On robust steady-state performance of feedback control systems

The steady-state performance of lumped LTI (linear time-invariant) feedback systems in the face of plant uncertainty is considered. The plant uncertainty considered here is the multiplicative perturbation of the output port. The necessary and sufficient conditions for various robust steady-state performances are obtained. Internal-model-principle-like results on the structure of controllers achieving various robust steady-state performances are derived from the necessary and sufficient conditions. The conditions are transformed into the measure of μ, thus enabling the synthesis of controllers achieving robust steady-state performance in the framework of μ synthesis and the generalized H^∞ control theory