JPH09135571A - Power converter for photovoltaic power generation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high efficiency power converter which facilitates the suppression of the voltage rise of a smoothing capacitor and the stable operation. SOLUTION: A power converter includes a stepup chopper 2 to which a DC voltage generated by a solar cell 1 is inputted, a smoothing capacitor 4 which is connected to the output of the stepup chopper 2 and an inverter 5 to which a DC voltage from the smoothing capacitor 4 is inputted and whose output is connected to a system. The DC voltage of the smoothing capacitor 4 is controlled by the control of the converted power of the inverter 5. The input voltage of the stepup chopper 2 is so controlled as to be a predetermined value beforehand by referring to the voltage of the smoothing capacitor 4 by feed-forward control to suppress the voltage rise of the smoothing capacitor 4 and prevent the decline of the conversion efficiency of the inverter 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar power generation power converter for converting DC power generated by a solar cell into AC power and supplying the AC power to a grid.

[0002]

2. Description of the Related Art When a power converter having no internal transformer is applied to a solar power generation system that is interconnected with a grid, the DC power generation voltage of a solar cell is generally lower than the peak value of the grid voltage. Since there are many, a booster of some kind is required in the power converter, and a booster chopper is usually used.

FIG. 4 shows an example of such a power conversion device. 1 is a solar cell, 2 is a boost chopper control circuit, 3 is a boost chopper control circuit, 4 is a smoothing capacitor, 5 is an inverter, and 6 is an inverter. The control circuit 7 is a system.
In FIG. 4, the solar cell 1 has an optimum voltage at which the generated electric power becomes maximum, and in order to efficiently take out the electric power from the solar cell 1, the DC voltage of the solar cell 1 is changed to a state such as temperature and solar radiation. It needs to be changed accordingly. In the conventional power converter shown in FIG. 4, in order to do this, the control circuit 3 of the boost chopper controls the input voltage of the boost chopper 2 so that the output power of the inverter 5 is always maximized.

[0004]

In such a power converter, the input voltage control of the step-up chopper 2 and the inverter 5 are performed.
Since the power control is separately performed, the control circuit has a complicated configuration, and the control of the both interferes with each other, which may cause unstable operation of the power conversion device.

As one of the methods for avoiding this problem, there is a method in which the boost chopper 2 is uncontrolled and the voltage of the smoothing capacitor 4 is controlled by the inverter 5. According to this method, since the boosting ratio of the boosting chopper 2 is fixed, the input voltage of the boosting chopper 2 can be indirectly controlled to the optimum voltage by controlling the voltage of the smoothing capacitor 4. In this case, since the boost chopper 2 is not controlled, the unstable operation as described above does not occur.

However, since the boosting ratio of the boosting chopper 2 is fixed, there arises a problem that the voltage of the smoothing capacitor 4 becomes very high when the output voltage of the solar cell 1 is high. For example, the minimum value of the optimum voltage of the solar cell 1 is 160
Assuming that the maximum value of V and the open circuit voltage is 340V and the voltage of the smoothing capacitor 4 is controlled to 320V which is necessary for the AC 200V interconnection, the required boosting ratio is the minimum value of the optimum voltage and the voltage of the smoothing capacitor 4. Although it is doubled from the relationship, the input voltage is the maximum value of the open circuit voltage with this boost ratio.
When it becomes 0V, the voltage of the smoothing capacitor 4 is 680
It will rise to V. It is necessary to use the smoothing capacitor 4 and the conversion element of the inverter 5 that can withstand this voltage. However, in general, these are not only large and expensive, but the loss increases due to switching of a high voltage, and There is a drawback that the conversion efficiency is significantly reduced.

An object of the present invention is to provide a high-efficiency power converter for photovoltaic power generation, which can suppress the voltage rise of the smoothing capacitor 4 and operates stably.

[0008]

In order to achieve the above-mentioned object, according to the present invention, a step-up chopper having a DC voltage generated by a solar cell as an input voltage, a smoothing capacitor connected to the output of the step-up chopper, and a smoothing capacitor In a power conversion device for photovoltaic power generation that includes a DC voltage of a capacitor as an input voltage and an inverter whose output is connected to a grid, the DC voltage of a smoothing capacitor is controlled by controlling the conversion power of the inverter, and the input of a boost chopper is controlled. The voltage control is performed by referring to the voltage of the smoothing capacitor so that the feedforward control is performed so that the voltage becomes a preset value.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the power converter for photovoltaic power generation according to the present invention, the DC voltage of the smoothing capacitor is controlled by controlling the converted power of the inverter, and the input voltage of the step-up chopper is controlled by the voltage of the smoothing capacitor. By referring to, the feedforward control is performed so that the value becomes a preset value, the voltage rise of the smoothing capacitor is suppressed, and the conversion efficiency of the inverter is prevented from lowering.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a power conversion device embodying the present invention. Components common to those in FIG. In FIG. 1, reference numeral 8 is a data table that stores the relationship between the voltage of the smoothing capacitor 4 and the input voltage of the boost chopper 2, that is, the boost ratio. FIG. 2 is a graph showing the relationship between the voltages stored in the data table 8. In this embodiment, the inverter 5 controls the voltage of the smoothing capacitor 4 according to the output power. The control circuit 3 of the step-up chopper refers to the voltage of the smoothing capacitor 4 and controls the input voltage of the step-up chopper 2 so as to have the relationship shown in FIG.

According to the voltage relationship of FIG. 2, since the input voltage is 160 V when the voltage of the smoothing capacitor 4 is 320 V, the step-up ratio at this time is 2 times, and the input voltage when the voltage of the smoothing capacitor 4 is 410 V. Is 340V,
The boost ratio at this time is about 1.2 times. That is, the control circuit 3 of the step-up chopper changes the step-up ratio according to the voltage of the smoothing capacitor 4, so that the input voltage of the step-up chopper 2 is as shown in FIG.
Feedforward control is performed so that the relationship shown in (1) is established.

With this control, even if the input voltage of the boost chopper 2 is 340V, the voltage of the smoothing capacitor 4 can be suppressed to about 410V.
It is not necessary to use high voltage capacitors for the smoothing capacitor 4 and the converter 5. Further, since the relationship between the voltage of the smoothing capacitor 4 and the input voltage of the boost chopper 2 is a linear relationship as shown in FIG. 2, if the voltage of the smoothing capacitor 4 is controlled, the input voltage of the boost chopper 2 can be controlled and the solar cell 1 Can be operated at the optimum voltage.

Further, since the input voltage of the step-up chopper 2 is uniquely determined by the voltage of the smoothing capacitor 4, there is no interference between the control of the step-up chopper 2 and the inverter 5, and the power converter can be operated stably. Further, the control circuit 3 of the step-up chopper only needs to output the step-up ratio by the data table 8 according to the voltage of the smoothing capacitor 4, and the configuration thereof is very simple.

According to FIG. 2, the ratio of the change in the input voltage of the boost chopper 2 to the change in the voltage of the smoothing capacitor 4 is double, but within the range that does not hinder the tracking of the optimum voltage of the solar cell 1. If the rate of change is increased, the voltage rise of the smoothing capacitor 4 can be further suppressed.

Further, the voltage relation of the data table is changed as shown in FIG. 3, and while the input voltage of the step-up chopper 2 is at the optimum voltage of the solar cell 1, the rate of change remains double.
If the voltage is higher than 10 times, the voltage increase of the smoothing capacitor 4 can be more effectively suppressed without affecting the tracking of the optimum voltage.

[0016]

As described above, according to the present invention, the DC voltage of the smoothing capacitor is controlled by controlling the conversion power of the inverter, and the voltage of the smoothing capacitor is referred to for controlling the input voltage of the boost chopper. As a result, the feedforward control is performed so that the value becomes a preset value, so even if the input voltage of the boost chopper rises, the voltage rise of the smoothing capacitor can be suppressed, and the smoothing capacitor and the conversion element of the inverter can be suppressed. In addition to being able to reduce the withstand voltage of, it is possible to prevent the efficiency of the inverter from decreasing.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an example of a relationship between a voltage of a smoothing capacitor and an input voltage of a boost chopper.

FIG. 3 is a diagram showing another example of the relationship between the voltage of the smoothing capacitor and the input voltage of the boost chopper.

FIG. 4 is a configuration diagram of a conventional power conversion device for photovoltaic power generation.

[Explanation of symbols]

 1 Solar cell 2 Step-up chopper 3 Control circuit for step-up chopper 4 Smoothing capacitor 5 Inverter 6 Inverter control circuit 7 System 8 Data table

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H02N 6/00 H02N 6/00

Claims (1)

[Claims] 1. A step-up chopper having a DC voltage generated by a solar cell as an input voltage, a smoothing capacitor connected to an output of the step-up chopper, and a DC voltage of the smoothing capacitor as an input voltage, and an output connected to a grid. In a power conversion device for photovoltaic power generation including an inverter, the DC voltage of the smoothing capacitor is controlled by controlling the converted power of the inverter, and the input voltage of the boost chopper is controlled by referring to the voltage of the smoothing capacitor. By doing so, the feed-forward control is performed so that the value becomes a preset value.