Design of fatigue-based specifications for the design of controllers in wind turbines

Abstract. Pitch controllers are critical components in wind turbines, and their design typically involves lengthy iterative processes of tuning and simulation-based validation. Using well-defined control specifications, rigorously linked to engineering requirements, can significantly reduce the effort needed to achieve optimal performance. This work presents a methodology for generating control specifications directly related to mechanical fatigue caused by driving loads in wind turbine applications. The method is tailored for frequency-domain controller design techniques, such as quantitative feedback theory (QFT) and H∞, and is based on Dirlik's method for fatigue assessment. It is tested through the design of controllers for a reference 15 MW wind turbine operating above rated conditions. The specification-driven design results in a validated reduction in fatigue, with simulation outcomes showing a mean error of 1.07 % between the fatigue value predicted by the specifications and the one obtained from simulations.