An Improved Isolated Single-Phase Buck-Boost AC–AC Converter With Inherent Commutation Using Only Three Switches

In this paper, an improved isolated single-phase buck-boost AC-AC converter with inherent commutation using only three switches is proposed. The proposed topology utilizes only one high-frequency switch along with two line-frequency polarity changer switches to achieve both inverting and non-inverting operation, which clearly distinguishes it from existing isolated AC–AC converters. Unlike converters that rely on positive/negative switching cells, the inherent commutation in the proposed structure ensures that all components remain active throughout both cycles of the voltage of input. As a result, input current remains continuous, snubber circuits and bidirectional high-frequency switches are eliminated and no dead times is applied, so the circuit structure, control and switching strategy are simplified. A comprehensive comparative analysis is conducted in terms of stresses of switch (voltage and current), peak and average switching device power (SDP) indices, component count, power density, and efficiency. The results demonstrate that the proposed converter achieves lower losses and reduced volume, offering a compact, cost-effective, and lightweight solution. The operating principles are analyzed across different modes, and key relationships are summarized for clarity. A laboratory prototype operating at 100Vrmsconfirms the theoretical analysis and validates the practical feasibility of the proposed converter.