LQG/LTR versus Smith Predictor control for discrete-time systems with delay

A simple LQG control with no control cost is considered for discrete-time systems with input delay. In such case the loop transfer recovery (LTR) effect can be obtained especially for minimum-phase systems. The robustness of this control is analyzed and compared with state prediction control whose robustness stability is formulated via LMI. The robustness with respect to uncertain time-delay is considered including the control systems with Smith predictor-based controllers. Computer simulations of a second-order stable, unstable and nonminimum-phase systems with time-delay are given to illustrate the robustness and performance of the considered controllers.