| From a deterministic perspective, the control of uncertain systems is based on two fundamental pieces of information: the origin and the size of the uncertainties. The first information provides an understanding of the structure of the uncertainty whereas the second describes the uncertainty growth rate. If both pieces of information are provided, the robust control problem is referred to as a structured uncertainty control scheme. By contrast, if only a bounding function on the uncertainty growth rate is known, the robust control problem is referred to as an uncertainty growth constrained scheme.;In this thesis, the problem of reducing and eliminating the nonmatching uncertainty and the normalized uncertainty envelope by state transformation is addressed. A robust controller design approach, based on the dependency of the normalized uncertainty envelope to the coordinate space and the uncertainty decomposition, is proposed to accommodate nonmatching uncertainty with large growth rate. The new threshold envelope on the uncertainty growth rate substantially improves the conservative results previously reported in the literature. For a certain class of nonlinear systems, the proposed design method provides a robust controller that guarantees stability in the presence of nonmatching uncertainty of arbitrarily large growth rate.;Some particular control problems encountered in the implementation of the robust controllers in the chemical industry are also investigated. Two robust corrections are proposed to control uncertain nonminimum phase systems. The first stabilizing correction minimizes the nonlinear behaviour that must be introduced in the input-output dynamics whereas the second correction places the eigenvalues of the nominal zero dynamics to a specific location.;Finally, the robust control problem of saturated systems is investigated. A robust controller based on the family of Leand/Artan algorithm is designed. The robust control parameter is selected according to the robust control feedback gain proposed by Barmish et al. (1984). Although the stability results are local and restricted to matched uncertain systems, the method based on the asymptotic behaviour of the logarithmic transformation constitutes a new and promising approach for the design of saturated controllers. |
