Differential Mode Circulating Current Reduction for Three-Level Modular Grid-Connected Photovoltaic System

       IEEE TENCON 2013——According to the problem that differential mode circulating current exists in the three-level modular grid- connected photovoltaic system with LC filter, the equivalent model of differential mode circulating current was proposed in this paper. Differential mode circulating current was divided into two types according to different loops. The admittance curve of differential mode circulating current between frequency and leakage inductance ratio was analyzed, and the conclusion was made that the first type of differential mode circulating current is much larger than the second type. Then, the parallel scheme with LCL filter is used, and the inductance ratio is reasonably designed to reduce the differential mode circulating current effectively. A three-level modular grid-connected photovoltaic system rated 10kW was built, and simulation results and experimental results demonstrate the correctness of the model analysis and reduction methods of zero-sequence circulating current.