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Addressing external disturbances has been a critical issue for control design to ensure reliable operation of systems. This article investigates the tracking control problem for the uncertain nonlinear systems with the strong external disturbance and the prescribed performance. The flexible performance-based control scheme is developed by introducing an external disturbance criterion into the prescribed performance. It is capable of guaranteeing the prescribed performance if the external disturbance is less than a specified threshold and degrading that in light of the user-appointed rule otherwise. Particularly, the disturbance interval observer is synthesized to generate the boundaries of the external disturbances and realize the judgment of that criterion. With the generated boundaries, the interval-type auxiliary system is designed to provide the modified performance functions (MPFs) that characterize performance requirement and degradation rule simultaneously. Based on the positive system theory and the Lyapunov method, it is theoretically shown that the system output can always track the reference signal and satisfy the constraints of MPFs. Finally, both the numerical simulation and the application of flight control design verify that the results are effective and valid.

It is always a challenge to design a resilient controller for nonlinear engineering systems, particularly for a system with external disturbance, uncertainties, and high couplings. This article systematically investigates the stability issues on complex resilient nonlinear systems with various disturbances and uncertainties. Initially, to address the difficulty in solving differential Hamilton–Jacobi inequalities, a resilient antidisturbance controller is designed by using the robust passive theory to guarantee that the closed-loop nonlinear system is asymptotically stable with ${H_\infty }$ property. To obtain the conventional design of the storage function, the equivalent robust passive system is introduced through a global diffeomorphism, and the corresponding stability analysis is conducted to verify the effectiveness of the method. The simulation results for a helicopter system are intended to demonstrate the practicality and validity of the proposed control method in solving nonlinear resilient control problems.