JP5755418B2 - Solar power system - Google Patents

Description

  The present invention includes a solar cell having a high output voltage at no load, such as a thin film system or a compound semiconductor system, and a low withstand voltage type converter that converts output power from the solar cell, and outputs the solar cell in the converter. The present invention relates to a photovoltaic power generation system that performs so-called MPPT (maximum power point tracking) control, and in particular, a high output voltage when the solar cell is unloaded in the photovoltaic power generation system is a low withstand voltage converter. It is related to restricting being applied to.

Solar cells are used in various ways such as lighting systems or interconnection systems with commercial power systems. The power generation output of the solar cell is converted by a converter (such as a DC / DC converter or a DC / AC inverter) and supplied to a load. The output characteristics of solar cells vary depending on temperature, illuminance, and the like. Therefore, in a photovoltaic power generation system, MPPT control is generally performed by the converter. This will be described with reference to FIG. 3. 1 is a solar cell, 2 is a power conditioner, 3 is a load, 4 is a commercial power source, and the power conditioner 2 indicates the output current and output voltage of the solar cell 1. A detection circuit 2a for detecting, a converter (including a DC / DC converter and a DC / AC inverter) 2b, and a controller 2c. The controller 2c controls the converter 2b based on the output of the detection circuit 2a to So-called MPPT (maximum power point tracking) control is performed to control the operating point to a substantially optimal operating point (for example, the output voltage Vp is controlled so that the solar cell 1 can output the maximum power) (see Patent Document 1). . Since the operation of MPPT control is well known, its description is omitted. FIG. 4A shows the temperature dependence of the solar cell 1, and FIG. 4B shows the illuminance dependence of the solar cell 1. 4A, for example, the optimum operating point is Pp (output voltage Vp, output current Ip) at a temperature of 25 ° C., and the optimum operating point is Pp (output voltage Vp) at an illuminance of 1000 W / m ² in FIG. , Output current Ip). For this reason, the optimum operating point varies with temperature and illuminance.

JP 2004-336842 A

  In recent years, low-cost solar cells such as thin film systems and compound semiconductor systems are being used in such solar cells. Although this type of solar cell is inexpensive, the output voltage at no load (output at no load) (Voltage) is high. The no-load output voltage is an output voltage when the output current Ip is 0 in FIG. On the other hand, converters having improved power conversion efficiency using low-voltage power MOSFETs have been used. Therefore, it is difficult to construct a solar power generation system by combining the above-described solar cell having a high output voltage at no load and a low withstand voltage converter.

  Therefore, the present invention provides a solar power generation system that can combine a low-cost solar cell and a converter with excellent power conversion efficiency, and is inexpensive as a whole system and excellent in the power usage rate of the solar cell. Is a problem to be solved.

  A photovoltaic power generation system according to the present invention includes a solar cell, a converter that converts the output voltage of the solar cell, and a converter that performs a conversion operation of the converter so as to control the operating point of the solar cell to a substantially optimal operating point with respect to the converter. In a photovoltaic power generation system comprising a controller for controlling, when the output voltage of the solar cell exceeds the withstand voltage input voltage of the converter, the input voltage input from the solar cell to the converter is input to the withstand voltage input of the converter. An input voltage limiting circuit for limiting the voltage to a voltage equal to or lower than the voltage is provided.

  Preferably, by connecting the input voltage limiting circuit in series with the input terminal of the converter, the input voltage limiting circuit bears a voltage component exceeding the withstand voltage input voltage of the converter among the output voltage of the solar cell. It is to be.

  Preferably, the input voltage limit circuit includes an input voltage detection circuit that detects an input voltage to the converter, a control circuit that controls the input voltage limit circuit based on a detection output of the input voltage detection circuit, and the control A delay circuit for delaying a control operation of the circuit.

  An input voltage limiting circuit to a converter according to the present invention controls a solar cell, a converter that converts an input voltage input from the solar cell, and the conversion operation in the converter so that the solar cell operates at a substantially optimum operating point. And an input voltage limiting circuit used in a photovoltaic power generation system comprising: a controller that converts the input voltage to the converter even when the output voltage of the solar cell exceeds the withstand voltage input voltage of the converter. It is characterized in that it is configured to be limited to a withstand voltage input voltage of or lower than this.

  According to the present invention, a photovoltaic power generation system is constructed by combining a solar cell with a low cost such as a thin film system or a compound semiconductor system but a high output voltage at no load and a converter with excellent power conversion efficiency but low withstand voltage. However, even if the output voltage of the solar cell at no load increases, an output voltage exceeding the withstand voltage input voltage is not applied to the converter as the input voltage. It has become possible to provide a solar power generation system with excellent power utilization.

FIG. 1 is a diagram showing a configuration of a photovoltaic power generation system according to an embodiment of the present invention. FIG. 2 is a diagram showing a circuit configuration of the input voltage limiting circuit in the system shown in FIG. FIG. 3 is a diagram showing a configuration of a conventional photovoltaic power generation system. FIG. 4 is a diagram illustrating an example of output characteristics of the solar cell.

  Hereinafter, an input voltage limiting circuit for limiting an input voltage to a converter that converts a solar cell output according to an embodiment of the present invention and a solar power generation system including the same will be described with reference to the accompanying drawings. With reference to FIG. 1, 1 is a solar cell, 2 is a power conditioner, 3 is a load, 4 is a commercial power source.

  The power conditioner 2 includes a detection circuit 2a that detects an output current and output voltage of the solar cell 1, a converter (including a DC / DC converter 2b1, a DC / AC inverter 2b2) 2b, and a controller 2c. MPPT control is performed to control the converter 2b based on the output of the detection circuit 2a to control the operating point of the solar cell 1 to a substantially optimal operating point.

  Here, the solar cell 1 is a solar cell with a low cost such as a thin film system or a compound semiconductor system but with a high output voltage at no load. The DC / DC converter 2b1 in the converter 2b has a low input voltage with a low withstand voltage. This is a withstand voltage input voltage type DC / DC converter, which converts the direct current input voltage of the solar cell 1 into a direct current output voltage. Further, the DC / AC inverter 2b2 in the converter 2b can convert the DC input voltage input from the DC / DC converter 2b1 into an AC output voltage and supply it to the load 3.

  The present embodiment is characterized in that the power conditioner 2 includes an input voltage limiting circuit 2d as described in detail below. That is, the input voltage limiting circuit 2d receives the input voltage Vp between the input terminals IN1 and IN2 of the DC / DC converter 2b1 as the input voltage Vp. Even if the solar cell 1 becomes unloaded and the high voltage fluctuates beyond the withstand voltage input voltage Vlimit of the DC / DC converter 2b1, the input voltage Vd to the DC / DC converter 2b1 is reduced to the withstand voltage input voltage Vlimit or less. It is a circuit to limit.

  Specifically, for example, when the withstand voltage input voltage Vlimit of the DC / DC converter 2b1 is 380V, the output voltage Vp at the time of no load is 500V between the pair of positive and negative output terminals OUT1 and OUT2 of the solar cell 1. When the input voltage Vd is to be applied as the input voltage Vd, the input voltage limiting circuit 2d bears 120V of the output voltage Vp = 500V as the burden voltage Vc, so that the pair of input terminals of the DC / DC converter 2b1 Limiting control is performed between IN1 and IN2 so that a voltage of 380 V or more, which is the withstand voltage input voltage Vlimit, is not applied as the input voltage Vd.

  Hereinafter, the input voltage limiting circuit 2d will be described with reference to FIG.

  The input voltage limiting circuit 2d includes an input voltage detection unit 10, a burden voltage calculation unit 11, a reference voltage unit 12, a delay unit 13, a ground fault detection unit 14, an excess voltage load unit 15, a temperature detection unit 16, and a lightning protection unit 17. The solar cell unsafe voltage protector 18 is included.

  The input voltage detection unit 10 is connected in parallel between the pair of input terminals IN1 and IN2 of the DC / DC converter 2b1 and detects the voltage between the input terminals IN1 and IN2. For example, the input voltage detection unit 10 uses a differential amplifier circuit as shown in the figure. It is configured. The input voltage detection unit 10 outputs a voltage having a level corresponding to a value 1/100 of the voltage Vd between the input terminals IN1 and IN2 as a detection voltage. On the other hand, the reference voltage unit 12 outputs a voltage having a level corresponding to 1/100 of the withstand voltage input voltage Vlimit of the DC / DC converter 2b1 as a reference voltage. Of course, these numerical values are merely examples and do not limit the present invention.

  The burden voltage calculation unit 11 is configured by, for example, the differential amplifier circuit illustrated in the drawing, compares the detection voltage output from the input voltage detection unit 10 with the reference voltage of the reference voltage unit 12, and inputs the input voltage limiting circuit 2d. The voltage to be borne is calculated, and the calculation result is output to the excess voltage load unit 15 via the delay unit 13. In this case, for example, an output voltage Vp of 500 V is output as a voltage exceeding the withstand voltage input voltage Vlimit of the DC / DC converter 2b1 from the solar cell 1, and the withstand voltage input voltage Vlimit is set between the input terminals IN1 and IN2 of the DC / DC converter 2b1. When an excess voltage of 500 V is to be applied as the input voltage Vd, the input voltage detection unit 10 outputs 5V, which is 1/100 of the voltage, as the detection voltage, while the reference voltage unit 12 outputs the withstand voltage input voltage. Since the reference voltage of 3.8V corresponding to 380V which is Vlimit is output, the calculation output from the burden voltage calculation unit 11 is 1.2V (= 5V-3.8V) in this example, and the excess voltage burden The voltage to be borne by the unit 15 is outputted as a voltage signal of 120V. Thereby, the gate of each power MOSFET which comprises the excess voltage burden part 15 is controlled, and these parallel synthetic | combination resistance bears 120V. Thus, even if the output voltage Vp of the solar cell 1 exceeds the withstand voltage input voltage Vlimit of the DC / DC converter 2b1, a voltage exceeding the withstand voltage input voltage Vlimit is applied to the DC / DC converter 2b1 as the input voltage Vd. You do n’t have to.

  In this case, the calculation result in the burden voltage calculation unit 11 is not directly input to the excess voltage load unit 15 directly, but is delayed by an appropriate time delay, for example, 0 to several seconds, in the delay unit 13. Therefore, the response is adjusted so that the control system does not hunting by being input to the excess voltage burden unit 15. This is because the DC / DC converter 2b1 performs MPPT control on the solar cell 1, so that the input voltage Vd is likely to fluctuate. Therefore, if the fluctuation follows this fluctuation, the control system can follow the fluctuation. This is because hunting occurs as a result.

  As shown in the figure, the excess voltage burden unit 15 is configured by connecting a plurality of power MOSFETs in parallel, and a calculation result signal from the burden voltage calculation unit 11 is input to each of the gates via the delay unit 13. In the above example, a predetermined voltage Vc of the output voltage Vp is borne from the solar cell 1 by the combined parallel resistance of the drain-source resistance of each power MOSFET. In the above example, when an output voltage Vp of 500 V is output from the solar cell 1, a voltage Vc of 120 V out of the 500 V is applied to each gate of each power MOSFET that constitutes it so that the excess voltage load unit 15 bears it. The calculation result signal is applied, and a drain-source resistance corresponding to the burden of the voltage Vc of 120 V is generated.

  Thus, the excess voltage load unit 15 is connected in series to the DC / DC converter 2b1 in parallel to the solar cell 1 together with the DC / DC converter 2b1, so that the converter 2b1 of the no-load output voltage 500V of the solar cell 1 is obtained. Since the voltage 120V exceeding the withstand voltage input voltage 380V is borne, the input voltage to the converter 2b1 is limited not to exceed the withstand voltage 380V. The overvoltage loader 15 is connected in series to the input terminal IN2 of the DC / DC converter 2b1, but it can also be implemented in parallel with both the input terminals IN1 and IN2.

  The ground fault detection unit 14 detects that the cable connected to the solar cell 1 is exposed and so on and is short-circuited due to contact with the ground and the like, and outputs the detected output to a circuit (not shown) using the detection output. It is provided for this purpose. The temperature detection unit 16 detects the temperature so that the power MOSFETs constituting the excess voltage burden unit 15 are not damaged by heating, and when the temperature exceeds a predetermined temperature, a signal corresponding to the detected temperature is sent to the unsafe voltage protection unit 18. Is applied to the gate of the SCR (thyristor) shown in FIG. 2 to make the SCR conductive, and the overvoltage loader 15 is made inoperative. Further, the unsafe voltage protection unit 18 is provided with the Zener diode shown in the figure, and when the output voltage of the solar cell 1 exceeds 500 V, the solar cell 1 can be protected by conducting. It has become. Further, the solar cell 1 can be protected by the lightning protection circuit 17. Although illustration is omitted, a cooling device such as a cooling fan may be arranged.

  As described above, in the present embodiment, the DC / DC converter 2b1 is a DC / DC converter that controls the conversion operation so that the controller 2c controls the operation point of the solar cell 1 to a substantially optimal operation point. Since the input voltage limiting circuit 2d for limiting the input voltage Vd to the converter 2b1 to be equal to or lower than the withstand voltage input voltage Vlimit of the DC / DC converter 2b1 is provided, the solar cell 1 has low costs such as a thin film system and a compound semiconductor system, but no load While a solar cell with a high output voltage is used, the DC / DC converter 2b1 is excellent in power conversion efficiency but has a low withstand voltage. Since the output voltage exceeding the withstand voltage input voltage is not applied from the solar cell 1, the entire system is inexpensive. It is possible to provide an excellent photovoltaic system to the power utilization of the solar cell 1.

DESCRIPTION OF SYMBOLS 1 Solar cell 2 Power conditioner 2b Converter 2c Controller 2d Input voltage limiting circuit 3 Load 4 Commercial power supply

Claims (1)

A solar cell, a converter that converts an input voltage input from the solar cell, and a controller that controls the conversion operation of the converter so as to control the operating point of the solar cell to a substantially optimal operating point with respect to the converter. In the solar power system provided,
When the output voltage of the solar battery exceeds the withstand voltage input voltage of the converter, an input voltage limiting circuit that restricts the input voltage input from the solar battery to the converter to the withstand voltage input voltage of the converter or a voltage lower than the input voltage. Provided,
The input voltage limiting circuit is
An input voltage detection unit that detects an input voltage to the converter that fluctuates due to a change in the substantially optimal operating point;
A calculation unit that calculates an excess voltage that exceeds the withstand voltage input voltage based on the detection output of the input voltage detection unit , and
A voltage load unit formed by connecting a plurality of power MOSFETs in parallel, which bears the excess voltage according to the calculation result of the calculation unit, is connected between the converter and the solar cell,
Furthermore, the photovoltaic power generation system includes a delay unit that delays the calculation result of the calculation unit and inputs the result to the voltage load unit.

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