Fault and unknown input reconstruction in VTOL aircraft system using sliding mode observer

This article presents a new approach to estimation of unknown inputs and faults in a class of nonlinear systems. The approach is based on the design of a cascade connection of two sliding mode observers. The first is used for estimation of state and unknown inputs and the second is used for fault detection. An important feature of the proposed approach is that the state trajectories do not leave the sliding manifold even in presence of unknown disturbances and faults. This allows for faults and disturbances to be reconstructed based on information retrieved from the equivalent output injection signal. The proposed approach is used to reconstruct unknown disturbances and faults in nonlinear model of Vertical Take-Off and Landing (VTOL) aircraft system.