JP2002027764A - Power conditioner and photovoltaic power generating system using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conditioner that causes no malfunction, converts the DC power of a solar cell into the same AC power with a system by the maximum power conversion efficiency, and transmits electric power in association with the system. SOLUTION: This power conditioner 1 without a transformer, which converts the DC power of the solar cell 2 into the AC power of the same commercial frequency with the system and supplies it to a system power supply, comprises a detection circuit 11 that detects a leakage current between the solar cell and the ground, an inverter circuit 12 that converts the DC power of the solar cell into AC power in response to a control command signal, and a control circuit 13 which is the circuit that inputs the control command signal into the inverter circuit to control its operation, changes over and controls the operation system of the inverter circuit to multiple systems in accordance with the detection of the leakage current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformerless power conditioner (non-insulated solar power generation) for converting the DC power of a solar cell into the same AC power as that of a system, and transmitting the power in connection with the system. Power converter).

[0002]

2. Description of the Related Art A power conditioner used in a photovoltaic power generation system for converting the DC power of a solar cell into AC power having the same commercial frequency as the system and supplying the AC power to a system power supply is provided with the DC power of the solar cell. There is a non-insulation type (transformerless) type which boosts the voltage and converts it into AC power of a commercial frequency by an inverter circuit.

In such a transformerless type power conditioner, when an inverter circuit having a plurality of switch elements in a full bridge circuit configuration is used, an AC voltage may be applied between the solar cell and ground depending on the operation method for each switch element. (Hereinafter, referred to as a single switching method for convenience of description) and a method of applying a DC voltage (hereinafter, referred to as double switching method for convenience of description).

[0004] In the conventional power conditioner, the operation method of the inverter circuit is fixed to one of the above-mentioned operation methods.

[0005]

The operating system of the inverter circuit is fixed to the single switching system because there is a stray capacitance (ground capacitance) which becomes particularly large in rainy weather between the solar cell and the ground in the above-mentioned system. When compared with the double switching method, the power conversion efficiency is excellent compared to the double switching method, and the power loss in the inverter circuit can be reduced.However, a large leakage current flows from the system side to the DC side via the stray capacitance in rainy weather or the like. As a result, the reliability of the system is affected, for example, the earth leakage breaker at home may malfunction.

When the operation system is fixed to the double switching system, the leakage current is small and the possibility of malfunction is small, but the power conversion efficiency is poor, so that the power loss in the inverter circuit is large.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a power conditioner capable of switching the operation mode of an inverter circuit, eliminating the possibility of malfunction, and having excellent power conversion efficiency.

[0008]

A first power conditioner according to the present invention is a transformerless power conditioner for converting DC power into AC power of a predetermined frequency and outputting the AC power. An inverter circuit for converting electric power into AC power, and a control circuit for switching and controlling the operation mode of the inverter circuit to a plurality according to the detection result of the leakage current and the power conversion efficiency.

A second power conditioner according to the present invention is a transformerless power conditioner for converting DC power of a solar cell into AC power having the same commercial frequency as the system and supplying the AC power to a system power supply. A detection circuit for detecting a leakage current between grounds, an inverter circuit for converting DC power to AC power, and an operation of the inverter circuit, wherein the inverter circuit operates in response to the detection of the leakage current. And a control circuit for switching and controlling a plurality of operation modes.

In the case of the first and second power conditioners according to the present invention, the operation mode of the inverter circuit is switched to a plurality of modes in accordance with the detection of the leakage current. The system can be switched. Therefore, when the leakage current is small, the operation method is switched to, for example, a single switching method having excellent power conversion efficiency. When the leakage current is large, the operation method is switched to, for example, an operation method with a small leakage current such as a double switching method. Malfunction can be prevented, and the reliability of the entire system using the same can be improved.

For example, when the operation system is fixed to the single switching system, the power conversion efficiency is approximately 96
%, And the power conversion efficiency when fixed to the double switching system is as low as approximately 95%. In the case of the first and second power conditioners of the present invention, both operation modes can be used in combination, so that the power conversion efficiency is lower than that of the fixed single switching mode.
It is higher than the fixed double switching method.

In particular, in the case of the fixed single-switching system, the earth leakage breaker may malfunction even if the power conversion efficiency is high. While the conversion efficiency is low, the first and second power conditioners of the present invention are extremely advantageous in that there is no risk of malfunction and the power conversion efficiency is higher than that of the double switching system.

Particularly, in the case of the second power conditioner of the present invention, when a large leakage current flows between the solar cell and the ground due to the stray capacitance that increases in rainy weather,
By switching the operation method of the inverter circuit, the leakage current is further reduced or substantially eliminated, and the reliability of the photovoltaic power generation system is improved by reliably preventing malfunctions such as earth leakage breakers and improving the power conversion efficiency. It is preferable because the improvement of the composition can be further improved.

In the above case, preferably, the inverter circuit has a full bridge circuit configuration including a plurality of switch elements, and each switch element performs a switching operation in response to a control input of the control circuit.

In the above case, preferably, the control circuit controls at least the inverter circuit so as to switch between an operation mode in which a voltage between the solar cell and the ground is a DC voltage and an operation mode in which an AC voltage is used.

A solar power generation system according to the present invention includes a solar cell, and a transformerless power conditioner for converting DC power of the solar cell into AC power having the same commercial frequency as the system and supplying the AC power to a system power supply, The power conditioner is a detection circuit for detecting a leakage current between the solar cell and ground, an inverter circuit for converting DC power of the solar cell to AC power, and controls the operation of the inverter circuit, A control circuit for switching and controlling a plurality of operation modes of the inverter circuit in accordance with the detection of the leakage current.

According to the system of the present invention, the power conditioner can switch the operation mode of the internal inverter circuit in accordance with the detection of the leakage current. When the switching system is used, and when the leakage current is large, a malfunction such as an earth leakage breaker can be prevented as a double switching system, so that a highly reliable system can be provided.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below based on embodiments shown in the drawings.

FIGS. 1 to 6 relate to an embodiment of the present invention, FIG. 1 is a circuit diagram of an entire photovoltaic power generation system according to an embodiment of the present invention, FIG. 2 is a detailed circuit diagram of an inverter circuit, and FIG. FIG. 4 is a timing chart in the case of the single switching system of the inverter circuit, FIG. 4 is a timing chart in the case of the double switching system of the inverter circuit, FIG.
FIG. 3 is a control operation flowchart of the control circuit.

Referring to FIG. 1, power conditioner 1
Is connected between the solar cell 2 and the system power supply 4 via the earth leakage breaker 3 via a pair of power wirings 5 and 6.

The solar cell 2 functions as a DC power supply, and the solar cell may be of any type as long as the present embodiment is applied.

The earth leakage breaker 3 does not perform an interruption operation when a current having a different direction flows from one of the wirings 5 or 6 to the other of the wirings 5 or 6. When the magnitude of the current exceeds a predetermined value, it is determined that a leakage has occurred, and a cutoff operation is performed.

The system power supply 4 is a 100/200 V single-phase 3
It is a linear system.

The power conditioner 1 converts DC power from the solar cell 2 into AC power synchronized with the system power supply 3, and a DC input unit (+) for inputting DC power from the solar cell 2. ) And an AC output unit 12 for outputting AC power, and a zero-phase current transformer (CT) 1
1. Inverter circuit 12 for system interconnection, interconnection relay 13
And a control circuit 14.

The zero-phase current transformer 11, the inverter circuit 12, and the interconnection relay 13 are connected in series between the solar cell 2 and the earth leakage breaker 3.

The zero-phase current transformer 11 detects, as a leakage current detection circuit, a current flowing from the power lines 5 and 6 to the ground via the stray capacitance C0 between the solar cell and the ground as a leakage current I0. As the leakage current I0, the inverter circuit 1
If the switching method in 2 is a single switching method, the switching becomes AC, and if the switching method is a double switching method, it becomes DC. However, the leakage current of the alternating current in the case of the double switching method is much smaller than that of the alternating current in the case of the single switching method.

As shown in FIG. 2, the inverter circuit 12 has input sections IN1 and IN2 and output sections OUT1 and OU.
T2, and its inputs IN1, IN2 and output OUT
1 and OUT2, a booster circuit unit 12a that boosts the DC voltage of the solar cell 2 to a constant DC voltage, and converts the DC power from the booster circuit unit 12a into AC power synchronized with the system power supply 4. A switch circuit section 12b for conversion and a filter circuit section 12c are provided.

In the inverter circuit 12, each switching element S of the booster circuit section 12a and the switch circuit section 12b
1 to S5 are controlled by a control input from the control circuit 14. Each of the switch elements S1 to S5 is in the form of a transistor in the embodiment. This transistor includes a bipolar transistor and an IGBT, and may be a GTO thyristor or the like without being a transistor.

The booster circuit section 12a includes a reactor L1, a diode D1, capacitors C1 and C2, and a switch element S1, and supplies a DC voltage of, for example, 350 V
To a constant voltage.

The switch circuit section 12b is composed of four switch elements S2 to S5 having a full bridge circuit configuration, and controls the output by changing the pulse width.
The switching operation is performed in the M system, and the DC voltage from the booster circuit unit 12a is converted into a rectangular wave AC voltage. In the embodiment, the switching operation of the switch circuit unit 12b is a PWM method in which frequency control and output voltage control are performed at the same time. However, another method, for example, a current control type or a voltage control type may be used. In short, in each system, any operation system that can control the driving of each of the switch elements S2 to S5 by a single switching system or a double switching system may be used.

FIG. 3 shows an operation timing waveform of the single switching system in the inverter circuit 12, and FIG. 4 shows an operation timing waveform of the double switching system.

3A and 4A are output voltage waveforms on the power line 5 side of the inverter circuit 12, and FIGS.
The output voltage waveform on the power wiring 6 side, (c) shows the switch element S2
ON and OFF waveforms of the switch element S3
N and OFF waveforms, (e) shows ON and O of switch element S3.
(F) shows the ON / OFF waveform of the switch element S5, and (g) shows the voltage waveform between the solar cell and the ground.

Since this operation is well known, a detailed description thereof will be omitted. In the case of the single switching system shown in FIG. 3, the switch element S2 is turned off, the switch element S3 is turned on in section A, and the switch elements S4 and S5 are turned off. ON, OFF
A positive sine wave voltage is output to the output part OUT1 and a negative sine wave voltage is output to the output part OUT2 by the PWM control described above.

In the case of the double switching system shown in FIG. 4, the ON and OFF cycles of the switch elements S2 and S5 are matched in the section A, and the ON and OFF cycles of the switch elements S3 and S4 are combined. Although the periods are matched, a negative sine wave voltage is output to the output unit OUT1 and a positive sine wave voltage is output to the output unit OUT2 by PWM control in which the ON and OFF periods of the above two combinations are reversed. And

According to such PWM control, in the case of the single switching system, as shown in FIG. 3 (g), the voltage between the solar cell and the ground has an AC waveform, and in the case of the double switching system, FIG. ), The voltage between the solar cell and the ground has a DC waveform.

In the case of the single switching system and the double switching system, the power conversion efficiency is as shown in FIG. In FIG. 5, the horizontal axis represents the output (k
W), the vertical axis indicates power conversion efficiency (%), a is a single switching system, and b is a double switching system. As is clear from FIG. 5, the power conversion efficiency of the single switching system is approximately 96%, which is approximately 1%, which is superior to that of the double switching system.

The filter circuit section 12c includes two coils L
0 and a capacitor C0, and converts the rectangular wave AC voltage from the switch circuit unit 12b into a sine wave AC voltage.

The control circuit 14 incorporates a microcomputer, and each switch element S of the inverter circuit 12
The control input for turning on and off the S1 to S5 is input. As shown in the operation flow of FIG. 6, the leakage current I0 is determined based on the output of the zero-phase current transformer 11. , The inverter circuit 12 based on the determination result.
Are controlled by switching between a plurality of operation methods, in this embodiment, a single switching method and a double switching method.

That is, during the system interconnection operation (S1), the control circuit 14 detects the detected current in response to the input of the current detection (S2) in the power wires 5 and 6 from the output of the zero-phase current transformer 11 It is determined whether or not the value exceeds the predetermined value I0. If it is determined that the value exceeds the predetermined value I0, the leakage current is large, so that the operation method of the inverter circuit 12 is switched to the double switching method in order to suppress the leakage current (S4). If it is determined that the current is less than the predetermined value I0, since the leakage current is small, the operation method of the inverter circuit 12 is controlled to be switched to the single switching method having excellent power conversion efficiency (S5).

The output of the zero-phase current transformer 11 has an AC waveform in the case of the single switching system, and has a DC waveform in the case of the double switching system. Is large,
Since the AC waveform of the double switching method is small, the AC
The determination at 3 can be made.

The present invention is not limited to the above embodiment, and various applications and modifications are possible.

(1) Although the system power supply 4 of the present embodiment is a single-phase three-wire system in the present embodiment, the present invention is not limited to this. Good
Other wire systems such as a three-phase three-wire system may be used. In the case where the number of output phases is a single phase, the inverter circuit has a full bridge circuit configuration of four transistors, and in the case of a three phase inverter circuit, it has a full bridge circuit configuration of six transistors.

(2) In the above embodiment, the switching of the operation mode of the inverter circuit 12 is of two types, the single switching mode and the double switching mode.
The present invention is not limited to this, and the operation method may be switched among a plurality of types.

(3) In the above-described embodiment, the leakage current is detected by arranging the leakage breaker in front of the inverter circuit 12. However, the present invention is not limited to this. It may be arranged on the side to detect leakage current.

(4) In the above embodiment, the control of the inverter circuit is PWM control. However, the present invention is not limited to this, and another control method may be used.

(5) In the above embodiment, the present invention is applied to any type of grid-connected photovoltaic power generation system connected to a distribution line of a power company. Can also be applied.

(6) In the above-described embodiment, the inverter circuit converts DC power into AC power at a commercial frequency, but may also convert AC power at an arbitrary frequency.

[0048]

As described above, according to the present invention, the operation mode of the inverter circuit can be switched to a plurality of types in accordance with the detection of the leakage current. Single switching system, if the leakage current is large, for example, double switching system can prevent malfunction such as earth leakage breaker,
As a result, malfunction can be prevented, and the overall power conversion efficiency can be made higher than in the double switching system.

[Brief description of the drawings]

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

FIG. 2 is a detailed circuit diagram of an inverter circuit.

FIG. 3 is a timing chart in the case of a single switching method of an inverter circuit.

FIG. 4 is a timing chart in the case of a double switching method of an inverter circuit.

FIG. 5 is a diagram showing power conversion efficiencies of the above two methods.

FIG. 6 is a control operation flow chart of a control circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power conditioner 2 Solar cell 3 Earth leakage breaker 4 System power supply 11 Zero-phase current transformer 12 Inverter circuit 12a Boost circuit part 12b Switch circuit part 14 Control circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshihiro Ueda O-Muron Co., Ltd. (10) Hanazono Todocho, Ukyo-ku, Kyoto-shi, Kyoto (72) Inventor Nobuyuki Touraura 10-Hanazono Todo-cho, Ukyo-ku, Kyoto, Kyoto (72) Inventor Katsutaka Tanabe Omron Co., Ltd. (10) Hanazono Todocho, Ukyo-ku, Kyoto, Kyoto Prefecture (72) Inventor Shigemitsu Kakizoe 1166, Hasemi, Hachizou-cho, Yokaichi, Shiga Prefecture 6 Kyocera Corporation Shiga Plant F-term (reference) in Yokaichi block 5G066 HA13 HA30 HB06 5H007 AA06 BB07 CA01 CB05 CC12 DB01 DC02 FA03 FA14 FA19 5H420 CC03 DD03 DD08 DD10 EA10 EA20 EA37 EA45 EB01 EB04 EB26 EB39 FF04 FF25 LL04

Claims (5)

[Claims] 1. A transformerless power conditioner for converting and outputting DC power to AC power of a predetermined frequency, a detection circuit for a leakage current, an inverter circuit for converting DC power to AC power, and the inverter circuit And a control circuit for switching and controlling a plurality of operation modes according to the detection result of the leakage current and the power conversion efficiency. 2. A transformerless power conditioner for converting DC power of a solar cell into AC power having the same commercial frequency as a system and supplying the AC power to a system power supply, wherein a leakage current between the solar cell and ground is detected. And an inverter circuit for converting DC power to AC power. The inverter circuit controls the operation of the inverter circuit, and switches and controls the operation method of the inverter circuit to a plurality of types according to the detection of the leakage current. A power conditioner comprising: a control circuit; 3. The power conditioner according to claim 1, wherein the inverter circuit has a full bridge circuit configuration including a plurality of switch elements, and each switch element performs a switching operation in response to a control input of the control circuit. A power conditioner, characterized in that: 4. The power conditioner according to claim 2, wherein said control circuit operates at least with respect to said inverter circuit in an operation mode in which a voltage between a solar cell and a ground is a DC voltage and an operation mode in which an AC voltage is used. A power conditioner characterized by performing switching control. 5. A power conditioner, comprising: a solar cell; and a transformerless power conditioner that converts DC power of the solar cell into AC power having the same commercial frequency as a system and supplies the AC power to a system power supply. A detection circuit for detecting a leakage current between a solar cell and ground; an inverter circuit for converting DC power of the solar cell to AC power; and controlling an operation of the inverter circuit, wherein the detection of the leakage current is performed. And a control circuit for switching and controlling a plurality of operation modes of the inverter circuit according to the following.