A design method for unknown input observer for non-minimum phase systems

In this paper, we examine a design method for unknown input observers for non-minimum phase systems. The unknown input observer has been used to estimate the state variable of the plant in the presence of unknown input. In addition the unknown input observer is applied to the systems with disturbance inputs or unknown varying parameters. Initially, the unknown input observer is examined by Kudva, Viswanadham and Ramakrishna. According to past studies, the unknown input observer for the plant (A,B,C,0) can be designed if and only if following 2 expressions hold true: (1) rankCB= rankB and (2) the plant (A,B,C,0) has no invariant zero in the closed right half plane. Many papers have been considered to design unknown input observers, even if above mentioned 2 expressions are not satisfied. In this paper, we propose a new design method of unknown input observers for non-minimum phase plants.