Blade Vibration Analysis and Pitch Control of Large-scale Wind Turbines

Abstract

The assumed modes method is developed to derive a set of linear differential equations describing the motion of a flexible wind turbine blade and to propose an approach to investigate the forced responses result from various wind excitations. In this work, we have adopted Euler beam theory and considered that the root of the blade is clamped at the rigid hub. And the aerodynamic parameters and forces are determined based on Blade Element Momentum (BEM) theory and quasi-steady aerodynamics. Numerical calculations show that this method gives good results and it can be used for modeling and the forced vibration analysis of wind-turbine blades including bending-torsion coupling effect, as well as turbo-machinery blades, aircraft propellers or helicopter rotor blades which may be considered as straight non-uniform beams with built-in pre-twist. In addition, an individual blade pitch control strategy is proposed by employing the developed blade model, in order to alleviate fatigue loads acting on the wind turbine blade and rotor shaft. Numerical simulation clearly demonstrates that the proposed control strategy is effective.