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Multivariable identification of an activated sludge process with subspace-based algorithms

control ENGINEERING PRACTICE 2003年第8期11卷 961-969页

作者： Sotomayor, OAZ Park, SW Garcia, C Univ Sao Paulo Polytech Sch LSCP Dept Chem Engn BR-05508900 Sao Paulo Brazil Univ Sao Paulo Polytech Sch LAC Dept Telecommun & Control Engn BR-05508900 Sao Paulo Brazil

This paper is aimed at identifying a linear time-invariant dynamical model (LTI model with lumped parameters) of an activated sludge process. Such a system is characterized by stiff dynamics, nonlinearities, time-variant parameters, recycles, multivariability with many cross-couplings and wide variations in the inflow and the composition of the incoming wastewater. In this simulation study, a discrete-time identification approach based on subspace methods is applied in order to estimate a nominal MIMO state-space model around a given operating point, by probing the system in open-loop with multi-level random signals. Six subspace algorithms are used and their performances are compared based on adequate quality criteria, taking into account identification/validation data. As a result, the selected model is a very low-order one and it describes the complex dynamics of the process well. Important issues concerning the generation of the data set and the estimation of the model order are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.

关键词： subspace methods multivariable identification state-space models activated sludge process environment engineering

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An observer for systems with nonlinear output map

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AUTOMATICA 2003年第5期39卷 909-918页

作者： Johansson, A Medvedev, A Lulea Univ Technol Control Engn Grp SE-97187 Lulea Sweden Uppsala Univ Dept Syst & Control SE-75105 Uppsala Sweden

A nonlinear observer, with the feedback gain weighted by the sensitivity of the output with respect to the state, is developed for systems with nonlinear output map.. The observer can be obtained from the extended Kalman filter by a special choice of time-varying weighting matrices. It is shown that the estimation error dynamics are asymptotically stable and a region of attraction is derived. The observer is applied to the top blown converter process for estimating the content of impurities in the liquid metal. Using plant data from the converter at SSAB Oxelosund AB, the observer is shown to provide accurate estimates of the carbon content. (C) 2003 Elsevier Science Ltd. All rights reserved.

关键词： nonlinear systems nonlinear observers region of attraction steel making

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Neural network-based identification of SMB chromatographic processes

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control ENGINEERING PRACTICE 2003年第8期11卷 949-959页

作者： Wang, C Klatt, KU Dünnebier, G Engell, S Hanisch, F Univ Dortmund Dept Chem Engn Proc Control Lab D-44221 Dortmund Germany

In this contribution, the identification problem for the control of nonlinear simulated moving bed (SMB) chromatographic processes is addressed. For process control the flow rates of extract, desorbent, and recycle of the SMB process, and the switching time are the manipulated variables. But these variables influence the process in a strongly coupled manner. Therefore, a new set of input variables is introduced by a nonlinear transformation of the physical inputs, such that the couplings are reduced considerably. The front positions of the axial concentration profile are taken as model outputs. Multilayer feedforward neural networks (NN) are utilized as approximating models of the nonlinear input-output behavior. The gradient distribution of the model outputs with respect to the inputs is used to determine their structural parameters and the network size is chosen by the SVD method. To illustrate the effectiveness of the identification method, a laboratory scale SMB process is used as an example. The simulation results of the identified model confirm a very good approximation of the first principles models and exhibit a satisfactory long-range prediction performance. (C) 2002 Elsevier Science Ltd. All rights reserved.

关键词： simulated moving bed process chromatography neural networks nonlinear identification

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Designing plant experiments for real-time optimization systems

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control ENGINEERING PRACTICE 2003年第8期11卷 837-845页

作者： Yip, WS Marlin, TE McMaster Univ Dept Chem Engn Hamilton ON L8S 4L7 Canada

This paper presents a new criterion to design plant experiments for model-based real-time optimization (RTO) systems. Experiments are designed by maximizing total expected profit over a future horizon. The objective function for designing plant experiments includes the gain in profit by reducing the offset and variability after the experiments and loss in profit before and during experimentation. Therefore, large plant movement from the optimum during experimentation and too many experiments are penalized by the profit loss term. By solving the experimental design problem, the time to start the experiments, the number of experiments and the experimental operating conditions are determined. The proposed experimental design approach is applied to the simulated Williams-Otto reactor, where it yields higher profit for several cases than achieved by standard RTO without experimentation. (C) 2002 Elsevier Science Ltd. All rights reserved.

关键词： real-time optimization experimental design dual control

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Inferential control of distillation compositions: selection of model and control configuration

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control ENGINEERING PRACTICE 2003年第8期11卷 927-933页

作者： Kano, M Showchaiya, N Hasebe, S Hashimoto, I Kyoto Univ Dept Chem Engn Sakyo Ku Kyoto 6068501 Japan

This article is concerned with a classical problem of how to design an inferential control system for enhancing the performance of distillation composition control. In this article, a new inferential control, termed "predictive inferential control," is proposed. In the predictive inferential control system, future compositions predicted from on-line measured process variables are controlled instead of the estimates of current compositions. The key concept of the predictive inferential control is to realize feedback control with a feedforward effect by the use of the inherent nature of a distillation column. The detailed dynamic simulation results show that the proposed predictive inferential control scheme integrated with cascade control works considerably better than other control schemes. Furthermore, the improvement of the control performance through iterative modeling or control-relevant identification is also demonstrated. (C) 2002 Elsevier Science Ltd. All rights reserved.

关键词： inferential control distillation partial least squares control-relevant identification cascade control

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Nonlinear control of a reactive distillation column

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control ENGINEERING PRACTICE 2003年第8期11卷 915-925页

作者： Grüner, S Mohl, KD Kienle, A Gilles, ED Fernholz, G Friedrich, M Univ Stuttgart Inst Systemdynam & Regelungstech D-70569 Stuttgart Germany Max Planck Inst Dynam Komplexer Tech Syst Magdebu D-39120 Magdeburg Germany Bayer AG Proc Technol Proc Control D-51368 Leverkusen Germany

control of reactive distillation columns is a challenging task due to the complex dynamics arising from the coupling of reaction and separation. In this paper, asymptotically exact input/output-linearization is applied in simulation studies to ail industrial reactive distillation column which is operated by Bayer AG. The resulting control law is rather general and can be easily adopted for other reactive distillation columns. This control scheme requires knowledge of the complete state of the process and therefore an observer is designed. Asymptotically exact input/output-linearization inherits robust stability from a robust observer. It is intuitively argued that the proposed observer is robust w.r.t. both model structure and parameter errors. In order to compensate for steady state observer offsets an outer control loop with simple PI-controllers is implemented. Simulation studies evidence that in comparison with a well-tuned linear controller the nonlinear controller shows a superior performance with respect to setpoint-changes and disturbances, even in the presence of unknown input delays. (C) 2002 Elsevier Science Ltd. All rights reserved.

关键词： nonlinear control observers robustness reactive distillation columns

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A new approach to defining a dynamic relative gain

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control ENGINEERING PRACTICE 2003年第8期11卷 907-914页

作者： Mc Avoy, T Arkun, Y Chen, R Robinson, D Schnelle, PD Univ Maryland Dept Chem Engn College Pk MD 20742 USA Univ Maryland Syst Res Inst College Pk MD 20742 USA KOC Univ Coll Engn Istanbul Turkey EI DuPont Nemours & Co Wilmington DE 19898 USA

A new approach to defining a dynamic RGA (DRGA) is presented. The approach assumes the availability of a dynamic process model which is used to design a proportional output optimal controller. The new DRGA is defined based on the resulting controller gain matrix. Two examples in which the traditional RGA gives the wrong pairings and an inaccurate indication of the amount of interaction present are discussed. One example involves transfer function models and the other an industrial recycle/reactor system. In both cases the new DRGA indicates the best pairings to use and it accurately assesses the extent of interaction present. (C) 2002 Elsevier Science Ltd. All rights reserved.

关键词： dynamic interaction relative gain loop pairing optimal control

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Engineering aspects of nonlinear H control for longitudinal vehicle dynamics 10

Engineering aspects of nonlinear H control for longitudinal ...

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10th IFAC symposium on control in Transportation systems 2003

作者： Ganzelmeier, Lothar Schnieder, Eckehard Institute for Traffic Safety and Automation Engineering Technical University ofBraunschweig Langer Kamp 8 Braunschweig38106 Germany

In this paper a nonlinear robust controller design task for longitudinal dynamics of autonomous road vehicles is considered. This work presents a longitudinal controller that covers the nonlinearities of the vehicle dynamics by a nonlinear model based controller design while the variation in vehicle parameters is covered by the unstructured robustness of the controller. How model nonlinearities in longitudinal vehicle dynamics are described and how they are taken into account during the controller design process is shortly presented. The used control concept for nonlinear plants in form of a nonlinear control task is described. The approach involves the numerical solution, by power series approximation, of the time-varying Hamilton-Jacobi-Isaac equation and results in a nonlinear controller approximating the optimal tracking control law for a specified desired trajectory and cost function. Mathematical and computational aspects of nonlinear control or of L2 gain synthesis are considered. The first practical results with a nonlinear robust control law for longitudinal dynamic of an autonomous vehicle are presented. Copyright © IFAC control in Transportation systems, Tokyo, Japan, 2003

关键词： Autonomous vehicles

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New strategy for optimal control of femtosecond pump-dump processes applicable to systems of moderate complexity

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EUROPEAN PHYSICAL JOURNAL D 2003年第1-3期24卷 177-180页

作者： Mitric, R Hartmann, M Pittner, J Bonacic-Koutecky, V Humboldt Univ Inst Chem D-12489 Berlin Germany Acad Sci Czech Republ J Heyrovsky Inst Phys Chem CR-18223 Prague Czech Republic

New pump-dump optimal control strategy applicable to the systems of moderate complexity has been developed which allows to drive the system to the desired objective in the ground state via electronically excited state. The strategy is based on the concept of the intermediate target in the excited state whose role is to select appropriate Franck-Condon window at a given time delay between pump and dump pulses in order to reach optimally the objective. The concept was applied on the isomerization process in Na3F2 employing our ab initio Wigner distribution approach. The pump and dump pulses have been found which suppress the radiationless transition through the conical intersection and drive the system via electronically excited state to the second isomer in the ground state with the maximal yield.

关键词： Molecular dynamics and other numerical methods Ab initio calculations

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Robust control of quantum systems in the presence of field fluctuations

Robust control of quantum systems in the presence of field f...

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1st International symposium on Fluctuations and Noise

作者： Rabitz, H Princeton Univ Dept Chem Princeton NJ 08544 USA

ISBN: (纸本)081944975X

The impact of control field fluctuations on the optimal manipulation of quantum dynamics phenomena is investigated. The presence of significant field fluctuations is shown to break down the evolution into a sequence of partially coherent robust steps. Robustness occurs because the optimization process reduces sensitivity to noise-driven quantum system fluctuations. This process takes advantage of the observable expectation value being bilinear in the evolution operator and its adjoint. The consequences of this. inherent robustness bodes well for the future success of closed loop quantum optimal control experiments.

关键词： quantum control laser fields laser noise optimal control

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