Robust model predictive control of integrating and unstable time delay processes.

Author(s)

Marcio André Fernandes Martins

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2014-09-05

Examining board members

Darci Odloak; Claudio Garcia; Oscar Alberto Zanabria Sotomayor; Marcelo Embiruçu de Souza; Antônio Carlos Zanin

• Advisor: Darci Odloak

Abstract

The design of stable model predictive control (MPC) strategies that explicitly incorporate the model uncertainty into the control formulation still remains an open issue, although a rich theory has been developed to the synthesis of robustly stabilizing MPC schemes. In fact, the existing solutions to the robust MPC problem seem far from an acceptable stage of practical imple mentations, chiey when the process system is composed of integrating and unstable poles, as well as time delays between its input and output variables. Within this perspective, the ultimate goal of this thesis is to develop a new framework for robust MPC synthesis which guarantees closed-loop stability of integrating and unstable time delay processes. On this subject, three different robust MPC strategies are developed. The two rst concerns on integrating time delay processes; the former is based on a two-step control formulation, whereas the latter is posed as a one-step control optimization problem and state-space model description is more general than that adopted in the former formulation. The third proposed strategy focuses on one-step control formulation-based unstable time delay processes. Aiming at practical implementation purposes, the controllers proposed herein comprise the following aspects: (i) the offset free control laws are obtained without the need to include an additional steady-state calculation op timization layer due to the enclosure of proper state-space models in the incremental form of the inputs, which are derived of analytical expressions of step response of the process system; (ii) the uncertainty of all model parameters, e.g. gains, time constants, time delays and so on, is considered in the problem formulation; (iii) the proofs of robust Lyapunov stability are easily carried out of an intuitive way by imposing terminal equality constraints and cost-contracting constraints; (iv) the suitable inclusion of slack variables, which does not commit the stabil ity properties of the controllers, ensure that the proposed optimization problems are always feasible; (v) stable integration with real-time optimization layer, seeing as the controllers are designed to work in the optimum target tracking scheme where they should drive the process to the optimum operating point, while maintaining the remaining inputs and outputs inside pre dened zones instead of xed set-points. Simulation examples typical of the process industry are exploited to illustrate the helpfulness of the proposed control methods and demonstrate that they can be implemented in real applications. (AU)

• FAPESP's process: 11/22313-5 - Development of a robust stable MPC for integrating systems with time delay
• Grantee: Marcio Andre Fernandes Martins
• Support Opportunities: Scholarships in Brazil - Doctorate