Robust MPC of constrained nonlinear systems based on

A robust MPC for constrained discrete-time nonlinear systems with additive uncertainties is presented. The proposed controller is based on the concept of the reachable sets, that is, the sets that contain the predicted evolution of the uncertain system for all possible uncertainties. If processes are nonlinear these sets are very difficult to compute. A conservative approximation based on interval arithmetic is proposed for the on-line computation of these sets. This technique provides good results with a computational effort only slightly greater than the one corresponding to the nominal prediction. These sets are incorporated in the MPC formulation in order to achieve robust stability. By choosing a robust positively invariant set as a terminal constraint, a robustly stabilizing controller is obtained. Sta-bility is guaranteed in case of suboptimality of the computed solution. In order to illustrate the proposed controller, it is applied to a Continuous Stirred Tank Reactor (CSTR) with an exothermic reaction. 1