A nonminimal representation of reduced-order observers

Abstract A new nonminimal representation of reduced-order observers of order n − k in the time and in the frequency domain is introduced. This reduced-order observer is based on a full-order plant model where the order reduction to n − k results from an infinite gain feedback of k outputs. This new representation is crucial for establishing the links between time and frequency domain design methods incorporating reduced-order observers. The main result are the doubly coprime fractional representations of a transfer matrix related to an observer of order n − k .