Preface
The book deals with understanding, analyzing and justifying Microgrids, as novel distribution network structures that unlock the full potential of Distributed Energy Resources (DER) and thus form building blocks of future Smartgrids. In the context of this book, Microgrids are defined as distribution systems with distributed energy sources, storage devices and controllable loads, operated connected to the main power network or islanded, in a controlled, coordinated way. Coordination and control of DER is the key feature that distinguishes Microgrids from simple distribution feeders with DER. In particular, effective energy management within Microgrids is the key to achieving vital efficiency benefits by optimizing production and consumption of energy. Nevertheless, the technical challenges associated with the design, operation and control of Microgrids are immense. Equally important is the economic justification of Microgrids considering current electricity market environments and the quantified assessment of their benefits from the view of the various stakeholders involved.
Discussions about Microgrids started in the early 2000, although their benefits for island and remote, off-grid systems were already generally appreciated. Nowadays, Microgrids are proposed as vital solutions for critical infrastructures, campuses, remote communities, military applications, utilities and communal networks. Bright prospects for a steady market growth are foreseen. The book is intended to meet the needs of practicing engineers, familiar with medium- and low-voltage distribution systems, utility operators, power systems researchers and academics. It can also serve as a useful reference for system planners and operators, technology providers, manufacturers and network operators, government regulators, and postgraduate power systems students.
The text presents results from a 6-year joint European collaborative work conducted in the framework of two EC-funded research projects. These are the projects “Microgrids: Large Scale Integration of Micro-Generation to Low Voltage Grids,” funded within the 5th Framework programme (1998–2002) and the follow-up project “More Microgrids, Advanced Architectures and Control Concepts for More Microgrids” funded within the 6th Framework Programme (2002–2006). The consortia involved were coordinated by the editor of this book and comprised a number of industrial partners, power utilities and academic research teams from 12 EU countries. A wealth of information and many practical conclusions were derived from these two major research efforts. The book attempts to clarify the role of Microgrids within the overall power system structure and focuses on the main findings related to primary and secondary control and management at the Microgrid and Multi-Microgrid level. It also provides results from quantified assessment of the Microgrids benefits from an economical, environmental, operational and social point of view. A separate chapter beyond the EC projects, provided by a more international authorship is devoted to an overview of real-world Microgrids from various parts of the world, including, next to Europe, United States of America, Japan, China and Chile.
Chapter 1, entitled “The Microgrids Concept,” co-authored by Christine Schwaegerl and Liang Tao, clarifies the key features of Microgrids and underlines the distinguishing characteristics from other DG dominated structures, such as Virtual Power Plants. It discusses the main features related to their operation and control, the market models and the effect of possible regulatory settings and provides an exemplary roadmap for Microgrid development in Europe.
Chapter 2, entitled “Microgrids Control Issues” co-authored by Aris Dimeas, Antonis Tsikalakis, George Kariniotakis and George Korres, deals with one of the key features of Microgrids, namely their energy management. It presents the hierarchical control levels distinguished in Microgrids operation and discusses the principles and main functions of centralized and decentralized control, including forecasting and state estimation. Next, centralized control functions are analyzed and illustrated by a practical numerical example. Finally, an overview of the basic multi-agent systems concepts and their application for decentralized control of Microgrids is provided.
Chapter 3, entitled “Intelligent Local Controllers,” co-authored by Thomas Degner, Nikos Soultanis, Alfred Engler and Asier Gil de Muro, presents primary control capabilities of DER controllers. The provision of ancillary services in interconnected mode and the capabilities of voltage and frequency control, in case of islanded operation and during transition between the two modes are outlined. Emphasis is placed on the implications of the high resistance over reactance ratios, typically found in LV Microgrids. A control algorithm based on the fictitious impedance method to overcome the related problems together with characteristic simulation results are provided.
Chapter 4, entitled “Microgrid Protection,” co-authored by Alexander Oudalov, Thomas Degner, Frank van Overbeeke and Jose Miguel Yarza, deals with methods for effective protection in Microgrids. A number of challenges are caused by DER varying operating conditions, the reduced fault contribution by power electronics interfaced DER and the occasionally increased fault levels. Two adaptive protection techniques, based on pre-calculated and on-line calculated settings are proposed including practical implementation issues. Techniques to increase the amount of fault current level by a dedicated device and the possible use of fault current limitation are also discussed.
Chapter 5, entitled “Operation of Multi-Microgrids,” co-authored by João Abel Peças Lopes, André Madureira, Nuno Gil and Fernanda Resende examines the operation of distribution networks with increasing penetration of several low voltage Microgrids, coordinated with generators and flexible loads connected at medium voltage. An hierarchical management architecture is proposed and functions for coordinated voltage/VAR control and coordinated frequency control are analyzed and simulated using realistic distribution networks. The capability of Microgrids to provide black start services are used to provide restoration guidelines. Finally, methods for deriving Microgrids equivalents for dynamic studies are discussed.
Chapter 6, entitled “Pilot Sites: Success Stories and Learnt Lessons” provides an overview of real-world Microgrids, already in operation as off-grid applications, pilot cases or full-scale demonstrations. The material is organized according to geographical divisions. George Kariniotakis, Aris Dimeas and Frank van Overbeeke describe three pilot sites in Europe developed within the more Microgrids project; John Romankiewicz and Chris Marnay provide an overview of Microgrid Projects in the United States; Satoshi Morozumi provide an overview of the Japanese Microgrid Projects; Meiqin Mao describes the Microgrid Projects in China and Rodrigo Palma Behnke and Guillermo Jiménez-Estévez provide details of an off-grid Microgrid in Chile. These projects are of course indicative of a continuously growing list, they provide, however, a good impression of the on-going developments in the field.
Chapter 7, entitled “Quantification of Technical, Economic, Environmental and Social Benefits of Microgrid Operation,” co-authored by Christine Schwaegerl and Liang Tao attempts to quantify the Microgrids benefits using typical European distribution networks of different types and assuming various DER penetration scenarios, market conditions, prices and costs developments for the years 2020, 2030 and 2040. Sensitivity analysis of the calculated benefits is performed. Although, the precision of these quantified benefits is subject to the high uncertainties in the underlying assumptions, the positive effects of Microgrids operation can be safely observed in all cases.
Next to the co-authors of the various chapters, there are many researchers who have contributed to the material of this book by their knowledge, research efforts and fruitful collaboration during the numerous technical meetings of the Microgrids projects. I am indebted to all of them, but I feel obliged to refer to some names individually and apologize in advance for the names I might forget. I would like to start with Profs. Nick Jenkins and Goran Strbac from UK; I have benefited tremendously while working with them and their insights and discussions helped clarify many concepts discussed in the book. I am indebted to Britta Buchholz, Christian Hardt, Roland Pickhan, Mariam Khattabi, Michel Vandenbergh, Martin Braun, Dominik Geibel and Boris Valov from Germany; Mikes Barnes, Olimpo Anaya-Lara, Janaka Ekanayake, Pierluigi Mancarella, Danny Pudjianto and Tony Lakin from UK; Jose Maria Oyarzabal, Joseba Jimeno and Iñigo Cobelo from Spain; Nuno Melo and António Amorim from Portugal; Sjef Cobben from the Netherlands; John Eli Nielsen from Denmark; Perego Omar and Michelangeli Chiara from Italy; Aleksandra Krkoleva, Natasa Markovska and Ivan Kungulovski from FYR of Macedonia; Grzegorz Jagoda and Jerszy Zielinski from Poland; my NTUA colleagues Stavros Papathanassiou and Evangelos Dialynas; and Stathis Tselepis, Kostas Elmasides, Fotis Psomadellis, Iliana Papadogoula, Manolis Voumvoulakis, Anestis Anastasiadis, Fotis Kanellos, Spyros Chadjivassiliadis and Maria Lorentzou from Greece. I express my gratitude to my PhD students and collaborators Georgia Asimakopoulou, John Karakitsios, Evangelos Karfopoulos, Vassilis Kleftakis, Panos Kotsampopoulos, Despina Koukoula, Jason Kouveliotis-Lysicatos, Alexandros Rigas, Nassos Vassilakis, Panayiotis Moutis, Christina Papadimitriou and Dimitris Trakas, who reviewed various chapters of the book and provided valuable comments. Finally, I wish to thank the EC DG Research&Innovation for providing the much appreciated funding for the research leading to this book, especially the Officers Manuel Sanchez Jimenez and Patrick Van Hove.
Nikos Hatziargyriou