JPH0895655A - Inverter control system for drive of solar battery - Google Patents

Abstract

PURPOSE: To stably control a solar battery at a point approximate to its maximum efficiency point by comparing the output frequency levels of an inverter set before and after the target voltage level is changed with each other and setting the target voltage level of output of the solar battery in accordance with the result of comparison. CONSTITUTION: The DC output of a solar battery 1 is converted into the AC output by an inverter 3 and supplied to a three-phase induction motor 7 to drive a pump 8. At this time, a controller 5 outputs a control signal in response to the difference between the read output voltage and the target voltage, and the analog signal that undergone the D/A conversion by a D/A converter 4 is applied to the inverter 3 as a frequency command signal. Thus, the output frequency is controlled. When the output frequency of the battery 1 is reduced, the output voltage of the battery 1 is increased, the output voltage of the battery 1 is set equal to the target voltage of the controller 5, and the pump 8 is driven. As a result, the battery 1 can be stably controlled at a point approximate to its maximum efficiency point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter control system in a drive system in which a driven device is driven by a solar cell without interposing a storage battery.

[0002]

2. Description of the Related Art When a solar cell is used to drive a pump, for example, a three-phase induction motor is generally used as a motor for driving the pump in terms of availability, maintenance, and cost. Need to be converted. An inverter is used for this quadrature conversion, but normally the AC output is a constant frequency output according to the ratings of the pump and motor.

The pump load is generally determined by the number of revolutions, but when the motor is rotating at a constant frequency, the pump number of revolutions is also almost constant, and the load is almost constant. On the other hand, since the output of the solar cell fluctuates due to sunlight, the pump cannot be driven when the output of the solar cell is small, and the output cannot be effectively used sufficiently when the output of the solar cell is large. Therefore, in order to effectively use the electric power of the solar cell, a method has been proposed in which the maximum electric power of the solar cell is constantly monitored, and the motor rotation speed is controlled according to the maximum electric power to effectively use the energy (Japanese Patent Laid-Open No. 2004-242242). 62-937
19 publication).

Further, when the maximum power is exceeded when the load is increased, the voltage drops sharply. Therefore, a method of monitoring the voltage and effectively using the power has also been considered.

[0005]

By the way, in order to monitor the electric power, usually, the voltage and the current are monitored and the product thereof is obtained. Therefore, a multiplier or a computer is required, and the hardware configuration is required. Will increase. On the other hand, the method of monitoring the voltage is a method that always keeps the user on the verge of power-down, although the hardware is simplified. Therefore, there is a problem that the operation becomes unstable unless the system is properly adjusted.

The present invention is intended to solve the above-mentioned problems, and a solar cell capable of controlling only a voltage without measuring a current and stably controlling a solar cell near a maximum efficiency point with a simple structure. It is an object of the present invention to provide an inverter control system in battery drive.

[0007]

According to the present invention, a solar cell output is converted into an AC output by an inverter, and an induction motor rotating at a speed proportional to the frequency of the AC output is driven to drive a driven device. In the driving method described above, the solar cell output voltage is input, the input voltage is compared with the set target voltage value, and the inverter output frequency is output by outputting the frequency command value to the inverter according to the comparison result. A controller for controlling the target voltage value is changed, the output frequencies of the inverters before and after the change of the target voltage value are compared, and the target voltage value of the solar cell output is set according to the comparison result. Is characterized by.

Further, according to the present invention, the target voltage value of the solar cell output is decreased, and when the output frequency of the inverter is increased, the target voltage value is decreased and set, and the target voltage value of the solar cell output is decreased. When the output frequency of the inverter decreases, set the target voltage value by increasing it.If the change of the inverter output frequency is small, decrease the target voltage value of the solar cell output. It is characterized by setting to the value of.

[0009]

In the present invention, when the maximum electric power of the solar cell is obtained by the variable frequency inverter, it is noted that the electric power has a positive correlation with the rotational speed of the pump, that is, the frequency of the inverter. Instead of monitoring the product, that is, the power, by controlling the voltage and monitoring only the frequency, the number of analog input points is reduced by one and the hardware configuration is simplified, and stable operation is performed by performing the constant voltage control. I will get it. That is, in general, the maximum output point of the solar cell is a substantially constant voltage point unless the temperature of the solar cell panel changes significantly, while the change in panel temperature is a slow change of several minutes or more,
Maximum power tracking can be performed by following a certain voltage point at a slow speed. Therefore, an appropriate target voltage is first determined in advance, and when the operating point is above the target voltage, the pump speed is increased, and when the operating point is below the target voltage, the pump speed is reduced to determine the operating point. The voltage is controlled so that the target voltage is achieved. Next, the target voltage is slightly changed and voltage control is similarly performed to set the operating point to the target voltage. Then, the output frequencies of the inverters before and after the slight change in the target voltage are compared, and if the frequency greatly increases, the operating point is changed in the same direction, and if the frequency greatly decreases, the operating point is changed in the opposite direction, and the frequency change is If it is smaller, it is determined to be the maximum power and the operating point is set to a value before the target voltage is slightly changed.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an overall configuration when the present invention is applied to a pump drive, FIG. 2 is a diagram illustrating control of the present invention, and FIG. 3 is a diagram illustrating an inverter control flow in the present invention. is there. In the figure, 1 is a solar cell, 2 is a voltmeter, 3 is a variable frequency control inverter, 4 is a D / A converter, 5 is a controller, 6 is an A / D converter, 7 is a three-phase induction motor, and 8 is a pump. Is.

The DC output of the solar cell 1 is
The output is converted to C output, and power is supplied to the three-phase induction motor 7 to drive the pump 8. The frequency control of the inverter 3 is performed by the controller 5. That is, the controller 5
Is read by the solar cell output voltage detected by the voltmeter 2 and converted into a digital value by the A / D converter 6. On the other hand, a predetermined target voltage is set in advance in the controller 5, a control signal corresponding to the difference between the read output voltage and the target voltage value is output, and D / A conversion is performed by the D / A converter 4. Add an analog signal to the inverter 3 as a frequency command signal,
Control the output frequency. The three-phase induction conductor 7 rotates according to the output frequency of the inverter 3, and the pump 8 is driven. The pump load is proportional to the rotation speed of the three-phase induction motor, that is, the frequency of the inverter. When the output frequency of the inverter 3 increases (load increases), the output voltage of the solar cell decreases and the output frequency of the inverter 3 decreases ( Load reduction)
Then, the output voltage of the solar cell increases, and the output voltage of the solar cell is controlled to reach the target voltage set in the controller 5.

By the way, generally, the maximum output point of the solar cell is a substantially constant voltage point unless the temperature of the solar cell panel changes significantly, and the change of the solar cell panel temperature changes at a slow speed of several minutes or more. In addition, the solar cell output has a positive correlation with the load, that is, the inverter frequency. Now, when the solar cell output voltage is plotted on the horizontal axis and the solar cell output (power) is plotted on the vertical axis, the characteristics shown in FIG. 2 are obtained. Since the power on the vertical axis has a positive correlation with the inverter frequency, the vertical axis has the same characteristics even when the frequency is f.
Now, when the frequency of the inverter is controlled by the controller 5 with the target voltage being Vset, the solar cell output voltage V
Is Vset, and the output frequency f of the inverter at that time is f1. In this state, if the target voltage Vset is lowered by ΔV and the output voltage of the solar cell is made to follow the target voltage by the inverter control in the same manner, the frequency changes to f2 and f1 <f2.
As shown in (a), since the target voltage Vset is a voltage higher than the maximum power point, it is possible to approach the maximum power point by lowering the target voltage. Note that f1 <f2
Occurs even when the sunshine increases, and similarly, the target voltage can be decreased to increase the inverter frequency to increase the load, and thus the maximum power point can be approached.

Assuming that the target voltage Vset is lowered by ΔV and the frequency is changed to f2 as a result of f1> f2 as a result of the inverter control, the target voltage Vset is maximum as shown in FIG. 2 (b). Since the voltage is lower than the power point, it is possible to approach the maximum power point by increasing the target voltage. It should be noted that f1> f2 occurs even when the sunshine becomes small, and the target voltage can be raised to lower the inverter frequency and control the load to be lightened to bring it closer to the maximum power point.

Further, as a result of lowering the target voltage Vset by ΔV and similarly performing inverter control, the frequency becomes f2,
If f1≈f2, then as shown in FIG.
Since the target voltage Vset is near the maximum power point, it is sufficient to maintain the target voltage Vset. In this case, the frequencies being substantially equal means that if the value is within 5% with respect to the frequency that gives the maximum power, power loss is small and stable operation is possible.

By the control as described above, the operating point can be brought to the maximum power point.

In the above description, the target voltage is slightly changed so that it is changed to the safe side where power down does not occur, and of course, the target voltage may be slightly changed so as to be increased. is there.

Next, the processing flow will be described with reference to FIG.

First, the controller is initialized (step 11), and in steps 12 to 19, the first constant voltage control process is performed. That is, parameters such as ΔV, Δf, and adjustment time are set (step 12), the output voltage of the solar cell is read (step 13), and the read voltage V is read.
Is compared with a preset voltage Vset, and V>
If Vset, f = f + Δf is set to increase the frequency to increase the load, and if V <Vset, f = f−Δf is set to decrease the frequency to reduce the load (steps 14, 1).
6). Since there is a time delay in the control system, after waiting for a certain time in step 18, the flag indicating whether or not V and Vset match (step 19). If V and Vset do not match, the output voltage of the solar cell is read again and the same processing is repeated. Then, the frequency f when V = Vset is set to f1 and the match flag is set to 1 (steps 15 and 17). Through the above processing, frequency control is performed so that the solar cell output voltage becomes the target voltage Vset.

Next, the match flag is cleared (step 2
0) and Vset as Vset-ΔV (step 2
1), V> V as in the first constant voltage control process
If set, f = f + Δf is used to increase the frequency and increase the load, and if V <Vset, f = f−Δf is used to decrease the frequency and lighten the load, and V = Vse
The frequency f at that time is set to f2 (steps 23 to 28).

Next, f1 and f2 are compared, and f1 <f2
If so, this corresponds to the case of FIG. 2A, and since the solar cell has a state of reserve, the target voltage is set to the second value and the load is increased to clear the match flag (step 3
1), returning to step 12, the above-described first and second processes are repeated.

On the other hand, if f1> f2, it corresponds to the case of FIG. 2B, and Vset + 2ΔV is set to be larger than the first target voltage by ΔV to reduce the load (step 3
0), similarly returning to step 12 and performing the same control again.

The case of f1 = f2 corresponds to the case of FIG. 2C, and since it is at the maximum power point, the target voltage is returned to the first value as Vset + ΔV (step 29).

By the above processing, the target voltage can be brought to the maximum power point.

In the above embodiment, the case of pump drive has been described, but the present invention is not limited to this, and can be applied to any fan drive type that can be driven by a solar cell. .

[0026]

As described above, according to the present invention, the maximum power is determined by using only the input voltage and the output frequency and by changing the frequency when the voltage value is slightly changed.
It can be stably performed with a simple hardware configuration, and the solar cell can always be operated near the maximum efficiency point.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram when a control method according to the present invention is applied to pump driving.

FIG. 2 is a diagram showing output characteristics of a solar cell.

FIG. 3 is a diagram for explaining a control flow.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Solar cell, 2 ... Voltmeter, 3 ... Variable frequency control inverter, 6 ... Controller, 7 ... Three-phase induction motor, 8 ... Pump.

Claims (4)

[Claims] 1. A drive system in which an output of a solar cell is converted into an AC output by an inverter, and an induction motor rotating at a speed proportional to the frequency of the AC output is driven to drive a driven device. Output voltage is input,
Comparing the input voltage with the set target voltage value,
A controller that outputs a frequency command value to the inverter according to the comparison result to control the inverter output frequency, changes the target voltage value, compares the output frequency of the inverter before and after changing the target voltage value, An inverter control method in solar cell drive, wherein a target voltage value of the solar cell output is set according to the comparison result. 2. The target voltage value of the solar cell output is reduced,
2. The inverter control method in solar cell drive according to claim 1, wherein when the output frequency of the inverter is increased, the target voltage value is decreased and set. 3. A solar cell output target voltage value is decreased,
The inverter control method in solar cell drive according to claim 1, wherein the target voltage value is increased and set when the output frequency of the inverter is decreased. 4. A target voltage value of a solar cell output is reduced,
The inverter control method in solar cell drive according to claim 1, wherein the target voltage value is set to a value before the change when the change in the output frequency of the inverter is small.