A multiple model gap-metric based approach to nonlinear quantitative feedback theory

We propose a simple quantitative feedback theory (QFT) technique for designing robust nonlinear feedback systems. In the proposed approach, multiple linear models are obtained by linearization of the nonlinear plant model at each operating condition, and local QFT controller/filter obtained using standard QFT techniques. Then, global controller/filter effective over the entire operating range are constructed from the local ones by soft switching based on the gap-metric concept. The proposed approach is much simpler and easier than the existing NLQFT approaches where the so-called linear time invariant equivalent (LTIE) plants need to be constructed from the original nonlinear plant set. The proposed method is illustrated via a challenging nonlinear continuous stirred tank reactor (CSTR) example.