Optimization of Wind Turbine Torsional Mitigation Procedures for Different Generator Classes

Wind turbine vibrations can result from periodic excitation caused by the wind and by both wind and seas for the case of offshore units. In particular, the turbine drivetrain is subject to torsional vibrations caused by both changes in the wind and grid disturbances. This paper uses a collection of different control schemes to damp the vibrations and seeks the best controller by optimizing each in terms of gain selection. Two 750 kW wind turbine models, one with a DFIG (doubly fed induction generator) and the other with a PMSG (permanent magnet synchronous generator) are used in the investigation. Numerical simulations of the wind turbines using the NREL developed software FAST 8 are the means of conducting the tests. In varying the gains, the work discovers that the best controller for a DFIG differs greatly from the best controller for a PMSG. In addition, the work found that the vibration damping in a DFIG turbine is different when the source of the vibration-causing disturbance is considered. The paper reports both the optimized gains and a set of questions raised by the behavior of the DFIG turbine where the response of the shaft torsion differs according to the source of the disturbance, i.e. either grid side or wind side.