Mixed-mode EMI noise in three-phase DC-fed PWM motor drive system

High density filter design for electromagnetic interference (EMI) noises is essential for the variable speed motor drive system in modern transportation applications. As often being one of the major causes of bulky and heavy filter designs, the mixed-mode (MM) noise phenomenon in the three-phase motor drive system is discussed in this paper. The generation schemes of the MM noises on both DC and AC sides of the system are analyzed. According to the three-phase voltage vector modulation, the MM noises at different switching conditions are compared and summarized. Based on experimental results from a specified prototype system, the existence of the MM noises and its impact on EMI filter design is verified. Investigations show that the implementation of both CM filter and balancing X-capacitors can help attenuate the MM noises effectively.