Nonlinear individual pitch control of large wind turbines for blade load reduction

As wind turbines (WTs) become larger in size, they are experiencing increasing structural loads on their flexible components. This may shorten the working life of WTs or even cause damage to them. This work proposes a nonlinear individual pitch control (IPC) strategy to mitigate blade fatigue load for WTs operating in the above-rated wind speed region. The controller consists of a blade vibration damper and a pitch angle lead compensator for each blade. The damper is used to damp the vibration of the blades, which is designed by nonlinear dynamic inversion (NDI) method to deal with the non-affine nonlinearity of the WT model. The lead compensator is used to compensate the delay between pitch angle command and actual angle caused by the pitch actuator. The simulation results with the aero-elastic model of FAST show that the nonlinear controller has a better system performance, compared with several other IPC controllers. Besides, the proposed approach is able to work well in large wind speed range, and is easy to implement for industrial applications.