Black start design for offshore wind–hydrogen energy Islands: Role of grid-forming battery and wind turbine technologies

Reliable black start capability is a critical design requirement for offshore wind–hydrogen energy islands, directly influencing system availability, asset utilization, and the levelized cost of hydrogen production. This paper investigates black start restoration strategies for autonomous offshore wind-to-hydrogen systems, focusing on the role of grid-forming converter technologies in enabling system recovery following total shutdown. A comparative analysis of grid-forming battery storage and grid-forming wind turbine generation is conducted using electromagnetic transient simulations of a 300MW offshore wind farm coupled with a 240MW electrolyzer plant. Both technologies are evaluated within a combined soft and hard energization framework incorporating controlled voltage ramping, switchable reactive compensation, and sequential feeder energization. Battery-based grid-forming achieves faster voltage restoration and higher short-term overload capability, while wind turbine-based grid-forming provides superior frequency damping through higher virtual inertia. The combined energization strategy significantly reduces converter sizing requirements compared to pure soft energization, while switchable reactive compensation reduces reactive power burden by 94 percent during multi-feeder restoration. Strategic activation of electrolyzer auxiliary systems provides controllable load management that further attenuates frequency excursions during staged restoration. The findings provide practical design guidelines for black start technology selection in offshore wind–hydrogen systems, with direct implications for converter sizing, capital investment, and hydrogen production continuity.