The control system design for ASV via discrete sliding mode control based on disturbance observer

Several challenge imposed on the aerospace vehicle (ASV) make the guidance and control task much more complicated than that of conventional aircraft due to its large attitude maneuvers and a large amount of uncertainty in ascent and descent modes. In order to provide accurate attitude tracking, the controller must be robust to external unknown disturbances, un-modeled dynamics and plant uncertainties and also be able to perform well under a wide range of operating conditions. Sliding mode controller is an attractive robust control algorithm for the ASV flight controller designs because of its inherent insensitivity and robustness to plant uncertainties and external disturbances. Such a robust controller would reduce risk and drastically decrease the amount of time spent in pre-flight analysis, thus reducing cost. The guidance commands Euler roll, pitch and yaw angles, and it commands the aerodynamic angles of bank, attack and sideslip in flight of ascent, cruise and descent. We present a relatively new sliding mode controller design technique driven by a disturbance observer, which can reduce the chatter of variable structure control, since it stabilizes a sliding quantity at zero in presence of matched disturbance and uncertainties. The controller employs an attitude loop, which are controlled via disturbance observer by perturbation principle. The salient feature is used to estimate external disturbances and model uncertainties, which improves robustness of the discrete sliding mode controller. We also address the stability and robustness of a discrete sliding mode control method based on disturbance observer. The novelty of the discrete sliding mode control based on disturbance observer is that both the sliding surface and the disturbance observer technique. The fine disturbance attenuation ability and robustness against the variation are illustrated through extensive numerical simulations for ASV stabilization system driven by a sliding mode observer design technique