Experimental and Simulation based Analysis of an Active EMI Filter for automotive PFC Applications

An On-Board Charger (OBC) within an Electric Vehicle (EV) is used to charge the high-voltage battery. The rectification of the AC-mains grid voltage is typically done with a Power Factor Correction (PFC) rectifier system. To ensure Electromagnetic Compatibility (EMC), an Electromagnetic Interference (EMI) filter is needed between the PFC stage and the grid. This paper proposes a Voltage Sense Current Inject (VSCI) Feedback (FB)-type Active EMI Filter (AEF) suitable for Common Mode (CM) EMI attenuation. Experimental and simulation-based results for the CM Insertion Loss (IL) of different EMI filter configurations are shown. The open loop gain of the AEF is evaluated to ensure system stability. Based on an EMC simulation of a Vienna-Rectifier type PFC, it is presented what operating cases of the AEF can be observed and how mitigation of unintended operation cases is possible. The full potential of the AEF is validated by EMC measurements taken from an OBC during 3-phase (3ph) charging operation at 11 kW. Two AEF designs, using different Common Mode Choke (CMC) sizes, are compared to a baseline Passive EMI Filter (PEF). As long as the CMC inductance stays the same, the AEF can provide up to 34 dB. of additional CM attenuation compared to the baseline PEF. It is also proven in an EMC measurement that the same CM performance can be achieved by an AEF, which uses CMCs whose CM inductance is roughly 60 % smaller than in the baseline PEF. Generally, the proposed AEF shows superior performance in comparison to the PEF up to a frequency of 1 MHz.