Robustness results of LQR-based systems with structured uncertainty

It is well known that linear quadratic regulator can have excellent stability robustness. However, some authors have recommended caution, by producing examples where the linear quadratic regulator may suffer from poor robustness. Specifically, small changes in the parameters of the system can cause fast unstable closed-loop poles. However, by comparing the bounds on allowable perturbations it is shown that the stability robustness properties are preserved in a general sense. The high parameter sensitivity gives a warning to those designers who favour high gain controllers.