Optimized Switching Frequency Voltage Balancing Schemes for Flying Capacitor Based Multilevel Converters

Abstract

The redundant switching states of flying capacitor-based (FC-based) multilevel converters are used to balance the voltages of the flying capacitors. Attempts to balance capacitor voltages have ignored the switching transitions between converter switching states. In this paper, we propose a generalized voltage balancing scheme with an optimized switching frequency scheme for FC-based multilevel converters, including the classic flying capacitor multicell (FCM) converter, which needs less computation. All the switching transitions between the switching states of adjacent voltage levels are considered by the overall priority index of switching frequency. In addition, an overall priority index is utilized to balance the voltages of flying capacitors. Using these two indexes, three criteria are developed to select the proper switching state of the converter. Using these criteria, the proposed decoupled SVM scheme is implemented intuitively and simply for FC-based multilevel converters. The proposed scheme is evaluated by simulation results of a five-level FCM converter. Moreover, experimental results demonstrate the robustness of the proposed method in the static load and transient conditions.