A Decentralized Fault-Tolerant Control System for Accommodation of Failures in Higher-Order Flight Control Actuators

In this paper, an effective integrated failure detection and identification (FDI) and fault-tolerant control (FTC) technique is developed for a class of nonlinear systems actuated by actuators that may undergo several different types of failures. Assuming that the actuator dynamics are fast, a baseline controller is designed and, using the singular perturbation arguments, shown to achieve the control objective. Typical failures in flight control actuators are considered next, and online FDI algorithms are derived for second-order actuator dynamics with non-measurable actuator rates, and third-order actuator dynamics when only output of the actuator is measurable. The FDI subsystem is decentralized in that an observer is run at each of the actuators, and the parameter estimates are adjusted using only the local information. The major issue of how to use this information to reconfigure the control law and assure the stability of the resulting closed-loop control system is addressed. An adaptive fault-tolerant controller that uses the parameter estimates from the FDI subsystem at every instant is designed next. It is demonstrated that all the signals in the system are bounded and that the tracking error converges to zero asymptotically despite multiple simultaneous actuator failures even in the case of second or third order actuator dynamics. The properties of the proposed FDI-FTC algorithms are evaluated through piloted simulations of the F/A-18 aircraft.