The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
|
|
|
Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Automation and Systems Technology for public examination and debate in Auditorium TU2 at Helsinki University of Technology (Espoo, Finland) on the 10th of November, 2006, at 12 noon.
Dissertation in PDF format (ISBN 951-22-8433-2) [2338 KB]
Dissertation is also available in print (ISBN 951-22-8432-4)
This study is concerned with the analysis and design of industrial robust model predictive control (MPC) for paper machine cross-directional (CD) processes, taking into account inherent uncertainty characteristics of the process. Paper machine CD control systems belong to the set of large scale, complex multivariable control systems, which are well known as ill-conditioned processes.
In this thesis, the concepts of structured model uncertainty and linear time-varying (LTV) systems with polytopic multi-models are exploited for describing uncertainty characteristics of the CD process. Complexity of the CD response system in terms of controller structure and inherent characteristics of the response model are evaluated based on the relative gain array (RGA) and the decentralized integral controllability (DIC). Results of the evaluation are utilized to select accurate CD response models for analysis of the primal robust MPC CD control strategy. An infinite horizon MPC problem with input and output constraints and polytopic system uncertainty is formulated as a convex optimization problem involving linear matrix inequalities (LMIs). The resulting time-varying state-feedback control law minimizes, at each time-step, an upper bound on the robust performance objective, subject to constraints.
Because the computation time of the primal robust MPC CD algorithm is too high for real time applications, a computationally efficient approach is adopted. The developed fast robust constrained state feedback MPC CD algorithm is based on a series of explicit control laws corresponding to a series of controlled invariant ellipsoids, calculated off-line, one within another in the state space. The concept of asymptotically stable invariant ellipsoid enables to provide robust stability without the demand of finding an optimum of the system at each sampling time. The advantage of this algorithm is that it gives off-line a set of stabilizing state feedback laws. Because no optimization is required, except a simple bisection search, the on-line computation time of the robust MPC CD algorithm is significantly reduced. The fast robust MPC CD algorithm is applied to the selected industrial large scale CD processes, and its efficiency is verified with numerous simulations and comparisons with the primal robust MPC CD algorithm. Simulations indicate that the loss of performance is minor and the benefit in on-line computation is over four orders of magnitude.
Keywords: paper machine, cross-directional (CD) control, robust model predictive control, linear matrix inequalities
This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.
© 2006 Helsinki University of Technology