Fatigue Load Reduction and Variable-Structure Control Techniques for DFIM-based Wind Farm Scenarios

Abstract

This paper proposes a trade-off approach between fatigue reduction and power extraction for wind farm scenarios, in which a simplified model for a Horizontal Axis Wind Turbine is developed. Both the aerodynamics and the electrical-mechanical model are implemented, considering a Doubly-Fed Induction Machine (DFIM). This model is controlled and connected to the grid by a back-to-back converter, composed of two bi-directional voltage source inverters. Moreover, the stator windings of the generator are directly linked to the grid and the rotor windings are connected to the grid through the power converter. The control of the VSIs is based on super-twisting sliding mode control, which guarantees robustness and low chattering effects. A wake model and an optimization problem for the reduction of the loads are included, to reduce the maximum fatigue load without compromising the power extraction. The results show a performance tracking of a desired rotational speed for the DFIMs and reduction of fatigue and damage, with a limited power reduction compared with the maximum power point tracking.