Active tip deflection control for wind turbines

This paper studies the use of blade tip sensors for load reductions and blade-tower clearance control. Typically, modern blade tip sensors measure flapwise tip deflection distances at a high sampling rate, and such measurements can be utilised as feedback signals for control operations. Thus, this paper proposes a novel blade pitch control design based on the tip deflection measurements and individual pitch control (IPC). Firstly, an IPC system design is presented, using the tip deflection measurements to alleviate turbine fatigue loads caused by differential loads such as wind shear, yaw misalignment and turbulence. Secondly, a novel implementation of IPC with tip trajectory tracking feature is proposed 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 and flexible rotors. The presented controller is implemented in HAWC2, and high fidelity load measurements are produced using the DTU10MW reference wind turbine. The simulation results showed that the fatigue damage reduction on key turbine components and the improved blade-tower clearance can be achieved simultaneously. Lifetime equivalent load reductions were seen in both rotating and fixed frame components under the normal operating conditions.