LOOP TRANSFER RECOVERY DESIGNS WITH AN UNKNOWN INPUT REDUCED-ORDER OBSERVER-BASED CONTROLLER

This paper presents a new approach to the loop transfer recovery (LTR) in linear multivariable control systems, based on the unknown input r educed-order observer-based controller. Two parametrization methods fo r all unknown input observers are presented; the first one is based on the matrix fraction description (MFD) and the second one is developed in RH(infinity). The LTR for both minimum and nonminimum phase system s are considered. An exact recovery, based on the unknown input observ er, is provided for minimum phase systems. For non-minimum phase syste ms, an approximate recovery is obtained by minimizing the H-infinity n orm of the recovery matrix.