Semi-global robust output tracking for non-linear uncertain systems in strict-feedback form

The problem of output tracking control is addressed for a class of non-linear strict-feedback form systems in the presence of non-linear uncertainties, external disturbances, unmodelled dynamics and unknown time-varying virtual control coefficients. A new design approach of robust controller is proposed by combining standard backstepping with signal compensation method. It is shown that semi-global robust stability and semi-global robust practical tracking property of the closed-loop system can be ensured and the tracking error can be made as small as desired. The designed controller is linear and time invariant, and so can be implemented easily.