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On the operability of continuous processes

IFAC Proceedings Volumes 2001年第25期34卷 65-76页

作者： Christos Georgakis Derya Uztürk Sivakumar Subramanian David R. Vinson Chemical Process Modeling and Control Research Center and Department of Chemical Engineering Lehigh University Air Products and Chemicals Allentown PA

This paper offers a brief overview of past work as well as a critique of the state of the art from the perspective of a recently introduced operability framework (Vinson and Georgakis, 1998, 2000). This framework aims to quantify the inherent operability of a process without having to specify the control structure. It enables the identification of inoperable processes, regardless of the feedback controller selected, necessitating process rather than controller changes. Evaluation of steadystate operability is a necessary first step which should subsequently be complemented by the examination of the dynamic operability. The defined concepts are based on some key operating spaces. These spaces define the available ranges of input variables, the desired ranges of output variables, and the expected ranges of disturbance variables of the process. The calculation of the operability index is demonstrated for linear and the more general case of nonlinear models. This is achieved by mapping the defined input and output spaces onto each other using the nonlinear steadystate model of the process. Dynamic operability is examined by solving an optimal control problem to find the minimum time within which the process can respond to a disturbance or move to a new operating point with the available ranges of inputs.

关键词： integration of design and control operability controllability operability index minimum-time optimal control

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Identification and control of Bilinear Systems

Identification and Control of Bilinear Systems

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American control Conference (ACC)

作者： James F. Bartee Christos Georgakis Chemical Process Modeling and Control Research Center and Department of Chemical-Engineering Lehigh University Bethlehem Pennsylvania Chemical Process Modeling and Control Research Center and Department of Chemical-Engineering Lehigh University Bethlehem PA USA

The research presented in this paper combines the problem of identifiction and control of nonlinear processes. This is done by approximating the process with a bilinear model and designing model-based control structures (Reference System controllers) based on the bilinear approximation. The identification of the bilinear model and the construction of the controller are described below. An example of the identification and control of an exothermic CSTR is also presented.

关键词： control systems Nonlinear systems control system synthesis Nonlinear control systems Linear systems process control chemical processes Continuous-stirred tank reactor control theory Algorithm design and analysis

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An Industrial Approach to Implementing MPC in Speciality chemical Plant

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IFAC Proceedings Volumes 1999年第2期32卷 6603-6608页

作者： Qiang Zhan Vincent G. Grassi Chemical Process Modeling and Control Center Dept. of Chemical Engineering Lehigh University Bethlehem PA 18015 USA Chemical Process Modeling Center Air Products and Chemicals Inc. 7201 Hamilton Boulevard Allentown PA 18195 USA

Model Predictive control Technology has been successfully applied to industry for more than two decades. Most of the applications appear in refining and petrochemical industry. Relatively few applications could be found in the chemical industry. In this paper, the approach to evaluate the benefit that could be obtained by implementing MPC as a supervisory controller to a specialty chemical plant is explained in detail. The process and the basic plantwide control structures are simulated in Speedup. The plant pie-testing and plant testing are both done in Speedup. DMC+ commercial software is used to identify the linear model from the plant, build the controller, and tune the controller. By using the interface software between Speedup and DMC+, the process operating under DMC+ can be successfully simulated. The benefits from DMC+ can also be clearly identified in the simulation study. Some important issues in this approach are also pointed out.

关键词： Model based control industrial control chemical industry simulation

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Issues in the Optimization, Estimation and control of Fed-batch Bioreactors Using Tendency Models

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IFAC Proceedings Volumes 1992年第2期25卷 71-76页

作者： P. Tsobanakis S.H. Lee J.A. Phillips C. Georgakis Bioprocessing Institute Chemical Process Modeling and Control Research Center and Department of Chemical Engineering Lehigh University Bethlehem PA 18015 USA

The tendency modeling approach for optimization, estimation, and control is applied to bioreactors. This approach uses a “tendency” or “grey” model based on the available fundamental knowledge of the process and emphasizes the incorporation of new process data. The technique is demonstrated on simulation studies and preliminary experimental results of the penicillin fermentation. The tendency model is based on reactor mass balances such as those proposed by Bajpai and Reuß (1980) while the number of overall reactions and their stoichiometry are derived by abstract factor analysis of experimental data. Actual process and equipment constraints, such as the power mounted to the fermentor, the oxygen transfer capacity, and the rheological characteristics of the broth, are added. The model can be updated periodically utilizing data collected both on-line and off-line. The updated model can be used off-line to develop optimal feeding policies. On-line, a Kalman filter can utilize the tendency model to estimate poorly, infrequently, or unmeasured states.

关键词： modeling tendency modeling factor analysis optimization estimation fermentation processes

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Performance assessment of constrained controllers 7th

Performance assessment of constrained controllers

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7th International Symposium on Advanced control of chemical processes, ADCHEM 2003

作者： Huang, Lilong Georgakis, Christos Chemical Process Modeling and Control Research Center Department of Chemical Engineering Lehigh University BethlehemPA18015 United States Department of Chemical Engineering Chemistry and Material Science 728 Rogers Hall Polytechnic University Six Metrotech Center BrooklynNY11201 United States

The paper presents a new deterministic framework for assessing constrained control loop performance. The proposed dynamic performance index is based on the dynamic operating work of Uztiirk and Georgakis (2002). It focuses on the time related characteristics of controllers' response to set-point changes or step-type disturbances. It explicitly takes into account the existence of constraints on manipulated variables. These constraints include minimum and maximum values as well as an upper limit on the rate of change of the input variables. © IFAC 2003

关键词： controllers

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Disturbance detection and isolation by dynamic principal component analysis

Disturbance detection and isolation by dynamic principal com...

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作者： Ku, Wenfu Storer, Robert H. Georgakis, Christos Chemical Process Modeling and Control Research Center Iacocca Hall Lehigh University 111 Research Dr. Bethlehem PA 18015 United States Department of Chemical Engineering Department of Industrial Engineering

In this paper we extend previous work by ourselves and other researchers in the use of principal component analysis (PCA) for statistical process control in chemical processes. PCA has been used by several authors to develop techniques to monitor chemical processes and detect the presence of disturbances [1-5]. In past work, we have developed methods which not only detect disturbances, but isolate the sources of the disturbances [4]. The approach was based on static PCA models, T2 and Q charts [6], and a model bank of possible disturbances. In this paper we use a well-known 'time lag shift' method to include dynamic behavior in the PCA model. The proposed dynamic PCA model development procedure is desirable due to its simplicity of construction, and is not meant to replace the many well-known and more elegant procedures used in model identification. While dynamic linear model identification, and time lag shift are well known methods in model building, this is the first application we are aware of in the area of statistical process monitoring. Extensive testing on the Tennessee Eastman process simulation [7] demonstrates the effectiveness of the proposed methodology.

关键词： Principal component analysis

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A control Performance Index Based on Minimum and Open-Loop Output Variance

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IFAC Proceedings Volumes 1999年第2期32卷 6704-6709页

作者： Stella Bezergianni Christos Georgakis Chemical Process Modeling and Control Research Center and Department of Chemical Engineering Lehigh University 111 Research Drive Bethlehem PA 18015 USA

The need to achieve reliable and effective automatic control systems has directed numerous research efforts towards the development of monitoring and assessment methods of the closed-loop performance. A new controller assessment index, called Relative Variance Index or RVI, is introduced in this work, according to which the closed loop performance is compared with the theoretically best control action (minimum variance control) and no control action. For the estimation of RVI, an identification method is employed to extract the system models and an estimate of the process unit delays. The proposed index, RVI, is in agreement with the classical deterministic closed-loop assessment measures and thus can be utilized for the controller performance evaluation more effectively.

关键词： controller Performance Assessment minimum variance control principal component analysis structure target factor analysis

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A systematic tuning approach for the use of extended Kalman filters in batch processes

A systematic tuning approach for the use of extended Kalman ...

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American control Conference (ACC)

作者： J. Valappil C. Georgakis Chemical Process Modeling and Control Research Center Lehigh University Bethlehem PA USA

State estimation methods, like the extended Kalman filter (EKF) are used for obtaining reliable estimates of the states from the available measurements in the presence of model uncertainties and unmeasured disturbances. The main open issue in applying EKF is the need to quantify the accuracy of the model in terms of the process noise covariance matrix, Q. The present paper proposes two methods that utilize the parametric model uncertainties to calculate the Q matrix of an EKF. The first approach is based on a Taylor series expansion of the nonlinear equations around the nominal parameter values. The second approach accounts for the nonlinear dependence of the system on the fitted parameters by use of Monte Carlo simulations that are easily be performed online. The value of the process noise covariance matrix (Q) obtained is not limited to a diagonal and constant matrix and is dependent on the current state of the dynamic system. The paper also discusses the application of these techniques to an example process.

关键词： Covariance matrix Q measurement State estimation Technological innovation Noise measurement Symmetric matrices Nonlinear systems Statistics Uncertainty Additive noise

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Designing Nonlinear control Structures by Reference System Synthesis

Designing Nonlinear Control Structures by Reference System S...

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American control Conference (ACC)

作者： R. Donald Bartusiak Christos Georgakis Matthew J. Reilly Chemical Process Modeling and Control Center and Department of Chemical Engineering Lehigh University Bethlehem PA USA

Reference system synthesis, an equation-based method for designing nonlinear feedforward/feedback controllers for general dynamic systems is presented. The control objective is expressed as a desired closed loop behavior in the form of a set of integro-differential equations which can, by design, be nonlinear. Realization of the desired closed loop behavior depends upon the solution of an operator equation relating the open loop system to the desired closed loop system for computing the necessary manipulated variable action. Analytical solutions of this operator equation can be found for simple systems. In general, numerical solutions can be determined using Newton's method, for example. The advantages of reference system synthesis are (i) it provides a general method for designing nonlinear feedforward/feedback controllers, (ii) it is simple, and (iii) its loop-shaping capabilities allow for the design of deliberately nonlinear closed loop behavior for higher performance and constraint-avoiding control. In this paper, we introduce the reference system synthesis procedure, illustrate its application to simple dynamical systems, and discuss the relationship of reference system synthesis to PID and Internal Model control design procedures.

关键词： Nonlinear control systems control system synthesis Nonlinear equations Design methodology Adaptive control Open loop systems Nonlinear dynamical systems Integrodifferential equations Closed loop systems Newton method

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Dynamic matrix control of a specialty chemical plant with different plantwide control structures

Dynamic matrix control of a specialty chemical plant with di...

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American control Conference (ACC)

作者： Qiang Zhan V.G. Grassi Chemical Process Modeling and Control Center Department of Chemical Engineering Lehigh University Bethlehem PA USA Chemical Process Modeling Center Air Products and Chemicals Inc. Allentown PA USA

Model predictive control technology has been successfully applied within the industry for more than 20 years. Most of the applications appear in the refining and petrochemicals industry, with few in specialty chemical plant. In this paper DMC+ commercial multivariable control software is evaluated for a specialty chemical process using offline simulation. The relative benefit that can be obtained from DMC+ above and beyond advanced regulatory plantwide control is carefully studied. In this study, DMC+ is built as a supervisory controller on the decentralized SISO plantwide control structure. DMC+ uses the setpoints of PI controllers as the manipulated variables. In this paper, different plantwide control structures are used and the performance of DMC+ on top of all these different plantwide control structures are compared. It will be shown that a well designed regulatory plantwide control structure is necessary to stabilize and linearize the process around some operating point. Good plantwide control design will give a better performance for DMC+.

关键词： chemical industry Predictive models Predictive control chemical technology Industrial control Application software Refining Petrochemicals chemical processes control design

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