Implementation of an Active Common Mode EMI Filter Considering High Conducted Differential Mode EMI in Electric Vehicle On-Board Chargers

Conducted and radiated Electromagnetic Interference (EMI) is of major concern in automotive On-Board Chargers (OBCs). Passive EMI Filters (PEFs) occupy a significant amount of space, whereas especially magnetic components like Common Mode Chokes (CMCs) and Differential Mode Chokes (DMCs) are the main cost and weight adders. Therefore, this paper proposes a Voltage Sense Current Inject (VSCI) Feedback (FB)-type Common Mode (CM) Active EMI Filter (AEF) that allows the usage of CMCs with smaller CM inductance. The AEF is part of the AC-input EMI filter of an OBC that can supply 11kW of charging power in 1-phase (1ph) and 3-phase (3ph) operation. Analytical analysis is provided, which relates the AEF's output voltage to the used CMC CM inductance and the fundamental switching frequency of the Power Factor Correction (PFC) system. It is shown that higher switching frequencies offer the possibility to decrease the CMC CM inductance without the risk to overload the AEF output. Furthermore, a leakage inductance estimation for current-unsymmetrical CMCs is provided and is experimentally validated. Conducted Emission (CE) measurements show the AEF performance and it is described how dedicated DMCs can be removed from the design. It was found that the benefit of a CM AEF in a Differential Mode (DM) dominant system is limited but can provide benefits for specific CM dominant harmonics within the regulated frequency range. A problem for AEFs is CM inductance degradation due to partial DM core saturation in CMCs. This phenomenon is experimentally investigated for ferrite and nanocrystalline CMCs.