Compared with the conventional two-level dual-active-bridge (DAB) dc-dc converter, the three-level DAB converter could operate with lower voltage rated switching devices and provide more control degrees of freedom, which enhances the control flexibility. This paper proposes a modulation strategy with five control degrees of freedom. In the previous work with multiple control degrees, the optimization strategies for efficiency or inductor current minimization are investigated; however, these strategies all need detailed mode analysis and complex mathematical optimization tools to obtain the optimal duty cycles. In this paper, an optimization strategy for the root-mean-square value of the inductor current is proposed. This method extracts the fundamental and third-harmonic components from the high-frequency voltages on both sides and adjusts the amplitude of the bridge voltages by the vector diagram to obtain the optimal duty cycles. The inductor current can be reduced significantly at light loads with the proposed strategy, so the efficiency of the converter can be improved. Moreover, the optimization process does not need the detailed operation analysis of the converter, nor does it require the complex mathematical optimization tools. Finally, the performance of the three-level DAB and the optimization strategy are verified by the experimental results.

中文翻译：

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五自由度三电平DAB转换器的优化调制策略


与传统的两电平双有源桥（DAB）dc-dc变换器相比，三电平DAB变换器可以使用较低额定电压的开关器件，并提供更多的控制自由度，从而增强了控制灵活性。本文提出了一种具有五个控制自由度的调制策略。在之前的多控制度工作中，研究了效率或电感电流最小化的优化策略；然而，这些策略都需要详细的模式分析和复杂的数学优化工具才能获得最佳的占空比。本文提出了一种电感电流均方根值的优化策略。该方法从两侧高频电压中提取基波和三次谐波分量，并通过矢量图调整桥电压的幅值以获得最佳占空比。采用所提出的策略可以在轻负载时显着降低电感器电流，从而提高转换器的效率。而且，优化过程不需要对转换器进行详细的运行分析，也不需要复杂的数学优化工具。最后，通过实验结果验证了三级DAB的性能和优化策略。