Non-ideal model of the common mode choke for EMI filters

In this article issues related to mathematical modelling of a three-phase common mode choke (CMC) are presented. Influence of the CMC characteristics on the electromagnetic interference (EMI) filter insertion losses is investigated. A novel behavioural model of a three-phase CMC including saturation and non-linear permeability effects in the frequency domain is proposed. Those two phenomena are considered simultaneously in the proposed CMC model. The magnetic hysteresis is based on a mathematical function, describing a dependency between current and inductance and the frequency dependent permeability is realized as a passive electrical network consisting of inductors, capacitors and resistors. The values of the passive components are determined according to permeability characteristics of a particular magnetic material, using the Foster network synthesis algorithm. CMC models based on four different soft-magnetic materials are implemented in LTspice and validated with measurements. A one-stage EMI filter is designed using the behavioural CMC model. Insertion losses of the designed filter with four different CMCs are measured and compared with mathematical models.