UC Berkeley

Flying capacitor multilevel (FCML) converters typically rely on natural balancing to achieve a balanced distribution of flying capacitor voltages. The mechanisms by which the flying capacitor voltages are able to balance have been extensively studied and theoretically there are certain combinations of level count and duty cycle at which the flying capacitor voltages do not balance. Although the flying capacitor voltages should diverge from the balanced distribution, in practice this behavior is rarely observed. To resolve this discrepancy between FCML converter theory and experiment, this article analyzes the impact of switch output capacitance on the flying capacitor voltage balancing dynamics, and illustrates that this capacitance has a naturally balancing effect. The additional mechanism of switch output capacitance induced balancing is analytically described and compared against experimental results on several FCML converter prototypes.