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Series Editor

Bernard Multon

Electrical Energy Storage in Transportation Systems

Benoît Robyns

Christophe Saudemont

Daniel Hissel

Xavier Roboam

Bruno Sareni

Julien Pouget

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Foreword

In this second book, called Electrical Energy Storage in Transportation Systems, Professor Robyns and his coauthors accomplish the aim they set upon from the beginning of their project, that is to present the reader with rigorous methodological approaches based on the concept of energy management supervisors for complex systems, including different sources and stock elements.

As indicated in the title, this new book is dedicated to electric transport, which is of particular relevance because of its broad applications – such as onboard networks in aeronautics, the integration of electric vehicles in the electric network, hybrid vehicles, or even hybrid railway traction and its installations. We have already highlighted, in our previous preface, the importance for our society of offering alternative solutions to currently available energy systems based on fossil or nuclear energy, via transitory solutions such as the hybrid vehicle. However, numerous scientific challenges still remain, the two principal ones being the limited performance of batteries and the difficulty to manage very complex systems in real time. This book particularly aims to provide an answer to this challenge. We can admit that the bet has been successful.

Indeed, pursuing the themes of the previous book, dealing with the management of energy production systems based on renewable sources and stock units, the authors deepen their methodology of fuzzy logic supervision. The presentation that they provide is highly pedagogic, and we follow with interest all the stages that lead to the elaboration of supervision (i.e. drafting the specifications, defining entry and exit variables, conceiving functional graphs corresponding to all necessary hierarchical levels, fuzzification of the problem and optimizing supervisor structures with the aid of genetic algorithms and experimental design).

In this book, apart from implementing the structured methodology based on the design of an energy management supervisor developed at the Laboratoire d'Electrotechnique et d'Electronique de Puissance of Lille, other complementary methods developed at Belfort and Toulouse Laboratories are equally explored. They concern fuzzy logics of type 2, filtering methods and explicit optimization.

Finally, they systematically propose an experimental validation of the studied structures, and this is not a minor contribution in the exposed works.

Thus, happily matching industrial theory and practice, this book will become an indispensable reference for all engineers and researchers working in the field of electric energy management of onboard systems.

Eric MONMASSON
June 2016

Introduction

At the end of the 19th Century, electrical energy was used in railway and road transport; the experimental electric vehicle "La Jamais Contente" (The Never Satisfied) exceeded 100 km/h in 1899. However, the difficulty of storing electrical energy in sufficient quantities, within reasonable volume and weight limits, represented one of the major obstacles in the development of autonomous electric vehicles that are able to travel medium- to long distances. At present, the development of renewable energy sources and the demand for low-carbon modes of transport are generating renewed interest in the storage of electrical energy, which becomes a key element for sustainable development. From this moment on, modern storage technologies make it possible to envisage the development of electric vehicles with acceptable performance levels, more efficient electrification of aircraft, the development of hybrid autonomous vehicles and locomotives, but also using storage to improve energy efficiency and to secure the supply of electrical transport systems. The aim of this book is to contribute to a better knowledge and understanding of these developing technologies within the framework of transport systems and more particularly with regard to their management and operation.

The aims of this book are to:

  1. – highlight the importance of storing electrical energy in accordance with the principles of sustainable development in transport, in the context of deploying smart electric power grids or “smart grids”, grids with which a certain number of transport systems will interact to an increasing extent, such as electric vehicles, plug-in hybrids, trains, underground trains, trams and electric buses;
  2. – present the variety of services provided with respect to the storage of electrical energy;
  3. – present methodological tools that make it possible to build an energy storage management system following a generic and pedagogical approach. These tools rely on artificial intelligence and explicit optimization methods. They are presented throughout the book with respect to practical case studies;
  4. – illustrate these methodological approaches using several practical and pedagogical examples regarding the electrification of transport units and their integration into electric power grids, in specific cases, with respect to the production of electrical energy from variable renewable energy sources.

The first chapter formulates the issues of storing electrical energy in transport systems. The storage requirements of these applications are highlighted, along with their numerous contributions. A design methodology for storage system management, relying on artificial intelligence, is introduced; it is particularly well adapted for the management of complex systems involving uncertainties related to the forecast of the production of variable renewable energy, the consumption induced by the trajectory or the power profile of the vehicle or aircraft, but also of the electrical grid when the system in question is connected to it. This methodology serves several objectives requiring real-time processing.

The second chapter presents the integration of electrical energy storage into aeronautic onboard grids. The increase in the number of electric charges as well as the gradual substitution of the actuators, originally hydrostatic or mechanical, by electro-hydrostatic or electro-mechanical actuators, are the main causes of the increased electrification of aircraft. The onboard electric power grids developed alternative solutions with fixed and variable frequency, and configurations of direct current grids (local or distributed) for the exchange of energy including storage are developed. Direct current grids, including storage, facilitate bidirectional electrical power flows, making it possible to recover the braking energy of the actuators, reduce the number of electronic power converters and the cable diameter between the main electrical grid and the actuators, thus allowing for gains in volume and mass. They also provide the possibility of increasing the reliability of these grids owing to the use of storage as a local emergency power supply. A structured methodology for the development of an energetic supervisor in real time, based on fuzzy logic, has been applied to the management of energy in a local energy exchange direct current grid, from the creation of a list of functional specifications (objectives and constraints) to the optimization stage of the supervisor parameters. A comparison is made between supervision strategies that use fuzzy logic only and solutions that do not resort to it (using, for example, a PI controller) together with combined solutions. Implementation on an experimental basis in real time is also addressed.

The third chapter refers to autonomous road vehicles. The first part refers to the charge management of electric vehicles, so as to incorporate them into the electric power grids harmoniously and to give priority to a charge using renewable energy as a guarantee of low environmental impacts. The design methodology of a supervisor based on fuzzy logic is implemented until the optimization of the parameter supervisor. The prospect of a more active contribution of electric vehicles to electric power grids (Vehicle to Grid and Vehicle to Home) is also addressed. The final part of this chapter provides an overview of various configurations of hybrid power trains which are implemented practically. The management of a hybrid vehicle, comprising electrochemical batteries, supercapacitors and a fuel cell, is then developed using fuzzy logic. A variant of fuzzy logic, referred to as type-2 fuzzy logic, which involves the uncertainty related to the determination of membership functions, is implemented.

The fourth chapter addresses hybrid electric traction for railway applications. The first part of the chapter, dedicated to rolling stocks, provides a detailed description of storage systems for the diesel hybrid traction unit, which includes two onboard technologies for storage systems: electrochemical batteries and supercapacitors. The energy management of these systems is carried out by combining digital filtering and explicit optimization methods. Experimental implementation on a real locomotive is also described. The second part introduces, in a pedagogical manner, practices dedicated to using onboard storage systems for electrical traction. The analysis is based on the kinematic profile to relate back to the basic energy requirements of the railway system. Starting from this description, the set of relevant applications of the energy storage systems is presented in more detail. In this part, numerical applications derived from real cases are presented to illustrate the scope and the energy issues of onboard energy storage systems in the railway sector.

The integration of systems for producing variable renewable energy (photovoltaic and/or wind) and for storing the energy directly in the feed system of the railway system introduces the notion of the railway “smart grid”. The fifth chapter describes this evolution, along with an analysis of the services that can be provided by the new hybrid railway power substations (HRPS) which supply the railway network. Reference is made to the services provided to the railway system itself, but also to electric power grids conducting and distributing the electrical energy and to local producers of renewable energy. A two-stage energy management process for an HRPS is then developed, with a first forecast stage (long-term management) and a different one in real time (short-term management), making it possible to adapt to fluctuations, as well as uncertainties in predicting the production of renewable energy, but also to deviations in the charge profile represented by the movement of trains. The supervision stage in real time is constituted following the structured methodology based on an artificial intelligence tool, namely fuzzy logic. The parameters of the supervisor are optimized and a sensitivity study, within an experimental platform in laboratories, makes it possible to evaluate the robustness of the supervisor. Finally, the development prospects for railway smart grids conclude this chapter.