Harris hawks optimization tuned exponential reaching law based integral SMC for pitch control of linear hydraulic actuated wind turbines

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Abstract
In the present study 5MW NREL horizontal axis wind turbine (HAWT) has been considered for pitch control to reduce fatigue loads and maintain rated power in region III of operation, that is, above rated wind condition. An electrohydraulic linear actuation system has been considered for blade-pitch revolve-motion of the rotor blade, based upon available wind speed. An augmented state improved exponential reaching law integral sliding mode controller (ASIERL-ISMC) has been designed for the HAWT pitch control application. In contrast to the previously reported improved exponential reaching law based controllers, in our ASIERL-ISMC, all state variables and the sliding variable have been considered together to define an augmented reaching law that can enhance the degree of freedom of the controller. Further, hyperparameters of the proposed ASIERL-ISMC have been optimized using Harris hawks optimization (HHO), to achieve superior control performance. The performances of this proposed HHO-ASIERL-ISMC have been compared with existing dynamic exponential term reaching law integral sliding mode controller (DETRL-ISMC) and improved exponential reaching law integral sliding mode controller (IERL-ISMC). The robustness and sensitivity of the proposed ASIERL-ISMC and HHO-ASIERL-ISMC have also been tested with three different available wind data. The proposed HHO-ASIERL-ISMC has been found to provide the most superior performance, in terms of both blade-pitch angle error (computed using integral absolute error (IAE)) and control energy (CE).

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