JPH0568722B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to maximum power control of a battery power source, such as a solar cell, for extracting maximum power from a battery power source, such as a solar cell, through a power conversion device comprising a chopper, an inverter, etc. Regarding the method.

[Technical background of the invention and its problems]

In recent years, battery power sources have been widely used in power supply systems that supply a predetermined amount of power by being connected to independent loads or other power supply systems via power conversion devices such as choppers and inverters. A solar cell, which is a typical example of this battery power source, has current-voltage characteristics (broken line) and current-power characteristics (solid line) as shown in FIG. 3, when solar radiation is used as a parameter.
The figure shows a tendency for current and power to increase as the amount of solar radiation increases. M ₁ , M ₂ , and M ₃ indicate maximum power points, and N ₁ , N ₂ , and N ₃ indicate points that give voltage and current at maximum power. The maximum power value varies greatly depending on the amount of solar radiation, but the voltage that provides the maximum power is almost constant regardless of the amount of solar radiation. Further, when the current increases beyond a certain predetermined value, the power shows a characteristic that the power decreases rapidly. In the case of a solar cell, the cause of electromotive force generation in a battery power source is the amount of solar radiation, so the magnitude of the amount of solar radiation is synonymous with a change in the cause of electromotive force generation.

Conventionally, there are two main methods for controlling the maximum power of a battery power source in order to effectively extract power from a solar cell having such characteristics.

The first method is to control the output voltage of the solar cell to a constant voltage by utilizing the fact that the maximum output point exhibits substantially constant voltage characteristics with respect to changes in solar radiation. However, if the voltage standard set under a certain condition remains unchanged, if the conditions change, such as a change in battery temperature, the voltage will fluctuate greatly due to the current fluctuation as shown in Figure 3. also occurred,
The disadvantage is that stable control cannot be performed.

The second method is a control method that constantly follows the maximum output point of the solar cell in order to compensate for the drawbacks of the constant voltage control. This control method is a method in which a solar cell is operated at two different points and its output power is compared so that the operating point of the cell becomes the maximum output point.

FIG. 4 shows an example of a device applying this second method to extract maximum power from a battery power source. In the figure, the DC output of a solar cell 10 is converted into AC by an inverter 11, and the DC output is converted to AC by an inverter 11.
It is supplied to the power system 13 via. solar cell 1
The output current and voltage of 0 are current detectors 21 and 22, respectively.
The detected values Is and Vs are detected by the A/D converter,
The signal is input to a maximum power control circuit 23 that includes a microcomputer, a D/A converter, and the like. This maximum power control circuit 23 has an input data storage function, a logical calculation function, a judgment function, etc., and calculates a voltage reference Vs ^* according to an algorithm described later and outputs the value. The voltage reference Vs ^* is compared with the voltage detection value Vs, and the deviation thereof is amplified by the error amplifier 24 and input to the gate control circuit 25. This gate control circuit 25 controls the gate phase of the inverter 11 according to the deviation from the error amplifier 24 so that this deviation becomes zero.

Here, the operation algorithm of the maximum power control circuit 23 will be explained with reference to FIG. As described above, a solar cell has current-voltage characteristics (broken line) and current-power characteristics (solid line) as shown in the figure under constant solar radiation and temperature. The operating region of this solar cell can be divided into a region where the voltage decreases relatively slowly as the current increases and a region where the voltage decreases significantly. When operating a solar cell, it is ideal to always operate at the maximum power point M. For this purpose, the circuit 23 sets the voltage reference Vs ^* according to the following algorithm. First, in the initial setting, the voltage reference Vs ^* is set to be the same as the ^voltage detection value ^Vs of the solar cell (if it is zero, the open voltage) Let me go. During this time, the power increases in the direction of arrow A in the figure. If the voltage reference Vs ^* continues to decrease as it is, the power will eventually exceed the maximum power point M and start decreasing as shown by arrow C. Therefore, by detecting this decrease in power, the voltage reference Vs ^* is moved in the direction of increasing by a constant width. As the voltage reference Vs ^* continues to increase, the power increases as shown by arrow D, but eventually begins to decrease as shown by arrow B. Therefore, this decrease is detected and the voltage reference Vs ^* is changed again in the direction of decreasing. By repeating the above operation, the voltage reference Vs ^* will reciprocate in the vicinity of the maximum power point M.

However, increasing or decreasing the voltage reference Vs ^* by a constant change width ΔVs ^* as described above has the following drawbacks. In other words, if the variation width ΔVs ^* is set to a small value, the variation width at the maximum power point M becomes smaller and the accuracy of maximum power control can be improved, but the tracking speed is slow for changes in characteristics due to sudden changes in solar radiation, etc. I get used to it. Also, the variation width ΔVs ^*
If the value of is set to a large value, the tracking speed can be increased, but the amplitude of fluctuation at the maximum power point M becomes large, and the accuracy and stability of the maximum power control decrease.

[Purpose of the invention]

The present invention has been made in view of the above, and the present invention has been made in view of the above.
With the maximum power control method, it is possible to accurately and stably control the output power of the battery power source to its maximum power, and it is also possible to quickly follow fluctuations in battery characteristics due to changes in conditions, etc. The purpose of the present invention is to provide a method for controlling the output power of a battery power source.

[Summary of the invention]

In order to achieve the above object, the present invention changes the range of change in the voltage reference applied to the power converter according to the amount of change in the output power of the battery power source caused by the change in the voltage reference. be.

[Embodiments of the invention]

Hereinafter, an embodiment of the method for controlling the output voltage of a battery power source according to the present invention will be described with reference to FIGS. 1 and 2.

This example is an example in which the present invention is applied to the case where the output power of a solar cell having characteristics similar to those shown in FIG. 5 is controlled by a device similar to that shown in FIG. 4. be. FIG. 1 shows a flowchart of this embodiment, and all of this processing is performed inside the maximum power control circuit 23.

As shown in FIG. 1, initial setting processing (step 1) is performed after starting maximum power control. In this process, the current detection value Is and voltage detection value Vs from the current detector 21 and voltage detector 22 are read, and the current output power Ps of the solar cell 10 is calculated from these values. Further, the same value as the voltage detection value Vs is initially set as the voltage reference Vs ^* and output to the error amplifier 24, and this voltage reference Vs ^*
A flag is set to indicate a mode for changing the value in the decreasing direction.

After this initial setting process is completed, the following routine is started which is repeated at every predetermined sampling period.

First, old data storage and new data reading processing (step 2) is performed. In this process, the voltage detection value read during previous sampling is
Vs' and the calculated output power Ps' are stored in the internal memory. Also, the current detected current value Is and voltage detected value from the current detector 21 and voltage detector 22
Vs is loaded. Next, a power calculation process (step 3) is performed, in which the current output power Ps is calculated based on the current detected value Is and the detected voltage value Vs that were read earlier.

Next, voltage reference change width calculation processing 4 is performed. In this process, the output power Ps′ at the previous sampling time is read from the internal memory, and the difference between this value and the value of the current output power Ps calculated earlier, that is, the power change amount ΔPs, is calculated, and the power change amount ΔPs is calculated. A power reference Vs ^* is set based on the amount ΔPs.

This variation width Vs ^* is set, for example, according to the relationship shown in FIG. In other words, if the absolute value of the power change amount ΔPs is smaller than the predetermined value ΔP ₁ ,
The change width ΔVs ^* is set in proportion to the power change amount ΔPs. Further, when the absolute value is larger than the predetermined value ΔP ₁ , the variation width ΔVs ^* is set to a constant value ±ΔV _S1 ^* . The sign of the change width ΔVs ^* is set to be the same as the sign of the voltage change amount ΔPs. in this case,
A positive change width ΔVs ^* indicates that the mode of change direction (increase, decrease) of the voltage reference Vs ^* is maintained as it is, and a negative value indicates that this mode is reversed, that is, if it is currently in a decreasing mode, it is switched to an increasing mode. It means that. In the following explanation, when we simply refer to the variation range ΔVs ^* , we mean its absolute value.

When this voltage reference change width setting process is completed, a mode determination process (step 5) is performed next. Here, it is determined from the flag whether the mode is currently decreasing or increasing, and
It is determined whether the current mode should be maintained or reversed based on the sign of the previously set change width ΔVs ^* , and if it is negative, the flag is switched to reverse the mode. Once either the decrease mode or the increase mode is determined in this way, the voltage reference setting process (step 6) is then performed. In this process, the previously set change width ΔVs is added to or subtracted from the voltage reference Vs ^* ' at the time of previous sampling, and a new voltage reference Vs ^* is set. In other words, if the mode determined earlier is the decreasing mode, the change width ΔVs ^* is subtracted from the previous voltage reference Vs ^* ′,
Furthermore, in the increase mode, the change width ΔVs ^* is added to the previous voltage reference Vs ^* ' to set a new voltage reference Vs ^* . Voltage standards set in this way
Vs ^* is output to the error amplifier 24.

By repeating the above routine, the operating point of the solar cell 10 is moved in the direction of increasing its output power Ps, as shown by arrows A and D in FIG. Maximum power point M
It will swing left and right around the center. At this time, the variation width ΔVs ^* that determines the amplitude of the operating point is set to be large as the power variation ΔPs is large and small as the power variation ΔPs is small, as described above. The amplitude of the fluctuation of the operating point becomes extremely small, so that the maximum power can be obtained accurately and stably. In addition, if the battery characteristics change due to sudden changes in solar radiation or battery temperature, and the operating point deviates significantly from the maximum power point M, the amount of power change ΔP
is large, the variation width ΔVs ^* of the voltage reference Vs ^* also becomes a large value, and the operating point moves toward the maximum power point M with a fast response speed. Furthermore, when the amount of solar radiation decreases and the operation of the solar cell 10 enters a region where it is unstable with respect to changes in the voltage standard Vs ^* , the amount of power change ΔPs becomes small, so the width of change in the voltage standard Vs ^* decreases. ΔVs ^* is also reduced, and fluctuations in battery voltage are reduced, making it possible to stabilize the voltage.

In the above embodiment, as shown in Fig. 2, the variation range ΔVs ^* of the voltage reference Vs ^* is varied in proportion to the power variation ΔPs, but it is also possible to vary it using another function similar to this. Of course, the same effect can be obtained even if Further, in this embodiment, a case has been described in which a solar cell is used as a battery power source, but similar effects can be obtained by using a power source with similar characteristics, such as a fuel cell. In the case of fuel cells, the cause of the electromotive force generated by the battery power source is the fuel (hydrogen,
This is a chemical reaction between a combustion agent (titanium, methanol, etc.) and a combustion agent (oxygen or air), and changes in the cause of this electromotive force are caused by the magnitude and speed of the electrochemical reaction amount of the fuel and combustion agent.

〔Effect of the invention〕

As explained above, according to the present invention, when changing the output voltage of the battery power source to make the operating point of the battery coincide with the maximum power point, the range of change in the output voltage is changed according to the amount of power change. Therefore, if the operating point moves away from the maximum power point due to a sudden change in conditions, the above tracking is performed at a fast response speed, and precise tracking is performed near the maximum power point. It becomes possible to obtain maximum power stably and accurately.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing an embodiment of the maximum power control method for a battery power source according to the present invention, FIG. The figure shows the characteristics of a solar cell.
FIG. 4 is a block diagram showing an example of a device for extracting maximum power from a solar cell, and FIG. 5 is a characteristic diagram of a solar cell for explaining an outline of maximum power control by the device. 10...Solar cell, 11...Inverter, 12
... Grid interconnection reactor, 13... Power system, 21...
...Current detector, 22...Voltage detector, 23...Maximum power control circuit, 24...Error amplifier, 25...
Gate control circuit.

Claims (1)

[Scope of Claims] 1. A battery having the characteristics that the voltage is constant regardless of changes in the cause of electromotive force generation when maximum power is obtained, and the power decreases rapidly when the current increases beyond a predetermined value. In a method of controlling the power taken out from a power source via a power conversion device to the maximum power, the output voltage of the battery power source is controlled to the maximum power by changing a voltage reference applied to the power conversion device by a predetermined change width. detecting the output power of the battery power supply at each value of the output voltage, and if the amount of change in the detected value of the output power is in an increasing direction, maintaining the direction in which the power reference is changed; On the other hand, if the change direction is in the decreasing direction, the change direction is reversed, and the change width of the voltage reference is changed depending on the magnitude of the change amount.