Design of Second-Order Sliding Mode Controller for Morphing Aircraft Based on NLFOEESO

This paper proposes a second-order sliding mode control method for morphing aircraft based on a nonlinear fractional-order error extended state observer (NLFOEESO). The proposed approach effectively maintains the stability of flight velocity and altitude despite complex factors such as center-of-mass variations and aerodynamic uncertainties and disturbances. Considering the highly uncertain, strongly nonlinear, and rapidly time-varying dynamics of morphing aircraft, sliding mode control is adopted as the fundamental control strategy. To enhance the system's disturbance rejection capability and alleviate the chattering phenomena, a second-order sliding mode control algorithm was designed. However, the disturbance rejection capability of sliding mode control remains limited. To address the aforementioned issues, a NLFOEESO was designed to dynamically estimate uncertainties such as aerodynamic uncertainties and disturbances during flight. Compared with the traditional extended state observer (ESO), the proposed NLFOEESO achieves a more optimal balance between response speed and estimation accuracy. This design enhances the system's adaptability to nonlinear high-frequency and low-frequency disturbances, further improving overall control precision. Simulation results validated the effectiveness and superiority of the proposed control method.