Effect of multiple load reduction control systems on the ultimate load and fatigue load of 4 MW class wind turbine

Wind turbines installed in external environments are subject to a combination of various environmental and operational conditions during their lifetimes, resulting in varying mechanical loads on each of their components. These loads directly impact the turbine lifetime; therefore, research aimed at reducing the load on each component of the wind turbine is required. In this study, load analysis was performed by applying various load reduction control systems. The effect of the load reduction was verified for each controller through individual simulations. Finally, the design load cases (DLC1.1-DLC8.1) required to evaluate the ultimate and fatigue loads based on the IEC 61400-1 ed.3 international standard were defined, and the loads with respect to a 4MW wind turbine with and without various load reduction systems were calculated. When applying all load reduction controllers, the turbine blades and the tower experienced ultimate load reductions of 1%-31% and 7%-21.7%, respectively, except the tower's side-to-side bending moment. This moment was observed in the idling condition, which was not affected by the control system; hence, no changes were observed in the load. Fatigue equivalent load reductions were also observed at the blade (3%-8.9%) and tower side-to-side load (4.8%-7.8%). Notably, however, the tower fore-aft fatigue load increased by 10% in most sections. This overall load reduction suggests that turbine components can be fabricated using less material, thereby increasing the wind turbine fatigue lifetime. This result is expected to reduce the levelized cost of energy.