An identical bipolar buck-boost AC-AC converter based on a coupled-inductor with safe-commutation, high gain, and high efficiency

Abstract

This article proposes a new identical bipolar buck-boost AC-AC converter with integrated coupled inductors. It possesses all the critical features of a bipolar buck-boost topology, providing both in-phase and anti-phase output voltages. Compared to its counterparts, a high boost factor is achieved without large duty ratios due to using magnetic coupling. Also, a high efficiency is obtained. A unipolar half-cycle modulation is employed in which only half of the switches of a phase-leg are modulated per half-cycle. Therefore, only two out of eight power switches operate at high frequency at any instant, ensuring high-efficiency operation. The safe-commutation operation is achieved by completely turning on the auxiliary switches of the main phase leg for a half-cycle, ensuring a continuous inductor current path during dead times. This results in voltage-spike-free operation. Additionally, this converter benefits from continuous input current and performs well with inductive and non-linear loads. The proposed topology can mitigate both voltage sags and swells due to bipolar operation when employed as a dynamic voltage restorer (DVR). Its high boost factor helps compensate for deep voltage sags (above 50%). This article presents the detailed theoretical aspects of the proposed topology, followed by experimental verifications on laboratory-built hardware.