Modeling and Analysis of a Differential Mode Active EMI Filter with an Analog Twin Circuit

Conventional passive EMI filters are bulky and occupy up to 30% of converter volume and weight. Active EMI filters are a key technology that enables the volume reduction of passive components in the EMI filter. The effectiveness of traditional active EMI filter for volume reduction is limited by the additional overhead from the passive components for noise sensing and compensation to ensure stability. In this article, a novel active EMI filter is proposed and demonstrated for differential mode noise attenuation. The filter consists of a twin circuit made up of low voltage/current components that mimic the high-power passive filter components in the main circuit. Unlike the conventional active EMI filter, the proposed filter uses compensation networks which consists of low-voltage surface-mount components only. The modeling of the entire circuit is carried out, and verified with small-signal measurements. The filter is then tested in a converter and the experimental results are shown to be consistent with the model and the small-signal measurements.