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 (LTR) of nonminimum phase systems, the authors study the set of recoverable target loops and establish necessary or/and sufficient conditions for a given plant to have at least one recoverable target loop. The authors also show that the compensator structure previously developed by them (Automatica, vol.27, pp.257-280, 1991) for minimum phase systems can recover any recoverable target loop for nonminimum phase systems as well, while retaining all its advantages over conventional observed-based controllers