Single-Stage AC/AC Converter for Solid-State Transformer (SST) Based on Modified DAB Topology

This paper presents a single-stage AC/AC converter for solid-state transformer (SST) application. The proposed solution exhibits a non-resonant topology based on a modified version of the Dual Active Bridge (DAB) and does not require four quadrant AC switches for direct AC/AC conversion, thus eliminating the associated commutation management and related issues. Also, the topology does not need Line-Frequency (LF) operated unfolding bridges, resulting in a reduced device count. Extended Phase-Shift (EPS) modulation is considered and full analytical calculations of the zero-voltage Switching (ZVS) regions are provided, demonstrating the capability to operate the converter over a wide range with complete ZVS. Experimental results are presented to validate the proposal and the associated analysis. Both rated and low power operation over a large part of the input AC cycle ranging from the peak value to near the zerocrossing point are shown and discussed.