Circulating Currents Control for Parallel Grid-Connected Three-Phase Inverters

When connecting two parallel three-phase voltage source inverters between the same DC power supply and AC bus, a zero-sequence circulating current will occur. The presence of these undesired currents increases the power losses and decreases the efficiency of the system. It has been demonstrated that circulating currents are basically influenced by null vectors. In this paper, modeling of the parallel grid-connected three-phase inverters and the cause of the zero-sequence circulating current are presented in detail. Hence, to deal with this issue, a method for suppressing the zero-sequence circulating current based on a PI controller is presented. Simulation results show that the proposed control strategy achieves to effectively suppress the circulating current.