Common Mode Filter for EMI Mitigation in Active Phase Converter

This paper proposes a common-mode (CM) filter based on a reduced switch active phase converter (APC) topology. The CM filter configuration provides a parallel path for CM currents in the unsymmetrical three-phase converter and reduces the EMI injected into the grid. The proposed CM filter facilitates the independent design of the differential-mode filter components of the converter. Analysis of the converter system is carried out using state-space approach. From the eigenvalue analysis of the system, it is shown that inclusion of the proposed CM filter does not affect the existing APC system poles. Hence, no filter redesign of the control structure is required. A design methodology is approved to select the CM filter components that can actively damp the CM resonance without any additional control loop. Efficacy of the proposed filter configuration is validated experimentally by measuring the common-mode voltage with the laboratory APC feeding a three-phase 3 hp induction motor from a single-phase grid