detection signal of the ground fault detection circuit 9 and turns off the parallel-off switch 14. Then, the commercial power system 3 and the system are separated.

When the DC circuit 21 is grounded, a relatively large ground fault current Ir flows through the DC circuit 21.
The detection core 1 of the zero-phase current transformer 10 is generated by the ground fault current Ir.
1 is magnetized, and the detection level of the ground fault detection circuit 9 changes due to the residual magnetism of the detection core 11. Therefore, in the photovoltaic power generation system of the present embodiment, a degaussing circuit 15 for degaussing the residual magnetism of the detection core 11 is provided.

The degaussing circuit 15 includes a first inductor 19 having one end connected to a portion on the solar cell 1 side with respect to the detection core 11 in the negative-side DC circuit 21, and one end connected to the other end of the first inductor 19. Is connected to the first capacitor 18
A resistor 17 having one end connected to the other end of the first capacitor 18, and a portion of the DC circuit 21 on the positive electrode side or the negative electrode side on the side of the booster circuit 5 with respect to the detection core 11 and the other end of the resistor 17. And switches 16a and 16b for connecting between them. The switches 16a and 16b are connected to the control circuit 8
When the control circuit 8 turns on the switch 16a, the first capacitor 18 is charged by the output voltage of the solar cell 1. When the control circuit 8 restarts the booster circuit 5 and the inverter circuit 6 and turns on the parallel-off switch 14 again after the detection of the ground fault,
The control circuit 8 turns on the switch 16b, discharges the electric charge accumulated in the first capacitor 18 through the first inductor 19, and causes the DC electric path 21 inserted through the through hole 12 of the detection core 11 to generate an attenuated oscillating current. After the residual magnetism of the detection core 11 is demagnetized by the damped oscillation current, the ground fault detection circuit 9 detects the ground fault.

As described above, when detecting a ground fault in the DC circuit 21 using the zero-phase current transformer 10, the detection core 11 is magnetized by the ground fault current, and residual magnetism is generated in the detection core 11. , Even if the detection level of the ground fault detection circuit 9 changes,
When the control circuit 8 restarts the distributed power supply 2 after the detection of the ground fault current, the demagnetizing circuit 15 demagnetizes the residual magnetism of the detection core 11, so that the detection level of the ground fault detecting circuit 9 can be kept constant. As a result, malfunction of the ground fault detection circuit 9 can be eliminated. When the control circuit 8 starts the distributed power supply 2 for the first time, the control circuit 8 uses the degaussing circuit 15 to detect the detection core 11.
When the distributed power source 2 is started up for the first time and when it is restarted, the degaussing circuit 15 degausses the detection core 11 and removes the residual magnetism of the detection core 11, thereby providing a ground fault. The detection level of the detection circuit 9 can be kept constant, and erroneous detection of the ground fault detection circuit 9 can be prevented. (Embodiment 2) FIG. 3 shows a circuit diagram of a photovoltaic power generation system of this embodiment. Since the basic configuration is the same as that of the first embodiment, the same components are denoted by the same reference numerals and description thereof will be omitted.

In the first embodiment, the demagnetizing circuit 15 is
1, the residual magnetism of the detection core 11 is demagnetized by flowing the damped oscillating current to the demagnetizing circuit 15 in this embodiment.
Flows decaying oscillating current through a detection secondary winding (not shown) wound around the detection core 11 based on a control signal of the control circuit 8, thereby demagnetizing the residual magnetism of the detection core 11. . Note that the demagnetizing circuit 15 may cause the damped oscillating current to flow through a secondary winding (not shown) wound around the detection core 11 separately from the secondary winding for detection.

As described above, the degaussing circuit 15 is connected to the detection core 11
A damped oscillating current is passed through the secondary winding wound around, and by flowing the damped oscillating current through this secondary winding, the residual magnetism of the detection core 11 can be demagnetized as in the first embodiment. . Thus, even if the detection core 11 is magnetized by the ground fault current when the ground fault current is detected, and the detection level of the ground fault detection circuit 9 changes, the control circuit 8 operates the booster circuit 5 and the inverter circuit after the detection of the ground fault current. When the controller 6 is restarted and the parallel-off switch 14 is turned on again, the control circuit 8
Since the residual magnetism of the detection core 11 is demagnetized using the reference numeral 5, the detection level of the ground fault detection circuit 9 can be kept constant, and the malfunction of the ground fault detection circuit 9 can be eliminated. (Embodiment 3) FIG. 4 shows a circuit diagram of a photovoltaic power generation system of this embodiment. Since the basic configuration is the same as that of the first embodiment, the same components are denoted by the same reference numerals and description thereof will be omitted.

In this embodiment, the resistor 17 having one end connected to the connection point between the second inductor 51 and the IGBT 52
A first capacitor 18 having one end connected to the other end of the resistor 17, and a detection core 11 in the DC circuit 21 on the negative side.
A switch 16c for connecting a portion on the side of the solar cell 1 to the other end of the first capacitor 18 with respect to the portion on the side of the solar cell 1 with respect to the detection core 11 in the DC circuit 21 on the positive side; Switch 1 that connects to the other end of 18
6d constitute the degaussing circuit 15, and the switches 16c, 1
6d is turned on / off by the control circuit 8. here,
When the switch 16 c is turned on by the output signal of the control circuit 8, the first capacitor 18 is charged by the output voltage of the solar cell 1. When the control circuit 8 restarts the booster circuit 5 and the inverter circuit 6 after the detection of the ground fault current, and when the parallel-off switch 14 is turned on again, the control circuit 8
Turns on the switch 16d, the first capacitor 18
Is accumulated in the resistor 17 and the second inductor 5
1, the damped oscillating current flows through the DC current path 21 inserted into the through hole 12 of the detection core 11, and the residual magnetism of the detection core 11 is demagnetized.

As described above, in the present embodiment, the second inductor 51 constituting the booster circuit 5 is connected to the first capacitor 1.
8 that discharges the electric charge accumulated in 8 and causes a damped oscillating current to flow.
, The number of components can be reduced, and the size of the distributed power source 2 can be reduced.

[0027]

As described above, the first aspect of the present invention includes a power conversion means for converting a DC voltage of a solar cell into a predetermined AC voltage, and is connected to a commercial power system via a disconnection switch. In a photovoltaic power generation system provided with a distributed power supply for supplying power to a load, a distributed power supply includes a current sensor having a DC current path inserted through a through-hole of a detection core made of a magnetic material, and a winding wound around the detection core. A ground fault detection circuit that detects a ground fault current flowing in the DC circuit from the output of the line, a control circuit that opens the disconnect switch when the ground fault detection circuit detects the ground fault current, and controls at least after the detection of the ground fault current The circuit is provided with a degaussing circuit for degaussing the detection core when the circuit breaker is turned on again.For example, when a DC circuit is grounded and a relatively large ground fault current flows in the DC circuit, the detection is performed. Ground fault current detection even when core is magnetized The degaussing circuit degauss the detection core when the parallel-off switch is turned on again, thereby demagnetizing the residual magnetism of the detection core, keeping the detection level of the ground fault detection circuit constant and malfunctioning the ground fault detection circuit. There is an effect that can be prevented.

According to a second aspect of the present invention, in the first aspect, the degaussing circuit is connected via a capacitor to a capacitor charged by an output voltage of the solar cell and to a direct current path inserted into a through hole of the detection core. A first inductor, and discharging the electric charge accumulated in the capacitor to the DC circuit via the first inductor, thereby causing an attenuated oscillating current to flow in the DC circuit to demagnetize the detection core. By flowing an attenuated oscillating current through the direct current path inserted into the through hole of the detection core, there is an effect that the remanence of the detection core can be demagnetized.

According to a third aspect of the present invention, in the first aspect of the present invention, the degaussing circuit is characterized in that a decaying oscillating current for degaussing the detection core flows through a winding wound around the detection core. By passing the damped oscillating current through the wound winding, there is an effect that the residual magnetism of the detection core can be demagnetized.

According to a fourth aspect of the present invention, in the second aspect of the present invention, the power conversion means includes a booster circuit for boosting the DC voltage of the solar cell to a predetermined voltage value, and the booster circuit is connected between the DC output terminals of the solar cell. , A series circuit of a second inductor and a second switching element, a diode having an anode connected to a connection point between the second inductor and the second switching element, and a second switching element via the diode. And a second capacitor for smoothing connected between both ends of the first and second terminals, wherein the second inductor also serves as the first inductor for flowing the damped oscillating current,
Since the second inductor constituting the booster circuit also serves as the first inductor for passing the damped oscillating current, there is an effect that the number of components can be reduced and the size of the distributed power supply can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a photovoltaic power generation system according to a first embodiment.

FIGS. 2A to 2C are explanatory diagrams illustrating the operation of the above.

FIG. 3 is a circuit diagram illustrating a photovoltaic power generation system according to a second embodiment.

FIG. 4 is a circuit diagram illustrating a photovoltaic power generation system according to a third embodiment.

FIG. 5 is a circuit diagram showing a conventional solar power generation system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solar cell 2 Distributed power supply 3 Commercial power system 4 Load 8 Control circuit 9 Ground fault detection circuit 10 Zero-phase current transformer 11 Detection core 12 Through hole 15 Demagnetization circuit 21 DC electric circuit

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hiroaki Koshin 1048 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Works, Ltd. (72) Inventor Tadayoshi Mukai 1048 Kadoma Kadoma, Kadoma City, Osaka Matsushita Electric Works Co., Ltd. (72) Inventor Hirotada Higashihama 1048 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside the Matsushita Electric Works Co., Ltd. (72) Inventor Hiroaki Yuasa 1048 Kadoma Kadoma, Kadoma City, Osaka Pref. AB29 AB49 AC19 5G066 HA06 HA13 HB06

Claims (4)

[Claims] 1. A solar system comprising: a power conversion means for converting a DC voltage of a solar cell into a predetermined AC voltage; and a distributed power supply connected to a commercial power system via a disconnecting switch and supplying power to a load. In a photovoltaic power generation system, a distributed power source is provided with a current sensor in which a DC circuit is inserted into a through hole of a detection core made of a magnetic material, and a ground fault current flowing in the DC circuit from an output of a winding wound around the detection core. A ground fault detection circuit for detecting, a control circuit for opening the disconnection switch when the ground fault detection circuit detects the ground fault current, and at least when the control circuit recloses the disconnection switch after the detection of the ground fault current. A photovoltaic power generation system comprising a degaussing circuit for degaussing a detection core. 2. A degaussing circuit comprising: a first capacitor charged by an output voltage of a solar cell; and a first inductor connected to a direct current path inserted into a through hole of the detection core via the first capacitor. And discharging the electric charge accumulated in the first capacitor to the DC circuit via the first inductor, thereby causing an attenuated oscillating current to flow in the DC circuit to demagnetize the detection core. 1. The solar power generation system according to 1. 3. The photovoltaic power generation system according to claim 1, wherein the degaussing circuit supplies a damped oscillating current for degaussing the detection core to a winding wound around the detection core. 4. The power conversion means includes a booster circuit for boosting a DC voltage of the solar cell to a predetermined voltage value, wherein the booster circuit includes a second inductor connected between the DC output terminals of the solar cell and a second inductor. A series circuit of switching elements, a diode having an anode connected to a connection point between the second inductor and the second switching element, and a second smoothing element connected between both ends of the second switching element via the diode. 3. The photovoltaic power generation system according to claim 2, wherein the second inductor also serves as the first inductor for flowing the damped oscillating current. 4.