Robust fault tolerant control of under-actuated VTOL aircraft

This paper presents a nonlinear robust fault tolerant control scheme to force the faulty system to asymptotically track a given desired trajectory via cascade observers. Focusing on the external disturbance and actuator faults of the nonlinear non-minimum phase vertical take-off and landing aircraft, two decoupled reduced order observers are designed to estimate the unknown disturbance and fault. By using the coordinate transformation and feedback linearization, two decoupled tracking subsystem are decomposed from the overall system, then two robust optimal feedback controllers are designed respectively to stabilize the two subsystems. And on this basis, the robust fault tolerant controller is proposed by using the fault estimation, which can make the overall close-loop system asymptotically stable. The effectiveness of the presented method is demonstrated by simulation results.