Individual blade repetitive control for horizontal-axis wind turbines

Horizontal axis wind turbine (HAWT) control is crucial for both increasing performance (quantity and quality of power harvested) and avoiding excessive stress of structural components. Indeed, both wind and corresponding torque are time-varying. In particular, boundary conditions over turbine blades are strongly affected by terrain boundary layer, which causes periodic inputs and then vibratory loads. In uncontrolled blades, high vibratory level might arise, along with reduction of generated power. The most effective and multipurpose way to control horizontal axis wind turbine is changing blade pitch in order to guarantee suited aerodynamic incidence, while other control strategies (as yaw or torque control) are mainly aimed at avoiding excessive rotational speed. Acting on blade pitch allows to reduce vibratory loads and regulate generated torque at the same time. In this work, this control approach is described, developed and validated by application to a lumped elasticity pylon/turbine system model.