A Variable Frequency Technique for EMI and Efficiency Improvements in High-Level Count Flying Capacitor Multilevel Converters

This work assesses the use of a variable switching frequency scheme specifically designed for a flying capacitor multilevel (FCML) converter in dc-ac operation to spread out the peaks of conducted electromagnetic interference (EMI) and improve efficiency. Ripple constraints of the flying capacitor voltages and inductor current set the basis for a deterministic switching frequency pattern, which can also be considered a targeted dithering scheme. Furthermore, by leveraging the constraints set by the passive components of the designed prototype and reducing the switching frequency, switching losses are mitigated and an increase in efficiency is gained. Hardware results are provided for a 2 kW 8-level FCML inverter and showcase improved conducted EMI peaks and efficiency for the high performance, high-level count prototype.