Evaluation of global structural load responses in wind turbines providing grid frequency support

As wind energy increasingly contributes to non-synchronous generation, wind turbines are expected to provide frequency-containment reserve (FCR), yet the associated structural impacts remain insufficiently quantified under realistic conditions. This study develops a coupled Simulink-OpenFAST framework to evaluate the structural response of a utility-scale reference wind turbine using turbulent inflow and measured Belgian grid-frequency data. Structural loading of blades, main bearing, and tower is assessed through normalized load-variation metrics linked to fatigue-relevant indicators. Results show that FCR provision primarily induces quasi-static shifts in the turbine operating point, while turbulence continues to dominate short-term load fluctuations. The structural impact is strongly regime-dependent: loads exhibit component-dependent behavior below rated wind speed - increasing for the blade, decreasing for the main bearing and tower - decrease more broadly under pitch-controlled operation above rated, and exhibit maximum sensitivity near rated conditions due to torque–pitch interaction. In this region, main-bearing and tower load variability jointly emerge as the dominant constraint. The proposed framework enables illustrative structural screening maps, supporting reserve allocation strategies that match commitment levels to local operating and grid-frequency conditions rather than applying uniform targets across the fleet.