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\iteman{io-port 02046421}
\itemau{Duarte-Mermoud, Manuel A.; La Rosa, Patricio S.}
\itemti{Designing SISO observers with unknown input.}
\itemso{IMA J. Math. Control Inf. 20, No. 4, 387-391 (2003).}
\itemab
Linear, finite-dimensional, time-invariant, strictly proper single-input, single-output $n$-order control systems with constant coefficients are considered. Using algebraic methods and the theory of linear differential equations, an observer design method for systems with unknown input is proposed and discussed. It is proved that the observer design procedure is possible only if the plant is of relative degree one and its zeros are located in the open left half of the complex plane. Therefore, an observer can be designed if and only if the plant is of unity relative degree and the numerator of the transfer function is of Hurwitz type. The paper contains also remarks and comments on design methods for linear control systems. Finally, it should be stressed that similar problems have been discussed by other authors [{\it C. C. Tsui}, ``A new design approach to unknown input observers'', IEEE Trans. Autom. Control 41, 464--468 (1996; Zbl 1034.93509); {\it M. E. Valcher}, ``State observers for discrete-time linear systems with unknown inputs'', IEEE Trans. Autom. Control 44, 397--401 (1999; Zbl 0958.93018)].
\itemrv{Jerzy Klamka (Gliwice)}
\itemcc{}
\itemut{observability; observer design; minimum phase relative degree}
\itemli{doi:10.1093/imamci/20.4.387}
\end