A terminal state contractive nonlinear MPC with output zones and input targets

Abstract

Terminal equality and inequality constraints along with terminal costs are known to be ingredients that grant stability in many Nonlinear Model Predictive Control (NMPC) approaches. Despite the availability of different methods for computing a suitable terminal set and cost, they usually rely on the linearization of the system and the design of terminal stabilizing control laws. Thus, approaches based on contracting constraints represent an alternative to circumvent the calculation of terminal sets and penalties. The present work proposes an NMPC based on a terminal state contracting constraint. This approach also avoids the need of large prediction horizon, helping to alleviate the computational burden usually associated with NMPC. Another contribution of this proposal is a formulation in terms of output zone control and input targets, designed for the common situation in the process industry where the number of degrees of freedom is not enough to independently track the setpoint of all controlled variables. A simulated case study is presented with the application of the proposed controller to the well-known quadruple-tank process.