Recovery of the voltage-dip speed increase in wind turbine by offline trajectory planning

In this paper, the performance of wind turbine speed control under line voltage dips is under scope. The focus is put on the post-fault behavior of the turbine mechanics, when the system has to be quickly steered back to the pre-fault optimal point without violating the generator torque limits, and avoiding to trigger drivetrain oscillatory modes. To this aim, a low computational burden control solution is proposed, combining a high-bandwidth-feedback pole placement strategy with a suitable state reference trajectory planning. A minimal recovery time is pursued in the trajectory design. The computational burden of optimization is shifted offline, evaluating the minimum time trajectories for a reasonable set of post-fault scenarios, and relying on a look up table to handle generic runtime faulty conditions. Simulations assess the promising performance of the proposed strategy.