A robust LMI-based pitch controller for large wind turbines

This paper utilizes the linear matrix inequalities’ techniques (LMI) for designing a robust collective pitch controller (CPC) for large wind turbines. CPC operates during up rated wind speeds to regulate the generator speed in order to harvest the rated electrical power. The proposed design takes into account model uncertainties by designing a controller based on a polytopic model. The LMI-based approach allows additional constraints to be included in the design (e.g. H∞ problem, H2 problem, H∞/H2 trade-off criteria, and pole clustering). These constraints are exploited to include requirements for perfect regulation, efficient disturbance rejection, and permissible actuator usage. The proposed controller is combined with individual pitch controller (IPC) that reduces the periodic blade’s load by alleviating once per revolution (1P) frequency fatigue loads. FAST (Fatigue, Aero-dynamics, Structures, and Turbulence) software code developed at the US National Renewable Energy Laboratory (NREL) is used to verify the results. ► The paper investigates designing robust pitch controller For 5MW wind turbine. ► The wind turbine model characteristics are first presented. ► An LMI robust controller is designed based on single model, then polytopic model. ► Individual pitch controller is designed to mitigate mechanical fatigue loads. ► Finally, simulation compares between the proposed controller and a PI controller.