Evaluation of Capacitor Voltage Balancing Control Approaches for NPC-based DAB Converters

Neutral-point-clamped (NPC)-based dual-active-bridge (DAB) converters face a crucial challenge with regard to capacitor voltage balancing. In order to suppress the negative effects caused by the voltage imbalance, e.g., overvoltage on certain devices, various control strategies for voltage balancing have been developed. To better design and implement the voltage balancing strategies, this paper benchmarks three voltage balancing approaches, i.e., modified-phase-shift (MPS) method, fixed-switching-state (FSS) method, and complementary-switching-state (CSS) method. The three voltage balancing approaches have distinct characteristics in terms of pre-calculation requirements, dynamics, efficiency, robustness, and implementation complexity. Therefore, a comprehensive comparison of these voltage balancing control strategies is conducted in this paper. Based on the evaluation results, the suitable applications of different voltage balancing methods are discussed.