High-frequency resonance (HFR) in the modular multilevel converter (MMC) has been reported in recent years frequently, yet, existing focuses on HFR are limited to the specific control strategy or grid condition, from which the conclusion may be not applicable if the control or grid changes. In this article, a unified MMC high-frequency impedance model (UHFIM) is proposed to fill this gap. By changing the gain of the model, UHFIM can reflect the high-frequency characteristics of the MMC under different control strategies in a unified form, which provides a theoretical basis for the general HFR suppression method. Analysis based on UHFIM reveals the worst cases of the HFR risk and the constraint of low-pass filter (LPF) order on the convergence of MMC high-frequency damping. In order to suppress HFR, this article proposes a joint design method for LPF and passive damper, which can completely remove the HFR risk from the entire high-frequency range without sacrificing too much dynamic performance of MMC, and it works no matter how the grid impedance varies. Besides, in the case that the damper cannot be installed, an alternative HFR suppression method based on delay time adjustment is also developed. Finally, the proposed unified model and the HFR suppression methods have been verified by simulation and experimental results.

中文翻译：

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基于统一MMC高频阻抗模型的高频谐振抑制

模块化多电平变流器（MMC）中的高频谐振（HFR）近年来被频繁报道，但现有对 HFR 的关注仅限于特定的控制策略或电网条件，如果该结论可能不适用控制或网格变化。在本文中，提出了一个统一的 MMC 高频阻抗模型（UHFIM）来填补这一空白。通过改变模型的增益，UHFIM可以统一反映MMC在不同控制策略下的高频特性，为通用的HFR抑制方法提供了理论依据。基于 UHFIM 的分析揭示了 HFR 风险的最坏情况以及低通滤波器 (LPF) 阶数对 MMC 高频阻尼收敛的约束。为了抑制 HFR，本文提出了一种LPF和无源阻尼器的联合设计方法，可以在不牺牲MMC过多动态性能的情况下，完全消除整个高频范围内的HFR风险，并且无论电网阻抗如何变化都能正常工作。此外，在无法安装阻尼器的情况下，还开发了一种基于延迟时间调整的替代HFR抑制方法。最后，通过仿真和实验结果验证了所提出的统一模型和 HFR 抑制方法。还开发了一种基于延迟时间调整的替代 HFR 抑制方法。最后，通过仿真和实验结果验证了所提出的统一模型和 HFR 抑制方法。还开发了一种基于延迟时间调整的替代 HFR 抑制方法。最后，通过仿真和实验结果验证了所提出的统一模型和 HFR 抑制方法。