Extension to standard system identification of detailed dynamics of a flexible wind turbine system

Provides two extensions to standard prediction error identification for the detailed dynamics observed from a real life flexible wind turbine system. From a theoretical modelling point of view the transfer function from blade pitch to flap moment (out of plane bending of the blades) is extremely interesting because it is mainly determined by aerodynamics and aeroelastics. These modelling aspects have not been properly validated in detail for full scale real life wind turbine systems yet. This is mainly due to the complexity of the wind field acting on the rotor. Although the wind drives the wind turbine it still is considered as a disturbance. In this paper rough knowledge of the wind field is used to structure the stochastic part in the identification procedure. Some disturbances clearly relate to rotor position. A transformation is proposed and applied to the original data in such a way that every rotation consists of the same number of samples (while the time to complete a revolution varies). This clearly improves the identification results obtained from experimental data