Global tracking sliding mode control for uncertain nonlinear systems based on variable high gain observer

An output-feedback sliding mode controller is proposed for a class of single-input-single-output (SISO) uncertain nonlinear systems. The sliding surface is generated using the state of a high gain observer (HGO) while the control signal amplitude is generated from a norm observer free of peaking. The proposed scheme achieves global tracking with respect to a small residual set by means of a time varying observer gain (HGO) synthesized from measurable signals.