Three-Phase AC Power Control Using Power Transistors

A three-phase ac power control circuit using power transistors which operate in a high-frequency chopping mode is described. The circuit is capable of handling several kilowatts of power at any lagging load power factor angle and the output voltage can be smoothly controlled from zero to full supply voltage. The circuit has inherently fast response and the high-frequency ripple at the output is easily filtered. The development, study, and experimental evaluation of the circuit with resistive and induction motor loads is described.