An improved common mode active filter for EMI reduction in vehicular motor drives

A novel common mode (CM) EMI active filter for automotive motor drives is developed. The active filter performs both the compensation of the CM voltage at the motor input and the mitigation of the leakage high frequency CM currents, so increasing the drive reliability and the vehicle electromagnetic compatibility (EMC). The proposed circuit represents an improvement of a previously EMI filter designed by the same authors. The filter scheme is based on a voltage feedback-action too. It includes a feed-forward action by exploiting the contribution to the error signal given by a suitably estimated CM current and an optimized design of the CM voltage detection/injection systems. Moreover, it is supplied by a smaller DC voltage and implements more performing amplifiers. The active filter behavior is investigated by experiments. The realized prototype shows a very good efficiency and compactness.