Isolated AC/AC Converter with LLC Resonant Converter High Frequency Link and Four-Quadrant Switches in the Output Stage

An AC-AC converter with high-frequency link employing LLC resonant converter operating in the vicinity of the resonance frequency is studied, in which the output stage is unique and formed by a high-frequency AC-AC converter employing four quadrant switches. The topology, its operation and the modulation strategy are presented. The high-frequency stage switches located on the primary side of the transformer operate with soft switching of the ZVS type, while the four quadrant switches that form the output stage operate with soft switching of the ZCS type. Experimental data on a 1.5 kW experimental prototype that was designed, built and tested in the laboratory, with 220 VRMS input, 220 VRMS output and 40 kHz switching frequency are given in the paper. The studied converter can be considered a candidate for the building block of medium voltage solid-state transformers (SST) for power distribution systems.