JPS5869469A - Inverter by solar battery - Google Patents

Abstract

PURPOSE:To always operate a load in the maximum efficiency by controlling an inverter so that the operating point always becomes the maximum output point even if the voltage-current characteristic of a solar battery is varied due to the variations in the sunshine amount and the environmental temperature. CONSTITUTION:A main inverter 2 is driven by a solar battery 1 to operate a load 3 such as an AC motor. At this time the output voltage V and the output current I of the battery 1 are detected and are inputted to a capacity control circuit 5, thereby calculating the power P as the product of the V and the I, the power P is differentiated by the I, and the output voltage and the frequency of the main inverter 2 are controlled by an auxiliary inverter 4 so that when the differentiated value is positive, the output of the inverter 2 is increased and when negative, it is decreased. Accordingly, the operating point can be always corrected to the maximum output point irrespective of the using condition of the solar battery 1, and the load 1 can be always operated in the maximum efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter (DC-AC converter) using solar cells.

Since conventional inverters use a rectified DC power source of a commercial AC power source or a battery as a power source, stabilization of the output voltage or output waveform has been considered first.

On the other hand, solar cells have voltage-current characteristics as shown in Figure 1, and the maximum output operating point is the voltage
There is only one fixed point where the product of current Ip and current Ip (VpxIp) is maximum, and this voltage-current characteristic changes depending on the environmental temperature and other factors.

Furthermore, solar cells are extremely expensive, and there is a demand for the most efficient use of solar energy.

The present invention has been made in view of the above, and its purpose is to eliminate fluctuations in the voltage-current characteristics of solar cells due to changes in the amount of solar cell sunlight, environmental temperature, etc.
An object of the present invention is to provide an inverter that automatically supplies maximum power to a load at all times.

Another object of the present invention is to provide an inverter that tracks the maximum output point of a solar cell using only an internal automatic control device without using an external temperature sensor or illuminance sensor.

First, the present invention will be explained in detail.

Figure 1 shows a voltage-current characteristic diagram of a solar cell.

Point Pmax is the maximum output point, and the diagonally shaded rectangle represents the magnitude of electric power at that point.

FIG. 2 shows a characteristic diagram in which electric power fiI is plotted on the horizontal axis and electric power P is plotted on the vertical axis. When the current value I is smaller than the current [1°] at the maximum output point, the power P increases as the peak current increases.
increases monotonically, and when the current l is larger than that, the power P decreases monotonically as the threshold current increases.

Therefore, the present invention detects the output voltage and output current of a solar cell, calculates q output power P=Vxl at that time, and determines whether the change in power P when the load current is slightly changed is positive or negative. By determining which side of the maximum output point P max the output point of the solar cell is located, it is determined which side of the maximum output point P max is located, and the output of the inverter is controlled in a direction closer to the maximum output point P max.

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

FIG. 3 shows a circuit block diagram of an embodiment of the present invention.

The main inverter 2 is driven by the solar cell 1, and the motor 3
is driven. The auxiliary inverter 4 generates control power necessary to operate the main inverter 2. - The capacity control circuit unit 5 detects the output voltage P and output current l of the solar cell 1 and controls the output of the main inverter 2, that is, the frequency and voltage, so that the solar cell operates at maximum power and effort. In the example, the output voltage of the solar cell 1 is 300 cm, and the maximum power 1 and W1 load 6 is a three-phase 200 cm, 400 W AC motor.

FIG. 4 shows an embodiment of the auxiliary inverter 4. solar cell 1
A dummy load 14 is connected to the b contact 12 of the relay 11, which is directly driven by the output of the relay 11, and an auxiliary inverter 15 is connected to the λ contact 13.

The auxiliary inverter 15 is of a thyristor series capacitor type consisting of two thyristors 16 and 17 connected in series and capacitors 18 and 19 connected in parallel to each thyristor, and the level transformer 2L is controlled by the output of the control circuit 20.
22, and various power sources for the main inverter 2 are independently taken out from the secondary winding of the output transformer 26. The auxiliary inverter 15 also has its own starting circuit 24.

This circuit consists of a Zener diode 25 and a resistor 26.2.
The output voltage of the solar cell is reduced by two series-connected transistors 28 , 29 whose base current is supplied through a series circuit of 7 and then supplied to the control circuit 20 through a diode 30 . Power supply to the control circuit 20 is normally performed by a power supply circuit that rectifies one of the secondary side outputs 23A of the output transformer 2B using a rectifier 61. The relationship between the starting circuit 24 and the steady power supply circuit is that the control circuit 20 is initially started by power supplied from the starting circuit 24, but when the auxiliary inverter 61 is activated and the rectifier 61 outputs DC, the rectifier Since the voltage of the DC output of 61 is higher, the diode 30 is cut off, and the starting circuit 24 is then stopped.
uses the output voltage (■) and output current (■) of the solar cell 1 as input signals, and outputs the power of the solar cell, which is the product thereof, P=VxI.

The differentiating circuit 42 outputs an H level when the power P is 0, and outputs an L level when the power P reaches 0. In the ramp function circuit 44, when the potential at point A is positive, the output rises in a gradient manner, and when the potential at point A is negative, the output decreases in a gradient manner. This ramp function circuit 44
A bidirectional Zener diode 45 connected between the input and output terminals of is used to clamp the upper and lower limits. The inverting circuit 46 decreases the oscillation frequency and power voltage of the inverter 2 when the output of the ramp function circuit 44 is increasing, and conversely decreases the oscillation frequency and the voice power voltage of the inverter 20 when the output of the ramp function circuit 44 is decreasing. Increase output voltage. An exclusive OR circuit (EX-OR) 48 outputs a positive voltage when both B and C are positive or both negative,
When one of the two manual forces B and C is positive and the other is negative, a negative voltage is output. The pie stable latch circuit 47 has an input A
When the control terminal is at H level, human power A is transmitted to output B. An OR circuit (OR) 49 outputs an H level when either the output C of the comparator 43 or the output of the clock pulse CP is at an H level. The clock pulse generator 50 outputs a clock pulse CP, for example, once every second.

In the circuit section 5 described above, the multiplier 41 constitutes the power calculation means I1, the differentiating circuit 42, the comparator 43, the bistable latch circuit 47, the EX-OR 48, and the OR gate 4.
9. The circuit network 40 including the clock pulse generator 50 constitutes a current differential calculation means, and the ramp function circuit 44, the inversion circuit 46, and the control section 71 of the main inverter 2, which will be described later, constitute an inverter control means.

Next, the operation of this capacity control circuit section 5 will be explained.

When the input terminal A point of the ramp function circuit is Hi, inverter 2
The output of the pump increases and the load pump rotation speed increases. On the contrary, when the input terminal A point of the ramp function circuit is LO, the output of the inverter 2 decreases and the pump rotation speed of the load decreases.

Also, when the output of the inverter 2 is increasing, the output terminal C of the threshold comparator 43 becomes Hi level, and on the contrary, when the output of the inverter 2 is decreasing, the output terminal C of the threshold comparator 43 becomes Hi level. It becomes Lo level.

On the other hand, when the output end of the comparator 43 at point C is at Hi level, the output of the OR gate 49 is always at Hi level, and at this time, when point A is at Hi level, both EX-OR outputs are at Hi level. If point A is LOOR then EX-OR
Similarly, since one of the two-manpower is Hl and the other is Lo, E
It matches the Lo level of the output point A of the X-OR and maintains the same state stably. On the other hand, comparator 43
When the output terminal C point is at Lo level, the output of the OR gate becomes Hi level only when the clock pulse is activated. When point C is at Lo level and point A is at Hi level, one of the two outputs of EX-OR becomes LO and the other becomes Hi due to the generation of the clock level, so the output of EX-OR is Lo.
Flip to level. When point C is at Lo level and point A is also at Lo level, EX-OR's 2
Since the human power is both at the KLo level, the output of EX-OR is inverted to the Hi level. After the EX-OR output is inverted from Lo to HiVc in this way, it is necessary to invert it again because the pulse width of the clock pulse is much shorter than the time constant of the integrating circuit made up of resistor k and capacitor C. Therefore, as shown in Figure 2, when the operating point of the solar cell is below the maximum output point and the inverter output is increasing, the A point is already at the LO1C point, and the LO1C point is at Hi level. When, and
As shown in Figure 2 ■, when the operating point of the solar cell is above the maximum output point and the inverter output is decreasing, if point A is already at Lo level and point C is at Hi level, both If the current state continues, the operating point of the solar cell will approach the maximum output point. In addition, as shown in Figure 2 ■, solar cells
・When the operating point is below the maximum output point and the inverter output is decreasing, point A is LO and point C is LOOR.
and when the operating point of the solar cell is below the maximum output point and the inverter output is increasing as shown in Figure 2 ■, when point A is already at Hi level and point C is at Lo level. In both cases, the operating point of the solar cell is far away from the maximum output point, but by reversing the output direction of EX-OR, the operating point changes toward the maximum output point.

FIG. 6 shows an embodiment of the main inverter of the present invention.

Switching transistors 53, 54, 55 are connected to the positive output line 51 of the solar cell 1, and switching transistors 56, 57, 58 are connected to the negative output line 52 in a bridge configuration to form a three-phase AC output terminal U.

■, connected to W, feedback diode 59, 60, 61, 62゜63.64 in parallel with each switching transistor
Connect. Each of the switching transistors 53 to 58 is connected to a respective drive circuit 65, 66° 67.68, 69, 7
0, and each of the drive circuits 65 to 70 is powered by an independent power source in a mutually busy circuit manner using the output transformer 23 of the auxiliary inverter 4. On the other hand, auxiliary inverter 4
The control unit 71, which is supplied with power, has a built-in oscillator, frequency dividing circuit, hexadecimal counter, one-shot multivibrator, gate circuit, etc., and generates six-phase square waves B, , B, ,
B.

B4. Outputs B,,B,. The frequency and pulse width of this six-phase square wave are controlled by the output of the capacity control circuit 5. Output of these 6 phases H”+ p Bt tBs
yB, , B, , B, and each of the drive circuits 65 to 70 are electrically insulated and coupled by photocouplers 72, 73, 74, 75, 76, and 77, respectively. Photocoupler 7
Reference numerals 2 to 77 each include a pair of light emitting diodes E, -E6 and phototransistors P1 to P.

FIG. 7 shows a waveform diagram of the main part of the main inverter shown in FIG. 6. The output frequency of the inverter is defined by the clock frequency, and the output current is controlled by the time width of the output BO of the one-shot multivibrator. Note that the output voltage is determined by the operating point of the solar cell. One period of AC output is formed using six square wave output signals BO. The output of the hexadecimal counter and the gate circuit extract two consecutive square wave outputs as shown in the figure to form six-phase square waves B, ~B-, and this signal causes switching transistors 56 to 58 to be output.
is controlled to open and close.

The capacity control circuit 5 of the present invention stores the output current at the maximum output point for each characteristic curve in the read-only memory of the microcomputer, and controls the main inverter by comparing the magnitude relationship between the output current and the stored value. According to the present invention, the operating point of the solar cell is always corrected to the maximum output point regardless of changes in the usage conditions of the solar cell, so that the load can always be operated at maximum efficiency. Therefore, for example, if solar cells are installed in a desert and used for purposes such as pumping underground water to the surface, the effect is particularly large.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams explaining the principle of the present invention. 3 is a circuit block diagram showing the entire embodiment of the present invention, FIG. 4 is a circuit diagram showing an embodiment of the auxiliary inverter 4 in FIG. 3, and FIG. 5 is a circuit diagram showing an embodiment of the auxiliary inverter 4 in FIG. 3. FIG. 6 is a circuit diagram showing one embodiment of the main inverter 2 in FIG. 3, and FIG. 7 is a waveform diagram showing the operation of the main inverter 2 in FIG. 1...Solar cell 2...Main inverter 3...AC load 4...Auxiliary inverter 5...Capacity control circuit section 41... ... Multiplier (power calculation means) 40 ...
... Current differential calculation means 44 ... Ramp function circuit Patent applicant Kyoto Ceramic Co., Ltd. Japan Inverter Co., Ltd. Representative Patent attorney Nishi 1) New construction Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] (1) In a device that drives an AC load such as an AC motor by converting the output of a solar cell into AC using an inverter, the output voltage and output current of the solar cell are detected and the product of the voltage and current (P = Vx I), non-current differential calculation means for calculating the power (P), and when the differential value (+) is positive, the output of the inverter is increased, and when it is negative, the output of the inverter is increased. An inverter using a solar cell, comprising an inverter control means for reducing an output of the inverter, and configured such that an operating point of the solar cell tracks a maximum power point.