JP2001103675A - Device and method for controlling solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly search the optimum operating point of a solar battery. SOLUTION: The control device is provided with a current voltage characteristic-grasping means 100 for approximately grasping current-voltage characteristics by measuring current the open voltage of a solar battery 3, short-circuiting current, and current when being controlled to a voltage that is slightly smaller than the open voltage, an optimum operation point determination means 101 for determining an optimum operating point according to the cross point between a first characteristic straight line L1 for indicating the open voltage and a current when being controlled to a voltage that is slightly smaller than the open voltage, and a second characteristic straight line L2 for indicating the characteristics of the short-circuiting current, and a control means 102 for controlling the current of the solar cell so that the solar battery voltage reaches the voltage of an optimum operation point P1 while a load is connected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell control device and a solar cell control method.

[0002]

2. Description of the Related Art Solar cells are used in various devices for supplying electric power and in cooling and heating devices in houses. The output characteristics of this solar cell are represented in FIG. 4 as current-voltage characteristics A, B, and C, and these characteristics change due to various factors (illuminance, temperature, individual difference, aging, etc.) in an actual operation state. .

That is, the characteristics of the solar cell voltage at which the maximum output is obtained change. Therefore, in order to increase the power generation efficiency in the actual operation state, it is necessary to obtain a solar cell voltage at which the maximum power can be taken out in that state by some method, and to control the voltage to be the voltage.

Conventionally, a generally used method for searching for an optimum operating point is called a hill-climbing method. In this method, the output voltage of a solar cell is gradually changed by an output current, and the power at that time is calculated. While searching for the maximum point of power.

[0005]

By the way, in the hill-climbing method, the amount of change in voltage near the optimum operating point is small even if the current is changed, and therefore the amount of change in power, which is the product thereof, is also small. Therefore, in the case of digital control, an A / D converter having a high resolution is required in order to accurately search for the optimum operating point, and the step size of the current to be changed must be narrowed. It takes time to search for an operating point.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a solar cell control device and a solar cell control method capable of searching for an optimum operating point of a solar cell in a short time. And

[0007]

Means for Solving the Problems In order to solve the above problems and achieve the object, the present invention has the following constitution.

According to the first aspect of the present invention, there is provided a method of measuring a current obtained by controlling the open-circuit voltage, short-circuit current, and voltage slightly lower than the open-circuit voltage of a solar cell to obtain a current-voltage characteristic approximately. An optimum operating point is determined from a voltage characteristic grasping means and an intersection of an open-circuit voltage and a first characteristic line indicating a current when controlled to a voltage slightly lower than the open-circuit voltage and a second characteristic line indicating a characteristic of the short-circuit current. A control device for controlling a solar cell current so that the solar cell voltage becomes an optimum operating point voltage with a load connected thereto. ].

According to the first aspect of the present invention, the current-voltage characteristic is approximately grasped, and the open-circuit voltage and the first characteristic line representing the current when the voltage is controlled to a voltage slightly lower than the open-circuit voltage are obtained. The optimum operating point is determined from the intersection with the second characteristic line indicating the characteristics of the short-circuit current, and the solar cell current can be controlled so that the solar cell voltage becomes the optimum operating point voltage with the load connected.

The invention according to claim 2 is characterized in that the control means for controlling the solar cell current uses a moving average result of the estimated value of the optimum operating point voltage as the target solar cell voltage. 3. The control device for a solar cell according to 1. ].

According to the second aspect of the present invention, the moving average result of the estimated value of the optimum operating point voltage is used as the target solar cell voltage, so that even if the amount of solar radiation fluctuates instantaneously, it is hardly affected. .

[0012] The invention according to claim 3 is based on "an open-circuit voltage of a solar cell, a short-circuit current, and a current when controlled to a voltage slightly lower than the open-circuit voltage to approximately grasp a current-voltage characteristic, The optimum operating point is determined from the intersection of the first characteristic line indicating the open-circuit voltage and the current when controlled to a voltage slightly lower than the open-circuit voltage and the second characteristic line indicating the characteristic of the short-circuit current, and the load is connected. A method for controlling a solar cell, comprising: controlling a solar cell current so that the solar cell voltage becomes an optimum operating point voltage in a state where the solar cell is in a de-energized state. ].

According to the third aspect of the present invention, the current-voltage characteristic is approximately grasped, and the open-circuit voltage and the first characteristic line indicating the current when the voltage is controlled to a voltage slightly lower than the open-circuit voltage are obtained. The optimum operating point is determined in a short time from the intersection with the second characteristic line indicating the characteristics of the short-circuit current, and the solar cell current is controlled so that the solar cell voltage becomes the optimum operating point voltage with the load connected. be able to.

According to a fourth aspect of the present invention, there is provided a method for controlling a solar cell according to the third aspect, wherein a moving average result of the estimated value of the optimum operating point voltage is used as a target solar cell voltage. ].

According to the fourth aspect of the present invention, the moving average result of the estimated value of the optimum operating point voltage is used as the target solar cell voltage, so that even if the amount of solar radiation fluctuates instantaneously, it is hardly affected. .

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a solar cell control device and a solar cell control method according to the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a control device for a solar cell, and FIG. 2 is a diagram for explaining calculation of an optimum operating point.

A battery 2 and a solar cell 3 are connected in parallel to the load 1, and the load 1 is driven by the power of the battery 2 and the solar cell 3. Output line 4 on the positive side of solar cell 3
Is connected to the diode D1 and the inductance 20, and the diode D1 prevents backflow of current.
The positive output line 4 and the negative output line 5 have:
The capacitor C1 is connected, and the capacitor C1 is in parallel with the solar cell 3.

A field effect transistor FET1 is connected to the positive output line 4 of the solar cell 3, and a field effect transistor FET2 is connected between the positive output line 4 and the negative output line 5. The gate of the field effect transistor FET1 is connected to the solar cell voltage control circuit 11 via the resistor 11 and the gate of the field effect transistor FET2 is connected to the solar cell voltage control circuit 11 via the resistor R12. The solar cell voltage control circuit 11 controls the field effect transistor FET1 and the field effect transistor FET2 to control the solar cell voltage.

When the power of the solar cell 3 is charged or supplied to a load, the field effect transistors FET1 and FET2 are operated so that the solar cell voltage becomes the target voltage. This field effect transistor FET
1 and the field-effect transistor FET2 are controlled by the capacitor C1 and the current fluctuation is stabilized by the inductance 20.

Between the positive output line 4 and the negative output line 5 of the solar cell 3, voltage dividing resistors R1 and R2 are connected in parallel with the solar cell 3, and these voltage dividing resistors R1 and R2 are connected in parallel. ,
The solar cell voltage divided by R2 is input to the CPU 10 and the solar cell voltage control circuit 11 via the operational amplifier OP1 as a voltage buffer.

A resistor R3 is connected to the output line 5 on the negative side of the solar cell 3, and a non-inverting input terminal of an operational amplifier OP2 is connected to the solar cell 3 side of the resistor R3 via a resistor R4. On the operational amplifier OP2 via a resistor 5
Are connected to each other, and the output terminal of the operational amplifier OP2 is connected to the CPU 10. The output of the operational amplifier OP2 is negatively fed back to the inverting input terminal via the resistor R6, and a voltage proportional to the solar cell current is amplified and input to the CPU 10.

The target voltage is output from the CPU 10 as a digital signal, converted into an analog signal by the D / A conversion circuit 12, and input to the solar cell voltage control circuit 11.

A voltage dividing resistor R7, R8 is connected between the positive output line 4 and the negative output line 5 of the solar cell 3 in parallel with the battery 2, and is connected between the voltage dividing resistors R7, R8. Is connected to the positive terminal of the comparison circuit 13, and the negative terminal of the comparison circuit 13 is connected between the voltage dividing resistors R9 and R10.
When the battery 2 is fully charged, the voltage of the positive terminal becomes larger than the voltage of the negative terminal in the comparison circuit 13, and outputs an overcharge prevention signal. The overcharge prevention signal is transmitted to the solar cell voltage control circuit 11. Is entered. Solar cell voltage control circuit 11
Then, the field effect transistor FET1 and the field effect transistor FET2 are controlled so that the battery 2 is not overcharged.

The CPU 10 measures the open-circuit voltage, the short-circuit current of the solar cell, and the current when controlled to a voltage slightly lower than the open-circuit voltage. A first characteristic line L1 showing an open voltage and a current when controlled to a voltage slightly lower than the open voltage, and a second characteristic line L showing a characteristic of the short circuit current
An optimum operating point determining means 101 for determining an optimum operating point P1 from an intersection with the control circuit 2 and a control means 102 for controlling a solar cell current so that the solar cell voltage becomes an optimum operating point voltage with a load connected. .

As described above, the current-voltage characteristic is approximately grasped, and the first characteristic line L1 representing the open voltage and the current when the voltage is controlled to be slightly lower than the open voltage, and the second characteristic line L1 representing the characteristic of the short circuit current. From the intersection with the characteristic line L2
1 can be determined in a short time, and the solar cell current can be controlled so that the solar cell voltage becomes the optimum operating point voltage with the load connected.

The actual characteristics of the solar cell are as shown by the dotted line in FIG. 2. The true optimum operating point P2 is located slightly lower than the optimum operating point P1, and the point P2 and the first characteristic straight line L1 There is a deviation from the optimal operating point P1 obtained from the intersection of the characteristic curve and the second characteristic line L2, but the optimal operating point voltage V1 is substantially the same in both characteristic graphs. From this, the field effect transistor FET1 and the field effect transistor FE are set so that the target solar cell voltage becomes V1.
If the solar cell current is controlled by changing the on / off duty ratio of T2, almost the maximum output can be obtained.

Next, the software operation of the solar cell control device will be described with reference to FIG. In step a1, it is determined whether or not one minute has elapsed since the previous processing. If one minute has elapsed, the target solar cell voltage is set to a value sufficiently higher than the open-circuit voltage (step a2), and the operational amplifier is turned on. The solar cell open circuit voltage V0 is measured from the output of OP1 (step a3).

The target solar cell voltage is set to a value sufficiently lower than the optimum operating point voltage V1 (step a4), and the solar cell current I0 is measured from the output of the operational amplifier OP2 (step a5).

Next, the target solar cell voltage is set to V0-ΔV (step a6), and the solar cell current I1 is measured (step a7). Here, ΔV is the optimum operating point voltage V1
And an appropriate value not higher than V0 and not higher than V0.

A first characteristic line L1 is obtained from the open circuit voltage V0 and the current I1 when the voltage is controlled to a voltage V0-.DELTA.V slightly lower than the open circuit voltage V0 (step a8). further,
A second characteristic line L2 is obtained from the short-circuit current I0 (step a9).

As described above, the open voltage V0, the short-circuit current I0, and the voltage V0-ΔV slightly lower than the open voltage V0 of the solar cell are obtained.
The current-voltage characteristic is approximately grasped by measuring the current I1 when the voltage is controlled to the minimum value. The optimal operating point P1 is determined from the intersection with the second characteristic line L2 indicating the current characteristic, and the intersection voltage V1 indicating the optimal operating point P1 is estimated from these intersections (step a10).

The solar cell voltage V indicating this optimum operating point P1
A moving average of 1 is obtained (step a11). For example, one solar cell voltage V1 is obtained and stored every one minute, an average of the past three times is always obtained from the stored solar cell voltage V1, and the moving average value is set as a target solar cell voltage. (Step a12) The process proceeds to Step a1, and the same control is repeated to control the solar cell current so that the solar cell voltage becomes the optimum operating point voltage with the load connected.

By using the moving average result of the solar cell voltage V1 indicating the optimum operating point P1 for the calculation as described above, even if the amount of solar radiation fluctuates instantaneously, it is hardly affected.

In this embodiment, the current-voltage characteristic is approximately grasped only by measuring the open voltage V0, the short-circuit current I0, and the current I1 when the voltage is controlled to be slightly lower than the open voltage of the solar cell 3. be able to. This makes the first
The optimum operating point P1 is determined in a short time from the intersection of the characteristic line L1 and the second characteristic line L2, and the solar cell current is controlled so that the solar cell voltage becomes the optimum operating point voltage with the load connected. be able to.

[0035]

As described above, in the solar cell control device according to the first aspect of the present invention, when the current-voltage characteristics are approximately grasped and the open-circuit voltage is controlled to a voltage slightly lower than the open-circuit voltage. The optimum operating point is determined from the intersection of the first characteristic line indicating the current of the current and the second characteristic line indicating the characteristic of the short-circuit current, so that the solar cell voltage becomes the optimum operating point voltage with the load connected. The solar cell current can be controlled.

In the solar cell control apparatus according to the second aspect of the present invention, the moving average result of the estimated value of the optimum operating point voltage is used as the target solar cell voltage, so that even if the amount of solar radiation fluctuates instantaneously, the influence is not affected. Hard to receive.

In the solar cell control method according to the third aspect of the present invention, the current-voltage characteristics are approximately grasped, and the first voltage indicating the open-circuit voltage and the current when the voltage is controlled to a voltage slightly lower than the open-circuit voltage. The optimum operating point is determined in a short time from the intersection of the characteristic line and the second characteristic line indicating the characteristics of the short-circuit current, and the solar cell current is adjusted so that the solar cell voltage becomes the optimum operating point voltage with the load connected. Can be controlled.

According to the solar cell control method of the present invention, the moving average result of the estimated value of the optimal operating point voltage is used as the target solar cell voltage, so that even if the amount of solar radiation fluctuates instantaneously, the influence is not affected. Hard to receive.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a control device for a solar cell.

FIG. 2 is a diagram illustrating calculation of an optimum operating point.

FIG. 3 is a software operation flowchart of the solar cell control device.

FIG. 4 is a diagram showing current-voltage characteristics of a solar cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Load 2 Battery 3 Solar cell 10 CPU 100 Current-voltage characteristic grasp means 101 Optimal operating point determining means 102 Control means L1 First characteristic straight line L2 Second characteristic straight line P1 Optimal operating point P2 True optimal operating point

Claims (4)

[Claims] An open-circuit voltage, a short-circuit current, and a current-voltage characteristic grasping means for approximating a current-voltage characteristic by measuring a current when controlled to a voltage slightly lower than the open-circuit voltage; Optimum operating point determining means for determining an optimum operating point from an intersection of a first characteristic line indicating a current when controlled to a voltage slightly lower than the open-circuit voltage and a second characteristic line indicating the characteristic of the short-circuit current; Control means for controlling the solar cell current so that the solar cell voltage becomes an optimum operating point voltage with a load connected. 2. The control means for controlling the solar cell current comprises:
The solar cell control device according to claim 1, wherein a moving average result of the estimated value of the optimum operating point voltage is used as a target solar cell voltage. 3. An open-circuit voltage, a short-circuit current, and a current when controlled to a voltage slightly lower than the open-circuit voltage, and a current-voltage characteristic is approximately grasped. The optimum operating point is determined from the intersection of the first characteristic line indicating the current when the voltage is controlled to a low voltage and the second characteristic line indicating the characteristic of the short-circuit current, and the solar cell voltage is optimized with the load connected. A method for controlling a solar cell, comprising controlling a solar cell current to reach an operating point voltage. 4. The method for controlling a solar cell according to claim 3, wherein a moving average result of the estimated value of the optimum operating point voltage is used as a target solar cell voltage.