JPH07109569B2 - Maximum power control method for solar cells - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention uses a solar cell as a power source,
The present invention relates to a solar cell maximum power control method for efficiently extracting maximum power from the solar cell via a power conversion device including an inverter.

[0002]

2. Description of the Related Art In recent years, attention has been paid to a power supply device that supplies predetermined power by using a solar cell as a power supply and connecting it to an independent load or another power supply system via a power conversion device such as an inverter.

This solar cell has a tendency that when the amount of solar radiation incident on the solar cell is used as a parameter, the electric power tends to increase as the amount of solar radiation increases, and the output power greatly depends on the operating point of the solar cell. It has the characteristic that it fluctuates.

As a control method for efficiently extracting the maximum power from the solar cell having such characteristics, Japanese Patent Laid-Open No. 206206/1987 discloses a method in which the maximum power point of the solar cell is always tracked, so-called mountain climbing. A law has been proposed.

This method is a method of operating the solar cell at two different points and comparing the output powers thereof so that the operating point of the solar cell becomes the maximum power point.

For example, when the solar cell has a voltage-power characteristic as shown in FIG. 4 under a constant amount of solar radiation, first, the reference operating voltage of the output voltage of the solar cell is determined from the open circuit voltage V _OP. Change width ΔV _S
Decrease with. During this time, the electric power increases in the direction of arrow i in the figure. Then, the power exceeds the maximum power point P and decreases in the direction of arrow ii. Detecting this decrease in power, this time the reference operating voltage is increased by the change width ΔV _S. This allows
The power increases in the direction of arrow iii in the figure, and eventually the maximum power point P
Begins to decrease in the direction of arrow iv. Therefore, the decrease in the electric power is detected, and the reference operating voltage is changed again in the direction of decreasing with the change width ΔV _S. By repeating the above operation, the reference operating voltage is reciprocated in the vicinity of the maximum power point P, and the maximum power point of the solar cell is always followed.

[0007]

However, the above-mentioned conventional method has the following problems because the reference operating voltage is increased / decreased with a constant change width ΔV _S.

That is, when the change width ΔV _S is set to a small value, the swing width of the operating point near the maximum power point becomes small, and the accuracy of maximum power control can be improved, but the maximum power of the solar cell is increased. It is not possible to move to the point P at high speed, and the follow-up speed for characteristic fluctuations due to sudden changes in the amount of solar radiation becomes slow, while on the other hand, when the change width ΔV _S is set to a large value, the follow-up speed for characteristic fluctuations is increased. There has been a problem that the fluctuation range of the operating point in the vicinity of the maximum power point becomes large, and the accuracy and stability of the maximum power control decrease.

The present invention has been made in view of the above points, and it is possible to perform the tracking of the maximum power point of the solar cell at high speed and to perform the maximum power control accurately and stably. An object of the present invention is to provide a method of controlling the maximum power of a solar cell that can be used.

[0010]

The present invention is a method for controlling the electric power extracted from a solar cell through a power conversion device to a maximum electric power, by changing a reference operating point given to the solar cell. If the output power from the solar cell is in the increasing direction, the direction in which the reference operating point is changed is maintained as it is. Conversely, if the output power is in the decreasing direction, the changing direction is reversed and the reference operating point is changed. The amount of change in the small value (0
(Excluding) is characterized by changing to.

[0011]

According to the present invention, when the reference operating point of the solar cell is changed to match the maximum power point, the change amount of the reference operating point is changed to a small value in the area near the maximum power point. Therefore, the amount of change in the reference operating point can be set large in a region that is not near the maximum power point, the solar cell can follow the maximum power point at high speed, and precise tracking can be performed near the maximum power point. .

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The maximum power control method for solar cells of the present invention will be described in detail below with reference to the drawings showing an embodiment thereof.
FIG. 1 is a block circuit diagram thereof. (1) is a solar battery power source (hereinafter referred to as DC power source), (2) is an inverter that converts the DC output of the DC power source (1) into AC, and (3) is the inverter
Transducer for detecting AC output power of (2), (4)
Is a sampler for setting the detection time, (5) is the DC power supply
It is a controller that generates the reference operating voltage Vref supplied to (1). The DC power source (1) has a voltage-as shown in FIG.
It has a power characteristic (curve I in the figure) or a voltage-current characteristic (curve II in the figure). 60H for the inverter (2)
A PWM (pulse width modulation) method that outputs a single-phase alternating current of z is used. A transducer having a response time constant of 0.5 seconds is used as the transducer (3). The controller (5) is equipped with an 8-bit microprocessor,
The sampler (4) is realized by software of the microprocessor.

The voltage V of the DC power supply (1) follows the reference operating voltage Vref to generate the DC output power P _DC .

The inverter (2) converts this DC output power P _DC into AC output power P _AC . The transducer (3) receives the AC output power P _AC as input, and
The detection value P ^* _AC is obtained by (4). Here, the sampling period T is sufficiently larger than the response time constant of the transducer (3), and T = 1 second is set.

The controller (5) is a function generator that gives the reference operating voltage Vref (t) at time t as the following equation using the outputs at times t-T and t-2T. Here, the gain K takes a positive value when P ^* _AC is increasing and a negative value when P ^* _AC is decreasing.

[0016]

[Equation 1]

Based on the above equation, the controller (5) takes in the output of the transducer (3) at the sampling period T = 1 second, calculates the reference operating voltage Vref, and outputs it.
Then, the outputs of the DC power source (1) and the transducer (3) are settled by the next sampling time.

FIG. 3 shows a DC power source (1) and an inverter (2).
FIG. 3 is an output voltage-power characteristic diagram of FIG. In this figure, the operating voltage of the solar cell, that is, the output voltage V = V of the DC power supply (1)
When the output power of the DC power supply (1) and the AC output power of the inverter (2) when ref = V _{1 are} at points A and a, respectively, the controller (5) determines that the AC output power P _AC is Vref is increased to move the operating point in the increasing direction.

If the output power of the DC power supply (1) and the AC output power of the inverter (2) when the output voltage V = Vref = V _{2 are} at point B and point b, respectively, The controller (5) reduces Vref.

In this way, the output voltage V of the DC power supply (1) is maintained near the voltage V _O which gives the operating point C at which the _AC output power P _AC of the inverter (2) becomes maximum.

Then, the gain K of the controller (5)
Is variable, and the change amount of the reference operating voltage Vref is ΔP _AC /
The operating voltage V of the DC power supply (1) is optimized by making it proportional to ΔV (ΔP _AC is the minute change in the output power of the inverter (2) and ΔV is the minute change in the output voltage of the DC power supply (1)). The amount of change in Vref when not in the vicinity of the operating voltage V _O can be made large, and the output power of the inverter (2) shifts to the optimum operating point C at high speed.

That is, the change amount of the reference operating voltage Vref is ΔP
Increased if _AC / [Delta] V is greater, because the [Delta] P _{A C} / [Delta] V is set small smaller, amplitude of the output voltage V in the vicinity of the [Delta] P _AC / [Delta] V is smaller maximum power point C becomes extremely small, therefore the maximum power It can be obtained accurately and stably. Further, in a region where the operating point is away from the maximum power point C, since ΔP _AC / ΔV is large, the change amount of the reference operating voltage Vref becomes a large value, and the operating point moves toward the maximum power point C at a fast response speed. .

Since the response speed of the output voltage V of the DC power supply (1) to the change of the reference operating voltage Vref is sufficiently faster than the time constant of the transducer (3), V = V
When Vref is slightly changed from the steady state of ref, the output voltage V can follow the reference operating voltage Vref during the elapse of the sampling period T.

Further, as described above, when controlling so that the AC output power of the inverter is maximized, the calculation of the reference operating voltage of the solar cell which does not need to be variably set at a high speed is performed with a slow response speed. The AC output power of the inverter is optimized based on the detected value of the AC output power of the inverter, and the output voltage of the solar cell, which has a faster response speed at the time of detection than AC, is made to follow the set reference operating voltage. In addition to being able to transfer the power to the solar cell at a high speed, it is possible to take out the power that maximizes the AC output power of the inverter from the solar cell, regardless of the power loss in the power conversion process in the inverter, and to make the solar cell power effective. Can be used.

[0025]

As described above, according to the present invention, when the reference operating point of the solar cell is changed to match the maximum power point, the change amount of the reference operating point is set to the region near the maximum power point. Since it is changed to a small value in, the amount of change of the reference operating point can be set large in the area that is not near the maximum power point, the solar cell can follow the maximum power point at high speed, and the maximum power point Precise tracking is performed in the vicinity, and maximum power can be obtained accurately and stably.

[Brief description of drawings]

FIG. 1 is a configuration block circuit diagram of a maximum power control method for a solar cell according to the present invention.

FIG. 2 is a characteristic diagram of output voltage-power (curve I) and output voltage-current (curve II) of a solar cell.

FIG. 3 is an output voltage-power characteristic diagram of a solar cell and an inverter.

FIG. 4 is an output voltage-power characteristic diagram of a solar cell under a certain amount of solar radiation.

[Explanation of symbols]

 1 DC power supply 2 Inverter 3 Transducer 4 Sampler 5 Controller

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hitoshi Tamura 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-58-157342 (JP, A) JP-A-56 -91633 (JP, A)

Claims (2)

[Claims] 1. A method of controlling electric power extracted from a solar cell through a power conversion device to a maximum electric power, wherein a reference operating point given to the solar cell is changed, and output power from the solar cell at that time is changed. If the output power is decreasing, the direction of changing the reference operating point is maintained as it is, and if the output power is decreasing, the changing direction is reversed, and the amount of change of the reference operating point is set near the maximum power point. The method for controlling the maximum power of a solar cell is characterized in that the value is changed to a small value (excluding 0) in the area of. 2. The maximum power of the solar cell according to claim 1, wherein the amount of change in the reference operating point is changed according to the rate of change in the output power when the reference operating point is changed. Control method.