Soft switched multilevel unidirectional high frequency link DC/AC converter for medium voltage grid integration

This paper describes a cascaded multilevel converter topology for direct medium voltage grid integration of photovoltaic sources. The topology uses high frequency magnetic isolation and hence, reducing volume and cost of overall system. The topology is single stage and does not have any inter-stage bulky filter capacitor, thus improving reliability. The low voltage DC side converter active switches are high frequency switched. These active switches are zero voltage switched (ZVS) for most part of the line cycle. The soft-switching is achieved without additional snubber elements. The active switches interfacing the medium voltage grid are switched at line frequency incurring negligible switching loss. The converter has modular structure which also has added advantages of easy repair-replacement. Modulation strategy and soft-switching technique are analyzed in detail. Key simulation results are presented to verify the circuit operation.