The circulating current of modular multilevel converter (MMC) has a great impact on the power losses, the submodule (SM) capacitor voltage ripples, and the rating of power devices. Existing analysis of circulating current has considered the capacitor voltage and the modulation signal. In this paper, the effect of semiconductor devices on the circulating current is further presented. In order to realize the different circulating current injection targets under different conditions, a unified online calculation scheme by using the instantaneous information of MMC is proposed in this paper to generate the circulating current injection references. It avoids detecting the amplitude and phase of the output current or using an extensive lookup table. Besides, a mathematical analysis model is built and it reveals the impact on the capacitor voltage ripple and the rms value of arm current with different injection references, thus guide the determination of the injection ratio. Experimental results based on a three-phase MMC prototype with six SMs per arm are presented to demonstrate the analysis of circulating current and the proposed circulating current injection references generating method is verified by different circulating current control targets with different loads.

中文翻译：

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模块化多电平变换器环流分析与注入控制


模块化多电平变换器（MMC）的环流对功率损耗、子模块（SM）电容器电压纹波以及功率器件的额定值有很大影响。现有的环流分析考虑了电容器电压和调制信号。本文进一步阐述了半导体器件对环流的影响。为了实现不同条件下不同的环流注入目标，本文提出了一种利用MMC瞬时信息的统一在线计算方案来生成环流注入参考。它避免了检测输出电流的幅度和相位或使用大量的查找表。此外，还建立了数学分析模型，揭示了不同注入基准对电容电压纹波和臂电流均方根值的影响，从而指导注入比的确定。基于每臂有六个 SM 的三相 MMC 原型的实验结果展示了环流分析，并且通过不同负载的不同环流控制目标验证了所提出的环流注入参考生成方法。