Robust Stability of Interval Plants and Quantitative Feedback Theory

This paper addresses the problem of judging how well a fixed compensator robustly stabilizes an interval plant. Design techniques such as the Quantitative Feedback Theory (QFT) confront the issue of deriving compensators which satisfy performance and stability robustness specifications for plants with known uncertainty. However, these procedures do not guarantee that stability robustness exists over the entire range of uncertainty. This is due to the fact that in QFT one chooses a series of arbitrary plants, and designs the controller solely from these points. This work presents a method of determining if a controller robustly stabilizes a plant with numerator and denominator uncertainty, and shows how to apply this technique in synthesis with the QFT compensator design procedure.