Design Theory and Implementation of a Planar EMI Filter Based on Annular Integrated Inductor-Capacitor Unit

Planar electromagnetic interference (EMI) filter has good application prospect in power electronics system with the advantages of small volume and good high-frequency performance. However, a complete theoretical system for the design of planar EMI filter has not been proposed yet. In this paper, an integrated structure formed by an annular "inductor-capacitor" (LC unit) is proposed first, which can be used as the basic cell of the planar EMI filter. A general arc transmission theory is also proposed, based on which the distributed-parameter model of the LC unit is established. Then, this LC unit can be equivalent to the two-port network by employing the model transformation method. Besides, the turn-to-turn electromagnetic parameter is extracted using finite element method, which provides the foundation for the research of LC unit and electromagnetic performance of the filter. The design method and the implementation of the whole planar EMI filter are elaborated in details, and the empirical initial values of the related structural sizes are also presented in this paper. In order to verify the proposed design theory, several EMI filters formed by LC units are designed according to the specifications. Common-mode insertion losses of the EMI filter are calculated and measured, respectively. The results verify the feasibility of the design theory.