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

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.