Disturbance decoupled observer design for descriptor systems

In this paper we study the observer design problem for descriptor systems with partly unknown inputs. We give necessary and sufficient conditions for the existence of a solution to the disturbance decoupled estimation problem with or without stable error spectrum requiring at the same time that the resulting combined system is regular and of index at most one. All results are proved based on a condensed form that can be computed using orthogonal matrix transformations, i.e., transformations that can be implemented in a numerically stable way. (C) 1999 Elsevier Science B.V. All rights reserved.