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This chapter presents a two-level combined control (TLCC) approach for voltage source converter-based multi-terminal high-voltage direct current (VSC-MTDC) networks that integrate offshore wind farms, aiming to enhance frequency support for the mainland grid. The TLCC operates across two hierarchical levels: the offshore wind turbine level and the onshore VSC station level. At the turbine level, each wind turbine employs adaptive inertial and droop control while maintaining maximum power point tracking (MPPT) without energy reserves. To mitigate secondary frequency drops (SFD), wind turbines are grouped into clusters based on rotor speed, and a step start-up control scheme is employed to sequentially activate these clusters, providing coordinated frequency support. At the system level, a communication-free allocation control strategy is used, leveraging local frequency signals from onshore VSC stations to efficiently distribute active power among them. This TLCC approach effectively enhances the frequency stability of the onshore grid and reduces SFD, while keeping the turbines in MPPT mode. Case studies conducted on a 3-area, 4-terminal VSC-MTDC system with integrated offshore wind farms validate the TLCC strategy’s effectiveness and adaptability across diverse scenarios.

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Two-Level Combined Control Scheme of VSC-MTDC Integrated Offshore Wind Farms for Onshore System Frequency Support

  • 章节

  • 发表日期：

    2025年

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  • Wei Yao,
  • Hongyu Zhou,
  • Yongxin Xiong,
  • Jinyu Wen

摘要

This chapter presents a two-level combined control (TLCC) approach for voltage source converter-based multi-terminal high-voltage direct current (VSC-MTDC) networks that integrate offshore wind farms, aiming to enhance frequency support for the mainland grid. The TLCC operates across two hierarchical levels: the offshore wind turbine level and the onshore VSC station level. At the turbine level, each wind turbine employs adaptive inertial and droop control while maintaining maximum power point tracking (MPPT) without energy reserves. To mitigate secondary frequency drops (SFD), wind turbines are grouped into clusters based on rotor speed, and a step start-up control scheme is employed to sequentially activate these clusters, providing coordinated frequency support. At the system level, a communication-free allocation control strategy is used, leveraging local frequency signals from onshore VSC stations to efficiently distribute active power among them. This TLCC approach effectively enhances the frequency stability of the onshore grid and reduces SFD, while keeping the turbines in MPPT mode. Case studies conducted on a 3-area, 4-terminal VSC-MTDC system with integrated offshore wind farms validate the TLCC strategy’s effectiveness and adaptability across diverse scenarios.