A direct adaptive control approach is used to track the tip speed ratio of wind turbine to maximize the power captured during the below rated wind speed operation. Assuming a known optimum value of tip speed ratio, the deviation of actual tip speed ratio from the optimum one is mathematically expressed as tip speed ratio tracking error. Since the actual tip speed ratio is not a measurable quantity, this expression for tip speed ratio tracking error is linearized and simplified to express it in terms of wind speed and rotor speed, where rotor speed can easily be measured whereas an estimator is designed to estimate the wind speed.
Important results from stability and convergence analysis of the proposed adaptive controller with state estimation and state feedback is also presented. From the analysis it was observed that the adaptive disturbance tracking controller can be combined with adaptive state feedback to achieve other control objectives such as reducing the wind turbine structural loading. Hence, an adaptive state feedback scheme is also proposed to reduce wind turbine tower fore-aft and side-side motions.