Necessary and sufficient conditions for a nonminimum phase plant to have a recoverable target loop - A stable compensator design for LTR

-In connection with loop transfer recovery of nonminimum phase systems, the purpose of this paper is two-fold: (1) to study the set of recoverable target loops and to establish necessary or/and sufficient conditions for a given plant to have at least one recoverable target loop, and (2) to show that the compensator structure developed earlier in Chen, Saberi and Sannuti [(1991) Automatica, 27, 257-280] for minimum phase systems, can also recover any recoverable target loop for nonminimum phase systems as well while retaining all its advantages over conventional observer based controllers.