Common mode leakage current analysis for transformerless PV system with long DC side cables

Due to the advantages of high efficiency and low cost, grid connected inverter based transformerless PV systems have been widespread during the last two decades. The key problem, which arises in absence of galvanic isolation, is the presence of a common mode (CM) leakage current on both AC and DC side of the inverter. In this paper, the influence of long DC side cable to the CM leakage current is taken into account for the first time. Moreover, an improved pai-structure model of the PV panel is proposed. It differs from the traditional single capacitance model in that the panel frame, the mounting rack as well as the connecting wire is all considered. Based upon the proposed model, the common mode leakage current is evaluated in both time domain and frequency domain. Simulation and experimental results give a firm support to the proposed model.