Evaluation of a communication-based fault ride-through scheme for offshore wind farms connected through high-voltage DC links based on voltage source converter

Offshore wind farms connected to the mainland through high-voltage DC links based on voltage source converters (VSC-HVDC) are subject to grid code requirements, such as fault ride-through (FRT) capability and dynamic voltage support. To address the challenge of FRT capability, sophisticated control strategies are required, capable of handling the power imbalance between the two interconnection ends during onshore grid faults. This study proposes an FRT method which combines a de-loading control strategy for the offshore wind turbines, utilising the communication infrastructure of the VSC-HVDC system, with a DC chopper to dissipate the power surplus that cannot be effectively curtailed via the communication link. The impact of communication system latency on the expected FRT response and the required rating of the DC chopper is investigated using a linearised small-signal model introduced in this study, whose results are validated against time-domain simulations using detailed electromagnetic transient-type models for the entire system. It is concluded that the required rating of chopper resistors can be substantially reduced when existing communication capabilities are exploited, even in the presence of relatively high communication delays.