The impact of model predictive control and supplementary aerodynamic actuators on extreme load mitigation of wind turbines

This thesis examines the impact of an additional pitch actuator near the blade tip on extreme load reduction of the Fraunhofer IWES 7.5MW wind turbine during full-load power production. To control the generator torque as well as inner and outer pitch systems simultaneously, a time-discrete 38-state linear 10 Hz model predictive controller (MPC) is designed. The corresponding state-space model is continuously updated to the current turbine state by four-dimensional interpolation among a set of priorly linearised models. As a first approach, perfect system observability is assumed. Evaluation simulations were performed with a normal turbulence model and a 50-year extreme operating gust during normal power production, specified in the German Lloyd certification guidelines. The subsequent comparison includes four MPC versions with and without a second pitch and a 5 s long wind forecast, respectively, that are benchmarked to the reference turbine's baseline PID-controller. The results show extreme load reductions of up to 56% for the tower base fore-aft moment and up to 75% for the blade flapwise moment as well as significantly reduced turbine motions for the MPCs compared to the baseline controller that is not equipped with a second pitch system.