Straightforward Modeling of Complex Permeability for Common Mode Chokes

Abstract

This paper presents a straightforward modeling method for the complex permeability of common mode chokes. The proposed model is obtained as an RL ladder network from a single RL parallel equivalent circuit by repeated manipulation called circuit dividing. Circuit dividing is the transformation of a single parallel RL circuit into two series-connected parallel RL circuits, and is used for expressing the complicated characteristics of inductive and resistive elements such as frequency-dependent complex permeability. The proposed model can be made to basically repeat the parameter fitting up to two parameters, so that the fitting procedure is straightforward. This is a great advantage for engineers because the model can be obtained without the need for special additional optimization programs, which were required in previous works. By using this model, the common mode impedance of a choke is fitted precisely, compared to the conventional single parallel RLC equivalent model. Moreover, not only the insertion loss of the EMI filter but also a time waveform is simulated precisely by both frequency and transient analysis with the proposed model.