Dynamic Characteristic of the Drive Train of DFIG Wind Turbines during Grid Faults

During a grid voltage drop, a problem is resonances in the drive-train shaft between the wind turbine and induction generator. Disadvantageous effects caused by this are noticeable vibrations and high mechanical stresses due to torque oscillations. The oscillations can be damped using the drive train damper, which is used to mitigate fatigue loading of drive train components, controller consisting of a nonlinear observer to estimate the torque in the rotor and computes a damping torque signal that is added to the driver´s demand. The control algorithm was implemented in the existing motor control unit without any additional hardware cost. The controller was successfully tested in a test. The resonances can essentially be eliminated.