ISSN:0020-7179    

DOI:10.1080/00207179408923095

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The nonlinearity of many chemical processes can be approximated by a static nonlinear element in series with a linear dynamic element. The model is called a Hammerstein model if the nonlinear static element precedes the linear dynamic element. It is a Wiener model if the order is reversed. This paper presents a simple method for the experimental determination of both the linear dynamic part and the nonlinear static part of the nonlinear model, simultaneously, by the use of nonlinear auto-tuning (relay feedback). A conventional linear auto-tune test, developed by Astrom and co-workers, is conducted by placing a relay in the feedback loop. The amplitude of the resulting oscillating output and the period of this cycle gives approximate values for the ultimate frequency and the ultimate gain of the linear system. The nonlinear auto-tune method described in this paper consists of the consecutive use of two or more relay-feedback tests with different relay heights and with different known dynamic elements inserted in the loop. For a Hammerstein model, the relays are displaced vertically from the origin such that the oscillations of the output of the process are symmetrical about the steady-state value. For a Wiener model, the relays are shifted horizontally from the origin such that the input to the process is a sequence of symmetrical pulses. The effectiveness of the method is demonstrated on two simulated example nonlinear processes: a simple second-order system with exponential static nonlinearity and a realistically complex distillation column.

ISSN:0020-7179    

DOI:10.1080/00207179408923096

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

How to represent an uncertain time delay in a form suitable for robust control in terms of the H∞-norm and the structured singular value (µ) is discussed. To use µ-synthesis the uncertain delay has to be approximated to yield a proper rational interconnection matrix M(s) and a purely complex perturbation matrix? (s). The parametric average of the delay is usually included in the nominal model, while the uncertain perturbation covers variation around the average delay. It is proposed to model the nominal time delay as uncertainty, i.e. using a larger uncertainty set. This yields a delay-free nominal model, which simplifies the controller synthesis. For the cases studied the delay free nominal model does not yield a more conservative design than the average delay model, despite its larger uncertainty set.

ISSN:0020-7179    

DOI:10.1080/00207179408923097

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A new procedure of robust control design is presented for nonlinear systems with parametric uncertainty and disturbance. This nonlinear optimization-based approach can design robust nonlinear controllers of widely different structures and arbitrary complexity. By taking the worst-case design approach, a minimax optimization problem is formulated. A number of state-of-the-art optimization procedures are explored as possible candidates for minimaximization. It is determined that the tools of non-smooth analysis and optimization are the most useful for the efficient solution of practical size worst-case design problems. Included in the paper are the significant details of a special two-tier structured minimax programming algorithm implemented in this work. The overall algorithm is used in solving two robust nonlinear control design problems. The controller designs produced by the minimax optimization algorithm are discussed and the performance of the controllers is studied by simulations.

ISSN:0020-7179    

DOI:10.1080/00207179408923098

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The design of robustly performing controllers for an important class of control problems is treated. The problem is dealt with in the structured singular value (μ)-framework. The systems considered are characterized by weak nonlineari-ties and parametric and unstructured uncertainties. Nonlinear effects are taken into account via linearization families. Parametric uncertainty is included in a non-conservative way. Both lead to a μ-synthesis problem with repeated scalar real perturbations. As no direct solution to such a μ-synthesis problem is known to date, an iterative approach comprising both μ-analysis of the actual problem and D-K-iteration for a modified problem is shown. This approach is applied to a realistic continuous stirred-tank reactor for production of cyclopen-tenol to show the applicability to non-trivial MIMO process control problems.

ISSN:0020-7179    

DOI:10.1080/00207179408923099

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This paper deals with the control of the temperature in non-isothermal stirred-tank reactors involvingM(M⩾ 1) chemical reactions. The proposed control algorithm is an input-output linearization controller which accounts for the well-known process nonlinearities. The control scheme is also adaptive in order to deal with the parameter uncertainty: in particular it is shown how to include explicit on-line estimates of theMactivation energies within the adaptive linearizing controller. The performance of the control law is illustrated in simulation.

ISSN:0020-7179    

DOI:10.1080/00207179408923100

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Large-scale industrial polymer reactors are typically multivariate, nonlinear, and often have significant time delays. Furthermore, key process measurements are sometimes not available at all, or they become available only after long laboratory analysis has rendered them obsolete. This paper reports on the development of a control system for such a reactor. The specific process in question is used to manufacture the polymer 'P' from three monomers 'A', 'B', and 'C, in a continuous stirred-tank reactor. Product quality measurements are available only by laboratory analysis from samples taken every two hours; however, the mole fraction of the monomers, catalyst, etc in the reactor are available every 5 minutes via chromatographic analysis. The control scheme involves a two-tier system in which the monomer, catalyst, etc, flow rates are used to regulate reactant composition in the reactor at the first tier level, every 5 minutes. At the second tier level, reactant composition target values are used to regulate final product properties. A dynamic kinetic model supplies on-line estimates of the product properties between the two-hour samples. The entire control scheme, implemented on a real-time process control computer, has resulted in significant reduction in product variability, with the consequent benefits of improved yield and product quality. Pertinent facts regarding the design and implementation of the control scheme are summarized along with some results representative of typical performance.

ISSN:0020-7179    

DOI:10.1080/00207179408923101

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This paper describes the results of a joint university-industry study to control a semi-commercial impact copolymerization reactor that produces ethylene-propylene-rubber, and mixes it with polypropylene homo-polymer at the molecular level. By changing operating conditions, the reactor can produce numerous grades of polymer according to consumer requests. An appropriate multivarible control system is necessary to achieve swift grade changeovers by changing pressure and concentrations of monomers in the reactor. Because measurements of concentrations, available every 6 minutes, occur less frequently than pressure measurements, we extend the Model Predictive Control (MPC) scheme to deal with this multirate output-sampled process. A 3×3 multirate MPC is developed and installed in the reactor. A thorough description of the features of this control algorithm is also included as well as experimental results to illustrate its performance.

ISSN:0020-7179    

DOI:10.1080/00207179408923102

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Novel ways of using multivariate statistical methods to develop process models for on-line monitoring and control are proposed. On a binary distillation column, PLS is used to develop a regression estimation using multiple tray temperature measurements and a manipulated variable to estimate and control distillate composition. Additionally, a feedback controller design based on a static PCA/PCR model is developed and demonstrated on the binary column. This controller's performance is compared with a PI controller for disturbance rejection and setpoint tracking. On a real-world chemical process, it is shown how both PLS and PCS are necessary to model normal plant operations. These models permit real-time monitoring and detection in a reduced subspace defined by the statistical independent variations in the data. Techniques for real-time monitoring and fault detection are demonstrated.

ISSN:0020-7179    

DOI:10.1080/00207179408923103

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

To overcome the limitations of the black-box character of the standard neural network approaches, a network with ellipsoidal units has recently been proposed. This novel approach addresses three main issues: (a) to understand better and represent the nature of fault classification boundaries; (b) to determine the network structure without the usual trial and error schemes; and (c) to avoid erroneous generalizations. In this paper, we develop the ellipsoidal units approach further by addressing the problem of real-time large-scale fault diagnosis. For such applications neural networks become very large and complex, making the training and interpretation tasks time consuming and difficult. Networks with ellipsoidal units naturally lend themselves to the development of decomposition techniques that result in the training of smaller networks with fewer training patterns. Three decomposition strategies, namely, network decomposition, training set decomposition, and input space decomposition, have been developed for large-scale industrial processes. The results for the real-time diagnosis of an Amoco model IV FCCU simulation case study are discussed. Network size and diagnostic performance are compared with alternative approaches, such as backpropagation networks and radial basis function networks.

ISSN:0020-7179    

DOI:10.1080/00207179408923104

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor