EMI noise mode transformation due to propagation path unbalance in three-phase motor drive system and its implication to EMI filter design

EMI filter design is often influenced by the noise transformations between the common-mode (CM) and differential-mode (DM), which is mainly due to the system unbalance. In this paper, the analysis of the intrinsic and EMI filter unbalance existing in the EMI noise propagation path of the dc-fed three-phase motor drive system is carried out. CM path unbalance in the circuit model is investigated with an example switching state in three-phase space vector pulse-width-modulation (SVPWM). Noise transformation from CM to DM is then verified with prototype experiments. The influence of the DM filter component unbalance on the DM propagation path is analyzed with simulation. After that, the transformation of the DM noise to CM is validated with tests. Influence of the unbalance and noise mode transformation on the EMI filter design is discussed and a comprehensive design procedure for high density EMI filter is proposed.