A High-Bandwidth Parallel Active Balancing Controller for Current-Controlled Flying Capacitor Multilevel Converters

This is the authors' abstract. We don't add key points for this paper.

This work presents a capacitor voltage balancing controller for current-controlled flying capacitor multilevel converters. A small-signal model of the converter derived from state–space averaging informs the parallel controller structure. The proposed controller incorporates nonlinear actions to decouple flying capacitor control loops and prevent adverse interaction between the capacitor voltage balancing and inductor current controllers. Experimental results of closed-loop line and load transient responses demonstrate significant performance improvements with the proposed balancing architecture compared to a converter relying on natural capacitor balancing. These improvements are quantified with experimental measurements of switch voltage stress and load current disturbance as a response to line voltage perturbations at different frequencies. Limits to control bandwidths in balancing controllers based on averaged models are discussed. The closed-loop stability of the converter operating with the proposed active balancing architecture is discussed as a function of the operating point, controller gains, and hardware parameters, such as output filter inductance and inductor current ripple.