Design of a High-Speed Motor-Alternator for Flywheel Energy Storage Systems
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Design of a High-Speed Motor-Alternator for Flywheel Energy Storage Systems by Marc J. Carlin S.B., Electrical Science and Engineering, Massachusetts Institute of Technology (1996) Submitted to the Department of Electrical Engineering and Computer Science in partial fulfillment of the requirements for the degree of Master of Engineering in Electrical Engineering and Computer Science at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 1997 © Massachusetts Institute of Technology, 1997. A uthor .................... Departmet El al Engineering and Computer Science 2 June 1997 I / V ~ ~') Certified by ........ ..... .................. .... ................. ........................ ..... James L. Kirtley Professor of Electrical Engineering and Computer Science Thesis Supervisor /,)fr2 "t, J Certified by .......... ........ ............ .................................... Jeffrey H. Lang -rotessdr of Electrical Engineerin and Computer Science TTiI Suwervisor Accepted by .................... Arthur C. Smith Chairman, Department Committee on Graduate Theses Design of a High-Speed Motor-Alternator for Flywheel Energy Storage Systems by Marc J. Carlin Submitted to the Department of Electrical Engineering and Computer Science 2 June 1997 in partial fulfillment of the requirements for the degree of Master of Engineering in Electrical Engineering and Computer Science Abstract High-speed motor-alternators are required in flywheel energy storage systems for hybrid electric vehicles (HEVs). Recent advances in permanent magnet materials and power electronics have stimulated research into the development of permanent-magnet synchronous machines (PMSMs) for this application. Flywheel systems have the potential to replace chemical batteries as HEV energy storage elements, but there are numerous design requirements that must be met before such systems become viable. The primary electromagnetic design challenge and the key contribution of this thesis is the analysis and characterization of eddy current losses in the permanent magnets arrayed around the rotor of the motor-alternator. Models of the relevant electromagnetic and electromechanical attributes of this type of machine, including power rating and electrical losses, are developed. The Ansoft Maxwell finite element software package is used to verify the torque and rotor loss models of the PMSM. A Monte-Carlo based integrated design process is then used to select the frontier of machine designs best suited for this application. The design frontier provides intuition into the design trends and tradeoffs inherent in this system, and investigates the viability of developing high-performance PMSMs with acceptably low rotor eddy current losses. Thesis Supervisors: James L. Kirtley and Jeffrey H. Lang Title: Professors of Electrical Engineering and Computer Science Acknowledgments Funding for this research was provided through a Small Business Technology Transfer Research Grant from the U.S. Department of Energy, with SatCon Technology Corporation as the prime contractor. I wish to thank my advisors, James Kirtley and Jeffrey Lang, for their invaluable insight into electromagnetics and their patience in helping me toward completion of this thesis. Their offices were always open when I needed a helping hand. I also wish to thank Dr. Mary Tolikas of SatCon Corporation, who provided not only key data and insights, but also good humor and cheer. I will take with me fonder memories of M.I.T. because of them. I cannot thank my family enough for the love and support they have shown me during my five-year journey. They were always there to listen and encourage me when I faced challenges and setbacks, and to share in the joy of my successes. My brother Erik has remained my best friend through it all, and to him I am eternally grateful. My roommate Jeff Roth is indeed a diamond in the rough. Without his companionship, advice, listening ear and gentle spirit I don't know how I could have persevered. "How good and pleasant it is when brothers live together in unity." Above all I thank the Lord my God, for it is by His grace that I have been saved and am sustained daily. All that I have is a gift from Him, and all that I am is the work of His hands. He has been faithful to His promise So do not fear for I am with you; do not be dismayed,for I am your God. I will strengthen you and help you; I will uphold you with my righteous right hand. Isaiah 41:10 Contents 1 Introduction ........................................................................................................... 12 1.1 O verview ................................................................................................................ 12 1.2 Research Background ...................................................... ...................... 12 1.3 Permanent-Magnet Synchronous Motor-Alternator ...................................... 14 1.4 Thesis Objectives and Scope................................................ ................... 15 1.5 Integrated Design Approach ...................................................... 16 1.6 T hesis O utline .......................................................................... ........................ 17 2 Development of Analytical Models ...................................................................... 18 2.1 Introduction ............................................... ....................................................... 18 2.2 Design Specification and Objectives ................................................ 18 2.3 Scope of Design Consideration .................................................... 20 2.3.1 Selection of Machine Configuration ....................................... ..... 20 2.3.2 Depth of Analysis ....................................................... ..................... 26 2.4 M otor Param eters ................................................. ............................................ 27 2.5 Analytical Machine Models ....................................................... 29 2.5.1 Machine Terminal Characteristics ........................................ ...... 29 2.5.2 Electromagnetic Torque Model..............................................33 2.5.3 Loss M odels ....................................................................... ...................... 37 2.5.3.1 Armature Loss ......................................................... 38 2.5.3.2 Rotor Eddy Current Losses ............................................... 39 2.5.4 Other Machine Attributes .................................................... 49 3 Model Verification by Finite Element Analysis ..................................................... 51 3.1 Introduction ............................................................................................................ 5 1 3.2 Stationary Field Analysis ........................................................ 52 3.3 Torque Analysis ........................................................................... .................... 54 3.4 Eddy Current Loss Analysis ..................................... ................ 55 4 Motor-Alternator Design Process ................................................... 84 4.1 O verview ........................................................ .................................................. 84 4.2 Construction of the Integrated Design Process ..................................... .... 85 4.2.1 Performance Requirements and Constraints ....................................... 86 4.2.2 Selection of Independent and Dependent Variables ................................... 88 4.2.3 Design Synthesis ...................................................... ...................... 90 4.2.4 Design Analysis........................................................92 4.2.5 Design Evaluation ...................................................... ..................... 92 4.3 Results of the Integrated Design ................................................... 93 4.3.1 Selection of the Optimal Design ............................................... 93 4.3.2 D esign Trends ...................................................................... .................... 93 4.3.3 Sum m ary .......................................................................... ........................ 98 5 Summary, Conclusion and Suggestions for Future Research.................99 5.1 Sum m ary of Thesis Results......................................... ..................................... 99 5.2 Suggestions for Future Research..........................................................................100 Appendix A Air Gap Armature Self-Inductance................. ...... 103 A. 1 Armature Winding Factor ..................................... 103 A.2 Armature Magnetic Field ...................................................... 105 A.3 Armature Self-Inductance ..................................... 111 Appendix B Armature Flux Linkage of Magnet-Produced Field .......................... 114 B. 1 Magnet-Produced Magnetic Field ..................................... 114 B.2 Armature Flux Linkage ......................................................... 121 Appendix C End Turn Analysis ...................................... ............... 125 Appendix D Armature Eddy Current Loss ............................................ 128 Appendix E 2D Rotor Eddy Current Loss Model .................................................. 131 E. 1 Transfer Relation Equations ..................................... ................ 131 E.2 Coupling Equations and Boundary Conditions ........................................