Analysis and proposal of an isolated DC/AC system using three-state switching cell

This paper presents an isolated dc/ac system using the three-state switching cell (3SSC). This converter is meant to operate as interface converter for microgrid or stand-alone applications in conjunction with a small power generating units. This system consists in two power processing stages. The first one is a dc/dc boost converter based in the 3SSC and the second one is a classical voltage source inverter (VSI) based in the full bridge inverter. The mentioned cell added in the dc/dc stage allows the use of only two windings in the isolation transformer, as well as, the series connection of only one dc current blocking capacitor to avoid its saturation. Other relevant characteristics of the system are, the blocking voltage across the controlled switches in the dc/dc stage is low, which allows the utilization of lower drain-to-source conduction resistances (R_DSon) MOSFETs, and the current through the autotransformer winding is almost continuous minimizing the hysteresis losses on the magnetic core. The operating principle of the proposed system has been analyzed in detail. In order to verify the feasibility of this topology, experimental waveforms are shown for a 1kW assembled prototype.