Vibration control in wind turbines during emergency shutdown based on nacelle velocity at the top of the tower

During malfunctions or in extreme conditions, wind turbines often resort to emergency shutdowns. This activity triggers the turbulent impact of dynamic loads, which result in structural imbalances of blades and vibrations—factors that foster increased structural fatigue and damage. Specifically focusing on an emergency shutdown setting prompted by grid loss, this paper utilizes a NREL 5 MW wind turbine as the key object of study. This study investigates the influences of changes in the angle of attack on the aerodynamic loads acting on the turbine blades and the consequent responses in tower vibrations. Derived from the findings, a novel emergency stop control strategy has been proposed. In this strategy, the tower top's vibration velocity is employed as a control input, which is used to adjust the blade pitch rate during the feathering phase in real time. This adjustment aims to reduce the aerodynamic loads and the tower's vibrations during the shutdown process. To achieve this, high-fidelity models coupling OpenFAST and Simulink have been used to carry out aerodynamic, hydraulic, and servo-elastic coupled nonlinear time-domain simulations, which study structural dynamic responses under various turbulent conditions. Compared to the baseline shutdown strategy, the newly developed method reduces tower vibration while having a minor impact on blade loads and the time required for feathering. Quantitatively, this results in a decrease in the maximum tower top displacement (by about 22 %) and bending moment at the bottom of the tower (by about 20 %).