A Single-Stage Soft-Switched LVDC to Three-Phase MVAC Converter for MV Grid Integration of Utility-Scale Solar PV

This paper presents a single-stage high-frequency link multi-level three-phase DC-AC converter for medium voltage grid integration of utility-scale solar park. On the DC side, three half-bridge legs are used. The converter employs three high-frequency transformers with multi-winding secondaries to provide galvanic isolation between the DC and AC sides. The output of each secondary winding is fed to an active rectifier followed by a full-bridge-based unfolder circuit to generate the line frequency AC. The rectifier-unfolder stages are then connected in cascade to build the medium voltage AC before connecting to the MV utility grid through line filters. The modulation strategy ensures zero-voltage switching of the DC side half-bridge legs throughout the line cycle. For DC-AC power flow, the secondary active rectifiers are soft-switched, and the unfolder circuits are line frequency switched, thus incurring negligible switching loss. The converter avoids using a bulky interstage DC- link filter capacitor. The operation of the converter is verified in MATLAB simulation, and critical simulation results are given in the paper.