Implementation of a transformer-less common mode active filter for off-line converter systems

This work presents a study and practical implementation of an active filter employing a HF power amplifier and passive filter components to be connected to the AC power lines in order to mitigate common mode conducted emissions of PWM converter systems. The filter topology is chosen from different possibilities listed in a literature survey and studied regarding practical implementation issues. Special attention is put on the stability analysis where the challenges for the feedback structure are discussed and a simple feedback structure is proposed. A prototype is designed and built, from which mathematical and experimental results are obtained demonstrating the potential and limitations of such a system.