JPH06309047A - Solar battery power source - Google Patents

Abstract

PURPOSE:To simplify a control circuit, to reduce the cost of a device and to improve the reliability as to the solar battery power source which converts the DC electric power outputted from a solar battery into AC electric power and outputs it. CONSTITUTION:The solar battery power source 1 has the solar battery PV, a converter 11 which converts the output of the solar battery into DC electric power having a different voltage, and an inverter 12 which converts the DC electric power outputted by the converter 11 into AC electric power; and the switching circuit 21 of the converter is controlled with pulses whose duty ratio is fixed and pulse width modulation control is performed for the switching circuit 31 of the inverter 12 so as to hold the input voltage to the inverter 12 constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell power source for converting DC power output from a solar cell into AC power and outputting the AC power.

[0002]

2. Description of the Related Art Solar cell power sources are used in various systems such as lighting systems, solar air conditioner systems, or systems that are connected to a power system, and greatly contribute to energy saving of the systems. The power generated by the solar cell fluctuates greatly according to the amount of solar radiation from the sun.Therefore, in the solar cell power supply, control is performed to reduce the effect as much as possible and to efficiently convert the power generated by the solar cell into AC power. ing.

FIG. 4 is a block diagram showing the structure of a conventional solar cell power supply 80. The solar battery power source 80 is the solar battery P.
V, DC voltage V1 output from the solar cell PV (for example, 10
DC / DC converter 81 for boosting 0V) to output DC power of voltage V2 (for example, 200V), and DC / D
Inverter 1 for converting the DC power output from the C converter 81 into AC power of voltage V3 (for example, 100 Vrms)
It consists of two.

The DC / DC converter 81 is a MOSFET.
It has a switching circuit 21 configured by using switching elements such as T and IGBT and a transformer for boosting, and a PWM control circuit 92 for controlling the switching circuit 21.

In the DC / DC converter 81, in order to use the generated power of the solar cell PV as efficiently as possible, the PWM control circuit 92 is set to a voltage close to the optimum operating point of the solar cell PV (here, 100 V). The constant input voltage is controlled by.

That is, in FIG. 3 showing an example of the output characteristics of the solar cell PV, the output characteristics of the solar cell PV change as curves CV1 to 3 when the amount of solar radiation to the solar cell PV changes. In these curves CV1 to CV3, the point at which the output power becomes maximum (the optimum operating point) changes like P1 to P3. Therefore, in the DC / DC converter 81, even if the amount of solar radiation fluctuates, It is desirable to perform the maximum power tracking control so that the battery PV always operates at the optimum operating points P1 to P3. However, as you can see from Figure 3,
Since the change in the voltage (optimal operating voltage) at the optimal operating points P1 to P3 is small, the voltage should be constant near the center (for example, 100V) within the variation range of the optimal operating voltage for the sake of simplification of the control circuit. The input voltage constant control is performed.

The inverter 12 has a switching circuit 31 formed by using switching elements similar to those of the DC / DC converter 81, and a PWM control circuit 34 for controlling the switching circuit 31. The inverter 12 is controlled so that the input voltage V2 and the output voltage V3 thereof are constant by varying the output current.

Next, the operation of the conventional solar cell power source 80 will be described. First, it is assumed that the amount of solar radiation is such that the output characteristic of the solar cell PV becomes the curve CV2. It is assumed that the DC / DC converter 81 performs PWM control so that the input voltage V1 has a constant value (100V), whereby the solar cell PV is operating at the operating point a. At this time, if it is assumed that the DC / DC converter 81 has no load, the output voltage V2 thereof is determined by the following equation (1) based on the duty ratio (Ton / T) determined by the PWM control. .

V2 = (Ns / Np) × V1 × (Ton / T) (1) where Ns / Np is the transformer winding ratio. However, since the inverter 12 is actually connected as the load of the DC / DC converter 81, the variable pulse width control (PWM control) is performed by the inverter 12 so that the output voltage V2 becomes a constant value (200V). The DC / DC converter 81 supplies a current to the inverter 12 to maintain the voltage V2. As described herein, the term “PWM control” may be used to mean that the pulse width is variably controlled in order to maintain or change the voltage.

In such a state, the amount of solar radiation decreases, and the output characteristics of the solar cell PV change from the curve CV2 to the curve CV.
Suppose it changed to 3. When the DC / DC converter 81 does not perform any control, the operating point of the solar cell PV is a
Although the point shifts to the point b, the operating point is the point b1 on the curve CV3 because the constant input voltage control is performed. This is because the DC / DC converter 81 acts as an impedance converter.

Then, the output voltage V2 of the DC / DC converter 81 will naturally change due to the change in the pulse width due to the constant input voltage control. The DC / DC converter 81 performs PWM control so that the output voltage V2 of the DC / DC converter 81 does not change. At this time, DC /
When viewed from the side of the DC converter 81, the inverter 12 is a load, but the impedance of the inverter 12 changes when the inverter 12 performs PWM control. Since the change in the impedance of the inverter 12 changes the input voltage V1 of the DC / DC converter 81, the DC / DC converter 81
Also performs PWM control. This also allows DC / D
Since the output voltage V2 of the C converter 81 changes, the inverter also performs PWM control.

By repeating the above series of operations, the control of the DC / DC converter 81 and the inverter 12 finally converges, and is stabilized in the state where the above-mentioned constant voltage is maintained.

When the amount of solar radiation increases and the output characteristic of the solar cell PV changes from the curve CV2 to the curve CV1, the PWM control is performed so that the operating point becomes the point c1 as described above.

[0014]

As described above, in the conventional case, the DC / DC converter 81 and the inverter 1 are used.
In 2 and 2, PWM control was individually performed. Therefore, complicated PWM control circuits 92 and 34 are required separately for each of them, resulting in a complicated overall circuit and an increase in the number of components, which is a problem in reducing the cost and improving the reliability of the device. Was becoming.

In view of such problems, it is an object of the present invention to simplify the control circuit, reduce the cost of the device and improve the reliability.

[0016]

In order to solve the above-mentioned problems, an apparatus according to the invention of claim 1 is a solar cell, and a DC / D for converting the output of the solar cell into DC power of different voltage.
In a solar cell power supply having a C converter and an inverter that converts DC power output from the DC / DC converter into AC power, a switching element of the DC / DC converter is controlled by a pulse with a fixed duty ratio. The pulse width modulation control is performed on the switching element of the inverter so that the input voltage to the inverter is constant.

The apparatus according to the invention of claim 2 is the DC /
The switching element of the DC converter is controlled by a pulse having a fixed duty ratio, and the maximum power tracking for maximizing the magnitude of the power input from the DC / DC converter to the switching element of the inverter is performed. The pulse width modulation control is performed so as to perform.

[0018]

Since the switching element of the DC / DC converter is controlled by the pulse having the fixed duty ratio, the ratio (step-up ratio) between the input voltage and the output voltage of the DC / DC converter becomes constant.

When the input voltage constant control is performed in the inverter, the input voltage of the inverter, that is, DC
The output voltage of the / DC converter is kept constant, so that the input voltage of the DC / DC converter is kept constant.

In the inverter, when the maximum power tracking control is performed, the power input to the DC / DC converter is controlled to be maximum, and as a result, the solar cell operates at the optimum operating point. Controlled.

[0021]

1 is a block diagram showing the configuration of a solar cell power supply 1 according to the present invention. In the solar cell power supply 1 shown in FIG. 1, the biggest difference from the solar cell power supply 80 shown in FIG. 4 is the control circuit 22 of the DC / DC converter 11. In FIG. 1, elements having the same actions as those described with reference to FIG. 4 are designated by the same reference numerals, and description thereof will be omitted or simplified.

The solar cell power source 1 includes a solar cell PV, a DC / DC converter 11 for stepping up a DC voltage V1 output from the solar cell PV and outputting a DC power of a voltage V2, and a DC.
The DC / DC converter 11 includes an inverter 12 for converting DC power output from the / DC converter 11 into AC power having a voltage V3.

The DC / DC converter 11 has a switching circuit 21 and a control circuit 22 for controlling the switching circuit 21. The control circuit 22 outputs to the switching circuit 21 a pulse signal S1 in which the duty ratio Rd is fixed to a constant value. Since the duty ratio Rd of the pulse signal S1 output from the control circuit 22 is constant, the ratio of the input voltage V1 and the output voltage V2 of the DC / DC converter 11 (( Boost ratio) becomes constant. Inverter 12
In the above, control is performed so that the input voltage V2 and the output voltage V3 are constant.

Therefore, the output voltage V1 of the solar cell PV is
Is boosted to a voltage V2 having a boosting ratio determined by the duty ratio Rd by the DC / DC converter 11 and input to the inverter 12. Since the inverter 12 is controlled to keep the input voltage V2 constant, D
The output voltage V2 of the C / DC converter 11 is kept constant, and eventually the input voltage V1 of the DC / DC converter 11 is kept constant. Therefore, the output voltage V1 of the solar cell PV becomes constant, and the solar cell PV always operates at a voltage close to the optimum operating point.

As described above, the solar cell power source 1 operates so that the output voltage of the solar cell PV is constant, and as a result, the solar cell PV is always operated in the vicinity of the optimum operating point and its generated power is effective. Can be used for. Moreover,
The control circuit 22 uses the pulse signal S with a constant duty ratio Rd.
Since only 1 should be output, the circuit configuration is extremely simple, and cost reduction and reliability improvement can be achieved. Further, the control circuit 22 does not have to make any response to changes in the amount of solar radiation or the load, and the PWM control circuit 32 performs the entire control. Therefore, the control is unified and the control is performed. Responsiveness is improved.

FIG. 2 is a circuit diagram showing the configuration of a solar cell power source 1a according to another embodiment of the present invention. The circuit is simplified. The solar battery power source 1a is a solar battery PV, DC
It is composed of a / DC converter 11a and an inverter 12a.

The DC / DC converter 11a has a switching circuit 21a and a control circuit 22a, and the inverter 12a has a switching circuit 31a and a PWM control circuit 32a.

The switching circuit 21a includes two transistors Q1 and Q2, a capacitor C1, a transformer T1, diodes D1 and D2, a reactor L1 and a capacitor C2.
Etc.

The control circuit 22a outputs an oscillator 51 which generates a pulse train having a constant duty ratio Rd, and a driver 52 which outputs two pulse signals S1 for switching and driving the transistors Q1 and Q2 based on the pulse train from the oscillator 51. It consists of

The switching circuit 31a includes two resistors R1 and R2 for voltage detection, four transistors Q3 to Q6 connected in a bridge, resistors R3 and R4, a reactor L2, a capacitor C3 and the like. The PWM control circuit 32a includes two resistors R5 and R6 for voltage setting, a differential amplifier 53, a multiplier 54, a bandpass filter 55,
It comprises a high-pass filter 56, a comparator 57, a driver 58, an insulating transformer 59 and the like.

Therefore, the transistors Q1 and Q2 are alternately turned on for a predetermined time by the pulse signal S1 from the driver 52, and in response thereto, currents in opposite directions flow to the primary side of the transformer T1 by the output of the solar cell PV. . On the secondary side of the transformer T1, a voltage boosted according to the winding number ratio Ns / Np of the transformer T1 is generated, which is rectified by the diodes D1 and D2, and the reactor L1.
And smoothed by the capacitor C2.

DC voltage V generated across the capacitor C2
2 is converted into an AC voltage by the switching of the transistors Q3 to Q6, and the reactor L2 and the capacitor C
It is output through a filter consisting of 3.

At this time, the DC voltage V2 input to the inverter 12a is detected by the resistors R1 and R2, and the waveform of the AC voltage output from the inverter 12a is the resistance R3.
It is detected by R4 and the transformer 59 for insulation. The detected input voltage V2 is input to the differential amplifier 53,
A voltage according to the difference from the set voltage set by the resistors R5 and R6 is output from the differential amplifier 53. This differential voltage is multiplied by the detected AC voltage waveform by the multiplier 54, and output from the multiplier 54 as a current command value. Then, it is passed through a high-pass filter 56 and input to a comparator 57, where it is compared with a triangular wave and pulse width modulation is performed. Then, from the driver 58, the transistors Q3 to Q
6 is output as a pulse signal S2 for switching driving.

That is, the inverter 12a performs constant input voltage control so that the difference between the input voltage V2 and the set voltage becomes zero. Such control operation of the inverter 12a is known.

Here, it is assumed that the output characteristic of the solar cell PV is such that the amount of solar radiation is such that the curve CV2 in FIG. 3 is obtained.
In the DC / DC converter 11a, since the duty ratio Rd of the pulse signal S1 is constant, the ratio (step-up ratio) between the input voltage V1 and the output voltage V2 is constant. Therefore,
A voltage V2 generated by boosting the input voltage V1 according to the boosting ratio is generated across the capacitor C2. Inverter 12a
Performs PWM control (input voltage constant control) so as to maintain the voltage V2 at a constant value. By PWM control, D
The impedance of the inverter 12a viewed from the C / DC converter 11a changes.

In such a state, the amount of solar radiation decreases and the output characteristics of the solar cell PV change from the curve CV2 to the curve CV.
Suppose it changed to 3. Since the duty ratio Rd in the DC / DC converter 11a is constant, the operating point tries to shift from the point a to the point b. However, if that happens, the output voltage V2 of the DC / DC converter 11a also decreases. Therefore, the inverter 12a performs PWM control so as to maintain it constant without lowering it. This PWM
By the control, the impedance of the inverter 12a becomes high, and the input voltage V1 of the DC / DC converter 11a, that is, the operating point of the solar cell PV becomes the point b1 instead of the point b.

That is, the input voltage constant control is performed in the inverter 12a, and the DC / DC converter 11 is controlled.
Since the step-up ratio is controlled to be constant at a, the input voltage V of the DC / DC converter 11a is consequently increased.
Control is performed so that 1 becomes constant, and the operating voltage of the solar cell PV becomes constant.

As described above, the solar cell power source 1a operates so that the output voltage V1 of the solar cell PV is constant, and as a result, the solar cell PV is always operated in the vicinity of the optimum operating point to generate its generated power. It can be used effectively. Moreover, since the control circuit 22a may have a simple circuit configuration including the oscillator 51 and the driver 52, the number of parts can be reduced, and the cost and the reliability can be improved.

In the above embodiment, for example, when the output voltage V3 of the inverter 12a is 200 Vrms, the input voltage V2 of the inverter 12a needs to be about 400V. Therefore, when the step-up ratio of the DC / DC converter 11a is "2", the output voltage V1 of the solar cell PV may be about 200V.

In the above embodiment, the inverter 1
2 and 12a have been described as performing constant input voltage control, but instead of this, DC / DC converters 11 and 1
The maximum power tracking control for maximizing the magnitude of the power input from 1a may be performed. By doing so, the operating point of the solar cell PV can always be maintained at the optimum operating point regardless of the change in the output characteristic of the solar cell PV due to the fluctuation of the amount of solar radiation, only by the maximum power tracking control of the inverters 12 and 12a. .

In the above embodiment, the solar cells PV, D
C / DC converters 11 and 11a and inverter 1
The circuit configurations of 2, 12a, the types of elements, and the like can be variously changed in accordance with the gist of the present invention.

[0042]

According to the present invention, the control circuit can be simplified, and the cost of the device can be reduced and the reliability can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a solar cell power source according to the present invention.

FIG. 2 is a circuit diagram showing a configuration of a solar cell power source according to another embodiment of the present invention.

FIG. 3 is a diagram showing an example of output characteristics of a solar cell.

FIG. 4 is a block diagram showing a configuration of a conventional solar cell power supply.

[Explanation of symbols]

1, 1a Solar cell power supply 11, 11a DC / DC converter 12, 12a Inverter 21 Switching circuit (switching element of DC / DC converter) 31 Switching circuit (switching element of inverter) Q1, Q2 Transistor (switching element of DC / DC converter) ) Q3, Q4, Q5, Q6 Transistors (switching elements of inverters) PV solar cells

Claims (2)

[Claims] 1. A solar cell, comprising a DC / DC converter for converting the output of the solar cell into DC power of different voltage, and an inverter for converting the DC power output by the DC / DC converter into AC power. In a solar cell power supply, a switching element of the DC / DC converter is controlled by a pulse having a fixed duty ratio, and a pulse width modulation is performed on the switching element of the inverter so that an input voltage to the inverter is constant. A solar cell power supply characterized by being controlled. 2. A solar cell, a DC / DC converter for converting the output of the solar cell into DC power of different voltage, and an inverter for converting the DC power output by the DC / DC converter into AC power. In the solar cell power supply, the switching element of the DC / DC converter is controlled by a pulse with a fixed duty ratio, and the DC of the switching element of the inverter is controlled.
The solar cell power supply is characterized in that pulse width modulation control is performed so as to perform maximum power tracking to maximize the amount of power input from the DC converter.