JPH0973327A - Solar light power generation controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an operation point from being misjudged by finding a control indication value at present sampling time from the output electric power of a solar battery and the control indication value of a control signal in each sampling cycle. SOLUTION: An arithmetic part of a control part 6 reads in the output current signal and output voltage signal of the solar battery in each sampling cycle and operates the output electric power PN. Then when the mode is not an excessive solar radiation quantity mode, the solar battery output electric power PN at the present sampling time is compared with the solar battery output electric power PB at last sampling time. When PN > PB, the same control indication value as that at the last sampling time is held as it is. When PN < PB, on the other hand, a control indication value which makes an input current increase or decrease opposite from that at the last sampling time is set. When PN equals PB continuously at a prescribed sampling frequency, the control indication value is set to the inverted value of that at the last sampling time and the excessive solar radiation mode is entered at next-time sampling time; and the control indication value is not re-set until PN becomes less than PB.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a photovoltaic power generation control device having a function of constantly generating maximum power from a solar cell.

[0002]

2. Description of the Related Art A solar cell has the IV characteristic shown in FIG. 4, and has an optimum operating point (Vop, Iop) at which the maximum output is obtained. Since the optimum operating point changes as shown in FIG. 5 according to the change in the amount of solar radiation, it is necessary to control the solar cell near the optimum operating point in order to efficiently obtain the output from the solar cell in the solar power generation system.

As a means for controlling the optimum operating point, there is a method in which a microcomputer is used to calculate the output power from the output current and output voltage of the solar cell, and the optimum operating point is tracked from the output voltage and the output power. A configuration diagram of the solar power generation system is shown in FIG. 1 and a control flowchart is shown in FIG. 7, and the method thereof will be described below.

In FIG. 1, the output power of the solar cell 1 is
Via the reverse connection prevention diode 2 and the smoothing capacitor 3,
Input to a DC / DC converter 4 including a choke coil 4a, a reverse connection prevention diode 4b, a smoothing capacitor 4c, a switching transistor 4d, etc.
The output power of the D converter 4 is supplied to the load 5.
The power supplied to the load 5 of the solar cell 1 is determined by the output voltage of the DC / DC converter 4. Therefore, D
By controlling the input current of the C / DC converter 9 with the control signal from the controller 6, the solar cell 1 can always generate power near the optimum operating point. The portion surrounded by the dotted line in FIG. 1 is the photovoltaic power generation controller CN.

The controller 6 outputs the output current signal and the output voltage signal of the solar cell 1 for each sampling period to the current detector 7,
The current output power P _N of the solar cell 1 is calculated by reading through the voltage detector 8 and the A / D converters 9 and 10 (FIG. 7).
Step 201). Based on P _N and the output voltage V _N at the time of the current sampling, and the output power P _B and the output voltage V _B at the time of the previous sampling, the region in which the operating point of the solar cell 1 exists in FIG. 6 is as follows. To estimate. Here, the area of is V1> V2 and P1 in FIG.
The area <P2, and the area is V3> V4 in FIG.
And it is a region of P3> P4.

When P _N > P _B and V _N > V _B , since the output voltage increases with the increase in output power, the operating point exists in the region of. (Steps 202 → 203 → 2
04) In the case of P _N > P _B and V _N <V _B , the output voltage decreases as the output power increases, so that the operating point exists in the region of. (Steps 202 → 203 → 205) In the case of P _N <P _B and V _N > V _B , the output voltage increases with the decrease of the output power, so that the operating point exists in the region of. (Step 202 → 206 → 207) When P _N <P _B and V _N <V _B , the output voltage decreases with the decrease in output power, and therefore the operating point exists in the region of. (Step 202 → 206 → 208) The input current control of the DC / DC converter 4 is performed corresponding to the region where the operating point exists. The input current control is performed by increasing or decreasing the duty ratio of the PWM pulse signal that is the control signal for driving the switching transistor 4d in the DC / DC converter 4, and when the operating point is in the region of, the duty ratio is corrected. The width is increased by Δd (steps 205 and 207), and Δd if it exists in the area of
Decrease (steps 204 and 208). Finally, the data is updated (step 209 → 210) and the PWM pulse signal is output (step 211). By repeating the above control, the solar cell 1 can generate power near the optimum operating point.

[0007]

As described above, according to the conventional control method, the present output power and output voltage of the solar cell are compared with the previous values, and the operating point exists in which region on the output characteristic curve. Is estimating what to do. However, this method has the following problems. (1) Since the output power and the output voltage are compared in two stages, an erroneous determination may occur depending on the measurement accuracy of the current value and the voltage value. For example, in FIG. 1, the current signal and the voltage signal are A
It is input to the control unit 6 via the / D converters 9 and 10. 8
In the case of a bit A / D converter, the resolution is 1 / of the measurement range.
Although it is 256, since the current value << voltage value in a normal solar power generation system, the measurement accuracy of the current value and the voltage value is different. Further, in the region of FIG. 6, since the voltage change is small with respect to the current change, the voltage change is small with respect to the resolution, and when the measurement accuracy of the voltage detector 8 is not good, the output voltage is increased with the increase of the output power. May result in an erroneous determination from an erroneous measurement result such as a decrease in the output voltage with an increase in the output voltage or a decrease in the output power. Conventionally, in order to solve such a problem, methods such as correction of measurement data and use of A / D converters having different accuracies have been taken. (2) As shown in FIG. 5, when the amount of solar radiation increases for a constant output power, the output voltage of the solar cell increases. Therefore, when the amount of solar radiation increases while the operating point of the solar cell exists in the region of FIG. 6, the output voltage also increases as the output power increases, so the operating point exists in the region of It will be in the same state as when doing, and erroneous judgment will occur.
Since erroneous judgments are repeated while the amount of solar radiation is increasing, there is a time loss in reaching the optimum operating point. When the amount of solar radiation is high,
Since the difference in output power due to the deviation from the optimum operating point is large, it affects the efficiency of the system.

An object of the present invention is to provide a photovoltaic power generation control device capable of preventing an erroneous determination of an operating point due to an output voltage measurement error of a solar cell and an erroneous determination of an operating point due to an increase in output voltage when the amount of solar radiation is increased. Is to provide.

[0009]

In order to achieve the above object, the present invention optimizes the solar cell by increasing or decreasing the input current of a DC-DC converter which receives the output power of the solar cell and supplies it to a load. In a photovoltaic power generation control device that performs operating point control, control of a control signal for increasing / decreasing the output power of the solar cell, the output power of the solar cell at the time of the previous sampling, and the input current of the DC-DC converter in each sampling cycle. The present invention is characterized in that the control instruction value at the time of current sampling is obtained from the instruction value.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A system configuration including a photovoltaic power generation control device according to an embodiment of the present invention is the same as that of the conventional one and is the same as that of FIG. In this embodiment, the input current of the DC / DC converter 4 is controlled by the control signal from the control unit 6. As this control signal, for example, a PWM pulse signal for driving the switching transistor 4d in the DC / DC converter 4 is used. In this case, if the duty ratio of the PWM pulse signal is increased, the output current of the solar cell 1 is decreased due to the increase of the input current of the DC / DC converter 4, and conversely, if the duty ratio is decreased,
The output voltage of the solar cell 1 increases as the input current of the DC / DC converter 4 decreases.

The details of the control unit 6 are shown in FIG. For example, the arithmetic unit 6a using a microcomputer calculates the solar cell output power from the output voltage and output current of the solar cell 1, and calculates the DC / DC converter 4 required to control the input current of the DC / DC converter 4 from the result. The control instruction value of the control signal to the DC converter 4 is output. The memory 6b uses the solar cell output power and control instruction value (input current increase = 1, input current decrease =
0) is stored and the data is updated every sampling. The PWM pulse generator 6c converts the control instruction value obtained by the calculator 6a into a PWM pulse signal that can directly control the DC / DC converter 4, and outputs it as a control signal.

The input current control procedure will be described below with reference to the solar cell characteristic diagram of FIG. 6 and the flowchart of FIG.

The calculation unit 6a reads the output current signal and the output voltage signal of the solar cell 1 for each sampling cycle, and calculates the output power P _N (step 101). The mode is selected (step 102), and when the solar radiation amount excess mode is not set, the solar cell output power P _N at the current sampling and the solar cell output power P _B at the previous sampling are compared.
Here, the excessive solar radiation mode refers to a state in which the electric power at the optimum operating point of the solar cell 1 at the present amount of solar radiation exceeds the maximum power consumption of the load 5.

When P _N > P _B and the control instruction value at the time of the previous sampling is 1, when the input current of the DC / DC converter 4 increases (the output voltage of the solar cell 1 decreases), the solar cell 1 Since the output power is increasing, the operating point of the solar cell 1 exists in the area of FIG. If the control set value at the time of the previous sampling is 0, the output power of the solar cell 1 is increasing with respect to the decrease of the input current of the DC / DC converter 4 (increase of the output voltage of the solar cell 1). Exists in the area of. If the operating point is in the region of, the optimum operating point can be approached by increasing the input current of the DC / DC converter 4 (control instruction value =
1), if the input current of the DC / DC converter 4 is decreased, it can approach the optimum operating point (control set value = 0). Therefore, P _N > P
_In the case of _B, the same control instruction value as in the previous sampling is held as it is (step 103).

If P _N <P _B and the control instruction value at the previous sampling is 1, the input current of the DC / DC converter 4 increases (the output voltage of the solar cell 1 decreases),
Since the output power of the solar cell 1 is decreasing, the operating point is in the region of. If the control set value at the time of the previous sampling is 0, the output power of the solar cell 1 is decreasing with respect to the input current decrease of the DC / DC converter 4 (increase of the output voltage of the solar cell 1). Exists in the area of. Therefore, when P _N <P _B, the control instruction value is set so that the increase / decrease in the input current is opposite to that in the previous sampling (step 104 → 105).

Further, when P _N = P _B continuously for the specified number of sampling times, it is judged that the amount of solar radiation is excessive with respect to the load (step 106), and the control instruction value is the value inverted from that at the previous sampling. Set to (Step 10
5) From the next sampling, the solar radiation excess mode is entered (step 102 → 107), and the control instruction value is not reset until the control instruction value is reset until P _N <P _B. An operation is performed to prevent the value from becoming an appropriate value (steps 107 and 108). Finally, the data in the memory 6b is updated (step 109), the PWM pulse generator 6c converts the control instruction value into a PWM pulse signal, and the PWM pulse signal is output to the DC / DC converter 4 as a control signal (step 110). By repeating this control, the solar cell 1 can generate power near the optimum operating point.

As described above, the operating point of the solar cell 1 is estimated from the output power and the control instruction value of the control signal, and the optimum operating point control is performed. Therefore, since the comparison is not performed by the output voltage, the voltage detector 8 Also, the influence of the measurement accuracy of the A / D converter 10 can be made extremely small. Also,
Even when the amount of solar radiation increases in the state where the operating point exists in the region, the control for the increase of the output power (in this case, the control instruction value to increase the input current = 1) is performed, and thus the erroneous judgment is made. It never happens. In the system configuration diagram of FIG. 1, a step-up DC / DC converter is shown as an example, but the present invention is not limited to this as long as the input current can be controlled. Further, in the case of a system in which the maximum output of the solar cell can always be used, such as an interconnection system having a reverse power flow with a commercial system, an excessive amount of solar radiation does not occur, so steps 106 and 107 in FIG. 108 is unnecessary.

[0018]

As described above, according to the present invention,
For each sampling cycle, the control instruction value at the current sampling is calculated from the output power of the solar cell and the control instruction value of the control signal for increasing or decreasing the solar cell output power at the previous sampling and the input current of the DC-DC converter. Since it is determined, it is possible to prevent the erroneous determination of the operating point due to the output voltage measurement error of the solar cell and the erroneous determination of the operating point due to the output voltage increase when the amount of solar radiation is increased. Further, when a microcomputer is used as a means for obtaining the control instruction value at the time of current sampling, the problem of the conventional control can be dealt with only by changing the software.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of a photovoltaic power generation system including a photovoltaic power generation control device, which is an embodiment of the present invention and is also a conventional example.

FIG. 2 is a block diagram showing details of a control unit that is an embodiment of the present invention.

FIG. 3 is a flowchart showing an operation of a calculation unit in FIG.

FIG. 4 is a diagram showing an IV characteristic and an output characteristic of a solar cell.

FIG. 5 is a diagram showing a transition of optimum operating point control of a solar cell due to a change in solar radiation amount.

FIG. 6 is a diagram showing movement of an operating point of a solar cell by optimal operating point control.

FIG. 7 is a flowchart showing conventional optimum operating point control.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Solar cell 2 Reverse connection prevention diode 3 Smoothing capacitor 4 DC-DC converter 5 Load 6 Control part 6a Calculation part 6b Memory 6c PWM pulse generator 7 Current detector 8 Voltage detector 9,10 A / D converter CN Solar power generation Controller P _N Solar cell output power at the current sampling P _B Solar cell output power at the previous sampling V _N Solar cell output voltage at the current sampling

Claims (3)

[Claims] 1. A photovoltaic power generation control device for performing optimum operating point control of a solar cell by increasing / decreasing an input current of a DC-DC converter which receives output power of the solar cell and supplies it to a load, at each sampling cycle. , The control instruction value at the time of current sampling is obtained from the output power of the solar cell and the control instruction value of the control signal for increasing or decreasing the solar cell output power at the previous sampling and the input current of the DC-DC converter. A solar power generation control device characterized in that 2. An optimum operating point of the solar cell by giving a control signal for increasing or decreasing the input current to a DC-DC converter having an input current increasing / decreasing function, which receives the output power of the solar cell and supplies it to a load. In a photovoltaic power generation control device for controlling, for each sampling cycle, current detection means and voltage detection means for detecting the output current and output voltage of the solar cell, and the current and voltage detected by the current detection means and voltage detection means. Calculate the output power of the solar cell from
A computing means for obtaining a control instruction value at the current sampling from the output power, the solar cell output power at the time of the previous sampling, and the control instruction value of the control signal for increasing or decreasing the input current of the DC-DC converter; A solar power generation control device comprising: a storage unit that stores a solar cell output power at the time of sampling and a control instruction value of a control signal for increasing or decreasing the input current of the DC-DC converter. 3. The calculation means compares the solar cell output power at the time of previous sampling stored in the storage means with the solar cell output power at the time of current sampling, and determines the solar cell output power at the time of current sampling. Is large, the control instruction value at the current sampling is set to the same as the previous sampling, and when the solar cell output power at the current sampling is smaller, the control instruction value at the current sampling is set. 3. The photovoltaic power generation control device according to claim 2, wherein is set to a control instruction value at which the increase / decrease in the input current at the time of the previous sampling is opposite.