Composite Hierarchical Pitch Angle Control for a Tidal Turbine Based on the Uncertainty and Disturbance Estimator

With the fast development of tidal turbines for sustainable energy generations, reliable and efficient tidal pitch systems are highly demanded. This paper presents a systematic design for a novel tidal pitch system based on hydraulic servo and bevel geared transmission. This system holds the characteristics of compact and triangular structure, making it easy to be installed in a narrow turbine hub. The pitch system dynamics are modeled by taking account of model uncertainties and external disturbances. An uncertainty and disturbance estimator (UDE)-based robust pitch control algorithm is developed to achieve effective pitch angle regulation, disturbance rejection, and generator power smoothing. The UDE controller is designed in a composite hierarchical manner that includes an upper level power smoothing controller and a low-level pitch angle tracking controller. The performance of the proposed pitch system and the UDE control is demonstrated through extensive simulation studies based on a 600-kW tidal turbine under varying tidal speeds. Compared with the conventional controller, the UDE-based pitch controller can achieve more reliable power smoothing and pitch angle tracking with higher accuracy.