Improving command tracking for QFT controllers

The two-degrees-of-freedom properties of controllers designed using QFT techniques are studied in this paper, giving an alternative proposal to change some aspects of the design in order to get improved command tracking and robustness of the design to changes in the controller. Thus, it is proposed to use a specific two-degrees-of-freedom structure, which through an adequate selection of the controller terms makes command tracking properties independent of the selection of the feedback controller. Then, the QFT technique can be used to design the feedback controller, without needing to redesign the prefilters if this feedback controller is re-designed. This technique is presented by way of an example using a process control problem.