Hybrid EMI filter design for common mode EMI suppression in a motor drive system

This paper first analyzes the common mode (CM) noise in a motor drive system. Based on the CM noise model, both CM noise voltage cancellation and CM noise current cancellation, which includes feedback and feed-forward current cancellations, are investigated. The feed-forward current cancellation is implemented and tested. It is found that due to the speed and gain bandwidth limitations, the active filter cannot suppress high di/dt and high amplitude CM noise current. Hybrid EMI filters which include a passive filter and an active filter is proposed and designed. The experiments show that the CM inductance of the passive filter can be reduced by 10 times because the active filter can well suppress low frequency noise.