A Single-Phase Isolated Bipolar Buck-Boost AC–AC Converter Without Commutation Issues

Abstract

This article presents a novel single-phase buck-boost ac–ac converter featuring a high-frequency built-in isolation transformer (HBIT). This topology offers several distinct advantages over its isolated counterparts, including a reduction in the number of semiconductor switching devices and passive elements while ensuring continuous input current with low total harmonic distortion (THD). It provides a wide range of symmetric bipolar step-down and step-up output voltages with better duty cycle utilization. The output frequency can be adjusted in discrete steps. The transformer’s winding ratio becomes an additional control variable for compensating shallow and deep voltage disturbances (sags and swells) without affecting buck-boost capability and magnitude coverage. The proposed converter is immune to the commutation issues of traditional ac–ac converters due to the absence of bidirectional ac switches and demonstrates consistent performance with inductive and nonlinear loads. Comparisons of peak and average device powers of the proposed converter are performed with the latest counterpart converters, indicating its smaller semiconductor requirements, costs, and losses. The comparisons of volumetric indices show its reduced passive component requirements and volume. Additionally, the converter shows a better power conversion efficiency. This article comprehensively analyzes the proposed topology and validates its performance through laboratory results.