JPH0625945B2 - Power supply system control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control method capable of constantly supplying maximum power to a load in a power supply system using a solar cell as a power supply device.

(Prior Art) As is well known, the output characteristics of a solar cell differ depending on the light irradiation amount and the temperature change of the photovoltaic element. For example, when the light irradiation amount is used as a parameter, the output as shown in FIG. Show the characteristics. In FIG. 2, the current-voltage characteristic is represented by a solid line and the power-voltage characteristic is represented by a broken line, and the current Id and the power Pd that can be taken out increase as the light irradiation amount increases. Further, the output power Pd, which is the product of the current Id and the voltage Vd, has maximum output power points Pm ₁ , Pm ₂ , Pm ₃ ...
, And there is a maximum power curve connecting those points. From such a point, by adjusting the output voltage Vd according to the amount of light irradiation, the maximum output power point P
A control method (maximum power tracking control method) for operating with m ₁ , Pm ₂ , Pm ₃ ... Has been proposed.

FIG. 3 shows a conventional power supply system based on this maximum power tracking control method. In the figure, 11 is a solar cell, and a converter 12 is connected to both ends of this solar cell 11. A load 15 is connected to the output side of the conversion device 12 via a power supply system 14 of an AC power supply 13. Also solar cells
DC current detector 16 and DC voltage detector on the output side of 11
17 is connected, and the DC current Id and the DC voltage Vd detected by these are input to the correction voltage generator 18. Then, the correction voltage ΔV ^* and the DC voltage Vd from the correction voltage generator 18 are input to the voltage controller 19, and the output signal thereof is added to the converter 12.

Here, the correction voltage generator 18 periodically detects the output current Id and the output voltage Vd of the solar cell 11, and internally calculates Pd = Id × Vd. Then, as a result of determining the combination of the changing direction of Vd and the changing direction of Pd, the correction voltage ΔV ^* is increased or decreased by a constant amount ΔV in the direction in which Pd is expected to increase, and the corrected voltage ΔV ^* is output to the voltage regulator 19. The voltage regulator 19 has a voltage command value V ^* inside, and by inputting ΔV ^* and Vd,
It is a constant voltage controller that operates to drive the converter 12 such that Vd is a voltage (V ^* + ΔV ^* ) that always gives maximum power under a certain amount of solar radiation.

FIG. 4 is a block diagram of the correction voltage generator 18. This generator 18 includes A / D converters 18a and 18b to which Id and Vd as analog signals are input, and a microcomputer to which these output signals are input. 18c and its output signal are input to obtain a correction voltage ΔV ^* as an analog signal D
/ A converter 18d.

Then, the CPU of the microcomputer 18c executes the program represented by the flowchart of FIG. That is, the CPU is 1 of the cycle for detecting Id and Vd.
A sampling timer corresponding to the period is started in step S1, and after the time is up, Id and Vd are read in in step S2, and in step S3, Pd = Id × Vd is calculated. Next, the process proceeds to step S4, and the increasing / decreasing tendency of the correction voltage ΔV ^* in the immediately preceding cycle (the electric power at this time is Pd ₋₁ ) is determined. If ΔV ^* is increased last time and Pd> Pd ₋₁ in step S5, Pd tends to increase with the increase of ΔV ^* , and the power / voltage characteristic is as shown in FIG. Presumed to be in. Therefore, ΔV
^Since it is considered that Pd will increase further if ^* is further increased, a process of increasing ΔV ^* by ΔV is performed in step S6.

Further, when ΔV ^* is decreased last time and Pd is decreased, the characteristic is predicted to be in the state of FIG. 6, so ΔV ^* is similarly increased by ΔV through steps S7 and S8. Further, as a result of increasing ΔV ^* last time, if Pd decreases, it is predicted that the characteristics are in the state of FIG. 6, and in this case, if ΔV ^* is decreased by ΔV in step S9, Pd Expect an increase. Similarly, when ΔV ^* is decreased last time and Pd is increased, the characteristics are as shown in FIG.
^Since a further increase in Pd can be expected due to a decrease in ^* , ΔV ^* is decreased in step S10.

As described above, the conventional maximum power tracking control method compares the current output power Pd with the previous output power Pd ₋₁ , and also considers the increasing / decreasing tendency of ΔV ^* so that the power / voltage characteristics of FIG. It is determined which of the following is present, and ΔV ^* is forcibly increased / decreased at the sampling cycle interval along the direction in which the increase of Pd is predicted based on the result, and this ΔV ^* is added to the voltage command value V ^*. The maximum output power is always obtained by operating Vd.

(Problems to be Solved by the Invention) However, this control method has the following problems. That is, with respect to the maximum solar radiation during power / voltage characteristic P ₁₀₀ of (insolation 100%) in Figure 7, the power / voltage characteristic P ₁₀ at the time of low solar radiation (e.g. about 10% or less of the maximum amount of solar radiation) of a wide range of It takes a value near the maximum power (hatched portion in the figure) across the voltage value (Vm ₁₀ '~Vm _10). That is, since the power / voltage characteristic is substantially flat characteristics, the operating voltage between the voltage Vm ₁₀ which corresponds to the true maximum power Pm _10, 'voltage Vm ₁₀ corresponding to' approximately equal Pm ₁₀ to Pm ₁₀ There is a problem that it wanders. In other words, it is difficult to accurately detect the true maximum power Pm ₁₀ due to factors such as instability of solar radiation and detection accuracy of Vd and Id.

Therefore, after temporarily detecting the maximum power at the point Pm ₁₀ ′ (voltage Vm ₁₀ ′) in the figure, the amount of solar radiation changes and the maximum amount of solar radiation is 50
%, In order to reach the true maximum power Pm ₅₀ in the power / voltage characteristic P ₅₀ , the voltage difference ΔV ₂ (= Vm ₅₀
A transition time of the voltage Vd corresponding to −Vm ₁₀ ′) is required. That is, the voltage difference ΔV ₁ (= from the true maximum power Pm ₁₀
Since relative vm ₅₀ -Vm ₁₀₎ transition time by ΔV ₂ / ΔV ₁ times the time it is required, the change of the voltage Vd is due [Delta] V ^* of increase or decrease of certain [Delta] V is moderated, [Delta] V ₂ In order to compensate for this, the flowchart of FIG. 5 must be executed several times, which causes a problem that the response delay of tracking control becomes significant.

The present invention has been proposed to solve the above problems, and its purpose is to prevent the operating voltage from becoming unstable when the amount of solar radiation decreases, and then to recover the amount of solar radiation rapidly. It is an object of the present invention to provide a control method for a power feeding system that enables a high-speed response even when the above is performed and can always provide the maximum power.

(Means for Solving the Problems) In order to achieve the above object, the present invention supplies the output power of a solar cell to a load via a conversion device, so that the output power of the solar cell is always maximized. By increasing or decreasing the correction voltage for the output voltage command value and operating the converter,
In a power supply system using a maximum power tracking control method that adjusts the output voltage of a solar cell, when the change in the output power with respect to the output voltage of the solar cell is almost constant (for example, the amount of solar radiation is about 10% or less of the maximum amount of solar radiation). During a certain low solar radiation), the correction voltage is set to zero to interrupt the maximum power tracking control, and the converter is operated under a constant solar cell output voltage command value that gives the true maximum power during the solar radiation. The solar cell is controlled by a constant voltage.

(Operation) In the present invention, under the maximum power tracking control, for example, when the amount of solar radiation is 10% or less of the maximum, the correction voltage is set to zero and the maximum power tracking control is interrupted. At the same time, the output voltage command value of the solar cell is fixed to a constant voltage that gives the maximum power at this time, and constant voltage control is performed. When the amount of solar radiation is recovered, the conventional maximum power tracking control is performed.

(Example) An example of the present invention will be described below with reference to the drawings. That is, in this embodiment, first, the correction voltage generator shown in FIG.
In the microcomputer 18c (see FIG. 4) in 18, the current output power Pd calculated from Id and Vd becomes smaller than the maximum output power Pm ₁₀ at the time of 10% of the maximum solar radiation, for example, when the solar radiation is low. It is determined whether or not. FIG. 1 is a flow chart of the program in this embodiment, and if the judgment result is true in step S11,
Since the fluctuation of the operating voltage Vd in the shaded area of the power / voltage characteristic P ₁₀ shown in FIG. 7 is expected, step S12
Then, the correction voltage ΔV ^{* is set} to zero and the maximum power tracking control is interrupted.

Then, the command value V ^* of the voltage regulator 19 in FIG.
_The solar cell is operated by fixing Vm ₁₀ corresponding to ₁₀ and maintaining Vd at a constant value Vm ₁₀ .

Since the hardware for realizing this control method is almost the same as that shown in FIGS. 3 and 4,
Detailed description is omitted to avoid duplication. Further, in the flowchart of FIG. 1, it is the same as that of FIG. 5 except for steps S11 and S12.

In the control method according to the present invention, when the amount of solar radiation recovers rapidly and reaches 50% of the maximum value, the power / voltage characteristic becomes P _{50 of} FIG. 7 as described above. Vd
Is fixed to a constant value Vm ₁₀ , and a voltage difference ΔV ₁ (= Vm ₅₀ − for continuously giving maximum power even when the amount of solar radiation is restored.
Since Vm ₁₀ ) is small, the voltage transition time is extremely short.

(Effect of the invention) As described above, according to the present invention, when the change in the output power with respect to the output voltage of the solar cell becomes almost constant, the correction voltage is set to zero to interrupt the maximum power tracking control. In order to operate the converter under the constant PV cell output voltage command value that gives the true maximum power at, and control the PV cell at a constant voltage, the fluctuation of the operating voltage during low solar radiation is controlled by the constant control by the optimum operating voltage. There is an effect that the maximum power can be immediately supplied with good response even when the amount of solar radiation is rapidly recovered.

Further, the present invention can be provided at a low cost because it can be realized mainly by adding some software to the conventional maximum power tracking control method.

[Brief description of drawings]

FIG. 1 is a flow chart of a program for controlling maximum power in one embodiment of the present invention, FIG. 2 is an output characteristic diagram of a solar cell using a light irradiation amount as a parameter, and FIG. 3 is conventional power supply by a maximum power tracking control method. Block diagram of system, FIG. 4 is a block diagram of correction voltage generator, FIG.
FIG. 6 is a flow chart of the maximum power tracking control program, and FIGS. 6 and 7 are output characteristic diagrams of the solar cell for explaining the operation of the conventional example. 11 …… Solar cell, 12 …… Conversion device 15 …… Load

Claims (1)

[Claims] 1. A converter is operated by supplying output power of a solar cell to a load through a converter and increasing or decreasing a correction voltage for an output voltage command value of the solar cell so that the output power is always maximized. Therefore, in the power supply system by the maximum power tracking control method that adjusts the output voltage of the solar cell, the correction voltage is set to zero and the maximum power tracking is performed when the change in the output power with respect to the output voltage of the solar cell becomes almost constant. A control method of a power supply system, characterized by interrupting control and operating a converter under a constant solar cell output voltage command value that gives a true maximum power at the time of solar radiation to control the solar cell at a constant voltage. .