Trade-Offs in LTR-Based Feedback Design

A number of fundamental trade-offs in LTR-based feedback design are investigated. First the trade-off between the recovery level and the controller gain is quantified based on a fundamental recovery matrix and the frequency-domain properties of LTR-controllers. The trade-off is illustrated graphically via socalled recovery diagrams. A major consequence of this trade-off is that the target and recovery design cannot always be performed independently as previously assumed. Further the performance limitation imposed by RHP-reros are analyzed and a new error function is derived, which expresses this basic recovery limitation. This result can be incorporated in the recovery diagram. The recovery diagram captures the fundamental trade-offs involved in LTR-designs. In the paper a technique for fast computation of the diagram is derived by invoking new results on weighted infinity-norm calculations. The results are illustrated by an example.