中文摘要：

针对多机T型三电平光伏并网逆变器的零序环流问题，在分析零序环流环路的基础上，建立零序环流的等效模型，并根据激励源的不同将零序环流分成3类：通态零序环流、开关零序环流和混合零序环流。提出一种共享中线的并联方案抑制通态零序环流，一种基于改进型LCL滤波器的并联方案抑制开关零序环流的高频分量。采用一种基于零序环流调节因子的控制方案抑制开关零序环流的低频分量，并确定调节因子的限幅范围，最后论证上述方案对混合零序环流抑制的有效性。搭建10kW的多机三电平光伏并网逆变器样机，实验结果证明了零序环流模型分析和抑制方法的正确性。

英文摘要：

According to the problems that zero-sequence circulating current （ZSCC） existed in T-type three-level grid-connected photovoltaic inverters, the equivalent model of ZSCC was proposed based on the loop analysis in this paper. ZSCC was classified into three types according to different exciting sources, namely, conduction ZSCC, switching ZSCC, and hybrid ZSCC. Firstly, a parallel scheme sharing neutral buses was proposed to reduce the conduction ZSCC. Secondly, a parallel scheme based on improved LCL filter was proposed to reduce high frequency component of the switching ZSCC. Based on the ZSCC regulatory factor, whose limitation was redefined, a control strategy was used to reduce low frequency component of the switching ZSCC. The schemes above were also effective to the hybrid ZSCC reduction. T-type three-level grid-connected photovoltaic inverters rated 10 kW were built. Experimental results verify the correctness of model analysis and reduction methods of ZSCC.