A Meshed MMC-Based MTDC System with Improved Voltage Margin Control for Robustness Towards Disturbances

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Department of Electrical and Computer Engineering


The voltage margin control strategy is often used for multi-terminal high voltage direct current (MTDC) transmission systems. It ensures a tight regulation of DC voltage similarly to the master–slave and sharing of voltage regulation task between two or more stations similar to the voltage droop, therefore combining desired features of those control strategies. However, for master stations of the voltage margin, the power delivered to the AC grid is controlled under assumptions that it can degrade the performance during grid disturbances. This paper proposes modifications in the voltage margin control to improve supportability in these situations. Thus, the power is closed-loop controlled, and feed-forward compensation is used to improve the system’s dynamic performance. The performance of the proposed improved voltage margin, voltage margin, and voltage droop was assessed in a four-terminal meshed MTDC system topology based on the multilevel modular converter, considering some of the most severe disturbance occurrences. The proposed control presented the best performance among the tested control strategies, obtaining a new power flow balance with less power and voltage oscillations.

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Journal of Control, Automation and Electrical Systems