JPS6252541B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solar cell utilization system that supplies power from a solar cell to an independent load or other power supply system via a power converter, and its purpose is to The purpose is to make the battery produce maximum output.

The voltage-current characteristic curve of a solar cell changes depending not only on the amount of light irradiation (incident energy) but also on the temperature of the solar cell. FIG. 1 and FIG. 2 illustrate characteristic curves of solar cell current I [A] and solar cell output [W] with respect to solar cell voltage V [V].
However, in the case of Figure 1, the temperature [℃] is used as a parameter under the condition that the incident energy is constant, and in the case of Figure 2, the incident energy [mW/cm ³ ] is used as a parameter under the condition that the temperature is constant. Each is illustrated. The curves indicated by broken lines in each of FIGS. 1 and 2 are maximum output characteristic curves.

By controlling the power converter to operate the solar cell at a current and voltage value that always provides the maximum power value, effective use of the solar cell can be achieved. In order to maintain the operating point of the solar cell at its maximum output point, an auxiliary solar cell with the same characteristics as the main solar cell is installed as a pilot cell, and the amount of light irradiated to the main solar cell is measured by the voltage of this pilot cell. Then, from this measured amount of light irradiation, the battery voltage that provides the maximum output is calculated using the characteristic relationship shown in Figure 2, and the power is converted so that the actual voltage of the main solar cell matches this calculated battery voltage. It has already been proposed to control devices. However, this method does not take into account the temperature dependence shown in Figure 1, and if the temperature changes depending on the installation location or ventilation cooling condition, the exact maximum output point cannot be determined. The drawback is that it cannot be detected. Another method is to directly find the maximum output point by repeatedly increasing or decreasing the solar cell current while monitoring the solar cell output, and then detecting the direction of change in the resulting solar cell output. Although this method is reliable, it is difficult to apply to low-priced products because the control is sophisticated.

An object of the present invention is to provide an apparatus that can detect the maximum output point accurately enough to satisfy even temperature changes while following the former simple method of using a pilot cell.

FIG. 3 is a block diagram showing an embodiment of the power supply device using solar cells according to the present invention. The main solar cell 1 that supplies electric power is connected to a power conversion device such as an inverter 2.
It is connected to the AC power supply system 3 via. 4 is a load connected to the system 3. An auxiliary solar cell 11 that is installed alongside the main solar cell 1 and does not supply power is prepared as a pilot cell. As this pilot cell, a cell having similar characteristics to the cell used as the main solar cell 1 is used, and care is taken so that both cells 1 and 11 are placed under the same conditions regarding the amount of light irradiation and temperature. ing. The pilot cell 11 is placed in a short-circuit condition, whereby the short-circuit current of the main solar cell during power supply is estimated. The short circuit current of the pilot cell 11 is input to a current command calculator 12. This current command calculator 12 has a function characteristic that simulates the relationship between the short circuit current of the main solar cell 1 and the current at maximum output, and the solar cell that produces the maximum output from a signal corresponding to the short circuit current of the pilot cell 11. Calculate the current. In this way, the current command value given by the calculator 12 is compared with the actual current value detected by the solar cell current detector 13,
The regulator 14 controls the inverter 2 according to the current control deviation. In this way, the current flowing from the solar cell 1 to the inverter 2 is adjusted according to the command value.

The reason why the current command value corresponding to the maximum output point is obtained by the current command calculator 12 is as follows.

In other words, among the various characteristics of solar cells, under normal temperature, clear sky and sunlight, I _P (t, L)/I _SC (t, L)=I' _P (t'
, L')/I _S ' _C (t', L') approximately exists. However, I _SC (t, L) is the short circuit current under the conditions of battery temperature t and solar radiation L, and I _P (t, L) is the current at maximum output under the same conditions. Also, I′ _SC (t′,
L') is the short circuit current under the conditions of battery temperature t' and solar radiation L', and I _P (t', L') is the current at maximum output under the same conditions. Therefore, for example, the short circuit current I′ _SC (t′, L′) and the current at maximum output I′ _P under a predetermined temperature t′ and solar radiation L′ that are considered standard.
By substituting (t', L') into the right-hand side of the above equation, the right-hand side becomes a constant value, and if this constant value is A, then I _P (t, L) = A・V _OC (t, L ) can be rewritten as In other words, an input signal corresponding to the battery open circuit voltage I _SC (t, L) is received, and an output signal corresponding to the maximum output current I _P (t, L) is generated by arithmetic processing according to the above formula. What is necessary is to provide the voltage command calculator 12. Short-circuit current of the main solar cell during power supply I _SC
Since it is difficult to directly detect (t, L), the corresponding current i _SC (t, L) is generated through the short-circuited pilot cell 11.
is extracted. The above-mentioned similar characteristics mean the relationship i _SC (t, L)=k·I _SC (t, L) (k is a constant).

According to the present invention, the signal corresponding to the short circuit current from the pilot cell is converted into a command value corresponding to the current at the maximum output by the calculation means having extremely simple functional characteristics that simulates the relationship between the short circuit current and the current at the maximum output. It is possible to operate the solar cell exactly at the operating point that provides maximum output, even compensating for the effects of changes in cell temperature.

[Brief explanation of the drawing]

1 and 2 are characteristic curve diagrams of a solar cell, and FIG. 3 is a block diagram showing an embodiment of the device of the present invention. 1... Main solar cell, 2... Power conversion device (inverter), 3... Other power supply system (commercial power supply system),
4...Load, 11...Auxiliary solar cell (pilot cell), 12...Current command calculator, 13...Current detector, 14...Adjuster.

Claims (1)

[Claims] 1. In a solar cell power supply device that supplies power from a solar cell to an independent load or other power supply system via a power conversion device, an auxiliary solar cell installed in order to estimate the short-circuit current of the main solar cell supplying power. and an arithmetic device that has a functional characteristic that simulates the relationship between the short-circuit current of the main solar cell and the current at maximum output, and calculates the current at maximum output of the main solar cell from the short-circuit current estimation signal obtained from the auxiliary solar cell. ,
A control device for controlling the power conversion device so that the actual current of the main solar cell matches the current at maximum output of the main solar cell calculated by the arithmetic device. Power supply device.