Fixed-time disturbance observer-based chattering-free sliding mode attitude tracking control of aircraft with sensor noises

The challenging attitude tracking control problem of aircraft with external disturbance and sensor noises is investigated. A disturbance observer-based control approach is presented. In this approach, a fixed-time disturbance observer is preliminarily developed. The external disturbance is estimated with the estimation error governed to zero after a fixed-time regardless of any initial state. Moreover, with measurement noises explicitly considered, a discrete tracking differentiator extracting the real signals from the polluted measurement is introduced into that fixed-time observer to improve its application potential. Invoking the estimation information, a sliding mode attitude controller is then synthesized. The main feature of the proposed approach is that the closed-loop attitude tracking system is guaranteed to be exponentially stable. External disturbance rejection is achieved, while its upper bound is not required to implement that approach. In contrast to the conventional sliding mode control schemes, the proposed controller is chattering-free. Numerical simulation and experimental tests are finally carried out to verify the effectiveness of the proposed approach.