Unknown input observer — A structural approach

This paper is concerned with Unknown Input Observers (UIO) design analysis. First the existence conditions for this kind of observer are expressed in terms of finite and infinite zeros of the system. Then structured linear systems are considered for which the entries of the system matrices are either fixed zeros or free parameters. To such systems, one can associate a directed graph to study generic properties. The existence conditions of UIO for structured systems are then expressed in terms of particular input-output paths in the associated graph.