JPH0827672B2 - Solar power generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a system in which DC power from a solar cell is converted into AC power by an inverter and an AC load such as an induction motor is driven. The present invention relates to a solar power generation device that controls an inverter so as to maximize it.

[Prior art]

In the solar power generation system that has been attracting attention in recent years,
There is a system in which DC power generated by a solar cell is converted into AC power by a variable frequency control inverter and the AC motor drives an induction motor connected to a pump or the like. In such a system, when the solar radiation amount and temperature of the solar cell are set to a certain constant value, as shown in FIG. 3, the voltage V-current I characteristic of the solar cell increases when the output current I increases above a certain level. The output voltage V drops sharply to zero. Therefore, so-called maximum power point tracking control has been developed in which the solar cell is operated at the point Pmax where the output power is maximum.

As a conventional example of the technique for performing the maximum power point tracking control of the solar cell, there is, for example, the one described in JP-A-58-69469. FIG. 2 is a block diagram showing the configuration of the maximum power point tracking control device. In the figure, 1 is a solar cell, 2 is a main inverter, 3 is a load such as an induction motor connected to a pump, 4 is an auxiliary inverter, and 5 is a control circuit. In the maximum power point tracking control device, the control circuit 5
Since the output power P-output current I characteristic of the solar cell is as shown in FIG. 4, the output voltage V and the output current I of the solar cell are detected to obtain the output power P = V × I at that time. By calculating and determining whether the change in the power P when the load current is slightly changed is positive or negative, it is possible to determine which side of the maximum power output point Pmax the solar cell output point is. It is configured to determine and control the output of the main inverter 2 in the direction in which the output point of the solar cell approaches the maximum power output point Pmax.

Further, as a technique for controlling the output power of the solar cell to the maximum power output point, there is another control device for an inverter device driven by a solar cell, which is described in Japanese Patent Laid-Open No. 56-132174. When the light quantity LQ of the solar cell is used as a parameter, the control device has an output voltage V-output current I characteristic as shown in FIG. 5, and an output power P-output current I characteristic as shown in FIG.
As shown in the figure, the frequency of the inverter device is controlled according to the detected value of the output voltage of the solar cell so that the output voltage of the solar cell is kept substantially constant regardless of the change in the amount of sunlight.

[Problems to be solved by the invention]

However, among the maximum power point tracking control techniques having the above-mentioned configuration, the one disclosed in Japanese Patent Application Laid-Open No. 58-69469 calculates the output power P = V × I in the control circuit and slightly changes the load current. The main inverter 2 is controlled by determining whether the change of the electric power P at time is positive or negative,
The control method for allowing the maximum electric power of the solar cell to be output to the induction motor connected to the pump is such that the response speed is slow, and, for example, when the output current has a ripple, the increase / decrease of the output of the main inverter 2 can be discriminated. The problem of not being able to
Furthermore, when the sun is zero and the power generated by the solar cell drops extremely, there is no information to find the maximum power output point Pmax, and the maximum power point tracking control becomes impossible. there were.

Further, as disclosed in Japanese Patent Laid-Open No. 58-69469, as shown in FIGS. 5 and 6, strictly speaking, even if the output voltage V at the maximum power output point Pmax of the solar cell is substantially constant, Therefore, even if the output voltage of the solar cell is controlled to be substantially constant regardless of the change in the amount of sunlight, the maximum power output point tracking cannot be performed accurately.

The present invention has been made in view of the above points, the response speed is fast, even if ripples occur in the generated power of the solar cell,
Another object of the present invention is to provide a solar power generation device capable of performing appropriate maximum power point tracking control even if the generated power is extremely reduced.

[Means for solving problems]

In order to solve the above problems, the present invention is a photovoltaic power generator that converts the output of a solar cell into an alternating current by an inverter via a control means, and drives a load with the alternating current power, wherein the control means outputs the output of the solar cell. A first control loop that detects the voltage V, controls the inverter according to the value of the output voltage V, and controls the output voltage of the solar cell to be substantially constant regardless of the amount of sunlight; A power calculating means for detecting the output voltage V and the output current I and calculating the power P from the product V × I is provided, and the power P is sampled at a plurality of points based on the output voltage. Compared with the sampling value before the time point, and when the sampling value at the certain time point is larger than the sampling value before the time point, the AC frequency of the inverter output is lowered to reduce the output power of the inverter. If the sampled value at a certain point is smaller than the sampled value before that point, the AC frequency of the inverter output is increased to increase the output power of the inverter and decrease the output voltage of the solar cell. It is characterized in that a second control loop for controlling so as to perform is provided.

[Action]

By configuring as above, the amount of sunlight in the solar cell
Solar cell voltage V-current I with LQ1 to LQ4 as parameters
The characteristics are as shown in FIG. 5, and the current I changes according to the amount of sunlight, but the voltage V hardly changes. Therefore, the detected value of the output voltage of the solar cell is set so as to keep the output voltage of the solar cell substantially constant. By controlling the output of the inverter according to the above, the solar cell is used near the maximum power output point Pmax as shown in FIG. Also, FIGS. 4 and 5
As is clear from the figure, even when the sun is clouded and the sunlight is shielded and becomes small, a substantially constant voltage value can be obtained, so that information for maximum power point tracking control is not lost.
In addition, the response speed is fast because there is no calculation or differentiation by the microcomputer for calculating the electric power P.

Further, the output power P of the solar cell is sampled at a plurality of points based on the output voltage, the sampling value at a certain time point is compared with the sampling value before the time point, and the sampling value at the certain time point is the sampling value before the time point. When it is larger, the AC frequency of the inverter output is lowered to lower the output power of the inverter and increase the output voltage of the solar cell,
Conversely, when the sampling value at a certain time point is smaller than the sampling value before that time point, the AC frequency of the inverter output is increased to increase the output power of the inverter and control the output voltage of the solar cell to drop, As will be described later in detail, more accurate maximum power point tracking control can be performed without being influenced by ripples and the like.

〔Example〕

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

FIG. 1 is a block diagram showing a system configuration of a control device for an inverter driven by a solar cell according to the present invention.
In the figure, 11 is a solar cell, 12 is a variable frequency control inverter, and 13 is an induction motor connected to a pump 14.
DC power from solar cell 11 is variable frequency control inverter
It is converted into AC power at 12, and the induction motor 13 is driven by the AC power at a speed according to the frequency. Reference numeral 15 is a current sensor for detecting the output current I of the solar cell 11, 16 is a voltage sensor for detecting the output voltage V of the solar cell 11, 17 is a voltage regulator, and 18 is a product of the output current I and the output voltage V. A multiplying circuit for obtaining the output power P of the solar cell 11 from I × V, 19 is an increasing direction discriminating circuit which will be described in detail later, 20 is a ramp number generating circuit,
Reference numerals 21 and 22 are comparators, 23 is a voltage setter, and 24 is an error amplifier. In the control device of the inverter driven by the solar cell having the above-mentioned configuration, the output voltage V detected by the voltage sensor 16 is adjusted to a voltage of an appropriate value by the voltage regulator 17 and input to the comparator 21, and the comparison unit At 21, the voltage is compared with the set voltage set by the voltage setter 23, and the difference is input to the error amplifier 24, amplified by the error amplifier 24, and output to the variable frequency control inverter 12. Here, if the set voltage of the voltage setting device 23 is set to the set voltage Vs such that the maximum power output point Pmax is as shown in FIG. 6, the variable frequency control inverter 12 causes the solar cell to be described in detail later.
The variable frequency control inverter 12 is controlled so that the output voltage of 11 becomes the set voltage. Also, the output current I detected by the current sensor 15 and the output voltage V detected by the voltage sensor 16
Is input to the multiplication circuit 18, and the multiplication circuit 18 obtains the output power P of the solar cell 11 from the product I × V of the output current I and the output voltage V. The output power P is input to the increasing direction discriminating circuit 19, and the increasing direction discriminating circuit 19 increases the output voltage so that the output power of the solar cell 11 becomes the voltage of the maximum power output point Pmax as described later in detail. A "+" or "decrease-" signal is generated and input to the ramp number generation circuit 20. The ramp number generation circuit 20 generates a voltage ΔV proportional to the “increase +” or “decrease −” signal of the voltage and inputs it to the comparison unit 22.

As described above, the control device of the inverter driven by the solar cell having the above-mentioned configuration is the voltage sensor 16-voltage regulator 17-
A first control loop CL1 including an error amplifier 24, a current sensor 15 and a voltage sensor 16-a multiplying circuit 18-an increasing direction discriminating circuit 19-a ramp number generating circuit 20-a second control loop including an error amplifier 24. And a control loop CL2.

FIG. 7 is a block diagram showing a system configuration of the increasing direction discrimination circuit 19 which constitutes the second control loop CL2.
In the figure, the parts denoted by the same reference numerals as those in FIG. 1 indicate the same or corresponding parts. Reference numerals 19a, 19b, 19c and 19d are sample and hold circuits, 19e and 19f are comparators, and 19g is an exclusive OR circuit. Sample and hold circuits 19a and 19c
Is inputted with the clock pulse CP2, and the sample hold circuits 19b and 19d are inputted with the clock pulse CP1. The operation of the increasing direction discrimination circuit 19 will be described below.

FIG. 8 is a timing chart showing potential changes at points a to o of the increasing direction discrimination circuit 19 when the output power P calculated by the multiplication circuit 18 changes with respect to the output voltage V as shown in FIG. is there. As shown in the figure, by inputting the clock pulse CP2 and the clock pulse CP1 delayed by 3/4 cycle, the voltage value at points I to I corresponds to the change in the output power P with respect to the output voltage V in FIG. , Pa, Pb, Pc, Pd,
Change to Pe. That is, the sample-hold circuit 19a holds the sampling value of the output power value P which is 1/4 cycle before the current output power value P (the voltage value at the point A), and the sample-hold circuit 19b holds 3/4 cycle before. The sampled value of the output power value P of is stored. Since the voltage value at the point G corresponds to the output power value P (voltage value at the point B) 1/4 cycle before the current output power value P, the comparator 19e indicates that the current power value P is 1/4 cycle. The previous output power value P and the output voltage value P one cycle before are input. The comparator 19 compares the output power value P 1/4 cycle before the current output power value P with the output power value P 1 cycle before (the voltage value at point C), and if the former is higher than the latter. When it is higher, it generates an "increase +" signal in the direction of increasing the output voltage P of the solar cell 11, and conversely, when the former is lower than the latter, it decreases the output power P of the solar cell 11 by "decrease-". Generate a signal. To the exclusive OR circuit 19g, the signal at the output point of the comparator 19e and the signal at the output point of the comparator 19f are input, and both the increase point and the output point are "increase +" signals. Decrease- "signal indicates" decrease- "
A signal is output, and when either one is "increase +" and the other is "decrease-", the "increased +" signal is output to the ramp frequency generator circuit 20.
Output to. The output of the ramp number generating circuit 20 is delayed by 2 cycles and 2 + 3/4 cycles from the signal voltage value at the point a by the clock pulses CP2 and CP1, respectively, as in the case of the sample and hold circuits 19a and 19b, and the sample and hold circuit 19c. And is held in the sample hold circuit 19d by sampling. The comparator 19f outputs an "increase +" signal when the voltage value at the J-point is higher than the voltage value at the F-point, and on the contrary, when the voltage value at the J-point is lower than the voltage value at the F-point, "decrease-" Output a signal. Due to the above-described operation of the increasing direction discrimination circuit 19, the output voltage of the solar cell 11 becomes the maximum power output point Pm of FIG.
Tracking control is performed so that the voltage value of ax becomes Vmax. That is, when the output signal of the exclusive OR circuit 19g is "increase +", the output of the variable frequency control inverter 12 is controlled to decrease,
When the output signal of the exclusive OR circuit 19g is "decrease-", the output of the variable frequency control inverter 12 is controlled to increase.

10 and 11 are diagrams showing the relationship between the total head of the pump 14 and the flow rate, and the relationship between the output of the induction motor 13 and the flow rate, respectively, in which the frequency of the AC output from the variable frequency control inverter 12 is shown. As a parameter, the frequency is 30H
These are the characteristics of the pump 14 when changed to z, 35Hz, 40Hz, 45Hz, 50Hz, 55Hz, 60Hz. As shown, by changing the frequency of the AC output of the variable frequency control inverter 12, the power consumption of the induction motor 13 changes. Therefore, when the output signal of the increasing direction discrimination circuit 19 is "increase +", the AC output frequency of the variable frequency control inverter 12 is lowered to reduce the output power of the variable frequency control inverter 12 to reduce the output voltage of the solar cell 11. When the output signal of the increasing direction discrimination circuit 19 is "decrease-", the AC output frequency of the variable frequency control inverter 12 is increased to increase the variable frequency control inverter 12
If the induction motor 13 is driven by configuring the control unit of the variable frequency control inverter 12 so as to increase the output power of the solar cell 11 and decrease the output voltage of the solar cell 11, the solar cell 11 is output at the maximum power output point Pm.
It can be used with ax.

As described above, in the above embodiment, the output power P is calculated from the output voltage V and the output current I of the first control loop CL1 that controls the tracking of the maximum power output point Pmax with the output voltage V of the solar cell 11. Is calculated, the output power P is sampled at a plurality of points based on the voltage, and the tracking control of the maximum output point Pmax is performed according to the magnitude of the sampling value.
And a configuration including. In the first control loop CL1, the output voltage does not drop so much even when the sunlight is blocked by the clouds and the generated power in the solar cell drops extremely, so even in such a case, maximum power output point tracking control can be performed. The control speed is fast because there is no processing such as calculation of output power P, sampling and comparison. Further, the second control loop CL2 is provided with a plurality of sample and hold circuits 19a to 19d and is configured to compare the sampled value at a certain point with the sampled value before that, so that the information is provided during the sampling period. Is stationary, unlike the conventional method of differentiating the output power with the current and controlling the inverter with the positive or negative of the differential value, even if a ripple occurs in the output voltage, the output increase / decrease of the variable frequency control inverter 12 Appropriate discrimination control is possible.

〔The invention's effect〕

As described above, according to the present invention, the following excellent results can be obtained.

The first control loop controls the output voltage of the solar cell to be substantially constant regardless of the amount of sunlight, so if the output voltage is appropriately determined, regardless of the amount of sunlight of the solar cell (for example, Control with a fast response speed can be performed near the maximum output voltage (even if there is solar radiation fluctuation due to weather fluctuations), and information for maximum power point tracking control is not lost at all times.

In the first control loop, a sampling value at a certain time point is compared with a sampling value before that time point, and when the sampling value at the certain time point is larger than the sampling value before that time point, the AC frequency of the inverter output is lowered. When the output voltage of the inverter is decreased and the output voltage of the solar cell is increased, and conversely, when the sampling value at a certain time point is smaller than the sampling value before that time point, the AC frequency of the inverter output is increased to increase the output power of the inverter. Since the output voltage of the rising solar cell is controlled to drop, accurate maximum power point tracking control can be performed without being affected by ripples and the like.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of a control device for an inverter driven by a solar cell according to the present invention, FIG. 2 is a block diagram showing a configuration of a conventional maximum power point tracking control device, and FIG. The figure which shows the voltage-current characteristic of a solar cell when the amount of light and temperature are made constant, FIG. 4 is a figure which shows the electric power-current characteristic of a solar cell, and FIG. FIG. 6 is a diagram showing the voltage characteristic, FIG. 6 is a diagram showing the power-voltage characteristic of the solar cell using the amount of sunlight as a parameter, and FIG. 7 is a block diagram showing the configuration of the second control loop CL2 of FIG. FIG. 9 is a timing chart showing a potential change at points I to W of the increasing direction discrimination circuit of FIG.
The figure shows the output power-output voltage characteristics of solar cells,
FIG. 11 and FIG. 11 are views showing the relationship between the total head of the pump and the flow rate, and the relationship between the output of the induction motor and the flow rate, respectively. In the figure, 11 ... solar cell, 12 ... variable frequency control inverter, 13 ... induction motor, 14 ... pump, 15 ... current sensor, 16 ... voltage sensor, 17 ... voltage regulator, 18 ... Multiplier circuit, 19 …… Incremental direction discriminating circuit, 20 …… Ramp number generating circuit, 21.22 …… Comparison section, 23 …… Voltage setting device, 24 …… Error amplifier, 19a to 19d …… Sample hold circuit, 19e, 19
f …… Comparator, 19g …… Exclusive OR circuit.

Claims (1)

[Claims] 1. A solar power generation device for converting an output of a solar cell into an alternating current by an inverter via a control means and driving a load with the alternating current power, wherein the control means controls an output voltage V of the solar cell. A first control loop for detecting and controlling the inverter according to the value of the output voltage V so that the output voltage of the solar cell becomes substantially constant regardless of the amount of sunlight, and the output of the solar cell An electric power calculation means for detecting the voltage V and the output current I and calculating the electric power P from the product V × I is provided,
The power P is sampled at a plurality of points based on the output voltage,
The sampling value at a certain time point is compared with the sampling value before that time point, and when the sampling value at the certain time point is larger than the sampling value before that time point, the AC frequency of the inverter output is lowered to reduce the output power of the inverter. If the sampled value at a certain time point is smaller than the sampled value before that point, the AC frequency of the inverter output is increased to increase the output power of the inverter and the output voltage of the solar cell. The solar power generation device is provided with a second control loop for controlling so as to lower the temperature.