This paper presents a distributed supplementary control for embedded Multi-Terminal VSC-HVDC (MTDC) grids to enhance the transient stability of the surrounding AC grid. Firstly, the need of supplementary controllers for embedded MTDC grids is demonstrated via the study of the Transient Energy Functions (TEF) of a simple hybrid AC/DC power system. Then, the proposed control structure is presented. This control aims to enhance the angle stability of the surrounding AC system via the modulation of the active power references of the converters. The objective of the control is to enhance AC transient stability while keeping the power balance of the DC grid even if converters reach their active power limits. The proposed control uses frequency, and angle measurements at the Point of Common Coupling (PCC) of the converters. The idea behind the proposed strategy is to match the control actions, and limits of each pair ($i,j$) of converters. If converter $i$ modulates its power, converter $j$ modulates the same amount of power in the opposite direction. The concept of virtual links is used in this paper to represent this matching. Finally, the proposed controller is tested on a modified version of the IEEE 39 bus system using EMT simulations.

中文翻译：

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一种用于增强交直流系统转子角稳定性的多端 VSC-HVDC 电网分布式补充控制

本文提出了一种嵌入式多终端 VSC-HVDC (MTDC) 电网的分布式补充控制，以提高周围交流电网的暂态稳定性。首先，通过对简单混合 AC/DC 电源系统的瞬态能量函数 (TEF) 的研究，证明了嵌入式 MTDC 电网对辅助控制器的需求。然后，提出了建议的控制结构。该控制旨在通过对转换器的有功功率参考进行调制来增强周围交流系统的角度稳定性。控制的目标是提高交流暂态稳定性，同时保持直流电网的功率平衡，即使转换器达到其有功功率限制。建议的控制在转换器的公共耦合点 (PCC) 处使用频率和角度测量。$i,j$) 转换器。如果转换器$i$ 调制其功率，转换器 $j$以相反的方向调制相同数量的功率。的概念虚拟链接在本文中用于表示这种匹配。最后，使用 EMT 模拟在 IEEE 39 总线系统的修改版本上测试所提出的控制器。