A Digital Self-Compensating Method for Integral-Cycle Power Control of RL Loads

A feedback controlled digital circuit which provides for integral-cycle control of power in RL loads is described. The significant feature of the circuit is that it rapidly and automatically adjusts the firing angle of the triac to eliminate the undesirable dc component in the current of RL loads. Another notable feature of the circuit is that the initial conduction is started with firing angle α = 90 ° which results in suppressed first peaks in the conduction bursts. Subsequently, the feedback takes over to make the firing angle α equal to the power factor angle Ø, thereby triggering conduction at the current zero in each burst. This scheme of automatic dc offset elimination can be utilized to good advantage in the case of motor loads with rapidly changing power factors.