Sliding Mode Output Tracking of Uncertain Nonlinear Systems with Unknown Control Direction

An output feedback sliding mode controller was recently introduced for linear uncertain systems with unknown control direction based on monitoring functions. Nonlinear systems were also considered but restricted to output dependent nonlinearities. Global or semi-global exact output tracking was obtained. Here, generalization is achieved to include nonlinearities depending on unmeasured states and to deal with multivariable systems. Furthermore, a new monitoring function to cope with control direction uncertainty is proposed which can lead to significantly improved tracking transient behavior.