Optimal Switching Transition-Based Voltage Balancing Method for Flying Capacitor Multilevel Converters

Abstract

This paper proposes a voltage balancing method for flying capacitor multilevel converters based on phase-disposition pulse width modulation (PD-PWM) using optimal transitions between converter switching states. The optimal transitions between converter switching states are possible due to the converter states’ redundancy and are decided with the continuous evaluation and minimization of a cost function. Simulation and experimental results verify the robustness of the proposed voltage balancing method against different load conditions. A significant reduction of the average switching frequency is achieved, when compared to the use of the optimal state voltage balancing method, where the optimal states are decided independently for each voltage level ignoring how transitions impact on the converter switching frequency. Moreover, the line-to-line output voltages are compared with the ones obtained with other modulation techniques in terms of total harmonic distortion values, and PD-PWM with the proposed voltage balancing method produces the best results.