JP3805953B2 - Power conditioner and solar power generation system using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transformerless power conditioner (non-insulated solar power converter) that converts the DC power of a solar cell into AC power that is the same as that of the system, and transmits the power in connection with the system.
[0002]
[Prior art]
For power conditioners used in photovoltaic power generation systems that convert the DC power of solar cells into AC power of the same commercial frequency as that of the system and supply it to the system power supply, the DC power of the solar cells is boosted, and the inverter circuit However, there is a non-insulated type (transformer-less) that converts AC power into commercial frequency.
[0003]
In such a transformerless power conditioner, when an inverter circuit having a plurality of switch elements having a full bridge circuit configuration is used, an AC voltage is applied between the solar cell and the ground depending on the operation method for each switch element. (Hereinafter referred to as a single switching method for convenience of explanation) and a method of applying a DC voltage (hereinafter referred to as a double switching method for convenience of explanation).
[0004]
In the conventional power conditioner, the operation method of the inverter circuit is fixed to any one of the above operation methods.
[0005]
[Problems to be solved by the invention]
In the above system, there is a stray capacitance (ground capacity) that becomes particularly large in rainy weather between the solar cell and the ground. If the operation method of the inverter circuit is fixed to the single switching method, it is compared with the double switching method. Excellent power conversion efficiency and less power loss in the inverter circuit, but a large leakage current flows from the system side to the DC side through the stray capacitance when it rains, for example, a leakage breaker in the home Affects the reliability of the system, such as possible malfunctions.
[0006]
In addition, when the operation method is fixed to the double switching method, the leakage current is small and the possibility of malfunction is small, but the power conversion efficiency is inferior, so the power loss in the inverter circuit is large.
[0007]
Therefore, an object of the present invention is to provide a power conditioner that can switch the operation method of the inverter circuit, eliminates the possibility of malfunction, and is excellent in power conversion efficiency.
[0008]
[Means for Solving the Problems]
The first power conditioner of the present invention is a transformerless power conditioner that converts DC power of a solar cell into AC power having a predetermined frequency, and detects a leakage current and converts DC power into AC power. An inverter circuit; and a control circuit that switches and controls an operation method of the inverter circuit in accordance with a detection result of the leakage current and a power conversion efficiency.
[0009]
The second power conditioner of the present invention is a transformer-less power conditioner that converts the DC power of a solar cell into AC power having the same commercial frequency as that of the system and supplies it to the system power supply. A detection circuit for detecting a leakage current of the inverter, an inverter circuit for converting DC power into AC power, and an operation of the inverter circuit, wherein an operation method of the inverter circuit is determined according to the detection of the leakage current. And a control circuit that controls switching to a plurality.
[0010]
In the case of the first and second power conditioners of the present invention, the operation method of the inverter circuit is controlled to be switched to a plurality according to the detection of the leakage current, so the operation method of the inverter circuit is switched according to the detection of the leakage current. It is done. Therefore, when the leakage current is small, the operation method is switched to, for example, a single switching method having excellent power conversion efficiency, and when the leakage current is large, the operation method is switched to an operation method with a small leakage current, such as a double switching method. Can be prevented, and the reliability of the entire system using it can be improved.
[0011]
For example, the power conversion efficiency when the operation method is fixed to the single switching method is as high as approximately 96%, and the power conversion efficiency when the operation method is fixed as the double switching method is as low as approximately 95%. In the case of the first and second power conditioners of the present invention, both operation methods can be used together, so that the power conversion efficiency is lower than the single switching method fixed, but higher than the double switching method fixed.
[0012]
In particular, when the single switching method is fixed, the earth leakage circuit breaker may malfunction even when the power conversion efficiency is high. When the double switching method is fixed, the power conversion efficiency is high even if there is little risk of malfunction. On the other hand, 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 method.
[0013]
In particular, 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 a stray capacitance that increases in the rain, the leakage current is further increased by switching the operation method of the inverter circuit. Therefore, it is preferable to improve the reliability of the photovoltaic power generation system by preventing the malfunction of the earth leakage circuit breaker and the like and improving the power conversion efficiency.
[0014]
In the above case, preferably, the inverter circuit has a full bridge circuit configuration including a plurality of switch elements, and each switch element is switched in response to a control input of the control circuit.
[0015]
In the above case, it is preferable that the control circuit switches and controls at least the inverter circuit between an operation method using a solar cell-ground voltage as a DC voltage and an operation method using an AC voltage.
[0016]
The photovoltaic power generation system of the present invention includes 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 that of the system and supplies the AC power to the system power supply. NA is a detection circuit that detects a leakage current between the solar battery and the ground, an inverter circuit that converts the DC power of the solar battery into AC power, and controls the operation of the inverter circuit. And a control circuit for switching and controlling the operation method of the inverter circuit to a plurality according to the detection of the above.
[0017]
According to the system of the present invention, since the inverter can switch the operation method of the internal inverter circuit according to the detection of the leakage current, the operation method is, for example, a single switching method having excellent power conversion efficiency when the leakage current is small. When the leakage current is large, for example, the double switching system can prevent malfunction of the earth leakage breaker and the like, thereby providing a highly reliable system.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, details of the present invention will be described based on embodiments shown in the drawings.
[0019]
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. 4 is a timing chart in the case of the double switching system of the inverter circuit, FIG. 5 is a diagram showing the power conversion efficiency of both systems, and FIG. 6 is a control of the control circuit. It is an operation | movement flowchart.
[0020]
Referring to FIG. 1, a power conditioner 1 is connected between a solar cell 2 and a system power supply 4 via a leakage breaker 3 via a pair of power wires 5 and 6.
[0021]
The solar cell 2 functions as a DC power source, and the solar cell may be of any type as long as this embodiment is applied.
[0022]
The earth leakage breaker 3 does not perform a breaking operation when a current having a different direction flows from one of the wires 5 or 6 to the other of the wires 5 or 6, but the current flows in the same direction in these wires 5 and 6. When the current flows and the magnitude of the current exceeds a predetermined value, it is assumed that there is a leakage, and an interruption operation is performed.
[0023]
The system power supply 4 is a 100 / 200V single-phase three-wire system.
[0024]
The power conditioner 1 converts DC power from the solar battery 2 into AC power synchronized with the system power supply 3, and a DC input unit (+) (−) for inputting DC power from the solar battery 2. ) And an AC output unit 12 that outputs AC power, and includes a zero-phase current transformer (CT) 11, an inverter circuit 12 for grid connection, a grid relay 13, and a control circuit 14.
[0025]
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 leakage breaker 3.
[0026]
The zero-phase current transformer 11 detects, as a leakage current detection circuit, a current flowing from the power wirings 5 and 6 to the ground via the stray capacitance C0 between the solar battery and the ground as a leakage current I0. The leakage current I0 is AC when the switching method in the inverter circuit 12 is the single switching method, and is DC when the switching method is the double switching method. However, the AC leakage current in the double switching method is very small compared to that in the single switching method.
[0027]
As shown in FIG. 2, the inverter circuit 12 has input parts IN1 and IN2 and output parts OUT1 and OUT2, and the DC voltage of the solar cell 2 is between the input parts IN1 and IN2 and the output parts OUT1 and OUT2. A booster circuit unit 12a that boosts the voltage to a constant DC voltage, a switch circuit unit 12b that converts DC power from the booster circuit unit 12a into AC power synchronized with the system power supply 4, and a filter circuit unit 12c. I have.
[0028]
In the inverter circuit 12, the switch elements S <b> 1 to S <b> 5 of the booster circuit unit 12 a and the switch circuit unit 12 b 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. As this transistor, there are a bipolar transistor and an IGBT, and a GTO thyristor may be used instead of the transistor.
[0029]
The booster circuit unit 12a includes a reactor L1, a diode D1, capacitors C1 and C2, and a switch element S1, and boosts the DC voltage of the solar cell 2 to a constant voltage of about 350V, for example.
[0030]
The switch circuit unit 12b is composed of four switch elements S2 to S5 having a full bridge circuit configuration, and is switched by a high-frequency PWM system that controls the output by changing the pulse width, and the DC circuit from the boost circuit unit 12a. The voltage 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 the frequency control and the output voltage control are performed simultaneously. However, other methods, for example, a current control type or a voltage control type may be used. In short, in each method, any operation method may be used as long as each switch element S2 to S5 can be driven and controlled by a single switching method or a double switching method.
[0031]
In the inverter circuit 12, the operation timing waveform of the single switching system is shown in FIG. 3, and the operation timing waveform of the double switching system is shown in FIG.
[0032]
3 and 4, (a) is an output voltage waveform on the power wiring 5 side of the inverter circuit 12, (b) is an output voltage waveform on the power wiring 6 side, (c) is an ON / OFF waveform of the switch element S2, ( (d) is the ON / OFF waveform of the switch element S3, (e) is the ON / OFF waveform of the switch element S3, (f) is the ON / OFF waveform of the switch element S5, and (g) is the voltage waveform between the solar cell and the ground. Show.
[0033]
Since this operation is well known, detailed description thereof will be omitted. However, in the case of the single switching system of FIG. In the PWM control, the output unit OUT1 outputs a positive sine wave voltage, the output unit OUT2 outputs a negative sine wave voltage, and vice versa.
[0034]
In the case of the double switching system shown in FIG. 4, in the A section, the switch elements S2 and S5 are combined to match the ON / OFF cycle, and the switch elements S3 and S4 are combined to match the ON / OFF cycle. However, 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 cycles of both the combinations are reversed, and vice versa in the B section.
[0035]
According to such PWM control, in the case of the single switching method, as shown in FIG. 3 (g), the voltage between the solar cell and the ground becomes an AC waveform, and in the case of the double switching method, it is shown in FIG. 4 (g). As described above, the voltage between the solar cell and the ground has a DC waveform.
[0036]
In the case of the single switching system and the double switching system described above, the power conversion efficiency is as shown in FIG. In FIG. 5, the horizontal axis indicates output (kW), 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% superior to that of the double switching system.
[0037]
The filter circuit unit 12c includes two coils L0 and a capacitor C0, and converts the rectangular wave AC voltage from the switch circuit unit 12b into a sinusoidal AC voltage.
[0038]
The control circuit 14 has a built-in microcomputer and performs input control of control inputs for turning on and off the switch elements S1 to S5 of the inverter circuit 12, and is shown in the operation flow of FIG. As described above, the leakage current I0 is determined based on the output of the zero-phase current transformer 11, and based on the determination result, a plurality of operation methods of the inverter circuit 12 are controlled, and in this embodiment, switching control is performed between the single switching method and the double switching method. It is supposed to be.
[0039]
That is, the control circuit 14 detects that the detected current is a predetermined value I0 with respect to the input of the current detection (S2) in the power wirings 5 and 6 from the output of the zero-phase current transformer 11 during the grid connection operation (S1). If it is determined whether or not the predetermined value I0 is exceeded, the leakage current is large, so that the operation method of the inverter circuit 12 is switched to the double switching method to suppress it (S4). If it is determined that the value is less than I0, the leakage current is small, so that the operation method of the inverter circuit 12 is controlled to be switched to the single switching method with excellent power conversion efficiency (S5).
[0040]
Note that the output of the zero-phase current transformer 11 is an AC waveform in the case of the single switching system and a DC waveform in the case of the double switching system, but the magnitude of the leakage current is large in the AC waveform of the single switching system, Since the AC waveform of the double switching method is small, the determination in S3 can be made by comparing the AC waveform in the control circuit 14 in magnitude.
[0041]
The present invention is not limited to the above-described embodiment, and various applications and modifications are possible.
[0042]
(1) The system power supply 4 of the present embodiment is a single-phase three-wire system in the present embodiment, but the present invention is not limited to this, and may be, for example, a single-phase two-wire system, Other wire methods such as a three-phase three-wire method may be used. Note that the inverter circuit in the case of a single-phase output phase has a full-bridge circuit configuration of four transistors, and the inverter circuit in the case of a three-phase has a full-bridge circuit configuration of six transistors.
[0043]
(2) In the above-described embodiment, the switching of the operation method of the inverter circuit 12 is two types, that is, the single switching method and the double switching method. However, the present invention is not limited to this, and more than one type is available. The operation method may be switched.
[0044]
(3) In the above-described embodiment, the leakage current is detected by arranging an earth leakage breaker on the front side of the inverter circuit 12. However, the present invention is not limited to this, and the leakage current is detected on the rear side of the inverter circuit 12. May be arranged to detect the leakage current.
[0045]
(4) In the above-described embodiment, the inverter circuit is controlled by PWM control. However, the present invention is not limited to this, and other control methods may be used.
[0046]
(5) In the above-described embodiment, the present invention is applied to a grid-connected photovoltaic power generation system of some form that is connected to a distribution line of an electric power company, but it is also applied to a photovoltaic power generation system that is independent of the system. be able to.
[0047]
(6) In the above-described embodiment, the inverter circuit converts DC power into AC power having a commercial frequency, but includes a case where it is converted into AC power having an arbitrary frequency.
[0048]
【The invention's effect】
As described above, according to the present invention, the operation method of the inverter circuit can be switched to a plurality of types according to the detection of the leakage current, so that the operation method is, for example, a single switching method having excellent power conversion efficiency when the leakage current is small, When the leakage current is large, for example, a double switching system can prevent malfunction such as an earth leakage breaker, and as a result, it is possible to prevent malfunction and at the same time, the overall power conversion efficiency can be made higher than that of 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 system of an inverter circuit. FIG. 5 is a diagram showing the power conversion efficiency of the both types. FIG. 6 is a control operation flow diagram of the control circuit.
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 Booster circuit part 12b Switch circuit part 14 Control circuit

Claims (5)

A transformer-less power conditioner for converting DC power of a solar cell into AC power having a predetermined frequency, a detection circuit for leakage current, an inverter circuit for converting DC power into AC power, and an operation method of the inverter circuit A power conditioner comprising: a control circuit that performs switching control in accordance with a detection result of the leakage current and a power conversion efficiency.   A transformer-less power conditioner that converts the DC power of the solar cell into AC power of the same commercial frequency as that of the system and supplies it to the system power supply, and a detection circuit that detects a leakage current between the solar cell and the ground, An inverter circuit that converts direct current power into alternating current power, and a control circuit that controls the operation of the inverter circuit, and that switches and controls the operation method of the inverter circuit to a plurality in accordance with detection of the leakage current. A power conditioner characterized by comprising.   The power conditioner according to claim 1 or 2, wherein the inverter circuit has a full bridge circuit configuration by a plurality of switch elements, and each switch element is switched in response to a control input of the control circuit. A power conditioner characterized by that.   3. The power conditioner according to claim 2, wherein the control circuit switches and controls at least the inverter circuit between an operation method using a solar cell-ground voltage as a DC voltage and an operation method using an AC voltage. Power conditioner characterized by   A solar cell, and a transformer-less power conditioner that converts the DC power of the solar cell into AC power having the same commercial frequency as that of the system and supplies the power to a system power supply. The power conditioner is a solar cell-grounding A detection circuit for detecting a leakage current between the inverter circuit, an inverter circuit for converting the DC power of the solar cell into an AC power, and an operation of the inverter circuit, wherein the inverter is detected in response to the detection of the leakage current. And a control circuit for switching and controlling a plurality of operation modes of the circuit.

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