Abstract
In this study, vibration control, a behavior which subordinates to stall-induced nonlinear vibration and amplitude control of a wind turbine’s blade section, based on unified pitch motion driven by slider-linkage mechanism, is investigated by using an iterative learning control (ILC) method. The nonlinear dynamical system is a nonlinear aeroelastic system. The aeroelastic system equations consist of three parts: the nonlinear structural equations derived by using Lagrange’s equations, the improved stall-induced nonlinear ONERA (ISNO) aerodynamic equations, and the pitch control equation. The ISNO model is not only suitable for the actual external pitch motion, but also suitable for the solution by using an ILC algorithm due to its fitted nonlinear aerodynamic coefficients. The ILC algorithm used here is an improved iterative learning algorithm (IILC) which considers the large-range, linearized, residual terms, and realizes gain adaptive tuning based on PID controller. On the one hand, it can control the amplitude of an unsteady flutter through trajectory tracking. On the other hand, when the preset value of the amplitude of the ideal trajectory is very small, it can make the system directly tend to convergence and stability of a nonlinear aeroelastic system. To simplify the extremely difficult iterative process, the pitch movement can track the elastic twist displacement in time, thus simplifying the aeroelastic equations and accelerating the IILC iteration process. Therefore, amplitude control for flap-wise/lead-lag displacements is realized by the unified pitch motion and the trajectory tracking controlled by using the IILC algorithm.
Highlights
The flutter instability of large-scale wind turbine blades usually includes two cases: classical flutter instability and stall-induced flutter instability
An ISNO aerodynamic model is applied, which is suitable for the actual external pitch motion for a large-scale wind turbine, and the bending/bending/twist coupling behaviors of the blades
The nonlinear stall aerodynamics are included by use of the ONERA aerodynamics equations [13] to investigate the nonlinear, large amplitude, aeroelastic behaviors of hingeless composite rotor blades during hovering flight, that can develop into flutter oscillations
Summary
The flutter instability of large-scale wind turbine blades usually includes two cases: classical flutter instability and stall-induced flutter instability. Flutter suppression and sliding mode control of TEF blade based on the adaptive reaching law and radial basis function ANN approximation were investigated to study and suppress a deep stall that was predicted by an improved B–L model, using fitted aerodynamic coefficients [10]. An ISNO aerodynamic model is applied, which is suitable for the actual external pitch motion for a large-scale wind turbine, and the bending/bending/twist coupling behaviors of the blades. The contributions of this study compared to other existing works in the literature can be summarized as follows: (a) The ISNO model, an improved ONERA model, is applied, which is suitable for the actual external pitch motion and bending/bending/twist coupling behaviors of rotating wind turbine blades. On the other hand, when the preset value of the amplitude of the ideal trajectory is very small, it can make the system directly tend to stability and convergence. (c) In terms of research methods and innovation, the ISNO model based on coefficient fitting is suitable for different kinds of stall-induced aeroelastic systems, and its supporting IILC algorithm is suitable for solving different kinds of stall-induced nonlinear aeroelastic systems
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