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Active strategies with TMDs for control of wind turbine vibrations
Fitzgerald, Breiffni
THESIS 10199 This thesis investigates the use of active structural control techniques for the mitigation of the dynamic response of wind turbines with particular emphasis on reducing the in-plane (edgewise) vibrations in wind turbine blades which have low aerodynamic damping. The rotating wind turbine blades with tower interaction represent time varying dynamical systems with periodically varying mass, stiffness and damping matrices. This thesis aims to determine whether active tuned mass dampers (ATMDs) or certain variations of these dampers could be employed to reduce vibrations in wind turbines with better performance than compared to their passive counterparts. Euler-Lagrangian structural dynamic mathematical models of wind turbines based on energy formulation have been developed for this purpose. These models consider the structural dynamics of the system and the interaction between in-plane and out-of-plane vibrations (coupled blade vibration model), the effects of gravity and that of centrifugal stiffening. Also, the interaction between the structurally twisted blades and the nacelle/tower has been considered. The wind turbine models have been subjected to gravity loading and turbulent aerodynamic loading. Aerodynamic loading has been simulated using the state-of-the-art modified blade element momentum (BEM) algorithm which accounts for the angle of attack, blade pre-twist, pitch angle and wind shear. Turbulence was generated from a Kaimal spectrum and a rotationally sampled spectrum. The model was reformulated by incorporating passive tuned mass dampers (TMDs) dampers inside the blades and at the top of the nacelle/tower. A schematic representation of the passively controlled edgewise blade model was experimentally validated in the laboratory. Active control in the form of active TMDs (ATMDs) has also been examined. The formulation of the rotating wind turbine blades with ATMDs has been proposed. The ATMDs were controlled by linear quadratic regulator (LQR), velocity feedback (VF) and acceleration feedback (AF) control algorithms. An investigation into the relative performance of the active controllers was carried out. Further, the vibration reduction achieved by using active control was compared with the uncontrolled and the passively controlled results. The application of ATMDs to the blades significantly reduced the in-plane blade vibrations. The stroke required by the ATMDs to operate was observed to be comfortably within the blade chord length limit. A new variation of an active control scheme with ATMDs was also proposed in this thesis. The new controller with an innovative hardware, called the cable connected ATMD (CCATMD) has been developed. CCATMDs consist of a pre-tensioned cable attached to an ATMD at one end and to the blade tip at the other end. When the ATMD moves a component of the cable tensile force acts to oppose the in-plane loading on the blade. It was shown that CCATMDs significantly reduce blade in-plane vibration and also improve upon the performance of the classical ATMDs requiring less control force to operate. The damper stroke again sits comfortably within the blade chord length highlighting the suitability of the proposed control scheme for use in the structural dynamic control of wind turbines. Finally, soil-structure interaction (SSI) was incorporated in the models to examine a more realistic model of a wind turbine system. A wind turbine foundation resting on flexible soil was modelled in a finite element code PLAXIS and incorporated into the wind turbine models developed in this thesis. It was shown that including SSI altered the nacelle/tower natural frequencies rendering passive control ineffective. LQR controlled ATMDs were designed to control nacelle/tower out-of-plane motion with SSI included. This active control algorithm achieved significant response reductions. This thesis investigates the use of active structural control techniques for the mitigation of the dynamic response of wind turbines with particular emphasis on reducing the in-plane (edgewise) vibrations in wind turbine blades which have low aerodynamic damping. The rotating wind turbine blades with tower interaction represent time varying dynamical systems with periodically varying mass, stiffness and damping matrices. This thesis aims to determine whether active tuned mass dampers (ATMDs) or certain variations of these dampers could be employed to reduce vibrations in wind turbines with better performance than compared to their passive counterparts. Euler-Lagrangian structural dynamic mathematical models of wind turbines based on energy formulation have been developed for this purpose. These models consider the structural dynamics of the system and the interaction between in-plane and out-of-plane vibrations (coupled blade vibration model), the effects of gravity and that of centrifugal stiffening. Also, the interaction between the structurally twisted blades and the nacelle/tower has been conside...
Keyword(s): Civil, Structural and Environmental Engineering, Ph.D.; Ph.D. Trinity College Dublin
Publication Date:
2012
Type: Doctoral thesis
Peer-Reviewed: Unknown
Language(s): English
Institution: Trinity College Dublin
Citation(s): Breiffni Fitzgerald, 'Active strategies with TMDs for control of wind turbine vibrations', [thesis], Trinity College (Dublin, Ireland). Department of Civil, Structural and Environmental Engineering, 2012, pp.286
Publisher(s): Trinity College (Dublin, Ireland). Department of Civil, Structural and Environmental Engineering
Supervisor(s): Basu, Biswajit
First Indexed: 2018-07-06 06:24:55 Last Updated: 2018-07-06 06:24:55