One-layer gradient-based MPC + RTO strategy for unstable processes: a case study of a CSTR system

Abstract

This paper proposes a single layer MPC + RTO strategy with guaranteed nominal stability, suitable for systems with stable and unstable modes. The control law applies an approximation of the gradient of an economic function, which drives the closed-loop system towards its desired economic performance, using a quadratic programming based optimization. Included in the optimization problem is a set of slack variables in order to provide a feasible solution at any time step. A reactor with unstable behavior is used to evaluate the effectiveness of the proposed controller and demonstrates its recursive feasibility and the convergence of the closed-loop system towards the desired economic performance. Two case studies are assessed: the first examines the nominal characteristics of the proposed strategy, while the second assesses the robustness of the proposed strategy by controlling the nonlinear model of the plant.