13.8 kV, 1MW Resonant Direct AC Medium Voltage Single Stage Solar PV Inverter

An inverter is generally employed with MV LFT to connect to the grid in a grid-tied PV system. However, in some single-stage topologies, the LFTs are replaced by HFT combined with an unfolder inverter. Generally, these topologies have limited use at high-power MV grids due to high switching losses on the primary side. This paper proposes a single-stage direct resonant AC medium voltage (MV) grid-connected solar PV inverter. It produces rectified sinusoidal AC current at the output of the rectifier and is then unfolded by a line frequency unfolding inverter. A combination of switching frequency and phase-shift modulation is used to reduce losses. Primary side LLC converter parameter selection is discussed, and an MV HFT is designed. A compact MV stage is designed, and the thermal performance of the cooling system is verified. A novel fiber optics-based sensor design is employed to address insulation challenges. The system performance is simulated for 1/3 MW at a single-phase 11.3 kV grid connection in MATLAB/Simulink. ZVS conditions are verified through experiments on a preliminary prototype.