Uncertainty and disturbance estimator-based control for uncertain LTI-SISO systems with state delays

In this paper, a robust control strategy based on the uncertainty and disturbance estimator (UDE) is proposed for uncertain Linear Time Invariant-Single Input Single Output (LTI-SISO) systems with state delays. The knowledge of the bounds of uncertainties and disturbances is not needed during the design process although it is required for the stability analysis. Both the cases with known and unknown delays are considered. In the case of unknown delays, the terms involving the delays are treated as additional disturbances to the system. The robust stability of the closed-loop system is analyzed in detail, and a stability condition is proposed. Simulations are given to demonstrate the excellent tracking and disturbance rejection capabilities of the UDE-based control strategy.