JPS60215224A - Output power controller of solar battery - Google Patents

Abstract

PURPOSE:To obtain a maximum output from a solar battery without causing a hunting state by controlling the solar battery with a voltage higher than the voltage for a maximum point of the solar battery output. CONSTITUTION:A motor 6 is started by a prescribed frequency (f), and a voltage VPMX for a maximum solar battery output after completion of start is detected, and the magnitude of the voltage is discriminated by a solar battery output voltage (VS) discriminating means 22. If the voltage VS is higher than the voltage VPMX, DELTAf1 is added to the frequency (f) through an output frequency increase/ reduction determining means 23, and the addition result is outputted as an inverter frequency reference signal FM through an addition/subtraction frequency output means 27 in accordance with an output frequency change number discriminating means 25. Meanwhile, if the voltage VS is lower than the voltage VPMX, DELTAf1 is subtracted from the frequency (f) by said means 23, and the signal FM is outputted through said means 27 in accordance with said means 25. When the device state is stable after the change of the output frequency, the voltage VS is read again, and similar control is performed.

Description

[Detailed Description of the Invention] "All #Can Aino" The present invention relates to a solar cell output power control device, and particularly when supplying power to a load using a solar cell as a power source, natural conditions such as a solar scene etc. The present invention relates to an output power control device for a solar cell that controls the output power so that the output power is always the maximum according to the conditions even if the output power fluctuates.

[Technical background of the invention and its considerations] In recent years, systems that use solar cells to convert solar energy into electric power have come into practical use. In this case, the maximum output power of the solar cell is controlled in order to efficiently convert solar energy into electric power.

Hereinafter, a configuration will be described as an example in which the speed of an AC motor is controlled by a variable frequency inverter to drive a pump, fan, blower, etc. as a solar type or pond load.

Figure 1 shows a variable frequency inverter using solar cells as a power source.
FIG. 2 is a diagram showing a circuit configuration for driving an AC motor with maximum power at night;

4 Power is supplied from the solar cell 1 through the backflow blocking diode 2 and the smoothing reactor 3 to the inverter 5 with variable frequency output, and the inverter 5 applies variable frequency AC voltage to the AC electric machine 6 to control the speed. is under control.

The inverter 5 includes semiconductor switching elements such as giant transistors GU-Gz1 and diodes DU'-DZ.
Since it takes pulsed power, a capacitor 4 is provided at its input terminal. Further, the capacitor 4 and the smoothing reactor 3 suppress the output current ripple of the solar cell and also suppress the surge voltage.

The output voltage V8 and the output current 8 of the solar cell 1 are detected by the pressure detection circuit 8 and the current detection circuit 9, and are input to the maximum power control circuit 20. The maximum power control circuit 10 inputs a control signal to the inverter control circuit 1 and controls the inverter r5.
is controlled so that it takes the maximum output power.

The output of solar cells varies greatly depending on changes in the amount of sunlight and temperature. FIG. 2 shows typical output characteristics of well-known solar cells.

Figure 2 shows the output current-voltage characteristics and output power characteristics when the amount of sunlight J+"L...Bn is used as a parameter, and the relationship between the size of the solar scene is Bl>B2>Is...
・〉B. The dash-dotted line is a plot of the solar cell output voltage at the maximum output point.

When controlling a variable frequency inverter using a solar cell having the above output characteristics as a power source, the frequency is controlled so that the output power from the solar cell is maximized (Pmax). That is, when the load 7 of the AC motor 6 driven by the variable frequency inverter 5 is a pump, blower, fan, etc. whose load torque is constant regardless of the rotation speed or increases according to the rotation speed, the frequency is changed. When it increases, the speed and output of the AC motor 6 increase, and the output current 8 of the solar cell 1 also increases. Generally, the inverter 5 is controlled to keep the voltage-frequency ratio V/F constant (that is, constant magnetic flux), so when the load torque is two constant with respect to the rotation speed or is proportional to the first power or more of the rotation speed, the above Similarly, the output current I8 increases.

Therefore, as the frequency of the inverter 50 increases, the solar cell 1
The output power of will also increase. However, when the frequency is increased beyond the output current I8 at the maximum output power PmaX of the solar cell 1, the output power of the solar cell 1 sharply decreases as shown in FIG.

In order to deal with the output characteristics of solar cells and to utilize solar energy that fluctuates greatly due to natural phenomena such as sunlight conditions with maximum efficiency, a maximum power control circuit IO is used to track the maximum power output point PmaX of the solar cells. control is in place.

FIG. 3 is a detailed circuit diagram of the maximum power control circuit IO. The output voltage 8 and the output current 18 of the solar cell 1 are supplied to the buffer amplifier 12. ], 3 is input to the multiplier 14, and the output power PsV of the solar cell is calculated and output.

This output power signal P8 is converted into a digital value by the A/D converter 15 and inputted to the microcomputer 16, which performs control as described below.

Make a judgment and output the frequency reference signal as a digital value,
It enters the inverter control (b) path 11 as an analog frequency reference signal FM through the D/A converter 17"-9-2
,. . . all uMtllRa$M@F9.8 A variable frequency control signal by V/F control, PWM control, etc. is output as a power to control the inverter 5 and drive the AC motor 6.

FIG. 4 is a flowchart for explaining the operation of the conventional device. In other words, when the microcomputer 16Fi starts up, it outputs the reference signal FM of a predetermined frequency f, starts the operation of the inverter 5, and starts the AC motor 6. , reads the solar cell output power P8 after completion of startup.

Next, the current frequency f is increased by a predetermined change frequency Δf to increase the rotational speed of the electric motor 6, and the solar cell output power P8 after completion of acceleration is read and compared with the value read last time. As a result, if the newly read output power has increased, the frequency is further increased by Δf to accelerate the motor, and the addition of Δf is repeated until the output power of the solar cell decreases. When the frequency is increased and the rotational speed of the motor is increased, the output current of the solar cell is increased and the output power increases. However, due to changes in natural conditions and the aforementioned output characteristics, the output power of the solar cell begins to decrease after a certain output current. When it is determined that the output frost f force has decreased, the frequency is decreased by Δf, contrary to the previous one, and the solar cell output power P after deceleration is completed is read and the increase or decrease is determined, and the output power is increased by Δf. Repeat increment or subtraction of f. However, the conventional maximum power control method described above has the following problems.

The maximum output point (voltage V
8M, current IsM), if the operating frequency is further increased, the negativity increases and the solar cell output current increases. As the solar cell output voltage increases, the voltage decreases. As the voltage decreases, the motor slip increases and the solar cell output JWL current increases. In other words, even if the inverter output frequency is not changed, the motor will eventually stall while repeating the above process.

If the engine is about to stall, the voltage will not return to its original level unless the operating frequency is drastically reduced.

In other words, a hunting state occurs between the maximum solar cell output power point, and the output of the solar cell cannot be used effectively.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and uses a solar cell as a power source to variably supply power to a load and control the supplied power so that the output power of the solar cell is maximized. The present invention provides an extremely stable solar cell output power control device that does not cause a hunting state across the maximum solar cell output point in a system that uses solar cells.

[Summary of the Invention] In order to achieve this object, the present invention provides a power supply means for supplying variable power to a load using a solar cell as a power source, and detecting the output power and voltage of the solar cell and detecting the maximum output power. In a solar cell output power control device equipped with a maximum power control circuit that sends a control signal to the power supply means so that A reading means, an output voltage determining means for determining whether the output voltage is larger or smaller than the voltage at the maximum output of the solar cell, and an output frequency addition/subtraction determining means for increasing or decreasing the output frequency by the output voltage determining means. FIG. 5 shows a power control circuit that controls the output frequency of the power supply means based on the output of the output frequency addition/subtraction determining means. Compared to the conventional maximum power control circuit shown in FIG. 3, a converter 18 for converting the solar cell output voltage v8 into a digital signal is added as a hardware configuration. The other configurations are the same as in FIG. 3.

A/D converter chip select terminal csFi solar cell output voltage v8. A, /D of solar cell output power P8,
:F inverter output is separated, and its control signal is output from the microcomputer's output ports Rs, I Pn.
, controlled by w.

The main circuit configuration is the same as that in FIG. 1, so a description thereof will be omitted.

FIG. 6 is a flowchart showing the operation of the solar cell output power control device according to the present invention.

FIG. 7 is a block diagram showing the microcomputer used in the present invention using functional blocks.

In the present invention, first, the electric motor 6 is started at a predetermined frequency f,
The voltage VPMX at the maximum solar cell output after completion of startup is detected. (The voltage detection method at the time of maximum output will be explained in detail later.) Thereafter, the magnitude of the voltage is determined by the solar cell output voltage determining means 22.

If the solar cell output voltage ■8 is larger than the voltage VPMX at the maximum output, Δfl is added to the frequency f via the output frequency addition/subtraction calculation means Yu, and the output frequency change [g
According to the I number determining means 2b, it is output as an inverter frequency reference signal FM via the addition/subtraction frequency output means 27.

On the other hand, if the output voltage of the solar cell (8) is smaller than the voltage VPMX at the maximum output point, the output frequency increase/decrease determining means n subtracts Δfl from the frequency f, and the output frequency is output to the inverter via the addition/subtraction frequency output means 27 according to the output frequency change number determining means 25. It is output as a frequency reference signal FM.

After the output frequency is changed and becomes stable, the solar cell output voltage (8) is read again and the same control is performed.

Here, the number of times the output frequency has been changed is counted by the output frequency change count means in addition to and subtraction of Δfl.

Next, the output frequency change number determination means 25 determines whether the output frequency change number N is larger or smaller than a preset number N.

When the number of output frequency changes N is smaller than NR (N<NR)
repeats the above control. In other words, the output of the output frequency increase/decrease determining means 23 is directly output from the addition/subtraction frequency output means 27.

On the other hand, if the number of output frequency adjustments N is equal to or larger than NR, the mode is shifted to a mode for detecting the voltage VPMX at the time of output from the solar cell.

Here, by changing NR, the time interval for detecting the voltage at the maximum output of the solar cell can be changed.

□゛After detecting the voltage at the maximum output of the solar cell, the new voltage after detection is taken into the pressure (v8) determining means 22 and control is performed using the new voltage.

Note that one method for finding the maximum output point of a solar cell is the fourth method.
As shown in the figure, the motor was first driven at the initial frequency f, the frequency was gradually increased, the solar cell output at that time was captured in the microcontroller, and as the output increased, the motor drive frequency was increased and the output frequency was increased. By repeating this process until the solar cell output decreases, the maximum solar cell output point and the output voltage at that time can be easily detected.

Further, since the method is well known, detailed explanation will be omitted.

``Effects of the Invention'' As described above, according to the present invention, since control is always performed at a voltage higher than the voltage at the maximum output point of the solar cell, the load power generator does not stall as in the conventional case, and the output Since the change in frequency is also extremely small, it provides extremely stable control, which is extremely effective.

[Brief explanation of the drawing]

Figure 1 is a circuit configuration diagram that uses a solar battery as a power source to drive an AC motor at maximum power using a variable frequency inverter, Figure 2 is a solar battery output characteristic diagram, and Figure 3 is the maximum power control circuit 10 of Figure 1. 4 is a flowchart for explaining the operation of the conventional device, FIG. 5 is a detailed circuit diagram for the maximum power control circuit of the present invention, and FIG. 6 is a detailed circuit diagram for explaining the operation of the present invention. 70-Chart, FIG. 7 is a diagram representing the microcomputer 16 by combining functional blocks.
...Solar cell 2...Diode 3...Reactor 4...Capacitor 5...Inverter 6...
AC power Iv1 machine 7...load 8...voltage detection circuit 9...current detection circuit lO...maximum power control circuit 1
1... Inverter control circuit 12, 'L3... Buffer amplifier 14... Multiplier 15... A/D converter 16... Microcomputer 17... D/A converter 21... Output 'voltage reading means 22...voltage determination means. 23...Output frequency increase/decrease determination means Sae...Output frequency change number counting means 5...Output frequency change number determination means 26...Voltage detection means at maximum output power 27...Addition/subtraction frequency (FM) Output means Fig. 1 Fig. 3 Fig. 4 Mete Fig. 6 Fig. 7 M

Claims (1)

[Claims] - (1) A power supply means that uses a solar cell as a power source to supply variable power to a load, and detects the output power and voltage of the solar cell and sends a control signal to the power supply means so that the output power is maximized. In an output power control device for a solar cell equipped with a maximum power control circuit, the output power and voltage reading means reads the detected output power and voltage, and the output voltage is set to the voltage at the maximum output of the solar cell. output voltage determining means for determining whether the output frequency is larger or smaller than the output voltage; and output frequency addition/subtraction determining means for increasing or decreasing the output frequency by the output voltage determining means; A solar cell output power control device characterized by controlling the output frequency of a solar cell.