Flying capacitor voltage balancing is critical for the performance of flying capacitor multilevel (FCML) converters. This paper investigates the intrinsic capacitor voltage balancing of multiphase FCML converters with coupled inductors. It is shown that the coupled inductor provides flying capacitor voltage balancing that minimizes steady-state imbalances due to periodic disturbances compared to converters with uncoupled inductors. A dynamic model of natural balancing of the converter is derived and used to estimate the time required for the flying capacitors to settle from an initial imbalance. The theoretical predictions are verified with analytical derivations, SPICE simulations, and experimental results.

This letter investigates the ripple reduction mechanisms of pulsed-width-modulated (PWM) coupled inductors based on the principles of multiphase interleaving. By adopting circuit duality and superposition analysis, the ripple reduction ratio of PWM coupled inductors is, for the first time, presented as a function of the ripple reduction ratio of multiphase interleaving and the coupling coefficient of the coupled inductor. The analysis simplifies the assumptions used in previous study, and results in concise and intuitive description of the ripple reduction mechanisms of coupled inductors. The results provide useful guidelines for designing interleaved and coupled PWM converters.