A 6-level Flying Capacitor Multi-level Converter for Single Phase Buck-type Power Factor Correction

This work investigates behavior of flying capacitor multi-level (FCML) converters in single phase buck-type power factor correction (PFC) applications. Recent developments in FCML converters using GaN transistors are leveraged to improve power density of a single-phase 240 VRMS ac to direct 48 V dc conversion stage in data center power delivery applications. Here, we experimentally demonstrate this concept by using a digitally controlled 6-level FCML converter. The experimental prototype achieves 163 W/in3 by box volume excluding heat sink and twice-line frequency energy buffer. A key contribution of this work is experimental exploration of flying capacitor natural balancing of an FCML buck converter in a single-phase ac-dc conversion where the flying capacitor voltages must swing at 120 Hz.