Analysis on Leakage Current in Transformerless Single-Phase PV Inverters Connected to the Grid

The removal of a transformer in grid-connected PV systems can reduce size, weight and costs. When no transformer is used, a galvanic connection between the grid and PV panels exists and leakage current appears due to parasitic capacitance. In this paper, the principle of leakage current is analyzed from equivalent resonant circuit and an equation is derived to evaluate the current. It will be shown that varying common-mode voltage, the imbalance of system as well as the grid contribute to the issue with different importance. Although the effect of grid could be ignored in most cases, it may cause potential danger especially when parasitic capacitance is large enough. In addition, simulation is conducted to verify the conclusions. The simulated waveform is consistent to the derivation and is similar to the measurements in engineering practice.