Robust controller and pre-filter design using QFT and interval constraint techniques

Robust control system design for uncertain systems (aka “plants”) is of great practical interest, and their automation is a key concern in the control community [1]. In the last few decades, several robust control methodologies in time as well as frequency domains have been proposed (cf. [1]). Quantitative Feedback Theory (QFT) [2] is a one such frequency-domain controller design technique based on the use of Nichols chart [3] in order to achieve a desired robust design over a specified region of uncertainty in the plant parameters.