JP2003084844A - Method for controlling maximum power of solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly make a target operating voltage follow the maximum output operating voltage even if an amount of solar radiation reduces. SOLUTION: When varying the target operating voltage Vref by controlling a current command value, the target operating voltage Vrefk+1 is varied in response to a value ΔVrefk+1 obtained by dividing a difference between an output power Pok-1 , at the target operating voltage Vref determined last time and an output voltage Pok at the target operating voltage Vrefk-1 determined this time by the output Pok at the recent target operating voltage. As a result, a variation range becomes relatively small when varying the target operating voltage Vref as an output power Po approaches to the maximum power Pmax, the target operating voltage Vref can be quickly made to follow the maximum output operating voltage Vmax by suppressing variation of the target operating voltage Vref in the vicinity of the maximum power Pmax even if an amount of solar radiation reduces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention controls the maximum output operating voltage of a solar cell, which changes with the amount of solar radiation, and maximizes the output power obtained from the solar cell via a power conversion device. It relates to a control method.

[0002]

2. Description of the Related Art In recent years, a power supply device which uses a solar cell as a power supply and supplies a predetermined electric power through a power conversion device such as an inverter has attracted attention. In general, when the amount of incident solar radiation is used as a parameter, solar cells tend to increase in power as the amount of solar radiation increases, and also have the characteristic that the output power greatly changes depending on the operating voltage of the solar cell. is doing.

In order to efficiently extract the maximum power from the solar cell having such characteristics, a method of maximum output tracking control called a hill climbing method has been conventionally proposed.

In the above mountain climbing method, the solar cell is shown in curves A and B in FIG. 3 (curve B represents a large amount of solar radiation and curve B represents a small amount of solar radiation) under a constant amount of solar radiation. In the case of having such a voltage-power characteristic, first, the target operating voltage of the output voltage of the solar cell is decreased from the open circuit voltage V _{OP in a} predetermined sampling period with a constant change width. During this time, the output power of the solar cell increases to the left in FIG. 3, and eventually exceeds the maximum power Pmax and decreases. When this decrease in output power is detected, the target operating voltage is increased by the change width. As a result, the output power increases to the right in FIG. 3, and eventually exceeds the maximum power Pmax and begins to decrease. Therefore, the decrease in the electric power is detected, and the target operating voltage is changed again in the direction of decreasing the change width. By repeating the above operation, the target operating voltage is reciprocated in the vicinity of the operating voltage (maximum output operating voltage) Vmax at which the maximum electric power Pmax is obtained, and is made to follow the maximum output operating voltage Vmax of the solar cell. Note that the target operating voltage of the solar cell can be changed by changing the output current of the power converter, and the target operating voltage is changed by giving a current command value that commands the output current of the power converter to the power converter. I am letting you.

However, in the above-mentioned conventional method, when there is a difference between the target operating voltage and the actual operating voltage of the solar cell, the current command value of the power converter is controlled so that the difference becomes zero. However, regardless of the size of the difference, the current command value was controlled with a constant change width. Therefore, for example, when the difference between the actual operating voltage of the solar cell and the target operating voltage is large, there is a problem that it takes a long time to reach the target operating voltage.

On the other hand, the applicant of the present invention controls the current command value to be applied to the power converter to change the target operating voltage according to the difference between the output power of the target operating voltage and the actual output power. Has proposed a maximum power control method for changing the current command value (see Japanese Patent Laid-Open No. 2001-60118).
That is, in this method, for example, when the actual output power greatly exceeds the output power at the target operating voltage, the current command value is greatly increased, and when the actual output power slightly exceeds the output power at the target operating voltage. Increases the current command value by a small amount.

[0007]

However, the output characteristics (output voltage-output power characteristics) of the solar cell greatly differ with the increase or decrease in the amount of solar radiation, and when the amount of solar radiation decreases as shown by the curve B in FIG. Since it is a gentle curve with little change near the maximum output operating voltage, even when the amount of change in output power is the same, when the amount of solar radiation is large and when the amount of solar radiation is small, the amount of solar radiation is smaller. The operating voltage of the solar cell fluctuates greatly. Therefore, when the target operating voltage is made to follow the maximum output operating voltage Vmax, the time required until the operating voltage of the solar cell is substantially matched with the target operating voltage increases, and the target operating voltage quickly reaches the maximum output operating voltage Vmax. You will not be able to follow.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solar cell capable of quickly causing a target operating voltage to follow a maximum output operating voltage even when the amount of solar radiation decreases. It is to provide a maximum power control method.

[0009]

In order to achieve the above-mentioned object, the invention of claim 1 controls the maximum output operating voltage of a solar cell so as to control the output power obtained from the solar cell through a power converter. This is the maximum power control method for the solar cell that maximizes the output power at the previous target operating voltage and the current target operation by changing the target operating voltage of the solar cell according to the current command value that commands the output current of the power converter. In a solar cell maximum power control method that obtains a difference from the output power in voltage and makes the target operation voltage approximately match the maximum output operation voltage that minimizes the difference, the current operation value is controlled to change the target operation voltage. At this time, the difference between the output power at the previous target operating voltage and the output power at the current target operating voltage is divided by the output power at the current target operating voltage to determine the target operating voltage. The range of change when changing the target operating voltage becomes relatively small as the output power approaches the maximum power, and even if the amount of solar radiation decreases, the variation in the target operating voltage near the maximum power can be changed. The target operating voltage can be suppressed to quickly follow the maximum output operating voltage.

According to a second aspect of the invention, in the first aspect of the invention, the direction in which the target operating voltage is changed is reversed when the output power at the current target operating voltage is smaller than the output power at the previous target operating voltage. Even if the target operating voltage exceeds the maximum output operating voltage, it is possible to reliably follow the maximum output operating voltage by reversing the changing direction of the target operating voltage.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to embodiments.

FIG. 2 is a block diagram showing an example of a power conditioner for implementing the maximum power control method of this embodiment. This power conditioner converts DC power of the solar cell 10 into AC power by a power converter 11 including an inverter, and is connected in parallel to a commercial power grid 13 via a protection relay (not shown) or the like to perform grid-linked operation. It is something to do.

The output current and output voltage of the solar cell 10 are
It is detected by the current detector 21 and the voltage detector 22, and the detected value is input to the maximum power control circuit 23. The maximum power control circuit 23 obtains the output power of the solar cell 10 from the input value and outputs a current command value for setting the target operating voltage set based on the value. The current detector 26 detects the current output from the power converter 11, the current command value is compared with the value detected by the current detector 26, and the deviation is amplified by the error amplifier 24 to control the current. It is input to the circuit 25. The current control circuit 25 controls the phase of the power converter 11 according to the deviation from the error amplifier 24 so that the deviation becomes zero.

Here, the maximum power control method of the present invention, that is, the operation of the maximum power control circuit 23 will be described with reference to the flowchart of FIG.

First, the maximum power control circuit 23 outputs a current command value that matches the target operating voltage with the open circuit voltage V _OP of the solar cell 10. The output current Io _{k of the} solar cell 10 and the output voltage Vo _k of the solar cell 10 are detected by the current detector 21 and the voltage while changing the target operating voltage Vref _k (k = 1, 2, ...) At a predetermined sampling period. The solar cell 10 is detected by the detector 22 (step 2 in FIG. 1).
Output power Po _k (= Vo _k × Io _k ) is calculated, and the obtained output power Po _k is stored in a memory (not shown) (steps 1 and 3 in FIG. 1).

Then, the maximum power control circuit 23 obtains the target operating voltage change amount ΔVref _{k + 1} for determining the target operating voltage Vref _{k + 1} at the next sampling (step 4 in FIG. 1).

ΔVref _{k + 1} = K × (Po _k −Po _k−1 ) / Po _k where K is a preset constant. Then, the maximum power control circuit 23 subtracts the target operating voltage change amount ΔVref _{k + 1} from the current target operating voltage Vref _k to obtain the next target operating voltage Vref _{k + 1} (= Vref _k −ΔVref _{k + 1} ). Request (Fig. 1
Step 5), the solar cell 10 is set to the target operating voltage Vref _{k + 1.}
The current command value for the operation is output (step 6 in FIG. 1).

As the target operating voltage Vref _k is decreased, the output power Po _k increases to the left in FIG. 3, and eventually the output power Po _k exceeds the maximum output power Pmax and begins to decrease. Become. Then, the maximum power control circuit 2
In 3, the current output power P is higher than the previous output power Pok _-1.
o _k detects the decrease in the output power Po _k from becoming small, the operating voltage to reverse the direction of change of the target operation voltage Vref _k in the direction of increasing, as the operating voltage to the target operating voltage Vref _k coincides To control the current command value. Output power Po _k from the solar battery 10 when the operating voltage is increased is increased in FIG. 3 the right, eventually it starts decreasing again exceeds the maximum power Pmax. When this decrease is detected again, the maximum power control circuit 23 decreases the operating voltage to the target operating voltage Vref _k.
That is, the direction of the change of is reversed and the current command value is controlled so that the operating voltage matches the target operating voltage Vref _k . Then, by repeating the above operation, the output power Po can be made to substantially match the maximum output power Pmax by the hill climbing method described in the prior art.

[0019] In this embodiment the way, in the output power Po _k-1 and the current target operating voltage Vref _k at the previous target operating voltage Vref _k-1 when controlling the current command value to change the target operating voltage Vref since the changing of the target operating voltage Vref _{k + 1} in accordance with the output power Po _k value .DELTA.Vref _k obtained by dividing the output power Po _k in the current target operating voltage Vref _k the difference between the output power Po is the maximum output power The variation width ΔVref _k when the target operating voltage Vref _k is changed becomes relatively smaller as it approaches Pmax, and even when the amount of solar radiation is reduced, the variation of the target operating voltage Vref near the maximum power Pmax is suppressed to reduce the target operating voltage Vref. Can quickly follow the maximum output operating voltage Vmax.

[0020]

The invention of claim 1 is a maximum power control method for a solar cell, which controls the maximum output operating voltage of the solar cell so as to maximize the output power obtained from the solar cell via the power converter. Then, the target operating voltage of the solar cell is changed according to the current command value that commands the output current of the power converter, and the difference between the output power at the previous target operating voltage and the output power at the current target operating voltage is calculated and the difference is calculated. In the maximum power control method of the solar cell that makes the target operating voltage approximately match the maximum output operating voltage that minimizes, the output power at the previous target operating voltage and the current power when changing the target operating voltage by controlling the current command value Since the target operating voltage is changed according to the value obtained by dividing the difference between the output power at the target operating voltage of and the output power at the current target operating voltage, the output power becomes the maximum power. As the target operating voltage changes, the range of change when changing the target operating voltage becomes relatively small, and even when the amount of solar radiation decreases, the target operating voltage is made to follow the maximum output operating voltage by suppressing the variation in the target operating voltage near the maximum power. The effect is that you can.

According to the invention of claim 2, in the invention of claim 1, when the output power at the current target operating voltage is smaller than the output power at the previous target operating voltage, the direction of changing the target operating voltage is reversed. Therefore, even if the target operating voltage exceeds the maximum output operating voltage, the direction in which the target operating voltage is changed can be reversed so that the maximum output operating voltage can be reliably followed.

[Brief description of drawings]

FIG. 1 is a flowchart for explaining an embodiment.

FIG. 2 is a block diagram showing the above power conditioner.

FIG. 3 is a waveform diagram showing voltage-power characteristics of a solar cell.

[Explanation of symbols]

10 solar cells 11 Power converter 13 Commercial power system 21 Current detector 22 Voltage detector 23 Maximum power control circuit 24 Error amplifier 25 Current control circuit 26 Current detector

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiromichi Inoue             1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works Co., Ltd.             Inside the company (72) Inventor Mutsumi Ichimura             1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works Co., Ltd.             Inside the company F term (reference) 5H420 BB14 CC03 DD03 EB16 EB26                       EB39 FF03 FF04 FF22 FF25

Claims (2)

[Claims] 1. A maximum power control method for a solar cell, which controls the maximum output operating voltage of the solar cell so as to maximize the output power obtained from the solar cell via a power converter.
The target operating voltage of the solar cell is changed according to the current command value that commands the output current of the power conversion device, and the difference between the output power at the previous target operating voltage and the output power at the current target operating voltage is calculated, and the difference is the most significant. In the solar cell maximum power control method that makes the target operating voltage approximately match the smaller maximum operating voltage, the output power at the previous target operating voltage and the current target when changing the target operating voltage by controlling the current command value A method for controlling maximum power of a solar cell, characterized in that the target operating voltage is changed according to a value obtained by dividing a difference between the output voltage at the operating voltage and the output power at the current target operating voltage. 2. The solar cell according to claim 1, wherein the direction in which the target operating voltage is changed is reversed when the output power at the current target operating voltage is smaller than the output power at the previous target operating voltage. Maximum power control method.