Disturbance-observer-based fixed-time second-order sliding mode control of an air-breathing hypersonic vehicle with actuator faults

This paper presents a disturbance-observer-based fixed-time second-order sliding mode approach for fault-tolerant control of an air-breathing hypersonic vehicle, where both partial loss of effectiveness faults and bias faults in actuators are considered. Firstly, a fixed-time second-order sliding mode control law is designed to guarantee the reaching time, independent of initial conditions. Then, by using a robust uniformly convergent differentiator technique, a fixed-time convergent disturbance observer is established to quickly estimate the lumped uncertainty, which consists of actuator faults and system uncertainties. Therefore, any information of actuator faults is not required by this design. Finally, simulation results of a generic air-breathing hypersonic vehicle are presented to demonstrate the effectiveness of the proposed controller.