Output-feedback sliding mode control for global tracking of uncertain nonlinear time-delay systems

An output-feedback sliding mode controller is proposed for multivariable nonlinear systems with time-varying state delays and unmatched uncertainties. The control strategy is based on unit vector control and a novel norm observer for the unmeasured state of time-delay systems. This approach guarantees global stability of the closed-loop system, exponential convergence of the output error and exact tracking of the reference signal. In addition, less restrictive conditions on the high frequency gain matrix are obtained.