Common-Mode EMI Noise Modeling and Reduction With Balance Technique for Three-Level Neutral Point Clamped Topology

This paper develops a common-mode (CM) electromagnetic interference noise model for a three-level neutral point clamped topology. Compared with existing modeling techniques with only one CM noise source, two extra important CM noise sources and their characteristics are identified and derived for an accurate CM noise model. The impedances of CM noise path are also extracted. Based on the developed CM noise model, the CM noise spectrum can be well predicted. The effect of CM noise paths on CM noise is discussed based on two different LCL filters. A CM noise reduction technique with a balance bridge at a large impedance ratio is proposed based on the developed model. The technique can be easily implemented at low cost. Both simulations and experiments validate the developed theory and technique.