A Scalable Passive Balancing Approach for Flying-Capacitor Odd-Level Converters

Flying-capacitor multilevel (FCML) converters usually incorporate active feedback loops for flying-capacitor (FC) voltage balancing, invariably requiring the sensing and regulation of multiple FC voltages. In this paper, a simple and scalable passive balancing approach is discussed for odd-level topolo-gies, based on a resistive balancing network (RBN) constructed around the converter. The RBN improves the open-loop balancing performance of the converter against duty cycle and phase shift mismatches in the control commands. The fundamental tradeoff between efficiency and sensitivity to timing mismatches inherent in the approach is studied through a simplified analysis and numerical simulations. Interesting beneficial effects of the proposed RBN on the converter start-up are also discussed. The efficacy of the RBN is demonstrated through experimental results using a reconfigurable 2-to-9-level FCML prototype.