A study of motor-end EMI filter on output common-mode noise suppression in DC-fed motor drive system

High density electromagnetic interference (EMI) filter design, especially on conducted common-mode (CM) noise emission suppression, is essential for variable speed motor drive system in modern transportation applications. As an alternative of the conventional inverter-end (IE) EMI filter, this paper discusses the possibility of implementing an EMI filter on the motor end for the CM noise attenuation. A functional comparison between the inverter and the motor-end CM filter is firstly carried out, concerning the CM noise propagation path in the DC-fed motor drive system. According to their features in the noise propagation, the authors focus on two typical kinds of motor-end CM filters in detail, namely the motor front-end (MFE) filter and the motor chassis-end (MCE) filter. Their performances on improving the output CM impedance and suppressing the CM noise emission are analyzed, based on experimental results from a specified prototype system. Investigations show that the implementation of the MFE filter has similar functions with the IE CM choke, while attaching the MCE filter with the motor can help save the magnetic size and weight from the conventional IE filter. However, special attentions are needed for the safety and parasitic concerns.