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Primary Frequency Support from Offshore Wind Power Plants Connected to HVDC Grids

Contribution to the power systems’ frequency support is expected to be one of the essential ancillary services that wind power plants (WPPs) shall provide. The high-voltage DC (HVDC) connected offshore WPPs may provide this service with and without using fast communication links between onshore and offshore. In the case of offshore HVDC grid, implementing the communication-less frequency support is challenging. Although it increases the reliability of the frequency control, among other challenges, it is not straightforward to comply with relevant grid code requirements. In this paper, this issue is mathematically described and a static model is developed to calculate the deviation of various electrical parameters of an HVDC grid in case of frequency drop on the land ac systems. A solution for the aforementioned problem is presented and its associated concerns are addressed. The study is verified by simulations of a four terminals dc grid with two offshore WPPs and two inland ac systems.