ISA Transactions abstracts on ControlGlobal.com

© 2005 ISA—The Instrumentation, Systems, and Automation Society.

---

Adaptive control of uncertain continuously stirred tank reactors with unknown actuator nonlinearities

By T. Zhang, M. Guay
Department of Chemical Engineering, Queen’s University, Kingston, Ontario, Canada K7L 3N6

Abstract
Adaptive nonlinear control is investigated for continuously stirred tank reactor (CSTR) systems using neural networks. The CSTR plant under study belongs to a class of nonaffine nonlinear systems, and contains an unknown parameter that enters the model nonlinearly. Using adaptive backstepping and neural network NN approximation techniques, an alternative adaptive NN controller is developed that achieves asymptotic output tracking control. A novel integral-type Lyapunov function, which includes both system states and control input as its arguments, is constructed to solve the difficulty associated with the nonaffine control problem. Numerical simulation is performed to show the feasibility of the proposed approach for chemical process control.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.

---

Continuous analysis of move suppressed and shifted DMC

By G. C. Kember, R. Dubay, and S. E. Mansour
Department of Engineering Mathematics, Dalhousie University, P.O. Box 1000, Halifax, NS, Canada, B3J 2X4; Department of Mechanical Engineering, University of New Brunswick, Fredericton, NB, Canada, E3B 5A3

Abstract
‘‘Shifted DMC’’ (shifted dynamic matrix control) has been empirically shown to have significant improved closed-loop control characteristics over ‘‘move-suppressed DMC’’ where, in the latter, diagonal terms of the dynamic matrix DMC prediction model are augmented to reduce numerical ill conditioning. An added benefit of shifted DMC was that the so-called ‘‘shifting parameter,’’ replacing the move suppression parameter, was easily found from the open-loop response. Therefore a novel analytical method, based on a closed form, continuous approximation to closed-loop DMC control, is introduced here and used to quantify the previous empirical results. The dependence of slow and fast time scales of the closed-loop response on the parameters is examined for move-suppressed and shifted DMC methods. It is found that in move-suppressed DMC the slow control time scale is sharply dependent upon the sampling time and move-suppression parameter and that these difficulties are eliminated in shifted DMC.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.

---

Design of controller using variable transformations for a nonlinear process with dead time

By R. Anandanatarajan, M. Chidambaram, and T. Jayasingh
Pondicherry Engineering College, Pondicherry, India; IIT, Chennai, India; St. Xaviers College of Engineering, Nagercoil, India

Abstract
In this work, a globally linearized controller (GLC) for a first-order nonlinear system with dead time is proposed. This is similar to the GLC proposed by Ogunnalke [Ind. Eng. Chem. Process. Des. Dev. 25, 241–248 (1986)] for nonlinear systems without dead time. Two methods are proposed. One is based on the Smith prediction from the model in the transformed domain and the other is based on Newton’s extrapolation method. The simulation study is made on the conical tank level process and the results are compared with those obtained using a conventional PI controller and the Smith PI controller based on the transfer function model about the operating point 39%. Finally, experimental results on the laboratory conical tank level process are also given.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.

---

Digital redesign of observer-based weighting switch controller for cascaded analog systems with state saturation and external loads

By J. S. H. Tsai, H. Cheng, M. M. Moussighi, and L. S. Shieh
Control System Laboratory, Department of Electrical Engineering, National Cheng Kung University, Tainan 701, Taiwan, R.O.C.; Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, 77204-4005, USA

Abstract
This paper presents an observer-based weighting switch controller for dealing with the problem of cascaded systems with state saturation and external loads. This method improves the generally poor transition response and output deviation caused by state saturation and external loads. In order to maintain the state-saturation limits, we adopt the evolutionary programming optimal search technique to find the optimal switching parameters for the weighted switch controller. Also, a digital redesign method is utilized to replace a designed high-gain analog controller with a low-gain digital controller. It is shown that the digitally redesigned outputs closely track the analogously controlled outputs. The digital redesign technique is then extended to find the digital version of the continuous-time observer. An illustrative example is demonstrated to show the effectiveness of the proposed procedure.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.

---

Second-order sliding mode controllers for nonlinear singular perturbation systems

By J. Wang, K. M. Tsang
Department of Electrical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

Abstract
Nonlinear systems are decomposed into slow and fast response subsystems using the singular perturbation theory and second-order sliding mode controllers are designed for each of the subsystems. The combined control action forms a suboptimal controller that can eliminate chattering in the continuous control output. Simulated examples are included to demonstrate the effectiveness of the proposed algorithm.