JPH09135583A - Inverter for photovoltaic power generation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent malfunction in an earth leakage breaker and radio-wave interference without using a transformer, by reducing a flowing-out of high-frequency current. SOLUTION: A DC voltage generated from a solar battery 1 is applied as an input voltage to an inverter, and the output is connected to a power system. The inverter includes a full-bridge circuit 2, in which a smoothing reactor 3 is inserted between all neutral points of arms and the system. A capacitor 4 is connected between each DC positive or negative input of the full-bridge circuit 2 and all smoothing reactors 3 on the system side. Then, malfunction or environmental radio-wave interference caused by a high-frequency current leaking into the DC circuit or the system can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter for photovoltaic power generation, which converts DC power generated by a solar cell into AC power and supplies the AC power to a grid.

[0002]

2. Description of the Related Art As a main circuit configuration of an inverter for photovoltaic power generation, a full-bridge circuit is generally used conventionally. FIG. 2 shows an example of the configuration of such an inverter. 1 is a solar cell, 2 is a full bridge circuit, 3 is a smoothing reactor, 4 is a smoothing capacitor, 5 is a transformer, 6 is a grid, and 7 is a sun. This is the ground capacity that a DC circuit such as a battery and wiring has with the ground.

In FIG. 2, a full bridge circuit 2 switches a DC voltage generated by the solar cell 1 at a high frequency of about 20 kHz and converts it into an AC voltage. Between the midpoints of the arms constituting the full bridge circuit 2, a pulse train whose peak value corresponds to a DC voltage and whose average value changes in a sine wave shape is generated by switching. And is supplied to the system 6 via the transformer 5. Therefore, the high-frequency current component accompanying switching flows into the smoothing capacitor 4 having a low impedance at high frequencies, and does not flow out to the system 6.

On the other hand, the high frequency voltage associated with switching is also generated between the DC input of the full bridge circuit 2 and the middle point of each arm, but the transformer 5 insulates the full bridge circuit 2 and the system 6 in terms of high frequency. As a result, the high-frequency current due to this does not flow out to the ground capacity 7 of the DC circuit or the system 6.

However, when such an inverter is installed in a general household, the transformer 5 is a transformer of a commercial frequency, so that the inverter is heavy and large. Therefore, the transformer 5 is omitted under the condition that the DC circuit of the solar cell 1 is not grounded.

[0006]

FIG. 3 shows a conventional example of an inverter in which a transformer is omitted from the inverter shown in FIG. 2, and the reference numerals are the same as those in FIG. In FIG.
Since the full bridge circuit 2 performs switching at a high frequency, between the DC input of the full bridge circuit 2 and the midpoint of the arm forming the full bridge circuit 2, as in the case where the transformer described in FIG. A high-frequency voltage whose peak value corresponds to the DC voltage is generated. This high frequency voltage is applied to the solar cell 1
Since a transformer for isolating the system 6 from the system is omitted and one wire of the system 6 is normally grounded, it is directly applied to the ground capacity 7 of the DC circuit through the ground. As a result, a high-frequency current that charges and discharges the ground capacity 7 flows out to the solar cell 1 and the system 6, and the high-frequency current causes a malfunction of the earth leakage breaker installed in the system 6 or causes a radio disturbance in the surroundings. There was a problem.

An object of the present invention is to provide an inverter for photovoltaic power generation in which malfunction of the earth leakage breaker and occurrence of radio wave interference are prevented by suppressing the outflow of such high frequency current, and a transformer is omitted. Especially.

[0008]

In order to achieve the above-mentioned object, in the present invention, a smoothing reactor is inserted between the midpoints of all the arms constituting the full bridge circuit and the system, and the system side of all the smoothing reactors. By connecting a smoothing capacitor between the DC positive input and the DC negative input of the full bridge circuit, high frequency voltage due to switching is prevented from being applied to the ground capacitance of the DC circuit.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the inverter for photovoltaic power generation according to the present invention, smoothing reactors are inserted between the midpoints of all the arms constituting the full bridge circuit and the grid, and the grid side and the full bridge of all the smoothing reactors are inserted. Connect a smoothing capacitor between the DC positive input or DC negative input of the circuit. With this configuration, the high frequency voltage associated with switching is not applied to the ground capacitance of the DC circuit, and malfunctions of the earth leakage breaker and electromagnetic interference to the surroundings can be prevented.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a photovoltaic power generation inverter embodying the present invention, and the reference numerals are the same as those in FIGS. 2 and 3. In FIG. 1, since the full-bridge circuit 2 performs switching at high frequency, a high-frequency voltage is generated between the DC input of the full-bridge circuit 2 and the midpoint of the arm forming the full-bridge circuit 2 as in the conventional case. This high-frequency voltage is applied to the smoothing capacitor 4 through the smoothing reactor 3 inserted between the smoothing capacitor 4 and the system 6, but since the high-frequency impedance of the smoothing capacitor 4 is extremely lower than the high-frequency impedance of the smoothing reactor 3, the smoothing capacitor 4 High frequency voltage is hardly generated at both ends of 4.

That is, in the embodiment of FIG. 1, the smoothing capacitor 4 is not provided between the phases on the system side of the smoothing reactor 3 as in the conventional example, but on each phase on the system side of the smoothing reactor 3 and the DC negative input of the full bridge circuit 2. Since it is connected between
High frequency voltage accompanying switching is smoothing capacitor 4
Is short-circuited, and is not applied to the ground capacitance 7 of the DC circuit. As a result, the high frequency current flowing out to the DC circuit of the solar cell 1 and the grid 6 can be significantly suppressed.

In the embodiment of FIG. 1, the smoothing capacitor 4
Was connected to the DC negative input of the full bridge circuit 2, but since a large-capacity capacitor is usually connected between the DC input phases of the full bridge circuit, the high frequency impedance between the DC input phases is extremely low. The same result can be obtained by connecting the smoothing capacitor 4 to the DC positive input.

[0013]

As described above, according to the present invention, the smoothing reactors are inserted between the midpoints of all the arms constituting the full bridge circuit and the system, and the system side of all the smoothing reactors and the full bridge circuit are connected. Since a smoothing capacitor is connected between the DC positive input or DC negative input, the high frequency voltage associated with switching is not applied to the ground capacitance of the DC circuit of the solar cell, and the earth leakage breaker is caused by the high frequency current flowing out to the DC circuit or grid. There is an effect that it is possible to prevent the malfunction of and the electromagnetic interference given to the surroundings.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an inverter for photovoltaic power generation according to the present invention.

FIG. 2 is a block diagram of a conventional inverter for photovoltaic power generation.

FIG. 3 is a block diagram of a photovoltaic power generation inverter in which a conventional transformer is omitted.

[Explanation of symbols]

 1 Solar cell 2 Full bridge circuit 3 Smoothing reactor 4 Smoothing capacitor 5 Transformer 6 System 7 DC capacity to ground

Claims (1)

[Claims] 1. An inverter for photovoltaic power generation in which a DC voltage generated by a solar cell is used as an input voltage and an output is connected to a grid, and the inverter is configured by a full bridge circuit, which constitutes the full bridge circuit. A smoothing reactor is inserted between the midpoint of all the arms and the system, and a smoothing capacitor is connected between the system side of all the smoothing reactors and the DC positive input or DC negative input of the full bridge circuit. Inverter for solar power generation.