Advanced Control Foundation: Tools, Techniques and Applications. Terrence Blevins Willy K. Wojsznis Mark Nixon

Transcription

1 Advanced Control Foundation: Tools, Techniques and Applications Terrence Blevins Willy K. Wojsznis Mark Nixon

2 1 Introduction The mathematical basis for many of the advanced control techniques in use today was known long before the technology was available to incorporate these techniques into process control systems. With the introduction of the first process control computers in the 1970s, it became possible to deploy advanced control as a layered application. Today, advanced control products are available as embedded applications within modern process control systems or as layered applications that may be easily added to older control systems. In this book, examples of commercially available products illustrate advanced control tools that are commonly used in the process control industry. The authors work in the design, development, and field testing of advanced control software products can in many cases be traced to the establishment in the early 1990s of an advanced control research and development program within Emerson Process Management. Many of the advanced control products embedded in the DeltaV control system came out of this program. The ISA book Advanced Control Unleashed Plant Performance Management for Optimum Benefit, published in 2003, included examples based on advanced control software products embedded in the DeltaV control system. Since then we have seen significant improvements made in advanced control tool capabilities and in user interfaces, improvements that make it easier to design and commission advanced control solutions. Also since then, new advanced control applications have been introduced for batch and continuous processes. This book provides a fresh look at some of the latest advanced control technologies that are available to the process industry. 1

3 2 ADVANCED CONTROL FOUNDATION: TOOLS, TECHNIQUES AND APPLICATIONS In this work, we benefited from the insight of many people we have worked with over the years in applying advanced control. Our goal in writing this book is to address concepts and terminology that are needed to understand and apply advanced control. The book will provide insight that will be helpful in applying advanced control techniques to improve plant performance. Whether the reader is working as a process control engineer in a manufacturing plant, in a controls group within an engineering department, or in an instrumentation department within a manufacturing plant, the information in this book sets a solid foundation for implementing advanced control solutions. Today, the process control systems installed in the process industry can be quite large and complex in design. Therefore, a person who is familiar with traditional control techniques may be reluctant to take the time needed to explore and work with the advanced control tools that are part of the control system. This is unfortunate, because in many cases advanced control techniques can provide significant advantages over traditional control techniques. The application examples in each chapter are designed to address multiple aspects of the design, implementation, and commissioning of advanced control solutions and how advanced control techniques compare to traditional control techniques. There are many aspects of advanced control, and this book is structured to allow engineers, managers, technicians, and others who are new to advanced control to quickly get up to speed on the technology and how it is applied. Experienced control engineers who are familiar with advanced control products will benefit from the application examples and solutions to workshops included in the book. The material is presented in a manner that is independent of the control system manufacturer. The workshops can be completed using a web browser to access the web site that has been created for this book. In general, the world of process control is broken into the control of batch and continuous processes. In this book we focus primarily on continuous process advanced control techniques, which in many cases can also be applied to batch processes. Many of the examples and workshops illustrate the control of both continuous and batch processes. The chapters in this book can be read in any order. If the reader has worked with advanced control tools in the past, it is possible to read only those chapters that address the topics of most interest. Even so, it is a good idea to at least review all chapters and associated workshops to gain a better appreciation of the latest features of advanced control

4 CHAPTER 1 INTRODUCTION 3 tools. In most cases these added features make it easier and faster to design and commission advanced control systems. Many of the concepts on justifying advanced control introduced in the first portion of the book establish a basis for understanding that can be helpful in assessing the benefits provided by techniques presented in later sections of the book. Also, with this understanding it should become clear that an advanced control strategy can and should be designed and justified independent of the advanced control software product that is selected to implement the solution. In each chapter on specific advanced control techniques, examples are used to show a typical application interface that is used to configure and commission advanced control solutions. When advanced control is embedded in the control system, the advanced control application interface can be fully integrated into the distributed control system. Also, in some cases, example displays are shown that can be used by the operator to access an advanced control solution. A significant part of the operator interface is directly tied to the control strategy. For example, the alarm system is often carefully designed to focus operator attention on the highest priority alarms first. Although the overall design of operator interface displays for advanced control implementation is beyond the scope of this book, many of the examples illustrate the working relationship between the control strategy and the operator interface displays The authors assume that the reader may not have worked with advanced control systems and concepts but does have a solid understanding of conventional control techniques and software tools for control implementation within a distributed control system. Thus, each chapter covers concepts and terminology that are helpful in working with advanced control. For example, the chapters on maximizing return on control system investment and evaluating control system performance address the basic principles that must be understood to estimate the economic benefits that can be achieved using advanced control products. In looking at whether advanced control is appropriate for a manufacturing plant, it is important to keep in mind the plant s requirements as well as the economic savings that may be achieved by using advanced control techniques. For example, what are the production and quality objectives that must be met? When the control goals and economic savings are clearly understood, it is usually a straightforward process to determine if advanced control products can be economically justified and, if so, to choose the appropriate advanced control technique.

5 4 ADVANCED CONTROL FOUNDATION: TOOLS, TECHNIQUES AND APPLICATIONS Background material on economic justification for an investment in advanced control is included in the first part of the book. Examples are used to illustrate techniques that the authors have found useful in justifying improvements that can be achieved within a variety of process operations. Having established a background in basic concepts and terminology, the book then addresses specific techniques such as on-demand or adaptive tuning that can be used to improve the operation of an existing control system. Later chapters address advanced control techniques such as fuzzy logic control and model predictive control, which may be used not only to replace traditional control techniques but to significantly extend control system functionality and the benefits obtained. As we address these new areas, the advantages of advanced control techniques will become obvious. At various points in the chapters on advanced control techniques, the reader has an opportunity to see an example of advanced control product by viewing the workshop solutions. The workshop solutions are provided on the web site and can be accessed without special software. The only requirement is access to a high speed Internet connection and a web browser. In the Appendix we provide detailed directions on how to access the web site. The workshop is designed to reinforce learning of the material in the chapter. The workshops are structured to be fun as well as informative. After viewing the workshop solution, it may be helpful to go back through the chapter if the workshop solution was not clearly understood. A dynamic process simulation is built into each of the book s workshops to show a realistic representation of the type of process response that may be achieved with the advanced control techniques presented in this book. The authors have found that during the pre-commissioning checkout of an advanced control system it is often helpful to create a dynamic process simulation that interacts with the control system. When a reasonable process simulation is tied to the control system, the control operation and the process response will usefully simulate those encountered in actual plant operation. Chapter 14 is dedicated to techniques that can be used to create a process simulation using the same tools that are commonly available within most process control systems. After the advanced control techniques that are most commonly used in industry are covered, techniques that can be used to integrate advanced control into an existing control system are addressed in Chapter 15. Some of the common issues that must be addressed in doing this are discussed in this chapter. Examples are used to illustrate

6 CHAPTER 1 INTRODUCTION 5 how advanced control can be layered on top of an existing control system. Throughout the book, as advanced control techniques are introduced, the manner in which each technique can be applied to address various process control requirements is illustrated using process examples and workshops. It should become clear by studying the examples how these control techniques can be applied to other processes with similar requirements. It is our hope that the understanding achieved by reading this book and viewing the workshop solution will set a foundation for addressing other control applications. The reader should feel free to contact the authors at their addresses with any questions about the book or about the use of the web-based workshops. All royalties from this book will be given directly to universities and educational programs to promote and enhance the understanding of advanced process control. A beneficiary of each year s royalties will be chosen by the authors.