UC Berkeley

The Flying Capacitor Multi-Level (FCML) converteris heralded as enabling the utilization of low-voltageswitches within a high-voltage converter by evenly distributingthe voltage stress on a series string of switches through the useof “flying” capacitors. However, this advantage of the converterrequires that the flying capacitors do not deviate too far fromtheir ideal voltage distribution regardless of transients, loaddisturbances, or other parasitics to ensure the switches are notovervolted among other concerns. Previous works have identifiedcertain theoretic combinations of duty cycle and level countwhere the flying capacitor voltages do not naturally balanceand instead diverge. Although seemingly problematic, in practicethis behavior is not observed in practical implementations. Toresolve this discrepancy between FCML theory and experiment,we analyze the impact of switch output capacitance on theflying capacitor voltage balancing dynamics, and illustrate thiscapacitance has a naturally balancing effect.