Sliding Mode Control of Uncertain Nonlinear Systems with Arbitrary Relative Degree and Unknown Control Direction

This paper considers the model reference tracking control for a class of uncertain nonlinear systems, based on sliding mode and output-feedback. No particular growth condition is imposed on the nonlinearity. Moreover, the design does not assume the prior knowledge of the control direction. For plants of arbitrary relative degree, global or semi-global asymptotic stability with respect to a compact set is guaranteed. Ultimate finite-time or exponential convergence of the tracking error to zero is achieved by using a hybrid lead filter based on 2-sliding mode exact differentiators. A monitoring function is used to determine the unknown control direction