Global tracking output-feedback sliding mode control design via norm estimators and variable high gain observer

An output-feedback sliding mode controller is proposed for a widely general class of single-input-single-output (SISO) time-varying uncertain nonlinear systems. Such a class encompasses plants in the state-of-the-art of global output-feedback control framework, possibly including strong polynomial nonlinearities in the unmeasured states. The sliding surface is generated by using the state of a high gain observer (HGO) while the control signal amplitude is obtained from norm estimators (or observers) free of peaking. The proposed scheme achieves global tracking by means of a time-varying HGO gain synthesized from measurable signals.