High-order disturbance observer for nonlinear systems using sliding-mode technology

A new sliding-mode based extended disturbance observer (SMEDO) for a class of nonlinear system is derived in this paper. Since the extended observer for high order external disturbance has been well studied in past literatures, we focus on the model mismatch confusion in such observer design issue. The brief idea is to combine a traditional nonlinear extended disturbance observer with the sliding-mode technology. And by designing sliding mode surface carefully, the robustness against model mismatch of the proposed observer can be guaranteed. Moreover, the stability analysis and the parameter tuning principles of proposed observer are given. Finally the performance of traditional nonlinear disturbance observer (NDOB), extended disturbance observer (EDOB) and proposed SMEDOB is compared in cases of variety disturbances. Simulations show that the proposed observer achieves lower tracking error than NDOB and EDOB for time varying and model uncertainty disturbances.