Dual active bridge converter with multilevel neutral point clamped topology has shown potential to be a viable solution for medium-voltage dc systems. However, it will face a crucial challenge with regard to capacitor voltage balancing. In order to mitigate 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 article evaluates several voltage balancing approaches, i.e., modified duty cycle (MDC) method, modified phase shift and duty cycle (MPSDC) method, fixed switching state (FSS) method, and complementary switching state (CSS) method. These voltage balancing approaches have distinct characteristics in terms of dynamics, efficiency, robustness, applicability with modulation strategy, and implementation complexity. Evaluation results show that the MDC and MPSDC methods have advantage of extending to various control strategies. However, they are affected by current polarity identification, and have large current and power fluctuations. The FSS method is the most robust and the simplest one, but it also has poor dynamics. On the other hand, the CSS method can deliver smooth dynamics and high efficiency, but it relies on identifying the polarity of inductor current, and it cannot be used to the single phase shift and triple phase shift control strategies. Based on the evaluation results, the suitable applications of different voltage balancing methods are discussed.

中文翻译：

---

多电平 DAB 转换器的电容器电压平衡控制策略评估


具有多级中性点钳位拓扑的双有源桥式转换器已显示出成为中压直流系统可行解决方案的潜力。然而，它将面临电容器电压平衡方面的严峻挑战。为了减轻由电压不平衡引起的负面影响，例如某些设备上的过压，已经开发了用于电压平衡的各种控制策略。为了更好地设计和实现电压平衡策略，本文评估了几种电压平衡方法，即修改占空比（MDC）方法、修改相移和占空比（MPSDC）方法、固定开关状态（FSS）方法和互补开关方法状态 (CSS) 方法。这些电压平衡方法在动态性、效率、鲁棒性、调制策略的适用性和实现复杂性方面具有独特的特征。评估结果表明MDC和MPSDC方法具有扩展到各种控制策略的优势。但受电流极性识别影响，电流、功率波动较大。 FSS方法是最稳健且最简单的一种方法，但其动态性也较差。另一方面，CSS方法可以提供平滑的动态和高效率，但它依赖于识别电感电流的极性，并且不能用于单相移和三相移控制策略。根据评估结果，讨论了不同电压平衡方法的合适应用。