Rejection of varying-frequency periodic load disturbances in wind-turbines through active disturbance rejection-based control

Abstract

Abstract Wind turbines are complex mechatronic systems subject to different kinds of disturbances. Among all disturbance sources, those from periodic nature are the most relevant and important for maintaining the structural health of the entire wind turbine. However, periodic disturbances in wind turbines, mainly given by wind shear, tower shadow and rotational sampling of turbulence, have a variable fundamental frequency that changes as function of the turbine angular speed. In consequence, conventional controllers have issues to mitigate such varying-frequency periodic loads. This paper proposes two individual pitch control schemes to attenuate the main periodic load components of blade flap-wise and hub yaw/tilt-wise bending moments in horizontal-axis wind turbines under varying-frequency conditions. Both proposals are founded on the paradigm of Active Disturbance Rejection Control (ADRC): the former is formulated in the time-domain using a Linear-Time-Invariant (LTI) standard controller, while the latter is designed in the angular position domain using a Linear-Position-Invariant (LPI) approach. Several realistic simulations with different wind turbulence intensities and average wind speeds are performed using a 5\u202fMW three-bladed horizontal-axis wind turbine implemented in the FAST code by NREL. Simulation results of the proposed control schemes show improved load reductions compared with other control techniques.