Conducted EMI Modeling and Analysis of Three-Phase Motor Drive Circuits

This paper conducts an in-depth investigation into the mechanisms of conducted electromagnetic interference (EMI) in variable-frequency motor drive systems. First, the system’s composition, control strategies, and key design parameters are introduced. Subsequently, the formation mechanisms of conducted EMI in three-phase motor drive circuits, the conduction paths of common-mode and differential-mode EMI currents, and corresponding suppression methods are analyzed. Equivalent circuit models for common-mode and differential-mode conducted EMI in both the front-end Boost PFC and back-end three-phase motor drive circuits are established. On this basis, the models’ validity is verified through experimental testing, and the characteristics of conducted EMI are thoroughly analyzed. The results demonstrate that EMI noise from the front- and back-end circuits superimposes, with common-mode interference arising from dv/dt generated by power device switching actions, while differential-mode interference is primarily dominated by the front-end circuit. The test data reveal severe exceedances in the low-frequency band and provide guidance on performance requirements for EMI filter design.