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| BOOK REVIEWS Power Systems
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| These book reviews have systems as the commonality among them, two textbooks on power systems, a book on energy, and one on control. The topics include renewable energy, stability and control, and analysis and operation, and frequency control. Renewable Energy in Power SystemsLeon Ferris and David Infield, Wiley, 2008.This book covers a variety of issues related to the integration and operation of renewable energy (RE) in power systems. Given the steady increase in demand for electricity, increased interest in protecting the environment and deployment of RE power generation sources, and their increased penetration into the power grid worldwide, the subject book is very timely. Congratulations to the authors! According to them, the book is based on a course module in the master’s program on RE at the Center for Renewable Energy System Technology (CREST) at Loughborough University, United Kingdom. The authors also say that this book assumes no previous knowledge in power systems engineering and guides the reader through the basic understanding of how a power system is put together and the way in which it ensures that the consumer demand is met from instant to instant. While I think the theme of the book, renewable energy in power systems, is timely, I have some comments about the statement made by the authors that the book assumes no previous knowledge in power systems. I will give my comments after I describe the topics covered in the book. The eight chapters of the book cover the following topics.
A possible expansion of the book, which the authors might consider for a future edition, could be for the topics which have been briefly covered (e.g., the interesting topics, dynamic demand control or demand response, power quality, islanding, and fault ride through). In fact, I encourage the authors to consider a second edition and add new topics and new regulatory information, which may be introduced for the integration and operation of RE in power system as the issue evolves. After such expansion, the book may also be used as text in a more advanced course on RE in power systems. I happen to teach a graduate course on RE power generation system modeling and control, with emphasis on wind and photovoltaic, where, in addition to modeling, maximum power operation of the generation devices, and other related topics are discussed. I certainly would like to see a more advanced text on RE in power systems to consider for a course to follow the course I teach on RE system modeling and control. In addition to being a text for a course on RE in power systems, the book can also be a handy reference for graduate students, practicing engineers, and academics working on grid integration of RE power generation sources and their management or in the general area of power system planning, where distributed generations are integral parts of the power system. In fact, I recommend the book for every field engineer who works in the area of planning, integration, and operation of distributed generation in power systems. —Hashem Nehrir Power System Dynamics— Stability and ControlJ. Machowski, J.W. Bialek, and J.R. Bumby, second edition, Wiley, 2008.This is a good introductory textbook on the subject of power system dynamic performance and control, and I would recommend it to both students of power system dynamics and practicing engineers. It is well written with a good balance between mathematical rigger and physically insightful discussions. The book provides a good broad coverage of dynamics, stability and control of power systems covering all the major issues such as voltage stability, angular stability, frequency stability and control, and modeling of power systems and their components. The book is presented out in a logical order starting with a basic introductory chapter, then leading into a chapter that discusses all the components that makeup a power system. Chapter 3 gives an overview and good solid mathematical basis for stead-state behavior and analysis of power system components. Chapters 4–10 cover the breadth of power system dynamics, including electromagnetic phenomena, electromechanical dynamics of generation for small and large disturbances, voltage stability, frequency stability and control, and methods for enhancing power system stability. In the last section of the book, Chapters 11–14, a series of more advanced topics are covered such as power system modeling, eigenvalue analysis, power system simulation, and model reduction. Having had the pleasure of owning a copy of the original 1997 first edition of this book, it is particularly interesting to discuss the enhancements made to the book in the second edition 2008 release. The new materials in this second edition, all of which are welcome additions, are as follows:
In general this is a nice textbook on the subject of power system stability and control and would well augment one’s library of books on the subject. In a perusal of the entire book I only found a few minor typos in some equations, nothing that would in anyway detract from the quality of the book. Also, the book has been further enhanced through the addition of fully worked-out problem examples in some sections, which are also quite beneficial for students of the subject. I enjoyed reading it and would recommend it to all students and practitioners in this fascinating area of power systems engineering. —Pouyan Pourbeik Electric Energy Systems—Analysis and Operationby Antonio Góméz-Expósito, Antonio Conejo, and Claudio Caňizares, Editors, CRC, 2008.This edited book covers a combination of topics in the area of power system analysis and operation. The various topics have been authored by a team of authors, and the three editors who are themselves authors have edited the contributions into a cohesive collection. The book includes 12 chapters and three appendices. The 12 chapters in the book do address very relevant contemporary topics in power system analysis and operation. However, the sequencing of the material in terms of providing a logical transition to the subsequent chapter could have been more carefully thought out. Since the book is a team effort, certain notational inconsistency is observed in the various chapters. In Chapter 2 which deals with steady-state models of power system component, the symbol U is used to represent voltage. However, in the very next Chapter 3, which deals with the topic of power flow, the symbol V is used to represent voltage. This notation for voltage is also used in Chapters 4 and 6 but reverts back to U in Chapter 7 where both U and V are used. A mature student or a practicing engineer would probably not have much problem with this change of notation, but for a person entering the field the notational inconsistency could pose some challenges. This inconsistency in notation does occur in other chapters in the book also. The book could serve as an excellent reference source or as material for multiple short courses. The book does not contain any problems or exercises at the end of each chapter and as a result would not be a convenient textbook of choice in a regular course taught at a university. The material covered in the 12 chapters provide an excellent mix of topics dealing with power system analysis and power system operation. The topics related to power system analysis provide the necessary building blocks and foundational material that transition smoothly into concepts and tools used for power system operation. The chapters are well balanced in the amount of detail provided and also include several useful examples. Chapters 1 and 2 provide an extensive overview of electric energy systems and basic material dealing with steady-state analysis of single phase ac systems. These chapters cover both traditional concepts as well as introduce concepts of market based power system operation. Chapter 3 covers the topic of power flow. I would have preferred this title to the title “load flow” used in the book. As a side note, I should point out that I was an impressionable graduate student at Iowa State University and on separate occasions at PES meetings heard two giants of our profession Charlie Concordia and Bill Tinney mention at meetings that “load does not flow, but power flows.” The chapter is extremely well written and addresses all major issues including both the polar and rectangular formulations of the power flow. I particularly liked the presentation of the material on the inclusion of regulating devices and associated limits, regulating transformers, and series compensators. The chapter ends with the treatment of large scale systems and introduces the topic of sparsity and optimal ordering. Chapter 4 introduces the topic of state estimation. A comprehensive treatment of the various elements of state estimation including problem formulation, solution techniques, observability analysis, alternative solution approaches, bad date detection and identification, non quadratic estimation, and topology and parameter errors is provided. The various sections also include several illuminating examples. Chapter 5 addresses the topic of the economics of electricity generation. This chapter begins with a solid treatment of economic dispatch and unit commitment. It then transitions to topics dealing with market operations, market-clearing procedures, self-scheduling and steps to develop offer strategies for producers, and various aspects of the impact on consumers and retailers. Optimal power flow and security analysis are introduced in Chapter 6. Contingency analysis using both distribution factors and power flows are introduced. The optimal power flow (OPF) problem is formulated and classified. Various applications of the OPF in power system operation and in the market environment are introduced and discussed. The examples in this chapter highlight several of the applications introduced. Three-phase linear and nonlinear models of power system components are developed in Chapter 7. The concepts of unbalanced system operation and symmetrical components are introduced. The traditional symmetrical component based modeling of transmission lines, transformers, and synchronous machines are then presented. In addition a very useful treatment of power system loads and filters and power electronic converters and controllers is also provided. The treatment in this chapter is quite detailed and has only one example. A few more examples in the latter sections of this chapter would have significantly enhanced the assimilation of the topics presented. Chapter 8 introduces the topics of faults analysis and protection. The principal elements of fault analysis for the different types of faults are presented together with examples. An overview of protection and the key aspects of different types of protection are introduced. Chapters 9 and 10 do an excellent job of introducing critical aspects of frequency and voltage control and also present element of rotor angle, voltage, and frequency stability. The material covered is comprehensive and provides important details of the various analysis techniques. These two chapters also contain very useful examples. Chapter 11 addresses the topic of three-phase power flows and harmonic analysis. The material is quite detailed and the examples provided are illuminating. A comprehensive treatment of electromagnetic transients is presented in Chapter 12. After an introduction of the basic concepts, a presentation of the analysis techniques including both analytical and numerical approaches is provided. Specific applications of overvoltage analysis are then examined. The chapter also includes a treatment of multiphase transmission lines. This book addresses a diverse set of topics in power system analysis and operation. It is a welcome addition to the collection of books currently available on these topics and complements the more traditional textbooks in this area by providing an expert's viewpoint on the relevant issues and intricacies associated with these topics. The development of the various power system operation topics in a market environment are particularly useful and highlight the rich experience of various experts who have conducted seminal work in this area. —Vijay Vittal Robust Power System Frequency ControlHassan Bevrani, Power Electronics and Power Systems Series, Springer, 2009.Automatic generation control has been one of my interests since I first read Nathan Cohn's standard text. Automatic generation control has several major components: load frequency control, tie line flow control, and economic dispatch that have been defined and redefined over several decades. Changes in the operational structure, due to competitive market requirements, have changed this function. This author has summarized over ten years of his active research based on the accepted control standards for the load frequency control component. This text is a summary of recent research in this area in a very timely manner for a large audience ranging from decentralized competitive markets, classical vertically operated systems, with the possibility of renewable resources such as wind and solar generation. This text would be suitable for a graduate course specializing in the application of robust control to power system frequency control. The text would also be valuable to practicing engineers who have to select, design, implement, test, or verify the operation of frequency control in an Energy management system. It would also be valuable to those involved in the present debate as to the role and scope of smart grid in these areas. The first chapter, “Power System Control: An Overview,” details the history of frequency stability problems and defines the problems that are addressed in this work. The range of resources considered not only includes the classical fossil fuel resources but also renewable energy resources. The description of the various disturbances that occur, the progressive response of the system to the disturbance, the general control structure, the impact of operating states, and the timescales are reviewed to clarify the problem in detail. The need for robust control, a sometimes misused term, is well defined with an abundance of references for additional examples. The chapter concludes with a list of specifications for proposed control techniques to address the robustness of the method, the dependency on decentralized structure, the structure simplicity, uncertainties, and constraints. This chapter concisely defines the problem at hand and how to rate the solutions presented in later chapters. Chapter 2, “Real Power Compensation and Frequency Control,” details the fundamental control loops, the unit and system response models, the use of synchronizing tie coefficient for multiple control areas, the calculation of ACE, and the LFC participation factor. A generalization of operating conditions and control actions follows with links to future chapters for such details. The chapter ends with a literature review of LFC synthesis and analysis that covers several decades of works in this area. Chapter 3, “Frequency Response Characteristics and Dynamic Performance,” explains the static and dynamic performance characteristics from the perspective of a simplistic transform-based solution to a far more detailed state-space solution. This chapter overviews the deregulated business environment and describes a simple auction method. The author does briefly discuss the various types of control in Europe. I would prefer that the PJM original control structure were included. Then the author could have pointed to that structure as the basis for the deregulated structures. The deregulated model for bilateral contracts is included were each GENCO has to provide for the demand changes at each DISCO that is under contract. A three-area system is used to demonstrate the models of this chapter. I would have preferred some additional discussion for the models used when the demand response is not required from the GENCO under contract and the DISCO has to purchase demand balance from another market. The physical constraints are discussed in detail including the unit rate limits, dead band, and time delays. Thus, the model is now highly nonlinear. The uncertainties in the system from each unit to the area response characteristics are discussed next. At this point in the text, the reader will find an appropriate model of the system to do practical frequency modeling and control. “PI Based Frequency Control Design” is Chapter 5. This chapter starts with the standard decentralized proportional integral control to synthesize an LFC for a multiarea power system. The author points out that this is the best starting place for the application of control design as it is the present state of the art. It is a means to introduce H∞ based static output feedback (SOF) control. This is solved by an iterative linear matrix inequality algorithm. This chapter details concisely with each part of the modeling process and transformation from PI to SOF control. The iterative LMI algorithm is presented in detail with a MATLAB-based pseudocode description. A case study (example) is provided to show the difference in controllers including simulation results. The last section expands the controllers to handle bilateral contracts where the GENCO has to follow the DISCO under contract. Chapter 5 expands the models to include frequency regulation with time delays. The author discusses the advances of wide-area measurement and phasor measurement units with respect to the delays of the communication system. This chapter develops a robust PI-based frequency control synthesis including the time delays presented by the communication system and the computer systems. The development is easy to follow. The text describes a very extensive analog power system simulator. It is historically interesting to find an extensive description of such a system as most laboratories now use personal computers. I have dreams about the analog computers at Purdue University even three decades later. The chapter includes the H∞ SOF-based PI controller with ACE delay adapted state-space model with results. The subsequent controller is simple without the need for an additional controller. “Multi-Objective Control Based Frequency Regulation” is the next chapter, Chapter 6. This chapter shows how to achieve a more rigorous solution in less time when the time delays are uncertain. Instead of a single norm control, a multiple norm control is used for better performance. The assumption that the nominal system transfer function should be strictly positive real (SPR) is relaxed in this solution. “The Agent Based Robust Frequency Regulation,” Chapter 7, details experiments to implement LFC objectives in a deregulated environment. A two-agent control model is used to demonstrate how the minimum number of required activities can be found to meet LFC objectives in a control area. The text demonstrates how to implement a decision and control agent receives data from a data acquisition and monitoring agent to calculate generation participation factors and a corresponding control signal using an H∞ robust proportional integral controller. The text assumes that the droop is set by the system operator. The required load relief under such an environment is calculated and related to the classical control response of a regulated system in a previous chapter. Chapter 8, “Application of Structured Singular Values in LFC Design,” presents how to apply structured singular value theory to LFC design. First, a design of a sequential decentralized LFC in a multiarea power system is presented. Second, a robust decentralized, deregulated control approach for LFC design is presented for a multiarea system. It is assumed that generators with robust LFC controllers bid and are selected in advance. Both cases include system uncertainties and demand variations. Chapter 9, “Frequency Control in Emergency Conditions,” examines system response during extreme frequency excursions. These excursions are outside the response capability of the plant. Thus, under-frequency load shedding has to be properly set to curtain the demand before additional generation is removed. An L step UFLS scheme is developed with an example to demonstrate the overall design. Then a multiarea example is developed with a proposed load shed decision in a decentralized design. The benefits of target load shedding is compared to conventional load shedding. The final chapter, “Renewable Energy Options and Frequency Regulation,” overviews the key issues of integrating renewable resources (wind and solar) on LFC systems. The impact on frequency excursions are reviewed. An updated LFC model is proposed as is the need to revise frequency performance standards. A survey of recent studies on frequency regulation with RESs is included as a conclusion. —Gerald B. Sheblé | |
