Leakage current suppression in non-isolated grid-tied photovoltaic inverters

In non-isolated grid-connected photovoltaic systems, system losses are increased by common mode leakage currents. Common-mode leakage current generates current harmonics, causes electromagnetic interferences and threatens personal safety. Therefore, common mode leakage current suppression is an important technical issue. First of all, this paper analyzes the causes of leakage current and then explains the most common leakage current suppression method by the mechanism of typical inverter topology, i.e., constructing a new continuity loop to disconnect the photovoltaic cell side from the AC grid side during the continuity stage, and combining it with the switching modulation method to keep the common-mode voltage unchanged, thereby effectively inhibiting the source of leakage current. Subsequently, the new topologies proposed by domestic and foreign scholars to suppress leakage current, namely the three-phase H7 voltage source topology and NDPGCI-6 topology, are reviewed, and their working principles are analyzed and compared regarding the effectiveness of leakage current suppression. Finally, these new topologies are summarized, and the feasibility of their application in practice is examined.