Voltage balancing of a five-level flying capacitor converter using optimum switching transitions

The flying capacitor (FC) multilevel converter requires a capacitor voltage balancing mechanism for proper operation. This paper proposes a voltage balancing scheme for a five-level FC converter based on phase disposition pulse-width modulation (PD-PWM) using transitions that produce the minimum number of switching events. This strategy will be called optimal-transition voltage balancing (OTVB) scheme. Since multiple optimum switching transitions between two consecutive voltage levels may be available, such a redundancy is used to regulate the FC voltages at their desired levels. Those transitions that produce more switching events are avoided. The rest of transitions are evaluated by means of a cost function and the one that produces the minimum value is selected. Simulation results show a significant reduction of the average switching frequency as compared to the use of the optimal-state voltage balancing (OSVB) scheme, while maintaining the balance of the FC voltages. Moreover, the proposed PD-PWM voltage balancing strategy is robust to static and dynamic load conditions.