An Analytical Model for Common-Mode EMI in Flying Capacitor Multilevel Converters

The increased popularity of the flying capacitor multilevel (FCML) converter, as well as the use of wide-bandgap devices in this topology has opened up a number of questions around conducted electromagnetic interference (EMI). Common-mode EMI is generated by parasitic capacitances throughout the circuit and the currents arising through them as a result of large dv/dt switching events. The mechanisms by which the FCML converter generates conducted common-mode EMI is an underexplored area of research, despite the critical nature of EMI. This paper proposes modeling a parasitic capacitance for each switch to understand how common-mode currents are generated in multilevel operation. Common-mode EMI scaling behavior from first principles for an FCML converter are derived, and hardware validation with a 6-level converter prototype provides concrete evidence in both the time and frequency domains that the level of modeled detail is sufficient to capture power-stage CM behavior for this converter topology.