JP2832667B2 - Solar cell output control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for controlling an output voltage from a solar cell and supplying the load to a load, and more particularly to an apparatus for always outputting maximum power from a solar cell.

[0002]

2. Description of the Related Art As shown in FIG. 6, when a solar cell plate that generates power by receiving solar light has a constant solar radiation amount and temperature, the output current Is has a certain constant value Iop as shown in FIG.
When the output voltage Vs increases as described above, the output voltage Vs rapidly decreases to zero. Maximum output power P of a solar cell having such characteristics
max occurs when the output current is Iop, and the Iop
And the product of the output voltage Vop at this time. The solar cell panel is configured by attaching 40 to 50 such solar cell plates to one panel and connecting them in series or in parallel.

In such a solar panel, when the temperature is kept constant and the amount of solar radiation is changed, the relationship between the output current Is and the output voltage Vs becomes as shown by the solid line in FIG. The curve changes from A1 to A2, and the maximum output point also changes from a1 to a2. As a result, the maximum output point changes as indicated by an a-dot chain line.

Further, in this solar cell panel, when the temperature is changed while the amount of solar radiation is kept constant, the relationship between the output current Is and the output voltage Vs is represented by a curve B1 when the temperature rises as shown by a broken line in FIG. From B1 to B2, and the maximum output point also changes from b1 to b2. As a result, the maximum output point changes as shown by a b-curve indicated by a two-dot chain line.

Accordingly, the maximum output that can be taken out of the solar cell panel in accordance with the change in the amount of solar radiation and the temperature changes in the shaded area in FIG.

[0006]

As described above, the maximum power that can be extracted from the solar cell changes in accordance with changes in temperature and the amount of solar radiation, and it is not possible to efficiently extract the maximum power from the solar cell as it is. There was a problem.

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a solar cell, voltage control means for controlling the output voltage of the solar cell to supply power to a load, and A driving unit that drives the control unit in accordance with a driving signal; a power detection unit that detects an output power of the solar cell; a voltage detection unit that detects an output voltage of the solar cell; A voltage fluctuation signal supply means for supplying a voltage fluctuation signal for gradually changing the output voltage to the means and continuing to supply the voltage fluctuation signal until a voltage optimum value detection signal is supplied; and a maximum value of the output power. Voltage optimum value detection means for generating the voltage optimum value detection signal at the time of occurrence, holding means for holding the output of the voltage detection means in response to generation of the voltage optimum value detection signal, and detection by the voltage detection means. It said drive control signal corresponding to a difference between the output of the output voltage and the holding means is a control means for supplying to said driving means, in which comprises.

[0008]

According to the present invention, the voltage fluctuation signal is supplied to the driving means by the voltage fluctuation signal supplying means every time the predetermined time elapses, and the driving means drives the voltage control means to output the output voltage of the solar cell and Change the output power gradually. These changes in the output voltage and the power are detected by the voltage detecting means and the power detecting means. When the output power reaches the maximum power, the voltage optimum value detecting means generates a voltage optimum value detecting signal. Thus, the voltage fluctuation signal from the voltage fluctuation signal supply unit stops. At the same time, the holding means holds the output voltage of the solar cell at that time by the voltage optimum value detection signal. The control unit supplies a drive control signal to the drive unit according to a difference between the voltage detected by the voltage detection unit and the voltage held by the holding unit. Thereby, the power taken out of the solar cell becomes the maximum power. When the predetermined time has elapsed, the maximum power is detected again in the same manner as described above, the output voltage of the solar cell at that time is held, and voltage control is performed using this as a reference signal. Therefore, even if the temperature or the amount of solar radiation changes during the elapse of the predetermined time, it can be handled.

[0009]

EXAMPLE In this example, as shown in FIG.
The solar cell 1 is connected to a voltage control means, for example, an input side of an inverter 3 via a protection diode 2. This inverter 3 includes a transistor or an IG
It is composed of switching elements 4 to 7 such as BT. A load 8 is connected to an output side of the inverter 3 via a reactor 15. The load 8 is connected to a commercial AC power supply 10 via a switch 9. The switch 9 is closed when a reverse power flow is made from the solar cell 1 to the commercial AC power supply 10.

A voltage detector 1 is connected between the inputs of the inverter 3.
1 for detecting a voltage applied from the solar cell 1 to the inverter 3. Similarly, a current detector 12 is provided in series between the inverter 3 and the solar cell 1, and detects a current supplied from the solar cell 1 to the inverter 3. The detected voltage and the detected current are supplied to the control device 13. Based on the detected voltage and the detected current, the control device 13 supplies a drive control signal to the drive device 14 as described later, and the drive device 14 controls the switch elements 4 to 7 of the inverter 3 to control the power supplied to the load 8 so that the voltage of the solar cell 1 becomes constant.

As shown in FIG. 1, the control device 13 includes a multiplier 21 for multiplying the voltage detected by the voltage detector 11 by the current detected by the current detector 12. Multiplier 2
The multiplied output of 1 indicates the output power extracted from the solar cell 1. The multiplier 21, the voltage detector 11, and the current detector 12 constitute a power detection unit.

The signal representing the output power is supplied to a resistor 22,
The divided voltage is supplied to a comparator 26. The output of the D / A converter 28 is supplied to the comparator 26 as a reference signal, and the comparator 26 generates an output “1” while the divided signal is larger than the reference signal. The output signal of the comparator 26 is supplied to an AND circuit 30. While the output of the comparator 26 is “1”,
A constant frequency clock pulse generated by the clock pulse generator 32 is supplied to the counter 34 via the AND circuit 30. The output of the counter 34 is supplied to the D / A converter 28.

Further, a divided voltage signal of the signal representing the power of the solar cell 1 is also supplied to a comparator 36, and further a D / A
The output of converter 36 is also provided to comparator 36, which is configured to generate an output "1" when the divided signal is less than the output of D / A converter 36. ing. The comparators 26 and 36, the AND circuit 30, the clock pulse generator 32, the counter 34, and the D / A converter 28 constitute voltage optimum value detecting means.

The output of the comparator 36 is supplied to a hold circuit 38, and a voltage signal is also supplied to the hold circuit 38. The output of the comparator 36 of the hold circuit 38 is "1". During the period, the voltage signal immediately before the output of the comparator 36 changes from “0” to “1” is held and output.

The hold output of the hold circuit 38 is
It is supplied to an error amplifier 40. This error amplifier 40
Is also supplied with a divided voltage signal, and an error between the two is amplified, and the error amplifier 40 supplies the amplified voltage to the driving device 14 via the diode 42.

Clock pulse generator 32, counter 3
4. The hold circuit 38 includes a clock pulse control circuit 46
Is reset by the reset pulse signal generated. The clock pulse generator 32 is configured to generate a reset pulse signal when a start signal is externally input to a start signal input terminal 48, and to generate a reset pulse signal every time a predetermined time elapses. ing.

The reset pulse signal is also supplied to the output setting device 50. When a reset pulse signal is supplied, the output setting device 50 supplies, via the diode 52, a drive control signal having a value capable of supplying the minimum voltage Vmin within the maximum current control range from the solar cell 1 to the inverter 3 via the drive device 14. To the inverter 3 over time.
Is configured to change the value of the drive control signal so that the voltage supplied to the maximum voltage Vmax increases toward the maximum voltage Vmax. The output setting device 50 is connected to the comparator 36
When the output “1” is supplied from the controller, the generation of the drive control signal is stopped.

In this embodiment, when the solar cell 1 is irradiated with sunlight, the solar cell 1 excites a voltage, and this voltage is supplied to the inverter 3 via the diode 2, and the voltage is controlled by the inverter 3. And supplied to the load 8.

The control of the inverter 3 is performed as follows. When a start signal is input to the start input terminal 48 at time t0 as shown in FIG. 3A, the clock pulse generator 32 generates a reset pulse signal as shown in FIG. The reset pulse signal causes the clock pulse generator 32, counter 34, hold circuit 3
8 is reset, and in order to gradually increase the voltage applied to the inverter 3 from the minimum voltage Vmin to the maximum voltage Vmax, the output setting device 50 changes the value of the drive control signal as shown in FIG. Change it gradually.

As described above, when the voltage is changed from Vmin to Vmax, the electric power P that can be extracted from the solar cell 1 gradually increases as shown in FIG.
x and then decrease.

In order to detect the state where the maximum power Pmax is obtained, the detection output of the voltage detector 11 and the detection output of the current detector 12 are multiplied by a multiplier 21 to obtain a state shown in FIG.
A signal representing power is generated as shown in (e). This signal is divided by resistors 22 and 23 and
Where it is compared with the output from the D / A converter 28.

However, since the counter 34 supplying the signal to the D / A converter 28 is initially reset and the output is 0, the output of the D / A converter 28 is also 0 and the divided voltage signal is output. Is larger than the output of the D / A converter 28, the output of the comparator 26 is "1" as shown in FIG.
Becomes

Since this output "1" is supplied to the AND circuit 30, as shown in FIG.
The clock pulse of the clock pulse generator 32 is supplied to the counter 34 via the counter, where it is counted and the count value is increased. This is converted by the D / A converter 28 into an analog signal and supplied to the comparator 26. Therefore, the comparator 26
Is increased as the voltage from the solar cell 1 increases from Vmin.

After the power detected by the multiplier 21 reaches the maximum power Pmax, and becomes slightly smaller than Pmax at time t1, the divided voltage signal supplied to the comparator 26 becomes larger than the D / A converter. Since the output is smaller than the output of the comparator 28 (corresponding to the maximum power), the output of the comparator 26 becomes “0” as shown in FIG. As a result, the supply of the clock pulse to the counter 34 via the AND circuit 30 is stopped as shown in FIG.

On the other hand, the comparator 36 also supplies the divided voltage signal and the D / A
Since the output signal of the converter 28 is supplied, the time t
At 1, the comparator 36 supplies the output “1” to the hold circuit 38 as shown in FIG. by this,
The hold circuit 38 holds a voltage signal (a voltage signal when the maximum power Pmax is generated) generated immediately before the output becomes “1”. Also, the output “1” of the comparator 36
Is supplied to the output setting device 50, and the output setting device 50 stops supplying the drive control signal as shown in FIG.

Thereafter, the difference between the holding signal (the voltage signal when the maximum power Pmax is generated) held in the holding circuit 38 and the voltage signal is amplified by the error amplifier 40 and passed through the diode 42 as a drive control signal. To the drive device 14. Thereafter, feedback control is performed so that the maximum power Pmax is extracted from the solar cell 1.

At time t2 when a predetermined time T2 has elapsed from time t0, the clock pulse control circuit 46 outputs a reset pulse to the clock pulse generator 32, counter 34, hold circuit 38, output setting Supply to the device 50. Thereafter, in the same manner as described above, the maximum power is detected, the output voltage when this maximum power is generated is held, and control is performed based on the held voltage.

Therefore, if the time T1 from time t0 to time t1 is selected to be sufficiently shorter (for example, 1/10) than the period (T2-T1) during which the maximum power Pmax is constantly output, , The period from time t1 to t2,
Maximum power can be extracted. Further, if the period T2 from when the reset pulse is generated to when it is generated again is set to be relatively short (for example, 1 minute), the maximum power after the change can be obtained even if the amount of solar radiation or the temperature changes. .

In the above embodiment, the two comparators 26, 3
6, the comparator 36 is removed, and the comparator 26
May be inverted by an inverter and supplied to the hold circuit 38 and the output setting device 50.

In the above embodiment, analog control is mainly performed, but digital control may be performed using a microcomputer or the like. In this case, FIG.
In the same manner as in the above case, the solar cell 1, the protection diode 2, the inverter 3, the voltage detector 11, and the current detector 12 are used, and the outputs of the voltage detector 11 and the current detector 12 are digitized and supplied to the microcomputer. The output of the microcomputer is converted into an analog signal by a D / A converter and supplied to the switching elements 4 to 7 of the inverter 3.

FIG. 5 shows a flowchart in this case.
First, the output voltage and output current of the solar cell 1 are detected (Step S2), and the output power is calculated (Step S4).
It is determined whether this power is the maximum value (step S6).
If it is not the maximum value, the voltage supplied to the inverter 3 is Vm
The control value is changed so as to slightly change from in to the Vmax side (step S8), and the inverter 3 is controlled according to the control value (step S10), and the process returns to step S2.
Until the power reaches the maximum value, steps S2, 4, 6, 8,
Execute 10 loops.

When the maximum power is eventually detected (the determination in step S6 is YES), the control value at that time, that is, the output voltage optimum value is stored (step S12), and the output power of the solar cell 1 becomes the maximum power. In other words, the constant voltage control is performed on the inverter 3 so as to correspond to the control value stored in step S12 (step S18). Then, it is determined whether a predetermined time has elapsed (step S2).
0), if it has not elapsed (the determination in step S20 is NO), the process returns to step S18, the loop of steps S18 and S20 is executed, and the constant voltage control is continued. Step S2
When the determination of 0 is YES, that is, when the predetermined time has elapsed, the process returns to step S2, and the control value is reset again.

[0033]

As described above, according to the present invention, the output voltage optimum value for generating the maximum power to be taken out of the solar cell is detected and held, and the held output voltage optimum value is used as a reference signal to determine a predetermined value. During the time, the voltage control means is controlled, and after a predetermined time elapses, the output voltage optimum value is detected and held again, and the voltage control is performed for a predetermined time using the held output voltage optimum value as a reference signal. Since the control of the means is repeated, the maximum power can always be taken out of the solar cell even if there is a change in the amount of solar radiation or the temperature.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a first embodiment of a solar cell output control device according to the present invention.

FIG. 2 is an overall block diagram of the first embodiment.

FIG. 3 is a timing chart for explaining the operation of the first embodiment.

FIG. 4 is a diagram showing a relationship between output current and power of the solar cell used in the first embodiment.

FIG. 5 is a flowchart of the second embodiment.

FIG. 6 is a diagram illustrating a relationship between an output current and an output voltage of a solar cell.

FIG. 7 is a diagram showing a state in which the relationship between the output current and the output voltage of the solar cell changes according to changes in the amount of solar radiation and the temperature.

FIG. 8 is a diagram showing a state in which the maximum power in a solar cell changes according to changes in the amount of solar radiation and the temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solar cell 3 Inverter (voltage control means) 8 Load 11 Voltage detector (power detection means) 12 Current detector (power detection means) 14 Drive device (drive means) 21 Multiplier (power detection means) 26 Comparator (voltage) Optimal value detecting means) 28 D / A converter (voltage optimal value detecting means) 30 AND circuit (voltage optimal value detecting means) 32 clock pulse generator (voltage optimal value detecting means) 34 counter (voltage optimal value detecting means) 36 Comparator (voltage optimum value detecting means) 38 Hold circuit (holding means) 40 Error amplifier (control means) 50 Output setting device (voltage fluctuation signal supplying means)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-70315 (JP, A) JP-A-63-36318 (JP, A) JP-A-62-85312 (JP, A) 97721 (JP, A) JP-A-60-118919 (JP, A) JP-A-53-81911 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G05F 1/67 H02M 7 / 48-7/98

Claims (1)

(57) [Claims] 1. A solar cell, voltage control means for controlling the output voltage of the solar cell to supply power to a load, driving means for driving the voltage control means in accordance with a drive signal, Power detection means for detecting the output power, voltage detection means for detecting the output voltage of the solar cell, and a voltage fluctuation signal for gradually changing the output voltage to the driving means every time a predetermined time elapses. Voltage fluctuation signal supply means for continuing to supply the voltage fluctuation signal until a voltage optimum value detection signal is supplied, voltage optimum value detection means for generating the voltage optimum value detection signal when the maximum value of the output power is generated, Holding means for holding the output of the voltage detecting means in response to the generation of the voltage optimum value detection signal; and a control means for controlling a difference between the output voltage detected by the voltage detecting means and the output of the holding means. A control unit for supplying the driving control signal to the driving unit.