Power and Energy Management of Multiple Energy Storage Systems in Electric Vehicles PhD Thesis Leon C Rosario June 2007 Department of Aerospace Power & Sensors Cranfield University, DCMT Shrivenham Swindon, Wiltshire, SN6 8LA, United Kingdom Power and Energy Management of Multiple Energy Storage Systems in Electric Vehicles A dissertation by LEON CHRISTOPHER ROSARIO Submitted in partial fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Electrical Engineering Supervisor: Dr Patrick Chi Kwong Luk THESIS COMMITTEE Dr Patrick C K Luk Dr John T Economou Prof Brian A White Department of Aerospace Power & Sensors Cranfield University, DCMT Shrivenham Swindon, Wiltshire, SN6 8LA, United Kingdom © Cranfield University 2007 All rights reserved No part of this publication may be reproduced without the written permission of the copyright owner Acknowledgements This journey would not have been as interesting without the fascinating people I met along the way I would first and foremost like to thank my supervisor, Dr Patrick Luk for the opportunity to carry out this research project I am indeed fortunate to have had him as my undergraduate lecturer and project supervisor many years ago and then the privilege of his insightful supervision for this work The trust, support and ‘the freedom to create’ that he has provided throughout the project is very much appreciated It is often said that in life, you will come across very few people that will take a chance on you and give you an opportunity to change your direction in life Dr Luk has taken such a chance, and I thank him for this A special thank you goes out to Dr John Economou for the many brainstorming sessions as well as the leisurely chats we had I am most grateful for the encouragement and support he gave me in writing my first conference paper The subsequent intimidating experience of presenting that paper for a large military audience was somewhat lessened knowing that Dr Economou was also there to back me up if the audience decided to use me as ‘target practice’ I wish to also thank Professor Brian White for his many insightful recommendations and his continuous support throughout my research My sincere appreciation for the tremendous support provided by Cranfield University’s technical staff A special thanks to Barry Grey, Chris Ransom, Colin Offer, Stuart Carter, Stacey Paget, Barry Luffman, Alan Norris, Chris Bland, Tony Low and all workshop staff Thanks to you folks, everything I build from now on has to be of a ‘proper-job’ calibre The postgraduate centre would not have been the same without Mr John Reynolds to keep us all sane I will certainly have fond memories of ‘wind-up Wednesdays’ And where would we be without fellow student Michael Gibson to rescue us when our computers crash It was also a pleasure to make the acquaintance of all the other research students at Heaviside Labs My heartfelt appreciation goes out to my parents, parents in-law, my two brothers, sister inlaws and my nephews, Jason and Kevin A special thank you to my Mum for allowing me to experiment with electricity as a little boy even though she would have preferred if I had expressed an ounce of interest in biology, and to my Dad for fuelling my interest to understand how things work and for teaching me the art of transforming imagination into something real I am an extension of both of them, and proud of it As an expression of my faith and appreciation of everything in my life, El shaddai, El shaddai, El-elyon na adonia Erkamka na adonai Finally, To my loving wife Vanessa, for tolerating my eccentric ways the past three years, and for agreeing to stand by me till the end of time… ii ABSTRACT This dissertation contributes to the problem description of managing power and energy of multiple energy sources for electric vehicle power system architectures The area of power and energy management in the application domain of electric vehicles is relatively new and encompasses several different disciplines Primarily, the challenges in electric vehicles having multiple energy storage systems lies in managing the energy expenditure, determining the proportional power splits and establishing methods to interface between the energy systems so as to meet the demands of the vehicle propulsion and auxiliary load requirements In this work, an attempt has been made to provide a new perspective to the problem description of electric vehicle power and energy management The overall approach to the problem borrows from the basic principles found in conventional management methodology The analogy between well-known hierarchical management concepts and power and energy management under timing constraints in a general task-graph is exploited to form a well-defined modular power and energy management implementation structure The proposed methodology permits this multidisciplinary problem to be approached systematically The thesis introduces a modular power and energy management system (MPEMS) Operation of the M-PEMS is structured as tri-level hierarchical process shells An Energy Management Shell (EMS) handles the long-term decisions of energy usage in relation to the longitudinal dynamics of the vehicle while processes within a Power Management Shell (PMS) handles the fast decisions to determine power split ratios between multiple energy sources Finally, a Power Electronics Shell (PES) encompasses the essential power interfacing circuitry as well as the generation of low-level switching functions This novel framework is demonstrated with the implementation of a power and energy management system for a dual-source electric vehicle powered by lead acid batteries and ultracapacitors A series of macro simulations of the energy systems validated against practical tests were performed to establish salient operating parameters These parameters were then applied to the M-PEMS design of a demonstrator vehicle to determine both the general effectiveness of a power and energy management scheme and to support the validity of the new framework Implementation of the modular blocks that composes the entire system architecture is described with emphasis given to the power electronics shell infrastructure design The modular structure approach is design-implementation oriented, with the objective of contributing towards a more unified description of the electric vehicle power and energy management problem i Nomenclature Notation Description Unit Ibatt Iuc Iload Ibattref Iucref Vbatt Vuc VDC Vbattref Vucref Vbusref PLoad Pbatt Puc Pbattmax Pbattmin Pucmax Pucmin Pavg Pucchg Lbatt Luc Cbatt Cuc CDC Voc Ah η fsw Gpbatt Gnbatt SoCbatt SoCuc D Battey current Ultracapacitor current Load current Battery reference current Ultracapacitor reference current Battery voltage Ultracapacitor volatge DC bus voltage Battery reference voltage Ultracapacitor reference voltage DC bus reference voltage Load power Battery power Ultracapacitor power Maximum Battery discharge power Maximum Battery charge power Maximum Ultracapacitor discharge power Maximum Ultracapacitor charge power Average load power UC reference charging power Battey converter inductor Ultracapacitor converter inductor Battery parallel input capacitance Ultracapacitor parallel input capacitance DC bus capacitance Open circuit voltage Ampere hour Efficiency Switching frequency Battery positive slew coefficient Battery negative slew coefficient Battery State of Charge Ultracapacitor State of Charge Duty cycle iii ampere ampere ampere ampere ampere volt volt volt volt volt volt watt watt watt watt watt watt watt watt watt henry henry farad farad farad volt amphour hertz watt/second watt/second - [A] [A] [A] [A] [A] [V] [V] [V] [V] [V] [V] [W] [W] [W] [W] [W] [W] [W] [W] [W] [H] [H] [F] [F] [F] [V] [Ah] [%] [Hz] [W/s] [W/s] Notation Description FTR Fla FgxT Froll FAD Tractive force Linear acceleration force Gravitational force Rolling resistance force Aerodynamic Drag Force AF Unit newton newton newton newton newton [N] [N] [N] [N] [N] β Vehicle equivalent frontal area Vehicle inclination angle square metre radians [m2] [rad] g m Gravitational acceleration constant Mass square metre kilogram [m2] ρ kilogram per cubic metre - [kg/m3] CD C0 ,C1 Air density Aerodynamic drag Rolling resistance coefficients E P I V Vs t Euc Ebatt Ekin k i n Energy Power Current Voltage Vehicle speed Time Ultracapacitor energy Battery energy Vehicle kinetic energy Time step Index Index watt hour ( Joule ) watt ampere volt metre per second second joule joule joule - [Wh] or [ J] [W] [A] [V] [ms-1] [s] [J] [J] [J] iv [kg] Abbreviations Batt (batt) DoD EMS EPR ESR EV HEV KVL LSB MOSFET M-PEMS MSB PES PMS PWM SLA SoC SoD UC (uc) VHDL VRLA Battery Depth of Discharge Energy Management Shell Equivalent Parallel Resistance Equivalent Series Resistance Electric Vehicle Hybrid Electric Vehicle Kirchoff's Voltage Law Least Significant Bit Metal Oxide Field Effect Transistor Modular Power and Energy Management Structure Most Significant Bit Power Electronics Shell Power Management Shell Pulse Width Modulation Sealed Lead Acid State of Charge State of Discharge Ultracapacitor Very high speed integrated circuit Hardware Description Language Valve Regulated Lead Acid v Contents CONTENTS List of Figures List of Tables Chapter Introduction 1.1 Motivation 1.2 The emerging area of Vehicle Power and Energy Management 10 1.3 Background on Electric Vehicles 12 1.4 Research Rationale 14 1.5 Problem Scope 16 1.6 Methodology 17 1.7 Contributions 20 1.8 Thesis Outline 22 1.9 Publications 24 Chapter 26 Literature Review 26 2.1 Overview 27 2.2 Multiple Energy Storage Systems in an EV 28 2.3 Power and Energy Management of Multiple Energy Storage Systems 29 2.4 EV Enabling Technology – The Ultracapacitor 35 2.5 Hybridisations of Batteries and Ultracapacitors in EV Power Systems 39 2.6 Ultracapacitor augmentation issues 48 2.7 Alternative ultracapacitor system configurations 48 2.8 Observations and Hypothesis 50 Chapter 55 EV Batteries and Ultracapacitors -Modelling and Application 55 3.1 EV Battery Systems 56 3.2 Basic configuration of secondary batteries 56 3.3 EV Battery systems 58 3.4 Battery Specific Energy (SEbatt) 61 3.5 Battery Specific Power (SPbatt) 61 3.6 Battery Capacity 61 3.7 Self Discharge 62 3.8 Faradic Efficiency (Amphour Efficiency) 63 3.9 Battery Energy Efficiency 63 3.10 Battery Modelling 65 3.11 Practical Application of Peukert’s Equation 67 3.12 Battery State of Charge (SoC) 69 3.13 Battery Internal Resistance (Ri) 70 3.14 Determining Battery Operating Constraints 71 3.15 EV Battery Management 74 3.16 Extended Battery equivalent circuit models 77 3.17 Ultracapacitors 82 3.18 Ultracapacitor Modelling 84 Contents 3.19 3.20 3.21 3.22 Ultracapacitor Power and Energy 87 Ultracapacitors in series 90 Hybridisation of Batteries and Ultracapacitors 94 Summary 97 Chapter 99 Electric Vehicle Power and Energy Requirements 99 4.1 Vehicle Longitudinal Dynamics 100 4.2 Vehicle Propulsion Power Demand 103 4.3 Vehicle Propulsion Energy Demand 104 4.4 Regenerative Braking 106 4.5 Vehicle Model - SIMPLORER 109 4.6 Case study of the effectiveness of combining batteries and ultracapacitors to service a vehicle power and energy demands 111 4.7 Summary 125 Chapter .126 The Management of Power and Energy 126 5.1 Adopting the general concept of management 127 5.2 Adaptation of hierarchical management concepts to Power and Energy Management 131 5.3 A Modular power and energy management structure (M-PEMS) 132 5.4 Energy Management Shell (EMS) 135 5.5 Power Management Shell (PMS) 136 5.6 Power Electronics Shell (PES) 138 5.7 M-PEMS implementation for a battery - ultracapacitor powered Electric Vehicle 139 5.8 Implementation of a PMS Policy 141 5.9 Implementation of an EMS Strategy 148 5.10 Extending the EMS strategy 154 5.11 Implementation of a Power Electronics Shell 155 5.12 Summary 162 Chapter .163 Hardware Description 163 6.1 The experimental vehicle 164 6.2 Battery System 165 6.3 Ultracapacitor System 166 6.4 Instrumentation and Control System 167 Chapter .172 Implementation framework 172 7.1 Design Rationale 173 7.2 Converter Topology 173 7.3 Theory of operation 174 7.4 Converter operating specification 175 7.5 Battery Boost Mode - Discharge mode (STATE 100) 177 7.6 Battery Buck Mode - Charging mode (STATE 111) 182 7.7 Ultracapacitor Boost Mode – Discharging mode (STATE 001) 186 7.8 Ultracapacitor Buck Mode – Charging mode (STATE 010) 191 7.9 Reactive component design 194 Contents 7.10 7.11 Converter Switching Components 204 Summary 207 Chapter 208 Experiments and Type Tests 208 8.1 Experiment 1: Model verification 209 8.2 Experiment 2: Empirical observations and instrumentation tests 213 8.3 Experiment 3: Power Management hardware in loop verification 218 8.4 PES Type Test 228 Chapter 232 Conclusions and Future work 232 9.1 Conclusions 233 9.2 Future work 237 References 239 Appendices 248 Appendix A: Schematics Appendix B: Selected Type Tests Appendix C: Images ... The Management of Power and Energy 126 5.1 Adopting the general concept of management 127 5.2 Adaptation of hierarchical management concepts to Power and Energy Management ... effectiveness of the hypothesized power and energy management implementation methodology The hardware is developed based on the application requirements and constraints of the test vehicle and energy. .. 7.11 Schematic and physical layout of the DC bus capacitor bank 204 Figure 7.12 Comparison of converter power losses as a function of demanded power transfer and State of Charge (SoC) of the ultracapacitors