Improvements on the computation of boundaries in QFT

Quantitative feedback theory (QFT) is an engineering design technique of uncertain feedback systems that uses frequency domain specifications. A key step in QFT is the mapping of these specifications into regions of the Nichols plane, whose borders are usually referred to as boundaries. Boundaries computation is a key design step, thus a precise and efficient computation is critical for both obtaining low bandwidth feedback compensators and simplification of the design process. In this work, the problem of boundaries computation is analysed, introducing a new algorithm based on the computation of level curves of a three‐dimensional surface. Besides magnitude boundaries, associated with some specification over the magnitude of a closed‐loop transfer function, phase boundaries are also considered. In addition, comparison with previous published algorithms is done in terms of precision and computational efficiency. Copyright © 2006 John Wiley & Sons, Ltd.