Integrated Strategy for Fault-Tolerant Flight Control System Design with Rate Saturating Actuators

In this paper, an integrated control scheme using fault diagnosis and reconfigurable control is investigated for the longitudinal motion of a commercial aircraft with actuator faults and rate limiting. Actuator faults and rate saturation are both important factors adversely affecting the stability and performance of flight control systems. The fault diagnosis process is designed based upon a modified multiple-model based unknown input observer and the reconfigurable control is constructed using adaptive control. Both additive and multiplicative faults are considered in the integrated design to deal with the three types of actuator faults: locked in place, loss of effectiveness, and bias. Moreover, the software rate limiters are implemented in the basic and fault-tolerant controller to improve the performance of control systems operating in the presence of actuator rate saturation. Proofs for the stability of the two modified controllers are proposed. Finally, a numerical example of the integrated fault-tolerant controller for a commercial aircraft is demonstrated. The stability and performance improvements can be accrued with the presented fault-tolerant control scheme.