A Study of the Leakage Current in Transformerless Three-Phase Photovoltaic Inverters Based on the B4 Topology

This paper outlines a new solution based on the B4 topology for reducing leakage currents in three-phase, grid-connected photovoltaic inverters. The effectiveness of this topology in reducing leakage currents, which are primarily caused by the relatively high capacitance to ground of the PV modules, is evaluated using both symmetrical and asymmetrical grid connection LCL filters. The results show that using an asymmetric filter is particularly effective in reducing leakage currents. The study is complemented by a presentation of the modelling and control procedure for grid-connected B4 inverters with an asymmetric filter, which differs from the conventional approach. The concepts introduced have been validated through experimentation involving the measurement and comparison of the leakage current produced by the B4 topology with that produced by conventional B6 topologies, as well as other previously proposed solutions. Additionally, the dynamic response and grid current distortion of the converter were measured to demonstrate the high performance of the proposed solution.