Discrete-time compensators with loop transfer recovery

Loop transfer recovery (LTR) has gained some prominence over the last years. In this paper, the authors briefly overview the main design features of the LQG/LTR controller both at the input and at the output of the plant, using the delta operator formulation developed in Middleton and Goodwin (1990). Two discrete-time compensators with LTR capability are then derived following the LTR design approach proposed in Chen, Saberi, and Sannuti (1991) for the continuous-time case. These compensators are shown to outperform their underlying LQG/LTR controllers from the perspective of recovery error. Of particular importance, they share the same degree of recovery as the continuous time compensators of the above papers when the sampling period goes to zero