Towards Pitch-Scheduled Drive Train Damping in Variable-Speed, Horizontal-Axis Large Wind Turbines

Given the prohibitive costs of replacement of damaged gearboxes, damping drive train osillations is of immense significance in large wind turbine control design. The Drive Train Damper (DTD) is an important constituent of the power production control routine in variable-speed, pitch-regulated large wind turbines. The DTD is used to mitigate fatigue loading of drive train components. This paper motivates the need for scheduling the parameters of the damper based on blade pitch angle. It is shown that due to the strong coupling between blade edgewise motion and the drive train torsion, the fundamental frequency associated with the drive train´s torsional motion can vary significantly across the range of blade pitch angles observed in practice. If left unaccommodated, this variation in fundamental frequency is shown to adversely affect the performance of the DTD.