A Multi-Function Common Mode Choke Based on Active CM EMI Filters for AC/DC Power Converters

It is widely believed that hybrid electromagnetic interference (EMI) filter (HEF) is one of the most optimized solutions for EMI elimination. Nevertheless, the desire for a smaller and lighter filtering method has never stopped. To further reduce the size and weight of a hybrid EMI filter, this paper proposes a multi-function common mode choke (MCMC) used in HEF. It differs from the traditional common mode (CM) choke in that two functions of (1) CM signal sensing and (2) CM noise suppression are integrated into one choke. In such a proposed MCMC design, the traditional current transformer (CT) is eliminated in the hybrid filter topology. This technique could reduce the size, weight, and cost of the filter to a great extent. Based on the MCMC, a novel CM filter is proposed to achieve high-performance noise suppression. System model and stability feature of the new filter are developed and investigated in detail. A filter prototype based on the proposed MCMC is constructed. It is tested on a 100-W commercial ac/dc converter. The experimental results show that the proposed CM filter can provide better EMI noise suppression with a smaller size. The insertion loss could reach 50 dB at low frequencies and 40 dB at high frequencies.