Robust Controller Design using Quantitative Feedback Theory (QFT)

Abstract

Most of the practical systems are characterized by high uncertainty which makes it difficult to maintain good stability margins and performance properties for closed loop system. In case of conventional control, if plant parameter changes we cannot assure about the system performance hence it is necessary to design robust control for uncertain plant. Among the various strategies proposed to tackle this problem, Quantitative Feedback Theory (QFT) has proved its superiority especially in the face of significant parametric uncertainty. The feature of QFT is that it can take care of large parametric uncertainty along with phase information. For the purpose of QFT, the feedback system is normally described by the two-degrees-of freedom structure. A chemical system common to many chemical processing plants, known as a continuous stirred tank reactor (CSTR).For an isothermal CSTR the product concentration can be controlled by manipulating the feed flow rate,which changes the residence time.