Circulation Current Suppressing for Parallel Three phase Inverters Based on CCVS

Parallel three phase inverters can improve operation reliability and increase transmission capacity, while the parallel structure provides path for circulating current, which worsen the power quality and increase energy losses. So it is necessary to suppress such circulating current. By transferring inverters into current controlled voltage sources (CCVS), the circulating current is suppressed through adding equivalent impedance in the circulating path in this paper. It can be seen from analysis that the zero sequence circulating current and harmonic circulating current that are caused by the unbalance of voltage output of inverter and line parameters flow through same path. Through multiplying detected circulating current of parallel inverter system and transfer impedance, the output voltage can be obtained. When it is added to the output voltage of control system in normal conditions, the circulating path is equivalent to add this transfer impedance. Analysis and simulation results show that both zero sequence and harmonic circulating current can be effectively suppressed when a pure resistance is chosen as the transfer impedance by using proposed method.