Optimality of two-degree of freedom controllers in H 2 - and H ∞ -norm space, their robustness and minimal sensitivity

Abstract A special generic structure of two-degree of freedom controllers and a connected closed-loop system parametrization with optimal regulator design methods are discussed. The optimality is expressed by two simple serial compensators based on the concept of the nearest inverse and can be performed in H 2 - and H ∞ -norm space. It is shown how these optimal filters are computed. The optimal sensitivity properties of this scheme are also analysed.