Modified Carrier-Based SPWM Technique for Zero Sequence Circulating Current Elimination in Parallel Inverters

For medium and high-power renewable energy applications, parallel four-leg inverters are highly recommended to increase the power capability, power rating, and the efficiency of the system. However, a zero-sequence circulating current (ZSCC) will be generated by the difference between the zero sequence voltages (ZSVs) due to unequal output currents and filter inductors, as well as other factors such as different switching frequencies and dead times when the inverters are connected in parallel via common DC and AC buses. The ZSCC will seriously distort the output currents and degrade the control performance and the dynamic response of the overall parallel system. This paper suggests a modified carrier-based SPWM to suppress the ZSCC by eliminating the difference between ZSVs through the adjustment of modulation voltages of the modified carrier-based SPWM. The proposed ZSCC suppression method can successfully achieve the ZSCC suppression even when the parallel four-leg inverters system has unbalanced output current sharing and filter inductances. The simulation results based on the parallel four-leg inverters distinctly confirm the effectiveness of the suggested ZSCC suppression method.