Nonminimum-phase output tracking in causal systems using higher order sliding modes

Asymptotic output tracking in a class of causal nonminimum-phase uncertain nonlinear systems is addressed via higher order sliding modes. Local asymptotic stability of the output tracking-error dynamics is provided. An output reference profile and an external disturbance forcing the internal dynamics are defined by an unknown linear exosystem. Its characteristic polynomial (which is used in the output-tracking control algorithm) is identified online by using a higher order sliding mode parameter observer. A numerical example illustrates efficiency of the developed higher order sliding mode (HOSM) control algorithm.