Leakage Current Suppression in Multilevel Cascaded H-Bridge Based Photovoltaic Inverters

Abstract

The transformerless inverters are more attractive due to their higher efficiency, lower cost, and lighter weight for grid-tied photovoltaic (PV) systems. However, the leakage current can flow through the system because of no galvanic isolation. This undesirable current leads to more losses, electromagnetic interferences, current harmonic distortion, and safety concerns. Therefore, the suppression of the leakage current in transformerless cascaded H-bridge (CHB) based PV systems is investigated in this article. First, the theoretical analysis is presented to model the leakage current for a five-level CHB inverter, and then a new modulation-based method is proposed to suppress this current. In contrast to most existing solutions, the proposed method can be easily generalized through the series connection of five-level CHB blocks. The validity of the proposed solution is verified by several simulations in the power systems computer aided design (PSCAD)/EMTDC environment. Then, experimental results on a five-level and nine-level CHB inverter are presented to confirm the theoretical and simulation results.