Single-Stage Isolated AC/AC Converter for Solid-State Transformer

Abstract

Single-stage AC to AC converter topology based solid-state transformers (SSTs) are being explored nowadays because of the higher efficiency of conversion. This paper presents a novel single-stage AC/AC converter topology for the solid-state transformer (SST), based on the LLC resonant converter. Four-quadrant ac switches are utilized on the primary side of the proposed converter to eliminate the folding bridge requirement and give a direct connection to the ac grid. Load-independent operation can be achieved by operating at the resonant frequency of the converter. Thin-film capacitors are used instead of bulky electrolytic capacitors to reduce the overall system capacitance and achieve high power density. Operating modes and soft-switching conditions are discussed in detail. Hardware prototype is developed to validate the operation of the proposed converter.