The four-level hybrid-clamped converter (HCC) is a new high-efficiency dc–ac converter. However, its dc-link capacitors face challenging voltage fluctuation issues at low frequencies, resulting in the distorted ac current and oversize converter volume. This letter presents a simple and effective control method of the HCC using open-loop common-mode voltage (CMV) injection. The mathematical model of the CMV and the capacitor voltage fluctuations is derived. The optimal CMV algorithm with the maximum suppression effect of capacitor voltage fluctuations is proposed as well as the implementation method. The microlevel mechanism of the proposed method in suppressing voltage fluctuation is clarified. The capability of the proposed method in improving dc voltage utilization is explored. Compared with existing methods, the proposed one reduces dc-link voltage sensors and computation complexity and mitigates CMVs at the load side. The optimal CMV is approximately 25% of the output voltage magnitude, and enhances the dc-bus voltage utilization by 12%. Results demonstrate that voltage fluctuations of HCC capacitors are reduced by over 60%. The proposed method has a solid dynamic balancing capability and works well for the wide-range frequency and modulation index.

中文翻译：

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具有开环优化共模电压注入的四电平混合钳位转换器的新型电压平衡控制

四电平混合钳位转换器 (HCC) 是一种新型高效直流-交流转换器。然而，其直流链路电容器在低频下面临具有挑战性的电压波动问题，从而导致交流电流失真和转换器体积过大。这封信介绍了一种使用开环共模电压 (CMV) 注入的简单有效的 HCC 控制方法。推导了CMV和电容器电压波动的数学模型。提出了电容器电压波动抑制效果最大的最优CMV算法及其实现方法。阐明了该方法抑制电压波动的微观机制。探讨了所提出的方法在提高直流电压利用率方面的能力。与现有方法相比，所提出的方案降低了直流链路电压传感器和计算复杂性，并减轻了负载侧的 CMV。最佳 CMV 约为输出电压幅度的 25%，并将直流母线电压利用率提高 12%。结果表明，HCC 电容器的电压波动降低了 60% 以上。所提出的方法具有可靠的动态平衡能力，并且适用于宽范围的频率和调制指数。