Extended State Observer-Based Optimized Terminal Sliding Mode Fault-Tolerant Controller for Wing-Rock Suppression in Subsonic Incompressible Flow

Abstract

This paper presents an adaptive fault-tolerant controller using terminal sliding mode theory to control the wing-rock motion in a slender delta wing. The governing equations of motion of have been obtained using the unsteady Vortex Lattice method for subsonic incompressible flow. A nonsingular terminal sliding mode controller (TSMC) is designed and robustified using an extended state observer (ESO) to ensure robustness against uncertainty, external disturbance, and certain actuator faults. The wing-rock dynamics are nonlinear and uncertain. Hence, first, a fast terminal sliding surface is designed to ensure finite-time convergence. Furthermore, an ESO is designed to estimate the roll-rate and uncertainty/external disturbances acting on the wing. The estimated disturbance is utilized to robustify the proposed terminal controller. The parameters of the fast terminal sliding surface are optimized using the genetic algorithm and an adaptive reaching law is designed. It is shown that the proposed controller is stable in the closed-loop. Simulations are performed to demonstrate the effectiveness of the controller for suppressing wing-rock motion in the presence of significant uncertainties, external disturbances, and servo/side slip dynamics. A comparison of the proposed controller is also carried out with existing controllers. The proposed controller significantly reduces the integral time absolute error (ITAE) and control efforts (CoE). Finally, certain actuator faults, such as lock-in fault and loss of effectiveness, are considered. It is observed that the controller achieves satisfactory performance even in the presence of these actuator faults.