ON ROBUST STABILITY AND PERFORMANCE WITH TIME-VARYING CONTROL

The analysis of time-varying control for robust stabilization and perf ormance improvement is considered. This problem has been investigated in recent years from the point of view of assessing the capabilities o f time-varying control to stabilize plants with structured norm bounde n perturbations. In this paper, it is shown that time-varying compensa tion provides no improvement over time-invariant compensation for the stability and performance robustness of discrete-time systems with str uctured, casual, time-varying, and norm-bounded perturbations, where t he norm on the perturbations is the l(2)-induced norm. The results of this paper help in completing the picture for the ease of time-varying perturbations.