Active Fault-Tolerant Control for Uncertain Nonlinear Systems: A Decoupling Approach

When disturbances or nonlinearities couple the observer and the controller, implementing active fault-tolerant control (AFTC) via the separation principle (SP) becomes challenging. This article proposes a novel AFTC framework with the goal of decoupling design for a class of uncertain nonlinear systems, thereby recovering the use of SP in AFTC design. An observer is developed for fault diagnosis and state estimation based on the system outputs, and the boundedness of the estimation errors is guaranteed. Next, an active fault-tolerant controller integrated with an adaptive mechanism is constructed for fault accommodation using the obtained fault information. To mitigate bidirectional influences between the observer and controller designs, all estimation errors and disturbances are treated as new disturbances in the AFTC system (AFTCS), and adaptive updating terms are designed to compensate for these disturbances. The stability of the AFTCS is analyzed, ensuring that all signals in the closed-loop system remain bounded and that the output tracking error converges to a neighborhood around zero. The effectiveness of the proposed approach is illustrated through a numerical simulation example.