1. Field of the Invention
The present invention relates to a circuit arrangement for feeding an electrical load from a solar generator comprising an input for connection to the solar generator and an output for connection to the electrical load, whereby a final control element is controlled by a control circuit and is arranged between the input and the output, the control circuit having a reference voltage input connected to a reference voltage generator which is controlled by a light sensor, and in which the reference voltage generator is an arrangement for measuring a signal for short-circuit current of the solar generator and the final control element is controlled by the control circuit such that the current drawn from the solar generator has a prescribed ratio to the respective measured value of the signal for the short-circuit current of the solar generator.
2. Description of the Prior Art
A circuit arrangement of the type set forth above has been disclosed in the German published application No. 20 43 423, fully incorporated herein by this reference. The known circuit arrangement is a two-stage action controller which is fed from a solar generator. The two-stage action controller is designed and dimensioned such that the current output by the solar generator has a prescribed ratio to the short-circuit current of a reference solar generator. This ratio is identified with the assistance of the characteristic field of the solar generator as the factor by which the short-circuit is to be multiplied in order to obtain the current in the operating point of maximum power. A test cell belonging to the solar generator serves as a reference solar generator. The solar generator feeding the load and the solar generator whose short-circuit current is measured are therefore of the same type. In this manner, the operating point of maximum power is obtained with good approximation in a great temperature range of the solar generator, and this is accomplished with relatively simple structure. The circuit arrangement serves, in particular, for charging a battery or for feeding loads which are buffered with the assistance of a battery. The proposed type of current matching, however, can also be advantageous in other loads when an optimally great load of the solar generator is desired. The circuit arrangement can be a component portion of a regulator or of an arrangement for what is referred to as forward-acting regulation wherein the final control element is controlled in a prescribed dependency on the measured short-circuit current.
Since the test cell is constantly loaded by a precision resistor, it is not available for a feed of the load. Moreover, the measured value of the short-circuit current of the test cell which serves as a signal for the short-circuit current of the solar cell is only an approximate value, since conclusions regarding the entire solar generator are drawn based on the properties of the test cell.
Given a circuit arrangement known from the periodical "Elektronik", 19/21, Sept. 1984, p. 96, a switching regulator is connected to a solar generator, the output voltage of the circuit arrangement being held at a described value with the assistance of the switching regulator. This is achieved in that the actual value input of the switching regulator is connected to a tap of a first voltage divider which is connected in parallel to the output of the circuit arrangement. The switching regulator comprises a further control input which is internally connected to a reference voltage source. This control input lies at a tap of a second voltage divider which is connected to the solar generator. A photodiode is connected directly adjacent the solar generator, the photodiode being arranged parallel to a resistor of the second voltage divider.
A maximum of power is to be gained from the solar generator with the assistance of the known circuit arrangement in that the reference voltage effective in combination with a voltage regulation is to be correspondingly influenced by the photodiode given a changing light irradiation. In addition to the radiation density, the temperature also has a significant influence on the generator voltage in the operating point of maximum power given a solar generator. In the known circuit arrangement, however, the latter is not taken into consideration.
A typical characteristic field of a solar generator may be found, for example, from the brochure "Solar Modules, Type Series SM36" of the Interatom Company.
A particularly simple type of matching would be to define the drawn current for a frequent mean radiation intensity. This, however, would have the disadvantage that the possible, higher current, given more intense radiation, could not be exploited and that the voltage would collapse given weaker radiation and charging would no longer be possible.
On the other hand, it can be conceived to continuously check the yield of the solar generator and to match the current to the value of the maximum power resulting from the yield in order to achieve a regulation to maximally-possible power. Such a regulator, however, involves a relatively great expense because of the circuit expense required.