Modeling and identification of drive-system dynamics in a variable-speed wind turbine

Active variable-speed control of wind turbines requires good knowledge of the dynamics to be controlled. This is particularly important when combined with the increasingly common soft concept, resulting in structural eigenfrequencies within the closed-loop bandwidth. The purpose of the authors´ work is to model the drive system in order to make possible the future design of an effective control system. In this paper, a physical model of the fundamental drive-system dynamics of a 400 kW horizontal axis variable-speed wind turbine is derived. The numerical parameter values in this model are then estimated from an identification experiment in closed loop on the real turbine using additional excitation (PRBS). Various identification schemes are compared and are shown to give consistent results in good agreement with the assumed physical model structure