This letter proposes a grid-forming control method for Modular Multilevel Converter (MMC) with AC-side current limitation capabilities under fault ride-through scenarios (balanced and unbalanced faults). The novelty of the proposed controller is that no physical capacitor bank at the AC-side connection is considered as it is usually done. This is achieved with two cascaded controllers (for voltage and current) and elliptic limitations in double synchronous rotating reference frame. In normal mode, the currents are imposed solely by the AC-side load and the current controller is in by-pass mode. In case of AC-side faults, the current controller is automatically enabled to effectively limit the currents if needed. This is achieved without switching logic between normal and limitation mode. Simulation results prove the effectiveness of the proposed strategy.

中文翻译：

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不平衡故障穿越下MMC电流限制的网格形成控制

这封信提出了一种在故障穿越场景（平衡故障和非平衡故障）下具有交流侧限流功能的模块化多电平转换器（MMC）的网格形成控制方法。所提出的控制器的新颖之处在于，无需像通常那样在AC侧连接处考虑任何物理电容器组。这是通过两个级联控制器（用于电压和电流）和双同步旋转参考系中的椭圆限制来实现的。在正常模式下，电流仅由交流侧负载施加，电流控制器处于旁路模式。如果发生交流侧故障，则在需要时会自动启用电流控制器以有效限制电流。无需在普通模式和限制模式之间切换逻辑即可实现。