Switched Adaptive Sliding Mode Disturbance Observer for Nonlinear Fault-Tolerant Flight Control

Typical fault scenarios such as actuator stuck, wingtip damage, and sudden center of gravity change usually bring great challenge to fault-tolerant flight control laws. In this paper, adaptive sliding mode disturbance observer (SMDO) is studied under the background of designing a fault-tolerant flight controller. This paper proposes a switched adaptive SMDO for observation of system uncertainties considering fault accommodation. It consists of two adaptive SMDOs: baseline gain-adaptation SMDO and fault-oriented gain-adaptation SMDO. The former is designed for observing slow-changing uncertainties, and can guarantee that the observer gains are small when disturbances are small; the latter aims at achieving fast observing and accommodating of sudden and large faults. Thereafter, a switching logic is developed for the switch between these two adaptive SMDO modes to ensure that the fast gain-adaptation SMDO only works in the case that the uncertainties are large and fast-changing. Finally, the switched adaptive SMDO is integrated with an incremental terminal sliding mode controller, and are validated using simulation experiments based on the nonlinear F-16 model.