Feedback Modelling of Passively Balanced Flying Capacitor Multilevel Converters

This work demystifies the fundamental principles of passive balancing of flying capacitor multilevel (FCML) converters by developing a feedback modelling method that is applied to natural balancing and coupled inductor balancing. Coupled inductors are a robust method of passively and inexpensively balancing large-order FCML converters. The feedback models are used to relate the role of loss and coupling ratio in the strength of passive balancing methods, thus showing how coupled inductors are superior to natural balancing when tightly coupled inductors are designed with a high quality factor. The feedback models are used to predict the steady-state imbalance of coupled inductor FCML converters under the influence of external disturbances and compare them to experimental results. A four-phase, five-level FCML converter is used to verify the feedback models and show the limitations of coupled inductor balancing at singular points.