Active Tip Deflection Control For Wind Turbines
J.Y. Liew (TU Delft - Aerospace Engineering)
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Abstract
This thesis presents an individual tip control (IPC) system based on blade tip deflection measurements. The controller is based on novel sensor inputs which measure flapwise tip deflection distance at a high sampling rate. IPC plays a key role in reducing fatigue loads in wind turbine components. These fatigue loads are caused by differential loads such as wind shear, yaw misalignment and turbulence. The presented controller is implemented in HAWC2 and high fidelity load measurements are produced using the DTU10MW Reference Wind Turbine. Lifetime equivalent load reductions were seen in both rotating and fixed frame components under extreme turbulence, inverse shear conditions and in normal operating conditions. A novel implementation of IPC is also presented where the blade tips are guided along a fixed trajectory to maximise blade-tower clearance. The motivation of this implementation is to reduce the chance of blade-tower interactions for large diameter turbine rotors. The theoretical background used in this study is presented first along with details of controller discretisation methods. Details of the iterative control design process is presented, and the simulated fatigue loads are compared for a number of control architectures. Finally, the implementation of the tip trajectory tracking control is presented along with an analysis of the pitch rate limits and the effect of IPC on electrical power output.