Fatigue load estimation and fatigue load reduction

Fatigue is the structural damage that leads the components of a wind turbine to sudden brittle failure when they suffers cyclic loading [6]. As the size of wind turbines is growing, fatigue loads become more and more significant for the design of major structural components. Concerning fatigue in a wind turbine tower, the fore-aft tower foot bending moment is considered as the most critical load. The benefits of fatigue load reductions, which can be achieved by appropriate design of a wind turbine control system, are increasing [4]. The purpose of this study is 1. to describe the estimation of tower bending fatigue load in the frequency domain [16] for control design. 2. to demonstrate, how a gain scheduled control system based on a "Linear Parameter-Varying" (LPV) model can be designed using this estimation. The control system provides active damping to the first tower eigen frequency (1. TEF) as well as to the 3p harmonic excitation.