Super twisting sliding mode control for a flexible air-breathing hypersonic vehicle based on disturbance observer

A robust finite time sliding mode control strategy is proposed in this paper for a flexible air-breathing hypersonic vehicle （FAHV） model with aerodynamic parameter uncertainty. The strong coupling among the aerodynamics, the propulsion system and the flexibility effects makes the problera more challenging. Firstly, to reduce the complexity of the controller design, the FAHV model is transformed into three subsystems （velocity subsystem, altitude and flight path angle subsystem, attack of angle and pitch rate subsystem）. Secondly, based on super-twisting algorithm, a novel finite time disturbance observer and an improved sliding mode controller are designed to ensure the finite time stability of each subsystem. The proposed disturbance observer can estimate the uncertainty and the derivative of virtual control in finite time. Finally, simulation results are presented to show the precision and rapidness in tracking the reference trajectory and validate the effectiveness of the designed controller.