Sliding-mode and back-stepping control for output tracking systems with unmatched uncertainties via a disturbance observer

In this paper, an alternative scheme to achieve output tracking for a class of uncertain systems which is designed using back-stepping control and sliding mode control (SMC) can provide exact tracking even in the presence of matched and unmatched disturbances. The newly proposed method is based on a nonlinear disturbance observer (NDOB) which can estimate the unmatched disturbance. Simulation verify the validity of the proposed approach.