A novel output-feedback sliding mode control (SMC) strategy is proposed for a class of single-input-singleoutput (SISO) uncertain time-varying nonlinear systems for which a norm state estimator can be implemented. Such a class encompasses minimum-phase systems with nonlinearities afinely norm bounded by unmeasured states with growth rate depending nonlinearly on the measured system output and on the internal states related with the zero-dynamics. The sliding surface is generated by using the state of a high gain observer (HGO) while a peaking free control amplitude is obtained via norm observer. In contrast to the existing semi-global SMC solutions available in the literature for the class of plants considered here, the proposed scheme is free of peaking and achieves global tracking with respect to a small residual set. The key idea is to design a time-varying HGO gain implementable only from measurable signals.
uncertain nonlinear systems; sliding mode control; output-feedback; global tracking; high gain and norm observer
