Prescribed performance-based fixed-time control of nonlinear systems with application to flight dynamics

This study presents a robust adaptive controller for strict-feedback nonlinear systems with dynamic uncertainties and external disturbances, aiming to achieve fixed-time convergence under prescribed performance constraints. The proposed approach employs fuzzy logic systems integrated with robust integral terms based on error signs for the effective estimation of uncertainties and disturbances. Using these estimates, a parallel identification system is constructed to maintain dynamic consistency with the original system dynamics. By embedding prescribed performance functions, the designed controller explicitly enforces transient constraints and ensures fixed-time convergence of tracking errors, independent of the initial states. Stability analysis rigorously demonstrates semi-global convergence of the identification errors and fixed-time convergence of the tracking errors. The simulation results verify the effectiveness and superior disturbance-rejection and tracking performance of the proposed scheme.