Topology Optimization Analysis of Leakage Current Suppression in Three-Level Four-Leg Photovoltaic Grid-Connected Inverter

The grid-connected non-isolated photovoltaic inverter system suffers from the leakage current, which increases the loss of the system, and the grid-connected current harmonics impact the normal operation of the equipment. To this end, first, the leakage current mechanism in a conventional three-phase three-level four-leg grid-connected inverter is analyzed and two circuit topology improvement schemes are proposed. Second, mathematical modeling of different circuit topologies is carried out. With the leakage current and the harmonic distortion rate of the grid-side current as the main suppression indicators, the advantages and disadvantages of each topology are analyzed. Finally, the optimal leakage current suppression circuit topology is proposed for the three-level four-leg grid-connected inverter. Meanwhile, the corresponding objective function and constraints are constructed to solve the problem of selecting key components parameter by non-linear programming. Without additional control strategy, the proposed optimal circuit topology has a significant leakage current suppression performance compared to the other three topologies, only 10.24% of the conventional topology, and ensures that the grid-connected current total harmonic distortion rate meets the highest relevant standards.