Observer design in receding-horizon predictive control

This paper considers the robust implementation of a class of predictive control methods represented by GPC. Such controllers are in two-degrees-of-freedom form where there are dynamics in both the forward and the feedback paths. The ‘tuning knobs’ of predictive controllers determine the characteristic polynomial PC , and for a given PC the observer or prefiltering polynomial T in the feedback path determines the robustness of the closed loop. Previous intuitive guidelines on the selection of T are shown to be limited in their effectiveness. For an open-loop stable plant, a simple criterion is provided which allows the feedback dynamics to be specified so as to enhance robustness. The T polynomial is then chosen to satisfy this criterion. In addition, robust design through T is related to an H∞ -optimal control scheme using the so-called Q-parametrization. Despite its simplicity, the new proposed approach to the design of T is seen to result in robustness comparable with that obtained from the H∞ method.