Analysis and Circuit Modeling of Mode Conversion in Non-Ideal EMI Filters

The performance of electromagnetic interference (EMI) filters is often degraded due to mode conversion, which can arise from imbalance due to the non-idealities of the filters themselves. To quantify and address this issue, this paper presents circuit models of EMI filters in the modal domain, including parasitics. The analysis is therefore developed entirely in the modal domain, where mode conversion contributions are represented by induced controlled sources. The models not only illustrate how small imbalances lead to unwanted common mode and differential mode noise, but also provide a physical interpretation for mode conversion at circuit level. The accuracy of the models is validated by comparison with traditional analysis in the SPICE solver. Finally, a statistical analysis is conducted to assess the impact of tolerances of real filter components on mode conversion.