JP2001060121A - Maximum power control method for solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly accurately judge whether output power is increasing or decreasing to the changing direction of a reference operating point by judging that the output power from a solar battery is decreasing in the case that the phases of the fluctuating waveform of the output power from the solar battery and the fluctuating waveform of the reference operating point are different. SOLUTION: In a maximum power control circuit 23, by superimposing fine fluctuation oscillated from an oscillator 26, the reference operating point is changed for a fixed amplitude at a preset fixed frequency. Then, by comparing the fluctuation waveform of the output power and the fluctuation waveform of the reference operating point, whether the output power is increasing or decreasing is judged. That is, by utilizing the fact that the phases are different between the fluctuating waveform of the reference operating point and the fluctuating waveform of the output power in an area on the left side of maximum output and the area on the right side in the output voltage - output power curve of the solar battery 10, whether the output power is increasing or decreasing is judged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the maximum power of a solar cell by using the solar cell as a power source and efficiently extracting the maximum power from the solar cell via a power converter composed of an inverter or the like. It is.

[0002]

2. Description of the Related Art In recent years, a power supply device that uses a solar cell as a power supply and supplies a predetermined power via a power conversion device such as an inverter has attracted attention. When the amount of solar radiation incident on the solar cell is used as a parameter, the solar cell has a tendency that power increases with an increase in the amount of solar radiation, and the output power greatly varies depending on the operating point of the solar cell. Has characteristics.

In order to efficiently extract the maximum power from a solar cell having such characteristics, Japanese Patent Laid-Open Publication No.
Japanese Patent Publication No. 29 and the like propose a maximum power point tracking control called a hill-climbing method. In this case, when the solar cell has a voltage-power characteristic as shown in FIG. 2 under a certain amount of solar radiation, first, the reference operating voltage of the output voltage of the solar cell is set to the open-circuit voltage VOP. From a predetermined sampling cycle with a constant change width ΔVS. During this time, the power increases in the direction of arrow a in the figure. Then
The power decreases beyond the maximum power point P in the direction of arrow c. When this decrease in power is detected, the reference operating voltage is increased by a change width ΔVS. As a result, the power increases in the direction of the arrow d in the figure, and eventually exceeds the maximum power point P to the direction of the arrow b.
Begin to decrease in the direction. Therefore, the decrease in the power is detected, and the reference operating voltage is changed again in the direction of decreasing the change width ΔVS. By repeating the above operation, the reference operating voltage is reciprocated near the maximum power point P, and the maximum power point of the solar cell is always followed.

[0004]

However, according to the above-mentioned conventional method, it is determined whether the output power from the solar cell is increasing or decreasing with respect to the change in the reference operating voltage at the time of the previous sampling. Since this is performed by comparing the output power with the newly sampled output power, if sudden noise occurs during the comparison, there is a problem that it is not possible to accurately determine whether the output power is increasing or decreasing. Was.

The present invention has been made in view of the above problems, and has as its object to determine whether the output power is increasing or decreasing with respect to the changing direction of the reference operating point. It is an object of the present invention to provide a method for controlling the maximum power of a solar cell, which is capable of judging accurately.

[0006]

According to the first aspect of the present invention,
In the method of controlling the output power taken from the solar cell through the power converter to the maximum power, when changing the reference operating point given to the solar cell, the reference operating point is set to a predetermined frequency and a predetermined amplitude. If the output power fluctuation waveform is the same as the fluctuation waveform of the reference operating point when it is changed, it is determined that the output power from the solar cell is in the increasing direction, and the fluctuation waveform of the output power and the reference operation point In the case where the phase is different from the fluctuation waveform, it is determined that the output power from the solar cell is in the decreasing direction.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a maximum power control method for a solar cell according to one embodiment of the present invention will be described in detail with reference to FIGS.

FIG. 1 shows an example of an apparatus for extracting maximum power from a solar cell. 10 is a solar cell, 11 is an inverter,
13 is a commercial power system, 21 is a current detector, 22 is a voltage detector, 23 is a maximum power control circuit, 24 is an error amplifier,
5 is a current control circuit and 26 is an oscillator.

The DC output of the solar cell 10 is
And is connected to the commercial power system 13 via a protective relay or the like. The output current and output voltage of the solar cell 10 are detected by a current detector 21 and a voltage detector 22, and the detected values are input to a maximum power control circuit 23. The maximum power control circuit 23 outputs a current command value based on the input value. The current command value is the current detector 21
Is compared with the value detected by the above, and the deviation is amplified by the error amplifier 24 and input to the current control circuit 25.
The current control circuit 25 controls the phase of the inverter 11 according to the deviation from the error amplifier 24 so that the deviation becomes zero. As a result, the solar cell 10 is controlled at a desired reference operating voltage.

The operation of the maximum power control circuit 23 will now be described with reference to FIG. The solar cell 10 has characteristics as shown in FIG. 2 at a certain amount of solar radiation and temperature, and it is ideal that the solar cell 10 is operated at the maximum power point P.

In the maximum power control circuit 23, first,
The operating point voltage of the solar cell is set to be the open circuit voltage VOP. Then, the reference operating voltage is reduced at a constant change width in a predetermined sampling cycle. At this time, the output power increases in the direction of arrow a. If the reference operating voltage continues to decrease as it is, the power exceeds the maximum power P,
The decrease starts as indicated by arrow C. In the present embodiment, in the maximum power control circuit 23, the reference operating point is changed by a constant amplitude at a preset constant frequency by superimposing a minute fluctuation oscillated from the oscillator 26.
Then, by comparing the fluctuation waveform of the output power with the fluctuation waveform of the reference operating point, it is determined whether the output power is increasing or decreasing. That is, as shown in FIG. 3, in the output voltage-output power curve of the solar cell 10,
From the maximum output P, in the left region I and the right region II,
Using the fact that the phase of the fluctuation waveform of the reference operating point differs from the phase of the fluctuation waveform of the output power, it is determined whether the output power is increasing or decreasing.

For example, in a region II on the right side of the maximum output P, the output power increases in response to a change in the reference operating voltage, but the fluctuation waveform of the reference operation voltage and the fluctuation waveform of the output power have the same phase. Becomes In a region I on the left side of the maximum output P, the output power is decreasing with respect to the change in the reference operating voltage, but the phase of the fluctuation waveform of the reference operation voltage is different from the phase of the fluctuation waveform of the output power.

According to the above-described criterion, it is possible to easily determine whether the output power is in the increasing direction or the decreasing direction without comparing the sampled output power. It is possible to accurately determine whether the output power is in the increasing direction or in the decreasing direction even if a periodic noise occurs.

If it is determined that the output power has started decreasing as shown by the arrow c, the reference operating voltage is moved in a direction to increase by a certain width. When the reference operating voltage is continuously increased, the output power increases as indicated by an arrow d, and starts to decrease as indicated by an arrow b. Therefore, this decrease is detected based on the above-mentioned judgment criterion, and the reference operating voltage is changed again in the direction of decreasing.

By repeating the above operation, the reference operating voltage comes close to the maximum power P. In addition, in order to enhance the following of the reference operating voltage near the maximum output P, the above-described change width may be changed according to the amount of change of the solar cell 10 caused by the change in the reference operating voltage.

[0016]

As described above, according to the first aspect of the present invention, in the method of controlling the output power taken out of the solar cell via the power converter to the maximum power, the reference operation given to the solar cell When changing the point, if the reference operating point is changed by a constant amplitude at a preset constant frequency, if the phase of the fluctuation waveform of the output power and the fluctuation waveform of the reference operation point are the same, the It is determined that the output power of the solar cell is in the increasing direction, and when the phase of the fluctuation waveform of the output power is different from the phase of the fluctuation waveform of the reference operating point, the output power from the solar cell is determined to be in the decreasing direction. It is not necessary to perform an operation of accurately sampling and comparing the output power, and the output power increases in the direction of change of the reference operating point only by comparing the phases of the reference operating point and the fluctuation waveform of the output power. It is possible to determine whether a downward direction or in a direction, an effect that it is possible to perform the maximum power control accurately the solar cell.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a device that extracts maximum power from a solar cell.

FIG. 2 is a characteristic diagram of a solar cell showing a maximum power control method.

FIG. 3 is a characteristic diagram of a solar cell illustrating a criterion for determining whether the output power of the solar cell is increasing or decreasing with respect to a change in a reference operating point.

[Explanation of symbols]

 Reference Signs List 10 solar cell 11 inverter 13 commercial power system 21 current detector 22 voltage detector 23 maximum power control circuit 24 error amplifier 25 current control circuit 26 oscillator

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Akira Yoshitake, Inventor 1048 Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Works, Ltd. 72) Inventor Hiroyuki Ohno 1048 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Works, Ltd. 5H420 BB14 CC03 DD03 EB39 FF03 FF04 FF22 GG01 GG04 KK10

Claims (1)

[Claims] 1. A method for controlling output power taken from a solar cell via a power converter to a maximum power,
When changing the reference operating point given to the solar cell,
When the reference operating point is changed by a constant amplitude at a preset constant frequency, when the phase of the fluctuation waveform of the output power and the phase of the fluctuation waveform of the reference operation point are the same, the output power from the solar cell is in the increasing direction. When the fluctuation waveform of the output power and the fluctuation waveform of the reference operating point have different phases, the maximum power of the solar cell is characterized in that the output power from the solar cell is determined to be in the decreasing direction. Power control method.