Current Source Optimization in AC-DC GTO Thyristor Converters

A digital interface for a three-phase PWM ac-dc GTO converter is described, and a microprocessor-based firing scheme for the PWM control system is proposed. Two modulation strategies, equal pulsewidth modulation (EPWM) and sinusoidal pulsewidth modulation (SPWM), are implemented and their efficiencies of operation considered. Applied as the inner current loop in a dc motor controller with constant-gain proportional-plus-integral (PI) control, a fast response to step reference input changes is obtained. The theoretical responses using an approximate z-transform analysis are used to obtain optimum operational parameters.