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

Abstract

This article presents a design methodology for an active electromagnetic interference (EMI) choke that enhances common-mode (CM) impedance through complex impedance modeling and loop-gain stability analysis. The feedback impedance is designed based on the measured impedance of the original CM choke and the EMI filter and is optimized to achieve both impedance boosting and stability across the target frequency range. A customized integrated circuit was developed to realize this function, enabling compact implementation within an 18 mm & times; 20 mm printed circuit board and supporting cost-effective mass production. Experimental validation using an 11-kW on-board charger demonstrated that the proposed active EMI choke increases CM impedance by more than five times near 300 kHz. Conducted emission tests confirmed that a two-stage EMI filter incorporating the active choke achieves comparable or improved suppression performance relative to a three-stage passive filter while reducing the overall weight by 38%. The proposed method was also applied to various magnetic core materials, with nanocrystalline cores providing the most effective impedance enhancement for broadband EMI suppression.