Aggregated electrolyzer modeling and coordinated frequency support of multi-GW offshore wind-hydrogen energy systems

Multi-gigawatt offshore wind-hydrogen energy systems (OWHESs) extend conventional high-voltage direct-current (HVDC)-connected offshore wind power plants (WPPs) by integrating large-scale electrolyzer plants (ELPs), offering a promising decarbonization path through coupling clean offshore wind and green hydrogen. For OWHES dynamic assessment, ELP models scalable to large plant capacities are needed to preserve key electrical dynamics and capture interactions with HVDC links and WPPs. However, existing studies lack an explicit scale-up modeling method for constructing such models, limiting integrated OWHES dynamic assessment. Moreover, existing frequency controls for HVDC-connected WPPs and ELPs are separately developed, without coordinating their complementary responses, leaving OWHES frequency support under-exploited. To address these gaps, this paper develops a module-based aggregated ELP modeling method and a coordinated fast frequency control strategy for OWHESs. The proposed model derives a capacity-scalable plant-level ELP equivalent through an explicit module-to-plant parameter-aggregation formulation, retaining stack, converter, hydrogen-buffer, and controller dynamics while reducing complexity. The proposed control coordinates HVDC, WPP, and ELP active-power responses, enabling fast frequency support and smooth, automatic post-support recovery. An integrated 2 GW OWHES model is established on a real-time simulator for system-level verification. Results demonstrate that the aggregated ELP model reproduces the detailed model with only 0.02% maximum power-response error, verifying the capacity-scalable ELP modeling. Compared with existing methods, the proposed frequency control achieves higher frequency nadir, lower frequency-change rate, and shorter settling time while avoiding deadband-induced oscillations. These results provide a modeling and control basis for offshore wind–hydrogen hubs to enable renewable power–hydrogen coupling while providing grid support.