Modeling, analysis and design of differential mode active EMI filters with feedforward and feedback configurations for AC-DC converters

This paper developed models for DM electromagnetic interference (EMI) input filters in AC-DC converters. The models are developed based on the circuit structures and control configurations. The models are developed for feedback, feedforward, feedforward-feedback and feedback-feedforward configurations. The closed loop gains are derived respectively. Based on the closed loop gain models, the open loop characteristics required for high performance active filters are determined. A passive filter topology which enhances the performance of the active filter is identified. The stability of active filters is analyzed and compared based on the developed models. The analysis is validated with both simulations and experiments. It is shown that the developed models can predict stability and help compensation design for active filters.