Structural load mitigation control for nonlinear wind turbines with unmodeled dynamics

This paper introduces an observer-based method to control nonlinear large-scale wind turbines to reduce structural loads while maintaining the rotor speed and extracted power in wind speed region III. The novel contribution is using a combination of proportional-integral observer and disturbance accommodating control to estimate nonlinearities, unmodeled dynamics, and wind disturbances, then cancel related effects by implying a suitable controller. The proposed approach is robust to unmodeled dynamics caused by the use of a reduced model for the controller design and wind speed variation. Besides the new load mitigating control design, simulation results are given. From the results it can be obtained that both load mitigation capacity and robustness of the system are improved using the proposed approach compared to PI controllers, typical for nowadays practically used controllers.