Output feedback sliding mode control in the presence of unknown disturbances

This paper examines the use of a sliding mode controller and an equivalent output injection sliding mode observer to control a nonlinear plant in the presence of an unknown disturbance. With only the measured output available for feedback, the observer reconstructs the full state in finite time and provides an estimate of the unknown disturbance. The controller ensures asymptotic reference trajectory tracking, or alternatively asymptotic convergence to the origin for the plant. Asymptotic stability of the closed loop system is proved under a set of nonrestrictive assumptions on the plant and the disturbance. These results are verified numerically through simulation.