基于谐振变换器的中压单级太阳能光伏逆变器损耗分析

In grid-tied PV systems, an inverter is typically used with a medium-voltage low-frequency transformer (MV LFT) to connect to the grid. However, in certain single-stage designs, high-frequency transformers (HFT) paired with an unfolder inverter replace the LFTs. These designs are usually less common in high-power medium-voltage grids because of significant switching losses on the primary side. This paper proposes a single-stage isolated 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. The losses at each stage are analyzed and a combination of phase-shift angle and switching frequency for optimal efficiency is proposed. A compact MV stage is designed, and performance is verified. 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 2400Vac single phase prototype.