Theoretical analysis of self-balancing function of capacitor voltages in flying capacitor multi-level converters

Among the various multi-level topologies, flying capacitor converters will be promising multi-level converters from the view point of the high power density because the size of the capacitors is expected to be minimized in small converters with higher switching frequency. Although the voltages of the flying capacitors theoretically can stay in the balanced condition, they tend to unbalance under some particular conditions in the practical converters. So far, the mechanism of the voltage balance of the flying capacitors associated with the circuit operation has not been clarified fully. In this paper, the self-balancing function of the capacitor voltage is analyzed quantitatively. Based on the analysis, the operating condition under which the capacitor voltages are balanced is clarified. The analytical results are useful to realize the simple flying capacitor converters without additional forced balancing control.