Inertial Response From Offshore Wind Farms Connected Through DC Grids

Inertial response from remote offshore wind farms (WFs) connected through point-to-point DC links relies on emulation of the onshore AC system frequency variation at each offshore wind turbine generator (WTG). This is not straightforward for a DC grid interconnecting WFs to multiple onshore AC systems. To address this problem, this paper builds up on a communication-less approach previously reported for provision of frequency services from offshore WFs connected through a DC grid. A weighted frequency scheme is adopted which relies on the fiber optic link embedded within the sub-sea cables for fast communication of onshore frequency variations up to the offshore converters. The effectiveness of the proposed approach is shown analytically and also through a case study on a 4-terminal DC grid interconnecting an offshore wind farm and two onshore AC systems.