Design Methods and Characteristics of Active EMI Choke Using a Custumized IC for Real 11kW On-Board Charger

Abstract

This thesis presents a design methodology for an active electromagnetic interference (EMI) choke aimed at enhancing common-mode (CM) impedance through complex impedance modeling and loop gain stability analysis. The feedback impedance is derived from the measured characteristics of a conventional CM choke and EMI filter, and is optimized to achieve both impedance boosting and system stability over the target frequency range. To implement this function in a compact form, a customized integrated circuit (IC) was developed and embedded within an 18 mm × 20 mm printed circuit board, enabling cost-effective mass production. The proposed design was experimentally validated using an 11kW on-board charger (OBC). Results showed that the active EMI choke increased CM impedance by more than five times around 300 kHz. Conducted emission (CE) measurements demonstrated that a two-stage EMI filter incorporating the active choke achieved comparable or superior suppression performance to a conventional three-stage passive filter while reducing overall weight by approximately 38%. Furthermore, tests with various magnetic core materials revealed that nanocrystalline cores provided the most effective broadband impedance enhancement.