Frequency support from a large-scale green hydrogen plant within an HVDC-connected offshore wind farm

• A large-scale HVDC-connected wind and electrolyser plant is modeled in detail. • Approaches to sizing and high-level control strategies for the electrolyser plant are discussed. • The connection of the electrolyser plant to the HVDC link eliminates the AC/DC stage. • Modular configuration of the electrolyser plant for high-voltage DC is discussed. • Simulations of case studies demonstrate reductions in wind curtailment and enhanced grid frequency support. Hydrogen electrolysers are power to gas conversion technologies that will be integrated with offshore wind farms in future power systems. Such systems will be required to operate flexibly, providing frequency support services to grids. This paper develops integrated modelling methods for large-scale electrolyser systems within an HVDC-connected offshore wind farm. The model includes a droop controller as the primary frequency controller and a model predictive control based secondary frequency response controller. An equivalent model for a DFIG-based wind farm is derived, by which the wind farm’s output power can be evaluated as a first-order system. We propose a dynamic electrolyser system model including stack circuit, power electronics interface and converter-level control loops incorporating large average models and control algorithms for Voltage Source Converter-based HVDC. The integrated model is applied to simulate plant operation, accounting for wind variations, HVDC and grid constraints, electrolyser characteristics, and frequency response scenarios. Approaches to sizing and high-level control and modular configuration for the electrolyser plant within the integrated system are explored. The results demonstrate that diverting excess wind power to an electrolyser plant for hydrogen production can reduce downward dispatch of wind, and that hybrid plants can provide faster frequency support than standalone wind farms. Configuration of the HVDC-connected OWF integrated with large-scale EL.