Influence of Higher-order Disturbance Estimation on Maximum Power Extraction of Wind Energy Conversion System using Sliding Mode Control

The demand for clean and renewable wind energy as an alternative energy source to fossil fuels that produce greenhouse emissions is ever-increasing. However, harnessing the maximum power from the wind source via the wind energy conversion system (WECS) requires precise estimation of aerodynamic torque and subsequently the reference generator speed. In this paper, the exponential disturbance observer-based sliding mode control (SMC) for extracting the maximum power of WECS using wind speed estimation is presented. As most of the existing research assumed the aerodynamic torque to be slowly varying, this study presented a comprehensive analysis of the influence of higher-order (fast-varying) aerodynamic torque for maximum power extraction of the WECS. The simulation results under different wind profiles for the zero-order, first-order, and second-order aerodynamic torque estimations were analyzed. Although the maximum power extraction has increased by 17% for an extremely-varying wind from 162.5 kW for the zero-order to 190 kW after incorporating the higher-order estimations, the zero-order estimation almost extracts the same power (151.7 vs 152.2 kW), and (6.85 vs 6.91 kW) for the fast varying wind and low magnitude wind force, respectively. Finally, the analyses showed that if the WECS is operating where the wind is not extremely fast-varying, the zero-order estimation is the ideal choice as the higher-order estimation increases the nonlinearity of the system.