Adaptive Disturbance Tracking Control to Maximize the Power Capture of Large Wind Turbines in below Rated Wind Speed Region
The amount of power captured by wind turbine depends on the wind speed and the power coefficient (Cp). When wind speed is above rated value, the rated amount of power is captured but in below rated wind speed operation or Region II operation, the power captured must be maximized. The power coefficient (Cp) further depends on the blade pitch angle and the Tip Speed Ratio (TSR). For a fixed blade pitch angle there exist an optimum TSR for which the power coefficient becomes maximum. In Region II turbine operation, blade pitch is kept constant and TSR is tracked to its optimum value to maximize the power capture. In this paper we introduce an Adaptive Disturbance Tracking Control (ADTC) Theory and make some modifications to implement it to maximize the power capture by tracking the optimum TSR in Region II operation of large wind turbines. Since ADTC requires measurement of wind speed, a wind speed and partial state estimator based on linearized lower-order model of wind turbine at Region II operating point was developed. The estimated wind speed was then used with the adaptive controller and the states were used for state feedback. The combination of partial state feedback and adaptive disturbance tracking control is implemented in National Renewable Energy Laboratory (NREL)'s 5 MW offshore wind turbine model and simulated in MATLAB/Simulink. The simulation result was then compared with existing fixed gain controller.