Three-phase ideal phase shifter using AC choppers

Abstract

A three-phase ideal phase shifter using pulse-width modulation (PWM) AC choppers is proposed. The ideal phase shifter is made up of three single-phase PWM AC choppers and transformers for series quadrature voltage injection. The proposed phase shifter uses PWM AC choppers to solve the commutation problem and produces phase shift without amplitude variation. In the PWM AC chopper, the required switching operation to solve the commutation problem is achieved using regenerative DC snubbers. Previous phase shifters have utilised the source voltage as the input to the tap changer, but the proposed phase shifter utilises, simultaneously, the output and source voltage as the input to the PWM AC chopper. The proposed phase shifter gives phase shift without amplitude variation, high efficiency, fast dynamics, high reliability, and significant reduction of the filter size. It is also shown via simulation and experimental results that the proposed ideal phase shifter gives good dynamic and steady state phase shift performances. Experimental results obtained on a 6kVA AC chopper are discussed.