Active Fault-Tolerant Control With Adaptive Estimation Error Compensation for Nonlinear Systems: Achieving Asymptotic Tracking

For active fault-tolerant control (AFTC) of nonlinear systems, inaccurate fault estimation caused by mismatched disturbances can result in compensation errors in the fault-tolerant controllers, making it difficult to achieve asymptotic tracking. This article proposes a novel AFTC strategy featuring an adaptive mechanism for compensating estimation errors for a class of strict-feedback nonlinear systems subject to mismatched disturbances. The strategy introduces an estimator, decoupled from the controller, to perform fault detection, fault estimation, and state estimation using measured output. By treating estimation errors and system disturbances as new process disturbances, adaptive compensation terms are constructed, while an active fault-tolerant controller is designed using the command-filtered backstepping method, ensuring the asymptotic convergence of the tracking errors. A prominent benefit of this strategy is that only bounded estimation needs to be implemented, thus weakening the bidirectional influence between the observer and the controller, and relaxing the accurate estimation demands often associated with existing AFTC methods. The effectiveness and suitability of the proposed AFTC strategy are demonstrated through a simulation example involving an underwater manipulator.