Modern Distributed Control Systems Research Articles

CURRENT TRENDS AND CHALLENGES IN DISTRIBUTED CONTROL SYSTEMS – AN OVERVIEW

In this paper, innovations in the field of distributed control systems have been considered. Without any claim for completeness, a short summary on current trends in this area has been provided. A special attention is paid to application of blockchain technologies in distributed control systems, game theoretical approach for distributed control applications, and advantages of distributed control for power systems. Also, one of the main issues of modern distributed control systems – cybersecurity has been considered.

Performance and Reliability Aspects of Clock Synchronization Techniques for Industrial Automation

Modern distributed control systems comprise multiple intelligent devices capable of performing complex time and mission-critical tasks both independently of each other or partly jointly with each other. To do so, they strongly depend on an accurate common notion of time as well as a reliable shared communication medium for timely data exchange. Traditional legacy communication technologies (field bus systems) supported time transport to a certain extent or provided at least a common frequency. Due to its numerous undisputed advantages, Ethernet has become the only viable communication medium effectively replacing such systems. Being inherently asynchronous time and frequency transfer has to be accomplished using a packet-based approach when moving to Ethernet. After explaining the basic principles of packet-based time transfer, the most common standards are explained compared with each other with respect to their intended application domains. Special emphasis will be put on the Precision Time Protocol (PTP) as defined in the underlying IEEE 1588 standard and its variant IEEE 802.1AS used for time-sensitive networks. Maintaining a highly accurate common notion of time under all circumstances is a crucial prerequisite for most distributed systems. Although PTP has proven to provide sub-microsecond accuracies, it can cope only with a limited number of error conditions. This paper describes all major sources that can either deteriorate the accuracy or cause a total loss of synchronization altogether. Selected countermeasures and enhancements are presented, which can greatly improve the resilience of PTP against errors as well as malicious attacks. This paper concludes by presenting the selected measurements' results of a novel proposed method.

Use of an industrial distributed control system in conjunction with Matlab/Simulink for process control education

The paper demonstrates how a four-tank laboratory process equipped with a modern distributed control system (DCS) is used in different control engineering laboratories for the undergraduate and graduate levels. This includes the utilization of commercial tools for DCS engineering as well as the design and commissioning of traditional and advanced control solutions. Matlab/Simulink tools are connected via OPC to extend the laboratory scope with rapid control prototyping and hardware-in-the-loop simulation. Using the same pilot plant, DCS and scientific computing environment in different courses lowers the costs, allows the reutilization of results and enables an efficient lab organization. It also supports the process of learning the inner context of different process control related subjects.

PID Advances in Industrial Control

Major advances that improve control in the process industry have been made over the last ten years in the basic PID technology of modern distributed control systems. This paper addresses the impact that international standards have on control implementation and the tools utilized in industry for monitoring and commissioning PID control. Examples are used to illustrate how new technologies, such as model switching for process identification, have allowed manufacturers to introduce a new level of ease-of-use in tools developed for on-demand and adaptive tuning. This paper discusses PID modifications that improve the speed of recovery from process saturation conditions that are common in industrial applications. Also, details are provided on PID modifications that enable effective control with non-periodic measurement updates by wireless transmitters. Finally, prospective future directions for industrial PID controllers are sketched.

Multiple use of an industrial‐distributed control system in control engineering education

AbstractThe paper demonstrates how a four‐tank laboratory process equipped with a modern distributed control system (DCS) is used in different control engineering laboratories for the undergraduate and graduate levels. This includes the utilization of commercial tools for DCS engineering as well as the design and commissioning of traditional and advanced control solutions. Using the same pilot plant and control system in different modules lowers the costs, allows the reutilization of results and enables an efficient laboratory organization. It also supports the process of learning the inner context of different process control related subjects. © 2011 Wiley Periodicals, Inc. Comput Appl Eng Educ 21: 313–321, 2013

NETWORKS IN CONTROL EDUCATION

Technological development has brought the use of networks in control to the mainstream. To reflect new trends in control technology a distributed control laboratory was developed. The laboratory is interdisciplinary and integrates a wide range of state-of-the-art technologies and standards representing modern industrial distributed control systems. The laboratory concentrates on developing of control algorithms operating under varying network conditions. A typical configurations of the laboratory experiment and basic steps of students work are described in the paper.

SOAP Message Structure for Web-based Distributed Control Systems

Emerging IT technologies, specially Internet communication and web-based applications are adopted to the modern distributed control systems. This paper defines a web-based application domain for a distributed control system connected by Internet. XML(eXtensible Markup Language) is used for representing a control system and control devices. These IT technologies makes a distributed control system flexible and scalable than existing distributed systems with the standard RMI protocols such as CORBA or DCOM.

Effect of Derivative Algorithm and Tuning Selection on the PID Control of Dead-Time Processes

Many control engineers try to avoid the use of derivative action in operating units. As Isaksson and Graebe have pointed out (in a presentation at Control Systems 2000, Victoria, British Columbia, May 2000), there is an “industrial myth that derivative action does not work.” They claim that some of this is due to the need to adjust the derivative filter constant, in addition to the usual three parameters of PID controllers. Modern distributed control systems offer a variety of choices for the PID algorithm, including both series (interacting) and parallel (ideal). The many PID tuning methods that have been developed over the years have used different algorithms, and some are limited to a narrow range of parameter values (dead times). Most tuning methods require setting three tuning parameters, but some propose setting four parameters. All this complexity presents a confusing picture to the practitioner who is faced with trying to tune a PID controller. This paper presents a quantitative comparison of alternative derivative algorithms and tuning methods for processes with a wide range of dead-time/lag ratios. Results show that, when the correct algorithm is used, the IMC tuning method proposed by Morari and Zafiriou (Robust Process Control; Prentice Hall: New York, 1989) gives good performance for large-dead-time processes. The correct algorithm has a four-parameter, parallel, output-filtered PID structure.

SFC++: a tool for developing distributed real-time control software

This paper describes a visual tool for developing real-time control software for distributed industrial systems. The aim of this project currently in progress, is to obtain a visual programming environment which integrates both the advantages of object-oriented modelling for the design and simulation of systems and the power of modern distributed control systems (i.e. computers with real-time operating systems interconnected by means of industrial real-time networks). To bridge the gap between the object-oriented system model and the implementation level, at which we have multiple parallel tasks running on a network, sequential function charts (SFCs) are used as a standard formalism [12,16] for the description of system dynamics and control software programming.

A novel performance monitoring strategy for economical thermal power plant operation

A need-based integrated performance monitoring strategy is proposed to economize the operation of a thermal power plant, exploiting the immensely powerful resources of newly retrofitted modern distributed control systems (DCS). After reviewing the performance monitoring practice of a typical 200 MW oil/gas fired thermal power plant at Ballylumford, N. Ireland, the paper analyses its shortcomings and then suggests remedial measures through the proposed strategy. A simulation of this plant has been used for investigation purposes. The twin key aspects of performance monitoring, i.e. monitoring of performance indices and controllable parameters, are addressed in more effective and novel ways. The achievable best efficiency values of plant components, needed for comparative performance evaluation, are shown to be more reliably and accurately obtainable through neural network performance models. A method based on histogram plots is shown to be highly effective in monitoring the performance of plant controllers in reducing the variability of plant variables and then modifying the set-points to improve the thermal performance of the plant.

Application of adaptive extended horizon control to a pyrometallurgical reactor

Abstract This paper discusses the application of adaptive feedback control to an industrial scale pyrometallurgical reactor. The control objective is to regulate the addition rate of coal to the reactor. In this continuous process coal creates a reducing environment to produce molten lead metal. The control algorithm comprises an extended horizon control law and a recursive model parameter estimator. The control law requires the specification of very few parameters a priori (estimated model order and maximum deadtime). The implementation of the controller on a modern distributed control system was relatively simple. Over a range of operating conditions and coal types, the new control system gives superior performance to a digital fixed parameter PI controller, which was used previously.

Real-time expert system implementation at monsanto-krummrich

Modern distributed control systems require reliable field inputs to operate effectively. Expert systems can provide the necessary sensor validation using material and energy balancing techniques. The expert system tightly coupled with a control system can better insure the reliable operation of a manufacturing process.

Strategies for implementing advanced process controls in a distributed control system (DCS)

Advanced controls are generally thought of as complex control schemes, traditionally implemented in a supervisory computer. However, with the tremendous increased functional capabilities, better interfaces, and ease of configuration of modern distributed control systems (DCS), the opportunities are now available for the user to realize significant economic benefits by implementing advanced controls along with the standard regulatory controls in the DCS. The paper presents some strategies to implement advanced controls using the tools available within the modern DCS. Application examples of implementing feed forward, non-interacting, model-based multivariable and constraint controls are discussed for common process units. Included are also examples for building quality estimators to substitute for analyzers. The article describes how the user can exploit the DCS not only to achieve regulatory controls, but to fully utilize its potential as a direct revenue generator.

A distributed fault diagnosis method based on digraph models: Steady-state analysis

We develop a highly modular fault diagnosis methodology using digraph models of process behavior. Digraph models are appealing because they are easy to understand, they can be developed from either empirical or fundamental knowledge, and they can be analyzed using the host of results available from graph theory. A modular approach is desirable for implementation in modern distributed control systems. All the available digraph methods rely on a global view of the process data, so they are not easily implemented in a highly distributed setting. The present method is developed carefully from graph theory, and uses off-line analysis of digraph structure to reduce the on-line computation wherever possible. The on-line work is specifically designed for a distributed implementation in which each sensor and controller currently in an abnormal state examines the states for a small number of adjacent measurements to suggest possible faults, including both measured and unmeasured variables. Attention is paid to the issues of diagnostic completeness, diagnostic resolution and computational effort.

Fluid catalytic cracking unit advanced control in a distributed control system

The quantity and complexity of advanced control implemented into first-level instrument/control systems continues to increase as today's modern distributed control systems progress. Several higher level advanced control schemes have been successfully implemented in the FCCU DCS at BP Oil Alliance Refinery. The advanced control concepts of advanced regulation, malfunction detection, distribution control, constraint/override control, multivariable control, and calculated performance variables are defined or reviewed in this paper. These concepts are illustrated by discussing specific advanced control applications installed in BP Oil's FCCU DCS.

Structures and criteria of distributed process automation systems

Modern distributed control systems are becoming increasingly difficult to compare with one another because of their diversity, heterogeneity and complexity. Most manufacturers do not specify any recognizable classification basis, and criteria for such a classification and judgment are missing. An attempt is made here to demonstrate the main new possibilities of distributed process control with microcomputers, data buses and video display units against a background of the orthodox method of totally parallel instrumentation and the totally centralized operation with conventional DDC process computers. References are made to suitable and advantageous structures for distributed systems, a list of criteria being adhered to at the same time. A general classification of distributed control systems is provided to permit the easier attainment of an overview.