A comparative analysis of the 5L-AH6 and 5L-SC topologies for grid-connected transformer-less multilevel inverters for PV systems

摘要

In this paper a comparative evaluation of the efficiency for two multilevel topologies used in grid-connected transformer-less applications is presented. The proposed analysis is focused in two of the most important characteristics in grid-connected converters, such as the leakage currents which appear between the stray capacitances and the ground path and the efficiency. The efficiency evaluation includes an analysis of power losses distribution in the semiconductors providing information to develop a good thermal design of the converter. For the evaluation is considered that the overall DC link is fixed to the desired voltage value and the capacitor voltages are balanced. Also, the topologies selected are connected to the grid by means of an ideal L filter to inject active power to the grid. In both cases, the proposed modulation strategy is based in the Sinusoidal Level Shifted Pulse Width Modulation (SLSPWM). Numerical results of the analysis of common mode voltage and the efficiency curves are presented.