Abstract
A novel experimental study on the use of individual pitch control to extend the fatigue life of wind turbines is conducted. The experiment is accomplished using a sub-scale model of a multi-megawatt turbine in both upwind and downwind configurations in a water towing tank. It is shown that individual pitch control based on a sinusoidal pitching scheme that is locked to the phase of the rotor rotation can mitigate unsteady loads caused by the velocity variation that is induced by the effect of rotor tilt and therefore extends the fatigue lifetime of blades. A positive pitching amplitude in the case of upwind configuration and a negative pitching amplitude in the case of downwind configuration eliminate the cumulative damage fractions due to the velocity variation.
Highlights
The development of advanced light composite materials allows three-bladed turbines to be made considerably lighter with larger and more slender rotor blade designs, which lead to a substantially reduced cost of wind-generated electricity [1]
It is shown that individual pitch control based on a sinusoidal pitching scheme that is locked to the phase of the rotor rotation can mitigate unsteady loads caused by the velocity variation that is induced by the effect of rotor tilt and extends the fatigue lifetime of blades
While a tilted rotor and a coned blade might have higher unsteady loads and lower power production due to the velocity variation that is induced by the effect of rotor tilt and blade cone, individual pitch control as an active approach can compensate for the influence of the velocity variation
Summary
The development of advanced light composite materials allows three-bladed turbines to be made considerably lighter with larger and more slender rotor blade designs, which lead to a substantially reduced cost of wind-generated electricity [1]. The lighter and larger wind turbine blades that are more flexible, have lower modal frequencies, and on the other hand, as there is an azimuthal variation of aerodynamic loads due to wind shear and turbulence as well as azimuthal variations of induced velocity due to tilt/yaw, larger wind turbine rotors are more susceptible to failure from fatigue [2][3]. As a design life of 20 years or longer is considered for the operation of a multi-megawatt wind turbine, an improved understanding of the impact of unsteady loads on wind turbines in different operating conditions is very important [2][4][5]. Collective pitch control is not capable of compensating for unsteady loads which vary azimuthally. Recent aero-elastic simulations suggest that individual blade pitch control may be a viable active approach to extend the fatigue life of multi-megawatt wind turbines [14][15]
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