Trade-off between power extraction maximisation and fatigue reduction in wind farms via second-order sliding mode control and min-max optimisation

In the last 10 years, with the increase of renewable energies, great attention is devoted to operation and maintenance of wind turbines and wind farms, which are the fundamental objectives to be guaranteed by the design of control systems. This study proposes a trade-off approach between fatigue reduction and power extraction for wind farm scenarios. The focus of this approach is to reduce maintenance costs for fatigue loads. This issue is solved by an optimisation problem, in which the maximum fatigue load among the turbines in the wind farm is minimised, then pitch angle and tip-speed ratio are given as reference points for each turbine in the wind farm. Furthermore, the super-twisting sliding mode algorithm is used for the rotor speed control and it shows that the turbines work at the optimised operating points. Moreover, the sliding mode controller produces continuous torques and improves the wind turbine performance by enhancing energy capture and reducing dynamic loads. The effectiveness of the method is illustrated through simulations of two wind farm scenarios. The results obtained with the proposed approach are compared with the case when each turbine in the wind farm tracks the maximum power operating point.