Analysis of common mode EMI for three-phase voltage source converters

A comprehensive analysis of common mode (CM) EMI is conducted for three-phase voltage source converters in various configurations. The analysis is based on the common mode equivalent circuit models derived from the detailed circuit models. Both frequency domain and time domain studies are performed for (a) three-phase PFC rectifier; (b) back-to-back connected rectifier and inverter; and (c) multiple back-to-back connected rectifiers/inverters with interleaved gating control. Contributions of the common mode voltage sources and coupling paths, as well as effect of a long cable and the common mode choke, are analyzed for both input-side and output-side conducted CM EMI. The analysis results give insights into the CM current generation, coupling, and mitigation methods for high power applications such as high performance double-conversion UPS, drives, microturbine generators, and doubly fed wind turbine-generators. Reduction of conducted CM current also mitigates the risk of radiated EMI issue for systems with long input or output cables.