Abstract
In this paper we study the use of individual blade pitch control as a way to reduce ultimate loads. This load alleviation strategy exploits the fact that cyclic pitching of the blades induces in general a reduction of the average loading of a wind turbine, at least for some components as the main bearing, the yaw bearing, or the tower.When ultimate loads are generated during shutdowns, the effect of the use of cyclic pitch results in reduced peak loads. In fact, as the machine starts from a less stressed condition, the response to an extreme gust or other event will result in reduced loading on its components. This form of load mitigation can be seen as a preventative load mitigation strategy: the effect on load reduction is obtained without the need to detect and react to an extreme event, but by simply unloading the machine so that, in case an extreme event happens, the result will be less severe.The effect of peak load mitigation by preventative cyclic pitch is investigated with reference to a multi-MW wind turbine, by using high-fidelity aeroelastic simulations in a variety of operating conditions.
Highlights
IntroductionThe ability of cyclic pitch control systems to lower fatigue loading on wind turbines has been thoroughly investigated and quantified, as witnessed by a significant body of literature devoted to this subject (cf. Refs. [1] to [11], and references therein)
In the last decade, the ability of cyclic pitch control systems to lower fatigue loading on wind turbines has been thoroughly investigated and quantified, as witnessed by a significant body of literature devoted to this subject
The wind turbine model operates in closed-loop with the controllers described above
Summary
The ability of cyclic pitch control systems to lower fatigue loading on wind turbines has been thoroughly investigated and quantified, as witnessed by a significant body of literature devoted to this subject (cf. Refs. [1] to [11], and references therein). Notwithstanding the several different possible implementations of such controllers, the majority of the results obtained by simulation or in the field show that the use of cyclic pitch is typically quite beneficial in the reduction of fatigue loading. This advantage comes at the price of an increased pitch activity, as for example quantified by the actuator duty cycle (ADC) or other similar metrics. Less can be found in the existing literature about the effects that cyclic pitch can bear on the ultimate loads affecting a wind turbine This is unfortunate, as ultimate loads rather than fatigue may drive the design of some wind turbine sub-systems.
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