Wind turbines with a large rotor span, often encounter inhomogeneous wind field, resulting into stress induced on the vital parts of the turbine. Some of these phenomenainthewindfieldarerepetitive, toacertain extend. By means of individual pitch control these disturbances can be minimized. This is investigated by first deriving a linearised state space model at a wind velocity of 18 m/s.
To drive the model, a wind profile is designed. The developed turbine model is verified with respect to the nonlinear NREL FAST 5 MW simulation model for wind velocities from 12 m/s to 24 m/s, the third operating region, for which it is desired to design the control scheme. Three controllers are designed. A collective pitch controller by means of PI controllers. An individual pitch controller using Multibladed Coordinate Transformation. The second individual pitch controller is done by using repetitive control scheme. In order to estimate the unmeasured states Kalman filter is used.
To validate, the designed controllers are implemented on NREL FAST 5 MW wind turbine for comparison with its baseline controller. According to the results, the Coleman transformation is outperforms the baseline controller in reducing the blade displacement. The repetitive controller on the other hand has better results, by minimising the fatigue on all the components of the turbine with one drawback, increased pitch actuation.