Single-Stage Isolated AC/AC Converter With Phase-Shifted Controller

Abstract

This article proposes a single-stage ac/ac converter with a high-frequency link, which is suitable for multilevel converters. The proposed topology is a direct ac/ac converter without commutation problems, which solves the common issue of direct ac/ac converters. Moreover, four-quadrant switches commonly used in matrix converters, and unfolding bridges normally essential in conventional circuits, are unnecessary in the proposed circuit, which enhances the efficiency and cost. The converter control strategy is adapted based on a single-phase shift technique with constant switching frequency and 50% duty cycle. The control strategy achieves a wide range of zero-voltage-switching (ZVS) turn-on without any auxiliary circuit. Furthermore, the high-frequency transformer (HFT) is free from line-frequency components with minimized rms value of current. Hence, an HFT with reduced size can be realized. The converter also has a low total harmonic distortion (THD) load current. A new continuous-time transient model of the proposed converter is proposed based on the generalized average model (GAM). The derived model is used to design the proposed phase shift controller. Moreover, a detailed closed-loop transient analysis is presented. A prototype circuit is implemented to validate the theoretical analysis and the feasibility of the proposed converter.