Investigation and Modeling of Combined Feedforward and Feedback Control Schemes to Improve the Performance of Differential Mode Active EMI Filters in AC–DC Power Converters

In this paper, the models of active differential mode electromagnetic interference input filters for ac-dc converters are first investigated. The models are developed for active filters with single feedback (FB) and single feedforward (FF) configurations, which include an active filter, passive filters, and the noise model for a converter. To increase the gain of the single active filter, the models for FB-FF, FF-FB, parallel FB, and series feedback (SFB) configurations are developed and investigated. Loop gains and insertion gains for all of these configurations are derived and compared. Stability has been analyzed based on the loop gains and a compensation technique is introduced to ensure stability. Based on the comparison among all these control configurations, it has been found that the SFB configuration can achieve the highest noise reduction. The loop gains and insertion gains of an active filter prototype with the SFB configuration are measured using a network analyzer to validate the developed model and compensation technique. Finally, spectrum measurements with a commercial boost power factor correction ac-dc converter have been conducted to verify the developed modeling and control techniques as well as the predicted performance for the SFB configuration.