Static VAR generator with time-related-error minimizer

摘要

A control circuit for a static VAR generator measures appropriate circuit variables during consecutive half cycles of line voltage. This information is utilized to determine the firing angles of the VAR generator thyristors for providing compensating current to the line for keeping the source current in phase with the source voltage, for balancing source current in three-phase electrical systems and for reducing the line voltage fluctuation. A time-related-error minimizer is provided in the control system of the VAR generator to reduce the deviation between the amount of compensating current which is predicted for proper compensation during a given half cycle and the actual amount of compensating current needed at the time of application. The error is related to the differential between the time of the calculation of the value of current needed and the time it is actually applied. In one case, an open loop-type computational technique is utilized to determine the required inductor current. In a second case, a feedback control for reducing error utilizes the desired or predicted current and the actual inductor current; and in a third case, the compensating error signal is indirectly determined by utilizing the difference between the instantaneous AC terminal voltage and its steady state average value. The error signal associated with the latter case is combined with the computed desired inductor current to reduce time related terminal voltage variations.