Error feedback sliding mode regulator

In this article, the problem of nonlinear sliding mode (SM) regulation is addressed for nonlinear systems in general and regular form that are subject to unmodelled disturbances. In particular, the error feedback SM regulator problem is defined, taking the concepts related to the zero output tracking submanifold as a starting point. Applying the internal model concept to the time-invariant SM equation, the solvability conditions to the problem are derived. A nonlinear extended observer is proposed, and using the observer states, a sliding manifold is formulated. A SM control algorithm is proposed to ensure the designed manifold to be attractive, achieving robustness with respect to allowed uncertainties resulting in the tracking error to be uniformly ultimately bounded. The effectiveness of the proposed method is demonstrated by the application of the regulator to a third order nonlinear non-minimum phase system.