Nonlinear control for load reduction on a variable speed pitch regulated wind turbine

A nonlinear controller is designed for load reduction on a variable speed pitch regulated wind turbine using the technique of extended linearisation. The tower first fore-aft bending mode is modelled as an Euler-Bernoulli beam using the Ritz method. A state-space representation based on extended linearisation, which depends on the varying wind speed, is used to design a nonlinear multivariable controller for the aboverated operation. This involves full state feedback, feedforward of desired values and proportional-integral control action, which are scheduled with the current wind speed. A discrete-time observer is designed to estimate the aerodynamic torque and the non-measureable states. In a further step, the wind speed is derived from the estimated variables. The controller is tested using a detailed wind turbine aeroelastic simulation code, and the performance is compared with that of the baseline controller for the wind turbine in question.