Common-mode Noise Reduction with Impedance Balancing in DC-fed Motor Drives

Unlike conventional passive or active filters, an impedance balancing circuit reduces the common-mode (CM) electromagnetic interference (EMI) noise by establishing an impedance balancing bridge. The EMI noise can be significantly reduced when the impedance bridge is designed to be well balanced. This paper investigates impedance balancing circuits in Dc-fed motor drive systems where both DC input and AC output need to meet EMI standards and thus EMI filters are needed for both sides. An impedance balancing circuit is proposed to reduce both DC and AC side CM noise. Two auxiliary branches are added to the conventional passive filters to establish an impedance bridge and reduce CM noise. The design criteria are presented, and the impact of the proposed impedance balancing circuit on both sides CM noise are investigated. It shows that the proposed impedance balancing circuit can reduce DC side and AC side CM noise based on different mechanisms. The CM noise reduction performance of the proposed method does not depend on the motor and cable models. Experiment results are presented to demonstrate the feasibility and effectiveness of the proposed method.