Abstract
In the design of control systems it is often necessary to construct estimates of state-variables which are not available by direct measurement. If the system is linear, its state vector can be approximately reconstructed by building an observer which is itself a linear system driven by the available outputs and inputs of a plant.
In this paper it is shown that the design of an observer for an n-th order plant with p available outputs can be reduced to the design of p separate observers for single-output subsystems under some conditions. This result is based on a canonical form developed in Lemmal and the theorem obtained by J.J. Bongiorno and D.C. Youla. The use of observers for indirect control systems is discussed. It is olse shown that if the nonlinear element φ(σ) contained in the indirect control system satisfies the Lipschitz condition, then the observer can be used without loss of absolute stability.
