An improved modulation method for zero-sequence circulating current suppression of paralleled inverter for PV/wind power applications

Paralleled inverter are regarded as an ideal capacity expansion solution widely used in the field of photovoltaic(PV) and wind power. However, the challenge of zero-sequence circulating current (ZSCC) is inevitable which degrades the output currents’ quality and reduces the stability of the system. ZSCC is categorized into high-frequency ZSCC and low-frequency ZSCC. We analyze the relationship between basic vectors and the rate of change of ZSCC. Based on this, an improved pulse-width modulation method based on common-mode voltage injection (CIPWM) is proposed in this paper. By selecting the optimal vector and vector sequence for each 60° sector, the method can reduce the high-frequency ZSCC peaks. By optimizing the three-phase duty cycle, the low-frequency ZSCC can be suppressed as well. In addition, the proposed method can reduce the output harmonics and switching losses. A carrier-based implementation approach based on common-mode voltage injection is also provided in this paper, which significantly simplifies the implementation process. Simulation results confirm the effectiveness of our proposed method.