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A formal graphical based process modeling methodology

COMPUTERS & CHEMICAL ENGINEERING 1997年第sup1期21卷 S835-S840页

作者： Drengstig, T Wasbo, SO Foss, BA NORWEGIAN UNIV SCI & TECHNOL DEPT ENGN CYBERNETN-7034 TRONDHEIMNORWAY

In this paper we present a representation scheme for chemical unit processes. The representation is based on a topological and a phenomenological abstraction of the process. The topological abstraction decomposes the process into control volumes and boundaries. The phenomenological abstraction represents the phenomena in the process using three general process characteristics, i.e. transport, reaction/generation and accumulation of mass and energy. For these entities we define a consistent set of graphical symbols that will be connected together in a network according to the modelers understanding of the process, giving a representation of the process. We further suggest to employ this representation in the development of a modeling methodology, where the symbols are related to differential and algebraic equations in order to represent a complete and consistent mathematical model. The methodology is successfully applied to two industrial processes, a ferromanganese furnace and an aluminum electrolysis cell. The latter will be used as an example. Simulations of the aluminum cell focusing on AlF3 dynamics are included.

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Hierarchical time-optimal control of a continuous co-polymerization reactor during start-up or grade change operation using genetic algorithms

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COMPUTERS & CHEMICAL ENGINEERING 1997年第Sup期21卷 S1037-S1042页

作者： Lee, MH Han, C Chang, KS POHANG UNIV SCI & TECHNOL CTR AUTOMAT RES POHANG 790784 SOUTH KOREA POHANG UNIV SCI & TECHNOL DEPT CHEM ENGN POHANG 790784 SOUTH KOREA

During start-up or grade-change operation of a continuous polymerization reactor, the transition time, required to reach the desired steady state from the initial state, decides the amount of off-specification polymer product which causes treatment problems. It is very important to calculate the minimum transition time and subsequently determine optimal control input trajectories. Due to complex reaction mechanism and highly nonlinear dynamics, however, this time-optimal control problem for a continuous copolymerization reaction during start-up or grade-change operation has been a challenging problem. We propose two level hierarchical time-optimal control methodology that is based on the discretization of transition time interval and application of genetic algorithms combined with heuristic constraints. The proposed methodology has shown better performance than IDP or SQP in terms of accuracy and efficiency. The methodology is illustrated by the application to the time-optimal control problem of continuous MMA-VA copolymerization to produce polymer with a desired molecular weight and composition of VA in a dead copolymer.

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The role of the human in intelligent control practices

The role of the human in intelligent control practices

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IEEE International symposium on Intelligent control (ISIC)

作者： G. Vachtsevanos Sungshin Kim School of Electrical and Computer Engineering Georgia Institute of Technology Atlanta GA USA

Operator's models are attracting the interest of industry as they relate to monitoring and control of complex engineered processes. Such processes are usually relying upon the expertise and ability of human operators for control purposes; they are often controlled sub-optimally owing to high personnel turnover, lack of fundamental understanding of plant dynamics, inaccuracy or unreliability of manual control actions, etc. Capturing and utilizing the expert's knowledge effectively and efficiently in an intelligent control framework promises to improve plant operational conditions particularly in the event of large-scale disturbances. Modeling the expert operator's experience is a perfect semiotic paradigm since the operator employs a variety of informational granules in order to establish an effect-cause relationship and take appropriate action in the event of an emergency. This paper focuses upon the role of the human in intelligent control, means to extract expert knowledge, represent it and employ it for control of complex systems. A neuro-fuzzy implementation strategy is suggested and the model is tested on a pH neutralization process.

关键词： Humans Intelligent control control systems Optimal control Large-scale systems Steady-state Open loop systems Marine vehicles Computer industry Industrial control

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Simultaneous structural/control optimum design of composite plate with piezoelectric actuators

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JOURNAL OF GUIDANCE control AND dynamics 1997年第6期20卷 1111-1117页

作者： Kim, Y Kum, D Nam, C HANKUK AVIAT UNIV DEPT AERONAUT & MECH ENGNKOYANG 411791SOUTH KOREA

An integrated structural/control design for the vibration suppression of a composite plate with segmented piezoelectric (PZT) actuators is examined, The electric power used by the PZT materials becomes a very important factor for real application to the control of flexible structures, The method to predict power required for the control is presented, and the power is used as a part of the objective functions, The structural weight, the state error energy, control energy, stability robustness, and the electric power required for vibration control are considered as the objective function. The locations of the PZT actuators are considered as control design variables, The ply orientation and thickness coefficients of the laminated composite plate are considered as structural design variables, The improved compromise multiobjective optimization by using a reduction factor of performance indices is applied to solve this optimization problem, The sequential linear programming method with move limits is used, The sensitivity analysis, which is required in the optimization process, is performed for the eigenstructure assignment control scheme and the performance indices with respect to the design parameters, The optimized results showed a significant amount of reduction in the structural weight as well as the control performance indices. The required electric power is also decreased.

关键词： Piezoelectric Actuators Electric Power Vibration Suppression Vibration control Structural Weight Structural Design Sensitivity Analysis Laminated Composites Sequential Linear Programming Closed Loop System

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Identification of a multistep-ahead observer and its application to predictive control

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JOURNAL OF GUIDANCE control AND dynamics 1997年第6期20卷 1200-1206页

作者： Lim, RK Phan, MQ Princeton University Princeton New Jersey 08544

State estimation is a fundamental component of modern control theory. In discrete-time format, the standard state estimator (observer) is one step ahead, It provides one-step-ahead estimation of the system state on the basis of information available at the current time step. To obtain multistep-ahead estimation, one can repeatedly propagate the one-step estimation a number of time steps into the future, but this process tends to accumulate errors from one propagation to the next. A multistep observer, which directly estimates the state of the system at some specified time step in the future, is identified directly from I/O data. One possible application of this multistep-ahead observer is in receding-horizon predictive control, which bases its present control action on a prediction of the system response at some time step in the future. It is possible to recover the usual one-step-ahead state-space model of the system from the identified multistep-ahead observer as well, although a stabilizing feedback controller can be designed directly from the identified observer. Numerical examples are used to illustrate the key identification and control aspects of this multistep-ahead observer concept.

关键词： State Space Representation Singular Value Decomposition High Alpha Research Vehicle Deep Space Network Output Feedback Vibration Suppression

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Unified cellular neural network cell dynamical equation using delta operator

Unified cellular neural network cell dynamical equation usin...

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IEEE International symposium on Circuits and systems (ISCAS)

作者： H.C. Reddy G.S. Moschytz Department of Electrical and Computer Engineering University of California Irvine CA USA Department of Electrical Engineering California State University Long Beach CA USA Institute of Signal and Information Processing ETH Zurich Zurich Switzerland

The signal processing algorithms based on conventional shift operator tend to be ill-conditioned in situations involving fast sampling and shorter wordlength. To alleviate this problem delta operator based analysis and design has been proposed for high speed digital signal processing and control systems. The advantage for delta (/spl delta/) operator seems to come from the fact as sampling period T/sub s//spl rarr/0, the discrete time system process resembles that of continuous time system. In this paper we develop a unified cellular neural network (CNN) cell model using the delta operator approach. The model gives a general discrete-time (DT) CNN cell dynamics in which the sampling period T/sub s/ is an explicit parameter. As T/sub s//spl rarr/0, we get the continuous time (CT)-CNN equation. Several results connected with the stability and robustness of CT-CNN and DT-CNN can be linked using this approach. This approach highlights the similarities, rather than the differences between discrete and continuous CNNs, thus allowing continuous insights to be applied to the discrete CNN case. Further, more importantly from the implementation point of view, delta operator based DT-CNN cell design can be obtained using /spl delta//sup -1/ as an integrator {instead of a delay (z/sup -1/)}. The /spl delta//sup -1/ integrator can be realized using switched current/switched capacitor circuits. The dynamic circuit element in the DT-CNN is thus "/spl delta//sup -1/".

关键词： Cellular neural networks Equations Signal sampling Robust stability Signal processing algorithms Signal analysis Signal design Digital signal processing process control control systems

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Dynamic behaviour of integrated plants

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JOURNAL OF process control 1996年第2-3期6卷 145-156页

作者： Morud, J Skogestad, S UNIV TRONDHEIM NTH DEPT CHEM ENGN N-7034 TRONDHEIM NORWAY

The effect of material recycle and heat integration on the dynamics and control of chemical processing plants is considered. In analogy to linear control theory, one may consider how plant interconnections affect the fundamental properties of the dynamics, such as the poles and zeros. This implies that recycle of mass and energy, which are feedback mechanisms, affects the poles and thus possibly the plant stability, whereas parallel interconnections in a plant affect the zeros and thus the achievable performance of the plant under feedback control.

关键词： process dynamics nonlinear systems positive feedback

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Piecewise linear controller improving its own reliability

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JOURNAL OF process control 1996年第2-3期6卷 129-136页

作者： Hashimoto, Y Katoh, T Shiina, T Yoneya, A Togari, Y McGreavy, C UNIV LEEDS DEPT CHEM ENGNLEEDS LS2 9JTW YORKSHIREENGLAND

Although the capability of neural networks in nonlinear dynamics modelling is well-established, the reliability of the output heavily depends on the training data. The reliability is a serious problem in applying it to real problems. in this paper, we propose a radial basis functions network (RBFN) which evaluates its own reliability and improves itself recursively. This network approximates the input-output relationships with a piecewise linear regression. An adaptive internal model control algorithm in which the reliability of the model is used to tune the controller performance, is also proposed.

关键词： neural network piecewise linear regression nonlinear control

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Performance enhancement by control law adaptation in slow-active road vehicle suspensions

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VEHICLE SYSTEM dynamics 1996年第Suppl期25卷 533-546页

作者： Pilbeam, C Sharp, RS

The paper is concerned with the possible performance improvements which can be obtained in an automotive active suspension system through the use of adaptive rather than fixed control The study is wholly theoretical and treats a quarter-car, slow-active, electro-hydraulic-pneumatic suspension with elastic limit stops. through simulation of running at a constant speed on randomly profiled roads. The adaptation is intended to adjust the system operation according to the prevailing road roughness level. road spectral properties being assumed average at all times. The road roughness estimation process is illustrated. The estimate is used to drive a gain scheduling adaptive scheme. Comparisons are made between adaptive slow-active systems, non-adaptive slow-active systems and a typical passive system. mainly by means of root mean square values of response variables. It is concluded that the assumptions made in such a study can exert a large influence on the nature of results obtained, giving rise to potentially conflicting interpretations. The present results indicate that adaptation of the type proposed has very limited value.

关键词： Automobile suspensions

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A system for simulation, monitoring and diagnosis of controlled continuous processes with slow dynamics

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KNOWLEDGE-BASED systems 1996年第8期9卷 525-530页

作者： Prang, J Huemmer, HD Geisselhardt, W [a] Gerhard-Mercator-University of Duisburg Electrical Engineering Department of Data Processing Bismarckstra?e 81 47057 Duisburg Germany

This paper presents a modelling approach specifically designed to be used in a monitoring and diagnosis system based on the simulation of relevant process and control system variables. The model is based on semantically extended data flow diagrams with each computational process representing the incremental behaviour of a component of the plant to be modelled. Variable as well as delay time behaviour is associated with each component model to support an event-driven simulation which, in turn, reduces computation time. This plant model of independent but interacting computational processes is easily extendable, modifiable and adjustable according to changes in the plant. The modelling approach is applied to a coal power plant process and is implemented in G2, an object-oriented, real-time expert system shell with built-in simulation and online external connection capabilities. Generic rules guiding the event-driven simulation and monitoring allow for modular adaptation of the model as the plant's structure and functionality change without requiring changes in the rule set. (C) 1997 Elsevier Science B.V.

关键词： behavioural modelling rule based diagnosis event-driven simulation process monitoring

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