Advanced system identification techniques for wind turbine structures with special emphasis on modal parameters

摘要

The goal of this research is to develop advanced system identification techniques that can be used to accurately measure the frequency response functions of a wind-turbine structure immersed in wind noise. To allow for accurate identification, the authors have developed a special test signal called the Pseudo-Random Binary Sequence (PRBS). The Matlab program that generates this signal allows the user to interactively tailor its parameters for the frequency range of interest based on the response of the wind turbine under test. By controlling NREL's Mobile Hydraulic Shaker System, which is attached to the wind turbine structure, the PRBS signal produces the wide-band excitation necessary to perform system identification in the presence of wind noise. The techniques presented here will enable researchers to obtain modal parameters from an operating wind turbine, including frequencies, damping coefficients, and mode shapes. More importantly, the algorithms they have developed and tested (so far using input-output data from a simulated structure) permit state-space representation of the system under test, particularly the modal state space representation. This is the only system description that reveals the internal behavior the system, such as the interaction between the physical parameters, and which, in contrast to transfer functions, is valid for non-zero initial conditions.