Simple time domain analysis of a 4-level H-bridge flying capacitor converter voltage balancing

Flying Capacitor (FC) multilevel Pulse Width Modulated (PWM) converters are an attractive choice due to the natural balancing property of the capacitor voltages. The balancing can be studied in the time domain, which results in easy to interpret expressions regarding parameter influence. Time domain analysis is normally done by time averaging of the system model over a PWM-period. In this paper a new method is presented starting from the “voltage unbalance” excessive energy which has to be dissipated in the converter load by switching harmonics in the load current. This is applied on a four-level H-bridge converter, which has dynamics of a high order and is normally hard to describe in the dime domain. The proposed method results in time domain parameters exactly describing the behaviour and the balancing of the capacitor voltages of the four-level H-bridge converter.