DOCSLIB.ORG

Air Gap Elimination in Permanent Magnet Machines

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Air Gap Elimination in Permanent Magnet Machines AIR GAP ELIMINATION IN PERMANENT MAGNET MACHINES By Andy Judge A Dissertation Submitted to the Faculty of the WORCESTER POLYTECHNIC INSTITUTE In partial fulfillment of the requirements for the Degree of Doctor of Philosophy In Mechanical Engineering by _________________________________________________________ March 2012 APPROVED: _________________________________________________________ Dr. James D. Van de Ven, Advisor _________________________________________________________ Dr. Cosme Furlong-Vazquez, Committee Member _________________________________________________________ Dr. Alexander E. Emanuel, Committee Member _________________________________________________________ Dr. Eben C. Cobb, Committee Member _________________________________________________________ Dr. David J. Olinger, Graduate Committee Representative ABSTRACT In traditional Permanent Magnet Machines, such as electric motors and generators, power is transmitted by magnetic flux passing through an air gap, which has a very low magnetic permeability, limiting performance. However, reducing the air gap through traditional means carries risks in manufacturing, with tight tolerances and associated costs, and reliability, with thermal and dynamic effects requiring adequate clearance. Using a magnetically permeable, high dielectric strength material has the potential to improve magnetic performance, while at the same time offering performance advantages in heat transfer. Ferrofluids were studied as a method for improved permeability in the rotor / stator gap with a combined experimental and computational approach. Results show promise for the ferrofluid technique. An off-the-shelf motor system showed improved performance with ferrofluids vs. fluids of equivalent viscosity, and improved performance vs. an air gap at low RPM. New generator designs showed design dependent performance gains, although some potential for negative performance effects. A proof of concept generator was built and tested, with increased voltage vs. RPM predicted through virtual prototyping, and validated through experimentation, showing ~10% improvement on voltage vs. RPM at the <600 RPM range. More repeatable engineering tests demonstrated a ~30% increase in the voltage / RPM relationship for designs with an isolated stator chamber and a large stator – rotor gap. However, the effects were negative for a similar system with a small stator-rotor gap due to leakage flux effects. i New contributions to the body of knowledge in this area include: • Application of the ferrofluid technique to axial flux designs. • Development of a virtual prototype, including variations in the fluid viscosity due to ferrohydrodynamic effects. • Consideration of negative effects of ferrofluid immersion, such as shear losses and increases in leakage flux. • Optimization of the design to eliminate increased viscous losses. The improved design has been designed, built, and tested, featuring isolation of the ferrofluid from the rotating region. This offers all of the performance gain of improved magnetic permeability, while minimizing the offsetting losses from increased shear effects. ii ACKNOWLEDGEMENTS To start, I would like to thank the faculty of Worcester Polytechnic Institute, including the members of my dissertation committee, and throughout the University. It had been a few years since I had last taken a class, and the overall graduate experience at WPI reminded me of why I became an engineer in the first place – my love of learning and technology. I am especially grateful to my advisor, Dr. James Van de Ven, who reminded me of what engineering research was all about, helping me get started, offering support whenever needed and giving me the freedom to make my own path throughout the process. None of this would have been possible without the financial support of my employers, ITT for the first three years of my PhD coursework and research, and DRS for the past few months. Also, I am appreciative of John Schneider and Mark St. Pierre, two former supervisors of mine, who wrote my recommendations to WPI, and were a pleasure to work for. I am also grateful to my co-workers, including those who helped me learn the basics of Permanent Magnet Machines when I started in the field, and those who taught me the fine points as my understanding of the topic grew. Of course, my most heartfelt thanks go to my family, including my father, for giving me his work ethic, and my mother, for giving me her love of life. To my children, Sawyer and Delaney, I am always grateful for, and want nothing more than to have you continue living happy, healthy lives. Finally, to my wife Wendy, thank you for supporting me in this, for loving me back, and for understanding me in such a complete way. iii TABLE OF CONTENTS Abstract……..…………………………..…………………………….…………………...i Acknowledgements………………………………………………………………………ii Table of Contents………………………………………..…………………….………...iii List of Tables…………………………………………………..………………………..vii List of Figures………………………………………………………..………………...viii Nomenclature………………………………………………………..……………….…xv Chapter 1…………………………………………………………………………………1 1.1 Background………………………………………………………………......1 1.2 Literature Review ……………………………………………….………..…2 1.2.1 Primary Sources …………………………………………………...3 1.2.2 Secondary Sources ……………………………………………….15 1.2.3 Citation Summary.………………………………………………..21 1.3 Overview….…………………………………………………………………22 Chapter 2 - Fundamentals of Magnetics….……………………..…………………….25 2.1 Magnetics……………………………………………………………………25 2.2 Fundamentals of Electromagnetism..……………………………………...32 iv 2.3 Permanent Magnet Machines – Air Gaps.………………………………..43 2.4 Fundamentals of Ferrofluids...…………………………………………….47 2.4.1 Tradeoffs to Ferrofluid Immersion..……………………….……50 Chapter 3 - Computational Model…………………………………………………….60 3.1 Background.………………………………………………………………...60 3.2 Computational Model…...………………………………………………….60 3.2.1 Macro-Scale Model..……………………………………………...61 3.2.2 Finite Element Analysis….……………………………………….66 Chapter 4 - Experiment 1 – Off the Shelf Motor……………………………………..83 4.1 Background…………………………………………………………………83 4.2 Experimental Results....…………………………………………………….83 Chapter 5 - Experiment 2 – Proof of Concept Generator……………………………97 5.1 Background…………………………………………………………………97 5.2 Experimental Results....…………………………………………………...101 Chapter 6 - Experiment 3 – Large Gap Ferrofluid Experiment..………………….109 6.1 Background………………………………………………………………..109 v 6.2 Experimental Results....…………………………………………………...109 Chapter 7 - Experiment 4 – Small Gap Ferrofluid Experiment...………………….119 7.1 Background..……………………………………………………………....119 7.2 Experimental Results......………………………………………………….119 Chapter 8 – Conclusions.....………………………………………………………..….129 8.1 Review....………………………………………………………...............…129 8.2 Conclusion......………...………………………………………............…...132 8.3 Recommendations for Future Work...…………………………………...135 References.……………………………………………………………………………..137 Appendix A: Magnetic Gears and Couplings.……………………………………….142 Appendix B: Experimental Part Drawings….……………………………………….148 vi LIST OF TABLES 2.3-1 – Losses in Permanent Magnet Machines. ………………………………..44 2.4.1-1 – Ferrofluid Viscosity and Density. ……...……………………………...51 3.2.2-1 – Summary, Mesh Sensitivity Study. …………………………………...73 3.2.2-2 – FEA Results, Increased Gap Permeability. …………………………...74 3.2.2-3 – FEA Results, Increased Permeability, Complete Immersion. ………...77 3.2.2-4 – FEA Results, Complete Immersion, 2.0” Leg Width.…………………80 3.2.2-5 – FEA Results, Increased Gap Permeability, Varying C-Channel Geometry…………………………………………………………………………82 6.2-1 – Experimental Data, Experiment 3. …………………………………….117 7.2-1 – Experimental Data, Experiment 4. ……………………………….........127 vii LIST OF FIGURES 1.2.1-1 - Nethe, et al. Magnetic Circuit. ……....…………………………….........6 1.2.1-2 - Nethe, et al. Force vs. Permeability for Various Air gap Distances….....7 1.2.1-3 – Nethe, et al. Analytical Model for Force vs. Relative Permeability for Various Air gap Distances………………………………………………………...8 1.2.1-4: Nethe, et al. Torque vs. Various Air Gap Distance for Various Maximum Levels of Magnetic Saturation. ……………………..…………………………….9 1.2.1-5 – Nethe, et al. Heat Flux Delta Versus Gap Width for Various Thermal Coefficients and Speed Ranges. …………………………………………….…...10 1.2.1-6 – Nethe, Et al. Linear Permanent Magnet Machine Experimental Fixture. ..…………................................................................................................11 1.2.1-7 –Nethe, Et al. Linear Permanent Magnet Machine Experimental Results....................................................................................................................12 1.2.1-8 – Nethe, et al. Rotating Permanent Magnet Machine CAD Model...........13 1.2.1-9 – Nethe, et al. Rotating Permanent Magnet Machine Experimental Results. …………………………………………………………………………..14 1.2.2-1 – Torque vs. Relative Angular Offset and Air gap Distance. …………...15 1.2.2-2 – Thingap Manufacturing Process. ………………………………….......16 viii 1.2.2-3 – Flux Guide for Permanent Magnet Machines. ………………………...17 1.2.2-4 – Ferrofluidic Generator, Heat Powered. ………………………………..18 1.2.2-5 - Ferrofluidic Generator, Rotary Motion Powered. …………………..…19 1.2.2-6 – Standard Halbach Array. ………………………………………….......20 1.2.2-7 – Extended Halbach Array………………………...……………...…......21 2.1-1 – Magnetic Element. ………………………………………………………26 2.1-2 – PMM Resistor Network. ………………………………………………...28 2.1-3 - Magnetic Flux Density vs. Magnetic Field Strength, D6ac Steel…..........30 2.2-1 - Traditional Brushed Motor / Generator. …………………………………33 2.2-2 - Demagnetization Curve for
Load more

Recommended publications
  • Permanent Magnet Guidelines
    MMPA PMG-88 PERMANENT MAGNET GUIDELINES I. Basic physics of permanent magnet materials II. Design relationships, figures of merit and optimizing techniques III. Measuring IV. Magnetizing V. Stabilizing and handling VI. Specifications, standards and communications VII. Bibliography MAGNETIC MATERIALS PRODUCERS ASSOCIATION 8 SOUTH MICHIGAN AVENUE • SUITE 1000 • CHICAGO, ILLINOIS 60603 INTRODUCTION This guide is a supplement to our MMPA Standard No. 0100. It relates the information in the Standard to permanent magnet circuit problems. The guide is a bridge between unit property data and a permanent magnet component having a specific size and geometry in order to establish a magnetic field in a given magnetic circuit environment. The MMPA 0100 defines magnetic, thermal, physical and mechanical properties. The properties given are descriptive in nature and not intended as a basis of acceptance or rejection. Magnetic measure- ments are difficult to make and less accurate than corresponding electrical mea- surements. A considerable amount of detailed information must be exchanged between producer and user if magnetic quantities are to be compared at two locations. MMPA member companies feel that this publication will be helpful in allowing both user and producer to arrive at a realistic and meaningful specifica- tion framework. Acknowledgment The Magnetic Materials Producers Association acknowledges the out- standing contribution of Rollin J. Parker to this industry and designers and manufacturers of products usingpermanent magnet materials. Mr Parker the Technical Consultant to MMPA compiled and wrote this document. We also wish to thank the Standards and Engineering Com- mittee of MMPA which reviewed and edited this document. December 1987 3M July 1988 5M August 1996 1M December 1998 1 M CONTENTS The guide is divided into the following sections: Glossary of terms and conversion tables- A very important starting point since the whole basis of communication in the magnetic material industry involves measurement of defined unit properties.
    [Show full text]
  • Analysis of Magnetic Field and Electromagnetic Performance of a New Hybrid Excitation Synchronous Motor with Dual-V Type Magnets
    energies Article Analysis of Magnetic Field and Electromagnetic Performance of a New Hybrid Excitation Synchronous Motor with dual-V type Magnets Wenjing Hu, Xueyi Zhang *, Hongbin Yin, Huihui Geng, Yufeng Zhang and Liwei Shi School of Transportation and Vehicle Engineering, Shandong University of Technology, Zibo 255049, China; [email protected] (W.H.); [email protected] (H.Y.); [email protected] (H.G.); [email protected] (Y.Z.); [email protected] (L.S.) * Correspondence: [email protected]; Tel.: +86-137-089-41973 Received: 15 February 2020; Accepted: 17 March 2020; Published: 22 March 2020 Abstract: Due to the increasing energy crisis and environmental pollution, the development of drive motors for new energy vehicles (NEVs) has become the focus of popular attention. To improve the sine of the air-gap flux density and flux regulation capacity of drive motors, a new hybrid excitation synchronous motor (HESM) has been proposed. The HESM adopts a salient pole rotor with built-in dual-V permanent magnets (PMs), non-arc pole shoes and excitation windings. The fundamental topology, operating principle and analytical model for a magnetic field are presented. In the analytical model, the rotor magnetomotive force (MMF) is derived based on the minimum reluctance principle, and the permeance function considering a non-uniform air-gap is calculated using the magnetic equivalent circuit (MEC) method. Besides, the electromagnetic performance including the air-gap magnetic field and flux regulation capacity is analyzed by the finite element method (FEM). The simulation results of the air-gap magnetic field are consistent with the analytical results. The experiment and simulation results of the performance show that the flux waveform is sinusoidal-shaped and the air-gap flux can be adjusted effectively by changing the excitation current.
    [Show full text]
  • University Physics 227N/232N Ch 27
    Vector pointing OUT of page University Physics 227N/232N Ch 27: Inductors, towards Ch 28: AC Circuits Quiz and Homework This Week Dr. Todd Satogata (ODU/Jefferson Lab) [email protected] http://www.toddsatogata.net/2014-ODU Monday, March 31 2014 Happy Birthday to Jack Antonoff, Kate Micucci, Ewan McGregor, Christopher Walken, Carlo Rubbia (1984 Nobel), and Al Gore (2007 Nobel) (and Sin-Itiro Tomonaga and Rene Descartes and Johann Sebastian Bach too!) Prof. Satogata / Spring 2014 ODU University Physics 227N/232N 1 Testing for Rest of Semester § Past Exams § Full solutions promptly posted for review (done) § Quizzes § Similar to (but not exactly the same as) homework § Full solutions promptly posted for review § Future Exams (including comprehensive final) § I’ll provide copy of cheat sheet(s) at least one week in advance § Still no computer/cell phone/interwebz/Chegg/call-a-friend § Will only be homework/quiz/exam problems you have seen! • So no separate practice exam (you’ll have seen them all anyway) § Extra incentive to do/review/work through/understand homework § Reduces (some) of the panic of the (omg) comprehensive exam • But still tests your comprehensive knowledge of what we’ve done Prof. Satogata / Spring 2014 ODU University Physics 227N/232N 2 Review: Magnetism § Magnetism exerts a force on moving electric charges F~ = q~v B~ magnitude F = qvB sin ✓ § Direction follows⇥ right hand rule, perpendicular to both ~v and B~ § Be careful about the sign of the charge q § Magnetic fields also originate from moving electric charges § Electric currents create magnetic fields! § There are no individual magnetic “charges” § Magnetic field lines are always closed loops § Biot-Savart law: how a current creates a magnetic field: µ0 IdL~ rˆ 7 dB~ = ⇥ µ0 4⇡ 10− T m/A 4⇡ r2 ⌘ ⇥ − § Magnetic field field from an infinitely long line of current I § Field lines are right-hand circles around the line of current § Each field line has a constant magnetic field of µ I B = 0 2⇡r Prof.
    [Show full text]
  • Power-Invariant Magnetic System Modeling
    POWER-INVARIANT MAGNETIC SYSTEM MODELING A Dissertation by GUADALUPE GISELLE GONZALEZ DOMINGUEZ Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY August 2011 Major Subject: Electrical Engineering Power-Invariant Magnetic System Modeling Copyright 2011 Guadalupe Giselle González Domínguez POWER-INVARIANT MAGNETIC SYSTEM MODELING A Dissertation by GUADALUPE GISELLE GONZALEZ DOMINGUEZ Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Approved by: Chair of Committee, Mehrdad Ehsani Committee Members, Karen Butler-Purry Shankar Bhattacharyya Reza Langari Head of Department, Costas Georghiades August 2011 Major Subject: Electrical Engineering iii ABSTRACT Power-Invariant Magnetic System Modeling. (August 2011) Guadalupe Giselle González Domínguez, B.S., Universidad Tecnológica de Panamá Chair of Advisory Committee: Dr. Mehrdad Ehsani In all energy systems, the parameters necessary to calculate power are the same in functionality: an effort or force needed to create a movement in an object and a flow or rate at which the object moves. Therefore, the power equation can generalized as a function of these two parameters: effort and flow, P = effort × flow. Analyzing various power transfer media this is true for at least three regimes: electrical, mechanical and hydraulic but not for magnetic. This implies that the conventional magnetic system model (the reluctance model) requires modifications in order to be consistent with other energy system models. Even further, performing a comprehensive comparison among the systems, each system’s model includes an effort quantity, a flow quantity and three passive elements used to establish the amount of energy that is stored or dissipated as heat.
    [Show full text]
  • Transient Simulation of Magnetic Circuits Using the Permeance-Capacitance Analogy
    Transient Simulation of Magnetic Circuits Using the Permeance-Capacitance Analogy Jost Allmeling Wolfgang Hammer John Schonberger¨ Plexim GmbH Plexim GmbH TridonicAtco Schweiz AG Technoparkstrasse 1 Technoparkstrasse 1 Obere Allmeind 2 8005 Zurich, Switzerland 8005 Zurich, Switzerland 8755 Ennenda, Switzerland Email: [email protected] Email: [email protected] Email: [email protected] Abstract—When modeling magnetic components, the R1 Lσ1 Lσ2 R2 permeance-capacitance analogy avoids the drawbacks of traditional equivalent circuits models. The magnetic circuit structure is easily derived from the core geometry, and the Ideal Transformer Lm Rfe energy relationship between electrical and magnetic domain N1:N2 is preserved. Non-linear core materials can be modeled with variable permeances, enabling the implementation of arbitrary saturation and hysteresis functions. Frequency-dependent losses can be realized with resistors in the magnetic circuit. Fig. 1. Transformer implementation with coupled inductors The magnetic domain has been implemented in the simulation software PLECS. To avoid numerical integration errors, Kirch- hoff’s current law must be applied to both the magnetic flux and circuit, in which inductances represent magnetic flux paths the flux-rate when solving the circuit equations. and losses incur at resistors. Magnetic coupling between I. INTRODUCTION windings is realized either with mutual inductances or with ideal transformers. Inductors and transformers are key components in modern power electronic circuits. Compared to other passive com- Using coupled inductors, magnetic components can be ponents they are difficult to model due to the non-linear implemented in any circuit simulator since only electrical behavior of magnetic core materials and the complex structure components are required.
    [Show full text]
  • 6.685 Electric Machines, Course Notes 2: Magnetic Circuit Basics
    Massachusetts Institute of Technology Department of Electrical Engineering and Computer Science 6.685 Electric Machines Class Notes 2 Magnetic Circuit Basics c 2003 James L. Kirtley Jr. 1 Introduction Magnetic Circuits offer, as do electric circuits, a way of simplifying the analysis of magnetic field systems which can be represented as having a collection of discrete elements. In electric circuits the elements are sources, resistors and so forth which are represented as having discrete currents and voltages. These elements are connected together with ‘wires’ and their behavior is described by network constraints (Kirkhoff’s voltage and current laws) and by constitutive relationships such as Ohm’s Law. In magnetic circuits the lumped parameters are called ‘Reluctances’ (the inverse of ‘Reluctance’ is called ‘Permeance’). The analog to a ‘wire’ is referred to as a high permeance magnetic circuit element. Of course high permeability is the analog of high conductivity. By organizing magnetic field systems into lumped parameter elements and using network con- straints and constitutive relationships we can simplify the analysis of such systems. 2 Electric Circuits First, let us review how Electric Circuits are defined. We start with two conservation laws: conser- vation of charge and Faraday’s Law. From these we can, with appropriate simplifying assumptions, derive the two fundamental circiut constraints embodied in Kirkhoff’s laws. 2.1 KCL Conservation of charge could be written in integral form as: dρ J~ · ~nda + f dv = 0 (1) ZZ Zvolume dt This simply states that the sum of current out of some volume of space and rate of change of free charge in that space must be zero.
    [Show full text]
  • Reluctance Network Analysis for Complex Coupled Inductors
    Journal of Power and Energy Engineering, 2017, 5, 1-14 http://www.scirp.org/journal/jpee ISSN Online: 2327-5901 ISSN Print: 2327-588X Reluctance Network Analysis for Complex Coupled Inductors Jyrki Penttonen1,2*, Muhammad Shafiq2, Matti Lehtonen1 1Department of Electrical Engineering, Aalto University, Espoo, Finland 2Vensum Ltd., Helsinki, Finland How to cite this paper: Penttonen, J., Abstract Shafiq, M. and Lehtonen, M. (2017) Reluc- tance Network Analysis for Complex The use of reluctance networks has been a conventional practice to analyze Coupled Inductors. Journal of Power and transformer structures. Basic transformer structures can be well analyzed Energy Engineering, 5, 1-14. by using the magnetic-electric analogues discovered by Heaviside in the 19th http://dx.doi.org/10.4236/jpee.2017.51001 century. However, as power transformer structures are getting more complex Received: December 16, 2016 today, it has been recognized that changing transformer structures cannot be Accepted: January 7, 2017 accurately analyzed using the current reluctance network methods. This paper Published: January 10, 2017 presents a novel method in which the magnetic reluctance network or arbi- Copyright © 2017 by authors and trary complexity and the surrounding electrical networks can be analyzed as a Scientific Research Publishing Inc. single network. The method presented provides a straightforward mapping This work is licensed under the Creative table for systematically linking the electric lumped elements to magnetic cir- Commons Attribution International License (CC BY 4.0). cuit elements. The methodology is validated by analyzing several practical http://creativecommons.org/licenses/by/4.0/ transformer structures. The proposed method allows the analysis of coupled Open Access inductor of any complexity, linear or non-linear.
    [Show full text]
  • Correlation of the Magnetic and Mechanical Properties of Steel
    . CORRELATION OF THE MAGNETIC AND MECHANICAL PROPERTIES OF STEEL By Charles W. Burrows CONTENTS Page I. Purpose and scoph op paper 173 II. Relation op the magnetic to the other characteristics op steel. 175 III. Magnetic behavior op steel under the inpluence op mechanical STRESS 182 1 Resimie of early work 182 2. For stresses below the elastic limit 184 3. For stresses greater than the elastic limit 188 (a) Experiments of Fraichet 189 IV. Inhomogeneities and plaws 200 I. Inhomogeneities in steel rails 203 T. Conclusions 207 VI. Bibliography 209 I. PURPOSE AND SCOPE OF PAPER So much work on this subject has been done during the last few years that the prospects are very bright that a magnetic examination of steel will furnish information of practical value as to its fitness for mechanical uses, without at the same time injuring or destroying the specimen imder test. This paper is a review of the work done in correlating the mag- netic and mechanical properties of steel. The International Association for Testing Materials has designated this as one of the important problems of to-day and has assigned its investi- gation to a special committee. A number of investigators are actively engaged on this problem. Among the mechanical properties that have been studied in connection with the magnetic characteristics are hardness, toughness, elasticity, tensile strength, and resistance to repeated stresses. The well-known fact that not only do these various properties depend upon the chemical composition and the heat 173 174 Bulletin of the Bureau of Standards {Voi.13 treatment, but that frequently very slight changes in the chemical composition or the heat treatment produce very appreciable effects on the magnetic and mechanical properties complicates the problem considerably.
    [Show full text]
  • Magnetic Circuit and Reluctance (How Do We Calculate Magnetic Field Or
    Magnetic circuit and reluctance (How do we calculate magnetic field or flux in situations where we have an air gap or two materials with diferrent magnetic properties?) 1. A magnetic flux path is interrupted by an air gap are of practical importance. 2. The problems encountered here are more complicated than in calculating the flux in a single material. 3. The magnet engineer is often of calculating the magnetic flux in magnetic circuits with a combination of an iron and air core 1 (i) In closed circuit case ( a ring of iron is wound with N turns of a solenoid which carries a current i) Ni N : Turns Magnetic field H L L : The average length of the ring Flux density passing → Ampere’s law → Ni H dl B μo(H M) circuit in the ring path Ni B μ ( M) Ni HL (B μH) o L B Ni L B B L μ Ni M L μo μ We can define here the magnetomotive N: the number of turns i: the current flowing in the force η which for a solenoid is Ni solenoid A magnetic analogue of flow Ohm’s law We can formulate a general : magnetic flux equation relating the Rm magnetic flux Rm : magnetic relutcance V i i R V Rm R 2 If the iron ring has cross-section area A(m²) permeability μ Turns of solenoid N length L Starting from the B A H A - The term L/μA is the relationship between Ni magnetic reluctance of A path. flux, magnetic induction L and magnetic field Ni - Magnetic reluctance is L series in a magnetic A circuit may be added is analogous to L R R m A A 1 3 Magnetic circuit Electrical circuit magnetomotive force electromotive force Flux () Current (i) reluctance resistance l l Reluctance Resistance R A A 1 Reluctivity Resistivity 1 conductivity permeability (ii) In open circuit case • If the air gap is small, there will be little leakage of the flux at the gap, but B = μH can no longer apply since the μ of air and the iron ring are different.
    [Show full text]
  • Energy Harvesting Using AC Machines with High Effective Pole Count,” Power Electronics Specialists Conference, P 2229-34, 2008
    The Pennsylvania State University The Graduate School Department of Electrical Engineering ENERGY HARVESTING USING AC MACHINES WITH HIGH EFFECTIVE POLE COUNT A Dissertation in Electrical Engineering by Richard Theodore Geiger 2010 Richard Theodore Geiger Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy August 2010 ii The dissertation of Richard Theodore Geiger was reviewed and approved* by the following: Heath Hofmann Associate Professor, Electrical Engineering Dissertation Advisor Chair of Committee George A. Lesieutre Professor and Head, Aerospace Engineering Mary Frecker Professor, Mechanical & Nuclear Engineering John Mitchell Professor, Electrical Engineering Jim Breakall Professor, Electrical Engineering W. Kenneth Jenkins Professor, Electrical Engineering Head of the Department of Electrical Engineering *Signatures are on file in the Graduate School iii ABSTRACT In this thesis, ways to improve the power conversion of rotating generators at low rotor speeds in energy harvesting applications were investigated. One method is to increase the pole count, which increases the generator back-emf without also increasing the I2R losses, thereby increasing both torque density and conversion efficiency. One machine topology that has a high effective pole count is a hybrid “stepper” machine. However, the large self inductance of these machines decreases their power factor and hence the maximum power that can be delivered to a load. This effect can be cancelled by the addition of capacitors in series with the stepper windings. A circuit was designed and implemented to automatically vary the series capacitance over the entire speed range investigated. The addition of the series capacitors improved the power output of the stepper machine by up to 700%.
    [Show full text]
  • Fundamentals of Magnetics
    Chapter 1 Fundamentals of Magnetics Copyright © 2004 by Marcel Dekker, Inc. All Rights Reserved. Introduction Considerable difficulty is encountered in mastering the field of magnetics because of the use of so many different systems of units - the centimeter-gram-second (cgs) system, the meter-kilogram-second (mks) system, and the mixed English units system. Magnetics can be treated in a simple way by using the cgs system. There always seems to be one exception to every rule and that is permeability. Magnetic Properties in Free Space A long wire with a dc current, I, flowing through it, produces a circulatory magnetizing force, H, and a magnetic field, B, around the conductor, as shown in Figure 1-1, where the relationship is: B = fi0H, [gauss] 1H = ^—, [oersteds] H B =— , [gauss] m cmT Figure 1-1. A Magnetic Field Generated by a Current Carrying Conductor. The direction of the line of flux around a straight conductor may be determined by using the "right hand rule" as follows: When the conductor is grasped with the right hand, so that the thumb points in the direction of the current flow, the fingers point in the direction of the magnetic lines of force. This is based on so-called conventional current flow, not the electron flow. When a current is passed through the wire in one direction, as shown in Figure l-2(a), the needle in the compass will point in one direction. When the current in the wire is reversed, as in Figure l-2(b), the needle will also reverse direction. This shows that the magnetic field has polarity and that, when the current I, is reversed, the magnetizing force, H, will follow the current reversals.
    [Show full text]
  • The Study of Magnetic Circuits Is Important in the Study of Energy
    MAGNETIC CIRCUITS The study of magnetic circuits is important in the study of energy systems since the operation of key components such as transformers and rotating machines (DC machines, induction machines, synchronous machines) can be characterized efficiently using magnetic circuits. Magnetic circuits, which characterize the behavior of the magnetic fields within a given device or set of devices, can be analyzed using the circuit analysis techniques defined for electric circuits. The quantities of interest in a magnetic circuit are the vector magnetic field H (A/m), the vector magnetic flux density B (T = Wb/m2) and the total magnetic flux Rm (Wb). The vector magnetic field and vector magnetic flux density are related by where : is defined as the total permeability (H/m), :r is the relative !7 permeability (unitless), and :o = 4B×10 H/m is the permeability of free space. The total magnetic flux through a given surface S is found by integrating the normal component of the magnetic flux density over the surface where the vector differential surface is given by ds = an ds and where an defines a unit vector normal to the surface S. The relative permeability is a measure of how much magnetization occurs within the material. There is no magnetization in free space (vacuum) and negligible magnetization in common conductors such as copper and aluminum. These materials are characterized by a relative permeability of unity (:r =1). There are certain magnetic materials with very high relative permeabilities that are commonly found in components of energy systems. These materials (iron, steel, nickel, cobalt, etc.), designated as ferromagnetic materials, are characterized by significant magnetization.
    [Show full text]