Robust fault tolerant control allocation for a modern over‐actuated commercial aircraft

Abstract

This paper presents a novel form of control allocation, designed within a sliding mode framework, for the fault tolerant control of over-actuated systems. The control allocation is designed in such a way as to allow a subset of the actuators to remain inactive under nominal fault-free conditions. In the event that the active set of actuators becomes unable to provide the desired performance, an adaption process takes place which allows the inactive actuators to compensate. A computationally light gradient descent algorithm is proposed to govern the adaption which guarantees that, if possible, actuator saturation is avoided and system performance is maintained - even in the event of severe actuator faults and failures. Rigorous conditions are derived, in terms of the faults/failures, uncertainties in fault reconstruction information and the adaptive process, which ensures sliding occurs in a finite time and that the resulting motion is stable. To demonstrate the effectiveness of the control scheme, a highfidelity blended wing body aircraft model is also proposed in this paper; this particular configuration of aircraft is nominally unstable, with poor control authority and a large amount of redundancy - making it a suitable candidate for testing reconfigurable fault tolerant control laws in the presence of input constraints.