Trade-offs between performance specifications, uncertainty and admissible models

The fundamental trade-off between performance specifications, the set of uncertainty over which this performance must be achieved and the set of admissible controller-design models is examined. This trade-off is inherent to feedback control, and may be alleviated by allowing the controller-design model to vary. Admissible controller-design models may be traded off in return for improved performance or robustness. A simple example illustrates that a qualitative trade-off between performance and stability robustness predicted by set-theoretic arguments may be quantified by the Bode sensitivity integral