Modeling of Capacitor Voltage Imbalance in Flying Capacitor Multilevel DC-DC Converters

This paper is focused on modeling of capacitor voltage imbalance in N-level flying capacitor multilevel (FCML) converters in the presence of imperfections in timing of control signals. A general state-space representation is developed to facilitate applications of two time-domain modeling methods: an exact numerical steady-state solution based on the augmented state-space approach, and a simpler approach based on linear-ripple inductor-current approximation. Examples of 4-level and 5-level FCML converters are examined to show how voltage imbalance depends on control signal timing mismatches, circuit parameter values, and N. It is shown how substantial differences between even-level and odd-level FCML converters can be related to rank reduction in the linear-ripple model under ideal timing conditions. Modeling results are verified by circuit simulations and experiments on a reconfigurable FCML prototype.