Dynamical Modeling and Control of the Flying Capacitor Multilevel Converter

Abstract: In recent works, solutions from the family of hybrid-switched-capacitor converters have been shown to meet the efficiency and power-density requirements of next-generation systems. Among these, the Flying Capacitor Multilevel (FCML) converter is promising for electric drives and dc-dc converters alike, as it incorporates smaller filter magnetics, uses high-figure-of-merit low-voltage switches, and is capable of faster dynamic response. The widespread adoption of this converter and related topologies, however, has been limited due to uncertainty about the behavior of the flying capacitor voltages under transient conditions. This talk studies the dynamic behavior of the capacitor voltages and presents solutions for regulating the capacitor voltages through “active balancing” control. Standard averaging methods are shown to be inadequate in accurately capturing the capacitor voltage dynamics under certain operating conditions, motivating new converter models developed from higher-order averaging techniques. The refined models obtained are capable of accurately describing the capacitor voltage behavior, and predict small-signal instabilities in standard active balancing control approaches. Subsequently, this talk will cover new modeling techniques and active balancing controllers that do not exhibit small-signal instabilities, and will highlight future directions for incorporating these controllers in physical systems.