Ground current suppression for grid connected transformerless PV inverter with unbalanced output filter inductors

This paper discusses the modulation methods for ground current suppression. It focuses on the ground current of the grid-connected three-phase transformerless photovoltaic (PV) inverter with unbalanced output filter inductors. The staggered SPWM modulation using three triangular signals displaced by 120 degrees is mentioned for comparison. Aiming at the case of unbalanced output filter inductors, an improved method of staggered SPWM is proposed. The comparison for the ground current´s harmonic spectrum and the effective value are presented. The comparison of effective value varying with the imbalance degree of the inductors is also studied. The simulation result will be given to verify the estimation. It is based on the circuit of PV inverter with parasitic capacitors, and use Simulink as the software. The calculation and simulation results will be compared. And the output filter inductor and the parasitic capacitor´s influence on ground current will also be referred.