JPH09285015A - Dc ground detector of photovoltaic power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid an electric shock caused by a leakage current, etc., by a method wherein, a DC ground judging means which judges that a DC ground of a solar battery exists and stops the operation of an inverter and an output reducing means which reduces an AC output from the inverter when a detection level by a ground detecting means is higher than a certain level are provided. SOLUTION: If the detection level of a ground detecting means 8 is higher that a certain value, the AC output of an inverter 2 is suppressed by the output reducing means of an inverter control unit 5 and, when the detection level of the ground detecting means 8 is lower than a second level, a fixed output operation is performed. Therefore, when a temporary leakage current is produced in a rainy state, etc., the operation of the inverter 2 is not stopped instantly by the mistaken judgement of a DC ground. Further, if a leakage current is not reduced below a 2nd level in spite of that the output of the inverter is suppressed to the lowest output value with which the system linkage is possible, the operation of the inverter is stopped, so that an electric shock caused by a leakage current, etc., can be avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC ground fault detector for a photovoltaic power generation system, and more particularly to a DC ground fault detecting a DC ground fault condition of a solar cell composed of a solar cell module circuit to stop an inverter. The present invention relates to a fault detection device.

[0002]

2. Description of the Related Art In recent years, a solar power generation system has been used in which a distributed power supply system of a comparatively small capacity of several kW using a DC power supply composed of solar cells is connected to a commercial power system via an inverter circuit to supply power to a load. Various systems have been proposed.

FIG. 3 is a schematic diagram of a conventional solar power generation system. In the figure, 31 is a solar cell module circuit in which a large number of solar cell elements that directly convert the energy of sunlight into a DC voltage are connected in series and parallel, and 32 is the DC power output from the solar cell module circuit 31. This is an inverter for converting into alternating current, and the direct current output from the solar cell module circuit 31 is converted into alternating current by the inverter 32, and then the load 34 is passed through the opening / closing means 33 such as an automatic recovery electromagnetic relay or a manual recovery breaker. And to the commercial power system 35.

On the output side of the solar cell 31, a voltage detecting means 36 for detecting the solar cell voltage is provided, and the output of the inverter 32 is maintained so that the operating point of the solar cell 31 is maintained at the reference voltage. Inverter control means 37 for controlling the current is provided.

Further, a ground fault detection device 38 has been conventionally provided to prevent electric shock and protect the electric path when a DC ground fault occurs in this solar power generation system. The ground fault detection device 38 detects the DC ground fault state of the solar cell 31 by utilizing the fact that the DC current values on the positive electrode side and the negative electrode side of the solar cell 31 are different during a ground fault. The inverter 32 is stopped when a DC ground fault condition is detected to ensure safety and protect the system.

[0006]

On the other hand, the solar cells in this solar power generation system are generally used outdoors in many cases, and are often installed on the roof of a house or the like. For this reason, it is often used in an environment exposed to wind and rain.

However, in the above-mentioned conventional apparatus, although the solar cell 31 is not in the DC ground fault state in rainy weather,
Frequent malfunctions that the inverter 32 is stopped when it is determined to be in the DC ground fault state occur. This is because water droplets adhere to the solar cell module circuit of the solar cell 31 to increase the capacitance component between the ground and the solar cell module circuit,
The increase in leakage current due to the influence of the capacity component
This is because it is erroneously detected that the DC ground fault state occurs.

The present invention has been made in view of the above problems, and distinguishes between a leakage current generation state due to water droplet adhesion on the solar cell module circuit and a DC ground fault state of the solar cell, and the leakage current Provided is a DC ground fault detection device for a photovoltaic power generation system, which improves the operation efficiency of the photovoltaic power generation system without immediately stopping the inverter upon determining that the DC ground fault has occurred.

[0009]

SUMMARY OF THE INVENTION A DC ground fault detector for a photovoltaic power generation system according to the present invention is a solar cell module circuit configured by connecting a plurality of solar cell elements in series and parallel, and the solar cell. Ground fault detection means for detecting the output ground fault of the solar cell comprising a module circuit, and output reduction means for reducing the AC output from the inverter when the detection level by the ground fault detection means is above a certain value, When suppressing the inverter output by the output reduction means, when the detection level by the ground fault detection means is equal to or higher than the certain value, it is determined that the solar cell is a DC ground fault and the operation of the inverter is stopped, and the DC ground fault determination means is stopped. It has and. By using this configuration, if a temporary increase in leakage current occurs due to water droplets adhering to the solar cell module circuit, such as in the case of rain, it will be judged as a DC ground fault and the inverter will be immediately stopped by mistake. There is no.

More specifically, it has an opening / closing means provided between the inverter and a commercial power system, and when the DC ground fault judging means judges that the solar cell has a DC ground fault,
The switching means is controlled to disconnect the inverter from the commercial power system. By using this configuration,
When a DC ground fault occurs in the solar cell, it is possible to reliably prevent electric shock and protect the electric path.

Further, preferably, when the output reduction means suppresses the inverter output, and the detection level by the ground fault detection means is smaller than the constant value, the inverter output is operated at that time. Alternatively, when the output level of the inverter is suppressed by the output reducing means, if the detection level of the ground fault detecting means is equal to or lower than the second level which is smaller than the predetermined value, the inverter output is operated to drive the inverter. By using these configurations, if a temporary increase in leakage current occurs due to water droplets adhering to the solar cell module circuit in rainy weather, etc., the leakage current value can be reduced and the photovoltaic power generation system can be used within the possible range. The operation of can be continued.

More preferably, the output reducing means gradually reduces the inverter output until the detection level of the ground fault detecting means becomes equal to or lower than the second level. By using this configuration, the operation of the photovoltaic power generation system is continued with the leakage current value reduced to a predetermined level, so that prevention of electric shock due to leakage current is reliably prevented.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A direct current ground fault detection apparatus for a photovoltaic power generation system according to an embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of a photovoltaic power generation system using a solar cell to which the present invention is applied.

In FIG. 1, a solar power generation system is a solar cell 1 (a solar cell module circuit comprising a solar cell module circuit configured by connecting a plurality of solar cell elements for converting sunlight energy into DC power in series and parallel. In the embodiment, an optimum operating voltage of 200 V and an optimum operating power of 3 kW) and an inverter 2 for converting a direct current power of the solar cell 1 into an alternating current power and supplying a predetermined alternating current voltage are mainly configured. Electric power is supplied to a load 4 such as various home appliances connected to a distribution line in an interconnected manner with 3.

The inverter 2 is composed of a plurality of bridge-connected switching elements, and a pulse width modulated switching control signal is given to the inverter 2 from an inverter control unit 5 which performs various processes described later. The inverter control unit 5 is constituted by a microcomputer.

Between the inverter 2 and the commercial power system 3, a system interconnection relay (hereinafter abbreviated as a relay) 6 and a manual reset type breaker (hereinafter, referred to as a relay) for system protection are provided in order from the output side of the inverter 2. 7) is provided, and the relay 6 and the breaker 7 open / close their contacts according to a control signal from the inverter control unit 5 to be connected to the commercial power system 3 or to be disconnected. . Here, the contact of the relay 6 is closed by the input of the interconnection command signal from the inverter controller 5, and the contact is opened by the input of the disconnection command signal from the inverter controller 5. Further, the breaker 7 is configured such that its contact is opened by the input of the disconnection command signal from the inverter control unit 5, and the contact is manually closed.

The ground fault detecting means 8 detects the difference between the direct current values of the positive electrode side and the negative electrode side of the solar cell 1, and detects the output ground fault of the solar cell 1 based on the detection result. The PWM generation circuit 10 sends the PW to the inverter 2 based on the inverter current control value from the inverter control unit 5.
Sending M switching signal. And this PW
The detection values of the inverter current detection means 11 and the inverter voltage detection means 12 are input to the M generation circuit 10, and PWM is performed so that the inverter current having the inverter current control value is output from the inverter 2 in the same phase as the system voltage. Sending a switching signal.

Then, the inverter control section 5 determines the inverter current control value so that the solar cell voltage detected by the solar cell voltage detecting means 9 is maintained at the preset reference voltage value, and the PWM generation circuit 10 is determined. Is output to.

Further, the detection result from the ground fault detection means 8 is input to the inverter control section 5, and when the detection level is a certain value or more (set to 50 mA in this embodiment), the output from the inverter 2 is output. In order to suppress the above, an output reduction unit 51 (not shown) is provided that changes the inverter current control value from the current value to a control value reduced by a predetermined amount and outputs the control value to the PWM generation circuit 10.

Further, the inverter control section 5 judges that the solar cell 1 is a DC ground fault and operates the inverter 2 when the level detected by the ground fault detecting means 8 is equal to or higher than the predetermined value when the inverter output is suppressed. And a DC ground fault determination unit 52 (not shown) that disconnects the power from the commercial power system 3 and supplies a PWM switching signal from the PWM generation circuit 10 based on a control signal from the inverter control unit 5. To stop the operation of the inverter 2 and open the relay 6 and the breaker 7 to disconnect the inverter 2 from the commercial power system 3.

On the contrary, when the inverter output is suppressed,
When the detection level by the ground fault detection means 8 becomes equal to or lower than the second level (which is set to 30 mA in this embodiment) which is smaller than the predetermined value, the inverter current control value at that time is set to the PWM generation circuit 10. Is output to the inverter for a fixed time to perform fixed output operation of the inverter 2.

In the inverter control section 5, the output reduction means 51 gradually reduces the inverter output until the detection level by the ground fault detection means 8 becomes equal to or lower than the second level, and the output reduction means 51 causes the inverter output to decrease. When the output becomes equal to or lower than the preset minimum output value (which is set to 100 W in this embodiment), the operation of the inverter 2 is stopped and the relay 6 is opened to commercialize the inverter 2 Disconnect from the grid 3
Keep the inverter in standby for a certain period of time.

Therefore, in rainy weather, water drops adhere to the solar cell module circuit of the solar cell 1,
The capacitance component C between the ground and the solar cell module circuit increases. Then, when the detection level in the ground fault detection means 8 becomes equal to or higher than the above-mentioned fixed value due to the increase in the leakage current due to the increase in the capacitance component C, the output reduction means 51 of the inverter control unit 5 causes the AC from the inverter 2 to change. Since the output is suppressed, the AC ripple voltage included in the solar cell output voltage is reduced, and as a result, the leakage current value due to the capacitance component C is also reduced.

Here, the capacitance component C between the earth and the ground has the following relationship with the permittivity ε, the area S, and the distance d between them, so that the capacitance component C increases with the increase in the permittivity ε due to water drops in rainy weather. C will increase. Further, since the AC ripple voltage corresponding to the inverter output is superimposed on the solar cell output voltage, the leakage current value increases as the inverter output increases. Therefore, the leakage current value is also reduced by suppressing the output of the inverter 2.

[0025]

[Equation 1]

Therefore, when the detection level of the ground fault detecting means 8 becomes equal to or higher than the predetermined value due to the increase of the leakage current due to the influence of the capacitance component C, the output reducing means 51 of the inverter control section 5 causes the inverter 2 to operate. The output fixed operation is performed in a state in which the AC output of is suppressed and the detection level of the ground fault detection means 8 becomes the second level or less. Therefore, in the case of a temporary increase in leakage current such as in the case of rain, it is not judged to be a DC ground fault and the inverter 2 is not immediately stopped by mistake. Further, even if the output of the inverter 2 is suppressed to the minimum output value that can be interconnected, the inverter operation is stopped when the leakage current value does not fall below the second level, so it is possible to reliably prevent electric shock due to leakage current. To prevent.

Next, the operation contents of the DC ground fault detecting device of the solar power generation system having the above-mentioned structure will be described with reference to FIG. First, in step S1, based on the detection result from the ground fault detection means 8, the inverter control unit 5 determines whether or not the detection level iL is 50 mA or more, and the process proceeds to the next step S3 only if YES.

In step S3, the output reducing means 51 controls the inverter output to be suppressed, and the process proceeds to step S5. Specifically, the inverter current control value is set to 1 from the current value.
The control value is lowered by A and output to the PWM generation circuit 10.

In step S5, the detection level iL of the ground fault detecting means 8 in the inverter control section 5 is again 50 m.
It is determined whether or not A or more, and if YES, step S7
If NO, the process proceeds to step S9.

In step S7, the DC ground fault judging means 52
It is judged that the solar cell 1 is in the DC ground fault state by
The inverter operation is stopped, the relay 6 and the breaker 7 are opened, the inverter 2 is disconnected from the commercial power system 3, and the inverter 2 is put into a failure state, and the processing is terminated.

On the other hand, in step S9, the detection level iL of the ground fault detection means 8 in the inverter control unit 5 is 30 m.
It is determined whether or not A or less, and if YES, step S1
If NO, the process proceeds to step S13.

In step S11, the current inverter current control value is sent to the PWM generation circuit 10 for 10 minutes to perform the output fixed operation of the inverter 2, and the process proceeds to step S15 to return the inverter 2 to the normal operation state and to step S1. Return.

In step S13, similarly to step S3, the output reduction means 51 performs the inverter output suppression control again, and the process proceeds to step S17. In step S17, it is determined whether the output of the inverter 2 is 100 W or more, and YES. If step S
Returning to step 9, if NO, the process proceeds to step S19.

In step S19, the operation of the inverter 2 is stopped, the relay 6 is opened, the inverter 2 is disconnected from the commercial power system 3, and the inverter 2 is placed in a standby state to end the processing.

Here, when the processing is terminated as a failure state of the inverter 2, the cause of the failure is removed, and when the open circuit voltage of the solar cell 1 and the system voltage of the commercial power system 3 are within the interconnection possible range, a fixed time period is reached. After a lapse of time (10 minutes or more after disconnection in the present embodiment), the operator manually resets the breaker 7 and automatically resets the relay 6 to start the operation of the inverter 2. Inverter 2
When the processing is terminated as the standby state of the above, if a certain period of time elapses (10 minutes or more after disconnection in the present embodiment, when the open circuit voltage of the solar cell 1 and the system voltage of the commercial power system 3 etc. After that, the relay 6 is automatically restored to start the operation of the inverter 2.

The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope.
Further, each configuration of the present invention is not limited to the above-described embodiment, but can be variously modified within the technical scope described in the claims. For example, in the above-described embodiment, when the output level of the inverter 2 is equal to or lower than the second level when the inverter output is suppressed, the inverter output at that time causes the inverter 2 to perform the output fixed operation. In addition to this, when the detection level by the ground fault detecting means 8 becomes smaller than the above-mentioned constant value, the inverter 2 may be operated with the output fixed at the output of the inverter at that time.

[0037]

As described above, according to the present invention, when a temporary increase in leakage current occurs due to the attachment of water droplets on the solar cell module circuit, such as in the case of rain, it is determined to be a DC ground fault and erroneous. The inverter will not be stopped immediately. Therefore, the operating efficiency of the system can be improved.

Further, when the DC ground fault judging means judges that the solar cell has a DC ground fault, the switching means is controlled to disconnect the inverter from the commercial power system, thereby generating a DC ground fault of the solar cell. In this case, it is possible to surely prevent electric shock and protect the electric circuit.

Furthermore, when the output level of the inverter is suppressed by the output reducing means, if the detection level of the ground fault detecting means is smaller than a certain value or is less than the second level, the inverter output is operated at that time. Therefore, if a temporary increase in the leakage current occurs due to the adhesion of water droplets on the solar cell module circuit, such as in the case of rain, reduce the leakage current value and continue the operation of the photovoltaic power generation system within the possible range. You can

In addition, the leakage current value is reduced to a predetermined level by gradually reducing the inverter output by the output reducing means until the level detected by the ground fault detecting means becomes equal to or lower than the second level. Since the operation of the solar power generation system is continued, the prevention of electric shock due to leakage current can be reliably prevented.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a photovoltaic power generation system according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating the operation content of the DC ground fault detection device of the solar power generation system in FIG.

FIG. 3 is a schematic configuration diagram of a conventional solar power generation system.

[Explanation of symbols]

 1 Solar Cell 2 Inverter 3 Commercial Power System 4 Load 5 Inverter Control Section 6 Grid Interconnection Relay 7 Manual Reset Type Breaker 8 Ground Fault Detection Means 9 Solar Cell Voltage Detection Means 10 PWM Generation Circuit 11 Inverter Current Detection Means 12 Inverter Voltage Detection Means 51 Output reducing means 52 DC ground fault judging means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H02H 3/32 H02N 6/00 H02N 6/00 H01L 31/04 K

Claims (5)

[Claims] 1. A photovoltaic power generation system for converting a direct current output generated from a solar cell element into an alternating current output having a predetermined voltage and outputting the alternating current output to a commercial power system to supply electric power to a load. A solar cell module circuit configured by connecting solar cell elements in series and parallel, and a ground fault detection means for detecting an output ground fault of a solar cell formed by the solar cell module circuit,
When the detection level by the ground fault detection means is a certain value or more, an output reduction means for reducing the AC output from the inverter, and a detection level by the ground fault detection means at the time of suppressing the inverter output by the output reduction means. Is a predetermined value or more, the DC ground fault determination means for determining the DC ground fault of the solar cell and stopping the operation of the inverter, and the DC ground fault detection of the photovoltaic power generation system. apparatus. 2. An opening / closing means provided between the inverter and a commercial power system, wherein the opening / closing means is controlled when the DC ground fault judging means judges that the solar cell is a DC ground fault. The DC ground fault detection device for a photovoltaic power generation system according to claim 1, wherein the inverter is disconnected from the commercial power system. 3. When the output reduction means suppresses the inverter output, and when the detection level by the ground fault detection means is smaller than the predetermined value, the inverter output is operated to drive the inverter. Item 1
Alternatively, the DC ground fault detection device of the solar power generation system according to item 2. 4. The level detected by the ground fault detecting means when the output of the inverter is suppressed by the output reducing means,
The DC ground fault detecting device for a photovoltaic power generation system according to claim 3, wherein when the second level is smaller than the predetermined value and is equal to or lower than the second level, the inverter is operated by the inverter output at that time. 5. The output reducing means gradually reduces the inverter output until the level detected by the ground fault detecting means becomes equal to or lower than the second level.
A DC ground fault detection device for the described solar power generation system.