EMI Filter Design and Analysis for an Isolated DC-DC Converter

As EV fast charging infrastructure has developed rapidly, electromagnetic compatibility (EMC) problems with DC-DC high-frequency converters have become more acute. In particular, multi-source multi-level active bridge (MS-ML-DAB) converters operating over a wide range of output voltages experience significant electromagnetic interference (EMI) due to rapid switching transitions and parasitic components. This study systematically analysed the electromagnetic interference (EMI) generated by the common mode (CM) and differential mode (DM) of the MS-ML-DAB converter for EV DC fast charging systems. A parasitic converter model is proposed to precisely identify the major noise processes in the EMI. Using FCC Class B emission-guided and impedance-based design concepts, the multi-stage EMI filter of the type π is analytically constructed for both input and output ports. The recommended filter shall provide impedance matching, adequate damping and stability in the event of significant voltage and current fluctuations. PSIM based simulations show significant noise abatement of DM and CM in the frequency range 150kHz to 30MHz in both working modes, confirming compliance with FCC Class B standards. This technique offers a practical and scalable solution to mitigate the EMF in high-power EV chargers.