A NEW STRUCTURE OF 12S-8P HYBRID

EXCITATION FLUX SWITCHING MOTOR USING

SEGMENTAL ROTOR

HASSAN ALI SOOMRO

UNIVERSITI TUN HUSSEIN ONN MALAYSIA

UNIVERSITI TUN HUSSEIN ONN MALAYSIA

STATUS CONFIRMATION FOR MASTER’S THESIS

A NEW STRUCTURE OF 12S-8P HYBRID EXCITATION FLUX

SWITCHING MOTOR USING SEGMENTAL ROTOR

ACADEMIC SESSION : 2015/2016

I, HASSAN ALI SOOMRO, agree to allow this Master’s Thesis to be kept at the Library under the

following terms:

1. This Master’s Thesis is the property of Universiti Tun Hussein Onn Malaysia.

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3. The library is allowed to make copies of this report for educational exchange between

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OFFICIAL SECRETS ACT 1972)

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conducted)

FREE ACCESS

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Permanent Address :

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A NEW STRUCTURE OF 12S-8P HYBRID EXCITATION FLUX SWITCHING

MOTOR USING SEGMENTAL ROTOR

HASSAN ALI SOOMRO

A thesis submitted in

fulfilment of the requirement for the award of the

Degree of Master of Electrical Engineering

Faculty of Electrical & Electronic Engineering

Universiti Tun Hussein Onn Malaysia

MARCH, 2016

ii

I hereby declare that the work in this thesis is my own except for quotations and

summaries, which have been duly acknowledged.

Student : ……………………………………………………

HASSAN ALI SOOMRO

Date : …………………………………………………….

Supervisor : …………………………………………………….

DR. ERWAN BIN SULAIMAN

DECLARATION

15 MARCH, 2016

iii

DEDICATION

To my beloved mother and father

DEDICATION

iv

ACKNOWLEDGEMENT

In the name of ALLAH, the most Gracious and the Most Merciful.

Alhamdulillah, all praises to Allah Almighty for His grace and blessings given to me

for the completion of my master’s studies successfully.

I also wish to express my gratitude to my supervisor, Dr. Erwan Bin

Sulaiman, for his guidance, invaluable help, advice, and patience on my project

research. Without his constructive and critical comments, continuous encouragement,

and good humour while facing difficulties, I could not have completed this research.

I am also very grateful to him for guiding me to think critically and independently.

I acknowledge, with many thanks, to the Office for Research, Innovation,

Commercialization and Consultancy Management (ORICC) for awarding me

scholarship for my master’s programme. I am much honoured to be the recipient for

this award. Receiving this scholarship has secured my financial position and

provided me the motivation and drive to successfully complete my studies.

Without support from the technical staff and my lab fellows of FSM research

group, this research would not have been undertaken. My sincere thanks to all my

FSM group friends who facilitated me every time with their technical knowledge.

It has been a very pleasant and enjoyable experience to work in UTHM with

a group of highly dedicated people, who have always been willing to provide help,

support, and encouragement whenever needed. I would like to thank all my friends

during my stay in UTHM. Life would never have been that exciting and joyful

without you.

Finally, I would like to give my sincerest gratitude to my parents for their

endless love, support, and for always making compromises to let me try whatever I

consider is worth doing.

v

ABSTRACT

The efficient use of energy enables commercial and industrial facilities to minimise

production costs, increase profits, and stay competitive. The majority of electrical

energy consumed in most industrial facilities is used to run electric motors.

Therefore, there is a need for researchers to develop advanced electric motors with

less cost and high efficiency. There has been a recent interest in flux switching motor

(FSM) in which all flux sources are positioned in stator that make the rotor simple,

robust, and brushless. The development of research has been with toothed rotor

structures, which exploit changes of paths for the stator teeth, but this structure

produces less torque and power. Hence, the use of a segmental rotor structure has

been developed, which gives significant gains. The primary function of the segments

is to provide a defined magnetic path for conveying the flux to adjacent armature coil

in stator as the rotor rotates. This design gives shorter end-winding than with a

toothed rotor structure, which requires fully-pitched coils. Hence, permanent magnet

FSM (PMFSM) and field excitation FSM (FEFSM) with segmental rotor have been

developed, but due to their infirmity of less torque generation inherit from less flux

linkage, a new structure of hybrid excitation FSM (HEFSM) is proposed. The

proposed design HEFSM I is analysed using a commercial 2D FEA package, JMAG-

designer software. Initially, HEFSM I has been improved and optimised by using

deterministic optimisation techniques and achieved torque and power of almost 48%

and 56% more than the initial HEFSM I, and almost 3% and 8% more than target

values respectively. Additionally, an alternate structure of HEFSM II has been

proposed, investigated, and optimised. Finally, optimised HEFSM II has achieved

torque and power almost 14% and 13% more than target values respectively. The

novel structure HEFSM II with segmental rotor has produced higher performances

than existing PMFSM and FEFSM, proving their suitability towards efficient and

reliable motors.

vi

ABSTRAK

Kecekapan penggunaan tenaga membolehkan kemudahan perdagangan dan

perindustrian bagi mengurangkan kos pengeluaran, meningkatkan keuntungan, dan

kekal berdaya saing. Sebahagian besar tenaga elektrik yang digunakan dalam

kemudahan perindustrian adalah untuk memacu motor elektrik. Oleh itu, adalah

perlu bagi para penyelidik untuk membangunkan motor elektrik dengan melibatkan

kos yang rendah dan kecekapan yang tinggi. Sejak kebelakangan ini, terdapat minat

yang dipamerkan oleh penyelidik di dalam motor fluks beralih (FSM) di mana semua

sumber fluks ditempatkan di dalam pemegun dan membuatkan pemutar lebih

ringkas, lasak dan tanpa keperluan berus karbon. Pembangunan penyelidikan telah

membuktikan bahawa struktur pemutar bergigi yang mengeksploitasi perubahan

laluan bagi gigi pemegun tetapi struktur ini menghasilkan tork dan kuasa yang

rendah. Oleh itu, penggunaan struktur pemutar bersegmen yang terkini telah

dibangunkan, yang mana telah memberikan beberapa kelebihan yang besar. Fungsi

utama segmen adalah untuk memberi laluan magnet yang ditetapkan untuk

mengalirkan fluks ke gegelung angker bersebelahan dalam pemegun pada ketika

pemutar berputar. Reka bentuk ini menjadikan hujung penggulungan lebih pendek

berbanding dengan struktur pemutar bergigi yang memerlukan gegelung sepenuhnya

bernada. Oleh itu, motor fluks beralih dengan magnet kekal (PMFSM) dan motor

fluks beralih dengan medan pengujaan (FEFSM) bersama pemutar segmen telah

dibangunkan namun disebabkan kelemahan mereka yang kurang baik dari segi

penghasilan tork akibat daripada kekurangan fluks yang berhubung, struktur baru

iaitu motor fluks beralih dengan pengujaan hibrid (HEFSM) adalah diperkenalkan.

Reka bentuk HEFSM I yang dicadangkan dianalisis menggunakan pakej komersial

2D-FEA, JMAG software ver. 13.0, yang dikeluarkan oleh JSOL Corporation. Pada

mulanya HEFSM I telah ditambahbaik dan dioptimumkan dengan menggunakan

teknik pengoptimuman berketentuan dan masing-masing mencapai tork dan kuasa

hampir 48% dan 56% lebih daripada HEFSM I yang dicadangkan dan hampir 3%

vii

dan 8% lebih daripada nilai sasaran. Sebagai tambahan, struktur alternatif HEFSM II

telah dicadangkan, disiasat dan dioptimumkan. Akhirnya HEFSM II yang

dioptimumkan telah mencapai tork dan kuasa hampir 14% dan 13% lebih tinggi

daripada nilai sasaran masing-masing. Struktur novel HEFSM II dengan pemutar

segmen menghasilkan prestasi yang lebih tinggi daripada yang sedia ada iaitu

PMFSM dan FEFSM, membuktikan kesesuaian mereka terhadap nilai kecekapan

motor dan boleh dipercayai.

viii

TABLE OF CONTENTS

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS viii

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF SYMBOLS AND ABBREVIATIONS xviii

LIST OF PUBLICATIONS xix

LIST OF AWARDS xxi

CHAPTER 1 INTRODUCTION 1

1.1 Research Background 1

1.2 Problem Statement 3

1.3 Objectives of the Study 3

1.4 Scope 4

1.5 Thesis Outline 6

1.6 Summary of the Chapter 7

CHAPTER 2 LITERATURE REVIEW 8

2.1 Introduction 8

ix

2.2 Permanent Magnet Synchronous Motor (PMSM) 11

2.3 Field Excitation Synchronous Motor (FESM) 12

2.4 Hybrid Excitation Synchronous Motor (HESM) 13

2.5 Flux Switching Motor (FSM) 14

2.5.1 FSM Using Toothed Rotor Structure 15

2.5.2 FSM Using Segmental Rotor Structure 24

2.6 Comparison of Toothed and Segmental Rotor

Structure 27

2.7 Performance Analysis of Toothed Rotor Motors 29

2.7.1 Performance Analysis of 12S-10P FEFSM

with Toothed Rotor 29

2.7.2 Performance Analysis of HEFSM with

Toothed Rotor 33

2.8 Performance Analysis of Segmental Rotor Structure 36

2.8.1 Analysis of Flux Lines and Flux Distributions

of FEFSM with Segmental rotor 36

2.8.2 Torque Analysis vs Ja at Various Je of

FEFSM with Segmental Rotor 37

2.8.3 Performance Analysis of PMFSM with

Segmental Rotor 38

2.9 Optimisation 43

2.9.1 Traditional FSM Design 43

2.10 Summary of the chapter 45

CHAPTER 3 METHODOLOGY 46

3.1 Introduction 46

3.2 Design and Investigation of PMFEM, FEFSM,

and HEFSM with Segmental Rotor 47

3.2.1 Design of PMFSM, FEFSM, and HEFSM

with Segmental Rotor 48

3.2.2 Investigation of Operating Principle for

PMFSM, FEFSM, and HEFSM 51

3.3 Performance Analysis of PMFSM, FEFSM, and

HEFSM with Segmental Rotor 53

x

3.3.1 No Load Analysis 54

3.3.2 Load Analysis 55

3.4 Optimisation and Comparison 57

3.5 Summary of Chapter 59

CHAPTER 4 RESULTS AND DISSCUSSION 60

4.1 Introduction 60

4.2 Design and Investigation Results of FEFSM,

PMFSM, and HEFSM I 60

4.2.1 Design Results of FEFSM, PMFSM, and

HEFSM I 61

4.2.2 Investigation of Operating Principles of

PMFSM, FEFSM, and HEFSM I 63

4.3 Performance Analysis on the Basis of 2-D FEA 69

4.3.1 No Load Analysis Results 69

4.3.2 Load Analysis Results 75

4.4 Design Improvement of Initial Design of

HEFSM I 78

4.5 Performance Comparison of Initial and Improved

Design of HEFSM I 80

4.6 Optimisation of Improved design of HEFSM I 82

4.6.1 Parameter Sensitivity of Optimised Design 82

4.6.2 Performance of Optimised Design of

HEFSM I with Segmental Rotor 84

4.6.3 Torque and Power vs Speed Characteristics

of Initial Design and Optimised Design 87

4.7 Losses Analysis and Efficiencies of PMFSM,

FEFSM, Initial HEFSM I, and Optimised HEFSM I 88

4.8 Alternate Proposed Design HEFSM II with

Segmental Rotor 92

4.8.1 Design and Investigation of HEFSM II

with Segmental Rotor 93

4.9 Performance Analysis and Comparison of Initial

Design HEFSM II and Optimised Design HEFSM I 96

xi

4.9.1 Flux Distribution of Initial HEFSM II and

Optimised HEFSM II at no Load Condition 96

4.9.2 Induced EMF of initial HEFSM II and

Optimised HEFSM I 98

4.9.3 Magnetic Flux Lines and Flux Strengthening

of Optimised HEFSM I and Initial

HEFSM II 98

4.9.4 Torque vs Various Je at Various Armature

Current Densities Ja of Optimised HEFSM I

and Initial HEFSM II 100

4.10 Optimisation of Initial Design of HEFSM II 102

4.10.1 Parameter Sensitivity of Optimised Design

HEFM II 102

4.10.2 Performance of Optimised Design of

HEFSM II with Segmental Rotor 104

4.10.3 Torque and Power vs Speed Characteristics

of Optimised HEFSM II and

Optimised HEFSM I 106

4.11 Rotor Mechanical Strength Analysis 108

4.12 Losses and Efficiencies of Optimised HEFSM II 108

4.13 Summary of the Chapter 113

CHAPTER 5 CONCLUSION AND FUTURE WORKS 114

5.1 Conclusion 114

5.2 Future Works 115

5.3 Summary of the Chapter 115

REFERENCES 116

xii

LIST OF TABLES

1.1 Design restrictions and specification of HEFSM 5

1.2 Material selection for stator, rotor, armature coil,

and FEC 5

2.1 Design restrictions and specification of HEFSM 28

3.1 Design parameters of PMFSM, FEFSM and

HEFSM 49

4.1 Design specification of PMFSM, FEFSM and

HEFSM I 63

4.2 Design parameters and specification of improved

and optimised design of HEFSM I with segmental

rotor 84

4.3 Design specification of initial HEFSM I and initial

HEFSNM II 94

4.4 Design parameters and specification of initial

HEFSM II and optimised design HEFSM II with

segmental rotor 103

4.5 Detailed loss analysis of all designs of HEFSM

with segmental rotor 112

5.6 Overall performance and comparison of all designs 113

xiii

LIST OF FIGURES

2.1 The classification of the main types of electric

motors 10

2.2 Interior permanent magnet synchronous motor 12

2.3 Field excitation synchronous motor 13

2.4 Field excitation synchronous motor 14

2.5 A simplified flux-switch alternator scheme 16

2.6 Principle Operation of E-Core HEFSM 17

2.7 Three-phase structure of FSM toothed rotor 18

2.8 12S-10P PMFSM with toothed rotor 19

2.9 Operation principle of PMFSM 19

2.10 18S-14P FEFSM with toothed rotor 21

2.11 Operation principles of FEFSM 21

2.12 (a) 6S-4P HEFSM (b) 12S-10P inner

FE HEFSM 22

2.13 The operating principle of the proposed HEFSM 23

2.14 Basic segmental rotor scheme with field winding

excitation 25

2.15 Basic segmental rotor scheme with PM

excitation 25

2.16 Flux distribution in stator teeth with field

excitation 26

2.17 Basic working principle of PMFSM with segmental

rotor 27

2.18 Open circuit field distribution of FEC at four rotor

positions, θr 30

2.19 EMF of various FEC 30

2.20 Cogging torque 31

xiv

2.21 Torque and power vs speed characteristics 32

2.22 Losses and efficiency 32

2.23 Flux lines of HEFSSM by permanent magnet 33

2.24 Flux lines of HEFSSM by both permanent magnet

and DC field excitation 34

2.25 Torque and power versus speed characteristics 34

2.26 Estimated motor loss and efficiency 35

2.27 FE Coil flux lines at Je of 30A/mm2

(a) 12S-8P FESF motor (b) 24S-10P FESF motor 36

2.28 FE Coil flux distributions at Je of 30A/mm2

(a) 12S-8P FESF motor (b) 24S-10P FESF motor 37

2.29 Comparisons of maximum flux vs Je for 12S-8P

and 24S-10P FESF motor 37

2.30 Torque Vs Je 6S-8P 38

2.31 Torque Vs Je 12S-10P 38

2.32 Induced phase EMF at 500 r/min. (a) Waveform

(b) Harmonic spectra 40

2.33 Static torque of PMFSM 41

2.34 Variation of torque and motor efficiency with

current at 500 r/min 42

2.35 Power factor and terminal voltage with current

at 500 r/min 43

2.36 Flow diagram of electric machine design process

commonly used by engineers 44

3.1 General work flow chart of project implementation 47

3.2 Work flow of design and investigation 48

3.3 Work flow for coil test analysis 51

3.4 Circuit for U, V, and W coil test 53

3.5 Performance analysis flow chart 54

3.6 General flow diagram of optimisation 58

4.1 Stators of FEFSM, PMFSM, and HEFSM I 61

4.2 Design of segmental rotor of PMFSM, FEFSM,

and HEFSM I 62

xv

4.3 Design of armature coil of PMFSM, FEFSM, and

HEFSM I 62

4.4 Design of FEC of FEFSM and HEFSM I 63

4.5 Graph of 6 coil flux pattern of PMFSM 64

4.6 Graph of 6 coil flux pattern of FEFSM 65

4.7 Graph of 6 coil flux pattern of HEFSM I 66

4.8 Armature coil arrangement of PMFSM, FEFSM,

and HEFSM I with segmental rotor 67

4.9 U, V, and W fluxes in the armature coil 68

4.10 Flux distribution of (a) PMFSM (b) FEFSM and

(c) HEFSM I with segmental rotor 70

4.11 Induced voltage of PMFSM, FEFSM, and HEFSM I 71

4.12 Cogging torque of PMFSM, FEFSM, and HEFSM I 72

4.13 Magnetic flux lines of (a) PMFSM (b) FEFSM and

(c) HEFSM I 73

4.14 Flux strenghtening of FEFSM and HEFSM I 74

4.15 U phase flux of PMFSM, FEFSM, and HEFSM I 75

4.16 Torque vs Armature current densities Ja Flux

strengthening of FEFSM and HEFSM I 77

4.17 Power vs Armature current densities Ja at maximum

field current density Je 30 A/mm2 78

4.18 Improved design 79

4.19 Flux lines of Initial and Improved design 79

4.20 Flux strengthening of Initial and Improved design

of HEFSM I 80

4.21 Torque vs field current density Je at maximum

armature current density Ja of 30 Arms/mm2 81

4.22 Power vs armature current density Ja at maximum

field current density of 30 A/mm2 81

4.23 Segment span at 390 and 40

0 83

4.24 Parameters of improved design HEFSM I with

segmental rotor 83

4.25 Parameters of optimised design HEFSM I with

segmental rotor 84

xvi

4.26 Flux distribution of optimised design of HEFSM I

with segmental rotor 85

4.27 Magnetic flux lines of optimised design of HEFSM I

with segmental rotor 85

4.28 Torque vs Je for optimised design of HEFSM I with

segmental rotor 86

4.29 Power vs Ja at maximum Je of 30 A/mm2 86

4.30 Torque vs speed characteristics of initial and

optimised design of HEFSM I 87

4.31 Power vs speed characteristics of initial and

optimised design of HEFSM I 88

4.32 Torque and power vs speed characteristic. 89

4.33 Estimated coil end length, Lend 89

4.34 Motor losses and efficiencies at different operating

points 91

4.35 Iron losses and copper losses distribution 92

4.36 Design of proposed HEFSM II with segmental rotor 93

4.37 Graph of 6 coil flux pattern of (a) Armature coil 1

(b) Armature coil 3 (c) Armature coil 2

(d) Armature coil 5 (e) Armature coil 3

(f) Armature coil 6. 95

4.38 Armature coil arrangement of initial HEFSM II 96

4.39 Flux distribution of optimised HEFSM I and initial

HEFSM II 97

4.40 Induced EMF of optimised HEFSM I and initial

HEFSM II 98

4.41 Flux lines of (a) Optimised HEFSM I (b) Initial

HEFSM II 99

4.42 Flux strengthening of optimised HEFSM I and

initial HEFSM II 100

4.43 Torque vs various Je at various Ja 101

4.44 Parameters of Optimised HEFSM II with

segmental rotor 103

xvii

4.45 Flux distribution and flux lines of optimisation

HEFSM II 104

4.46 Torque characteristics of Optimised HEFSM II 105

4.47 Comparison of torque characteristics of FEFSM,

PMFSM, initial HEFSM I, optimised HEFSM I,

and optimised HEFSM II at maximum Ja of 30

Arms/mm2 105

4.48 Power characteristics vs Ja of FEFSM, PMFSM,

initial HEFSM I, optimised HEFSM I and optimised

HEFSM II at maximum Je 106

4.49 Torque vs speed characteristics of optimised

HEFSM I and HEFSM II 107

4.50 Power vs speed characteristics of optimised

HEFSM I and HEFSM II 107

4.51 Mechanical stress analysis of initial and optimised

designs of HEFSM I 109

4.52 Torque vs speed characteristics of optimised

HEFSM II 110

4.53 Motor losses and efficiencies at different operating

points 111

4.54 Iron losses and copper losses distribution 111

xviii

LIST OF SYMBOLS AND ABBREVIATIONS

A Ampere

AC Alternating Current

B Flux Density [T]

f Frequency [Hz], [rad/s]

I Current [A]

J Current Density [A/m2]

L Length [m]

N Number of turns

p Number of Poles

R Resistance [ohm]

r Radius [m]

rpm Revolution Per Minute

T Torque [Nm]

t Time [s]

V Voltage [V]

EMF Electromotive Force

FEA Finite Element Analysis

FEC Field Excitation Coil

FEFSM Field Excitation Flux Switching Machine or Motor

FSM Flux Switching Machine or Motor

HEFSM Hybrid Excitation Flux Switching Machine or Motor

HEV Hybrid Electrical Vehicles

IMs Induction Motors

PM Permanent Magnet

PMFSM Permanent-Magnet Flux Switching Machine or Motor

SRM Switched Reluctance Machine or Motor

SRM Synchronous Reluctance Machine or Motor

xix

LIST OF PUBLICATIONS

Journals:

(i) Hassan Ali, Erwan Sulaiman, Mohd Fairoz Omar, Mahyuzie Jenal,

“Design studies and performance of a novel 12S- 8P HEFSM with

segmental rotor”, Journal of Electrical Systems, 5-6 December 2015, Shah

Alam, Malaysia. (ISI).

(ii) Hassan Ali, Erwan Sulaiman, F. Khan and S.M. Naufal, “Magnetic Flux

Analysis of Various Flux Switching Motors Using Segmental Rotor for

Hybrid Electric Vehicles”, Journal of Electrical Systems, 5-6 December

2015, Shah Alam, Malaysia. (ISI).

(iii) Hassan Ali Soomro, Erwan Sulaiman and Faisal Khan, “Comparative

Performance of FE-FSM, PM-FSM and HE-FSM with Segmental Rotor”,

Applied Mechanics and Materials. Vol. no 773-774, pp. 776-780 (2015).

(SCOPUS).

(iv) Hassan Ali Soomro, Erwan Sulaiman and Mohd Fairoz Omar,

“Performance Comparison and Analysis of (HEFSM) and (FEFSM) Using

Segmental Rotor Structure”, Applied Mechanics and Materials, vol. 695,

pp. 778-782 (2015).(SCOPUS).

(v) Hassan Ali, Erwan sulaiman, Mubin Aizat and Zhafir Aizat, “Improved

Design of Three Phase Hybrid Excitation Flux Switching Motor with

Segmental Rotor”, Applied Mechanics and Materials, vol. no. 785, pp. 295-

299, (2015). (SCOPUS).

xx

Proceedings:

(i) Hassan Ali, Erwan Sulaiman, Mahyuzie Bin Jenal, Faisal Khan, “A novel

structure of hybrid excitation flux switching motor with segmental rotor”

Malaysian Technical Universities Conference on Engineering And

Technology (MUCET 2015).

(ii) Hassan Ali, E. Sulaiman, Mohd Fairoz Omar and Mahyuzie Bin Jenal,

“Comparison of Three Phase and Single Phase FEFSM with Segmental

Rotor”, 8th Malaysian Technical Universities Conference on Engineering &

Technology (MUCET 2014).

(iii) Hassan Ali Soomro, Erwan Sulaiman and Faisal Khan, “Comparative

Performance of FE-FSM, PM-FSM and HE-FSM with Segmental Rotor”,

International Integrated Engineering Summit Conference (IIES 2014).

(iv) Erwan Sulaiman, Hassan Ali, Mubin Aizat and Zhafir Aizat, “Improved

Design of Three Phase Hybrid Excitation Flux Switching Motor with

Segmental Rotor”, 9th International Power Engineering and Optimisation

Conference, (PEOCO2015).

(v) E.Sulaiman, H. Ali, and M.Z.Ahmad, “Magnetic Flux Analysis of Various

Flux Switching Motors Using Segmental Rotor for Hybrid Electric

Vehicles”, IEEE International Magnetics Conference (Intermag 2015).

xxi

LIST OF AWARDS

(i)

(ii)

Silver Medal at Malaysia Technology Expo, The Leading International

Invention and Innovation Expo, Putra World Trade Centre, Kuala Lumpur,

12-14 February, 2015.

Certificate of Participation at Research and Innovation Festival 2014,

Dewan Tunku Mahkota Ismail (DTMI), Dewan Terbuka and Dewan Sekitar

(DTMI).

1CHAPTER 1

INTRODUCTION

1.1 Research Background

As the term electrical machine includes motors and generators, machines operating

as motors utilise energy conversion, to give a greater variety of configurations and

sizes. Much of the insights in the proceeding discussion is applicable to the motoring

class of electrical machines, which is estimated to account for 60-70% of the

electrical energy utilisation in the developed world [1, 2]. The global trends and

influence of new technologies on the development of the electrical machines, in

response to economic and environmental pressures, are briefly recounted with a

reference to the position of developing flux switching machines [3].

The first concept of flux switching machine (FSM) was founded and

published in mid-1950s. FSM consists of all flux sources in the stator. Besides the

advantage of brushless machines, FSM has a single piece of iron rotor structure that

is robust, and can be used for high-speed applications, and the total control is

maintained over the field flux [4]. Firstly, a permanent magnet flux switching

machine (PMFSM), which is a permanent magnet (PM) single-phase limited angle

actuator, or more well known as Laws relay, with four stator slots and four rotor

poles was developed. It is extended into a single-phase generator with four stator

slots, and four or six rotor poles. Over the past ten years, many new FSM topologies

have been developed for various applications, ranging from low-cost domestic

appliances, automotive, wind power, aerospace, and others [5].

2

There are major advantages if both the field and armature windings of a

synchronous machine can be on the stator and all brushes are eliminated, whilst

complete control is maintained over the field flux. The operation of the motor is

based on the principle of switching flux. FSM is a form of salient rotor reluctance

machine with a novel topology, combining the principles of the induction generator

and the switched reluctance machine (SRM). The concept of FSM involves changing

the polarity of the flux linking the armature winding by motion of the rotor [6].

In general, there are three main classes of FSM, namely PMFSM, having only

permanent magnet for their main flux source; field excitation flux switching machine

(FEFSM), having only field excitation coil (FEC) for their main flux sources; and

hybrid excitation flux switching machines (HEFSM). Hybrid excitation flux

switching machines (HEFSMs) are those which utilize primary excitation by

permanent magnets (PMs) and secondary excitation by means of DC field excitation

coil (FEC). Normally, PMFSMs have relatively poor flux weakening performance

but can be operated beyond base speed in the flux weakening region by means of

controlling the armature winding current. By applying negative d-axis current, the

PM Field can be counteracted but with the disadvantage of increase in copper loss

and thereby reducing the efficiency, reduced power capability, and also possible

irreversible demagnetization demagnetisation of the PMs. Thus, HEFSM is an

alternative option where the advantages of both PM machines and DC FEC

synchronous machines are combined. As such, HEFSMs have the potential to

improve flux weakening performance, power and torque density, variable flux

capability, and efficiency, which have been researched extensively over many years

[7, 9].

On the other hand, recently researchers have developed the use of segmental

rotor construction for SRMs and two-phase flux switching motors, which give

significant advantages over other topologies. Whereas segmental rotors are used

traditionally to control the saliency ratio in synchronous reluctance machines, the

primary function of the segments in this design is to provide a defined magnetic path

for conveying the field flux to adjacent stator armature coils as the rotor rotates. As

each coil arrangement is around a single tooth, this design gives shorter end-

windings than the toothed rotor structure, which requires fully-pitched coils. There

are significant advantages with this arrangement as it uses less conductor materials

and may improve the overall motor efficiency. There is a choice to use either a field

3

winding or PM, or a combination of both for primary excitation [10]. More recently,

rotors with segments have been used in a novel way to produce bipolar flux linkages

in the armature windings, promising higher torque densities. This arrangement

enables use of single-tooth concentrated windings, reducing power loss, and saving

copper [11]. Topologies for three-phase segmented-rotor flux-switching machines

employing a DC field winding are presented in [12] and examined on the basis of the

peak armature flux linkage, induced phase EMF, and torque capability. The basic

principle of these types of machines is based on an unconventional configuration,

using a segmental rotor to modulate and switch polarity of the flux linkages in the

armature windings.

1.2 Problem Statement

In recent researches, segmental rotor FSM is designed in a manner such that bipolar

flux is achieved in armature winding. However, the main problems of three-phase

segmented-rotor flux-switching machines employing a DC field winding and PM are

less torque generation, high cost, and low efficiency. Besides these, flux in PMFSM

with segmental rotor cannot be controlled because of constant flux production. On

the other hand, flux strengthening in FEFSM with segmental rotor is very weak. [13,

14]

A new structure of hybrid excitation flux switching motor HEFSM using

segmental rotor is proposed in this work to overcome these problems, and designed

in which both permanent magnet and field excitation coil are used to generate bipolar

flux in armature coil to produce maximum torque and high efficiency. The amount of

copper losses and the weight of this new structure will be compared with the

PMFSM and FEFSM to see if significant reduction can be achieved. Also, due to the

use of FEC, flux can be easily controlled, and due to PM, flux strengthening will also

be increased.

1.3 Objectives of the Study

The main objective of this study is to develop a new structure of HEFSM using

segmental rotor that will have a much lower copper losses and lighter than PMFSM

4

and FEFSM. To achieve the main objective, there are some specific objectives that

have to be fulfilled, which are:

(i) To design and investigate the operating principle of PMFSM, FEFSM,

and HEFSM using segmental rotor.

(ii) To analyse the performance of PMFSM, FEFSM, and HEFSM

including no load and load conditions such as cogging torque, flux

distribution, EMF, and torque characteristics.

(iii) To optimise the performance characteristics of HEFSM with

segmental design.

1.4 Scope

The design restrictions, target specifications, and parameters of the proposed

12Slots-8Poles HEFSM using segmental rotor for HEV applications are listed in

Table 1.1. The electrical restrictions related with the inverter such as maximum 415V

DC bus voltage and maximum 100 A inverter current are set. Assuming the water

jacket system is employed as the cooling system for the machine, the limit of the

current density is set to the maximum 30Arms/mm2 for armature winding and

30A/mm2

for FEC, respectively. The outer diameter, the motor stack length, the rotor

diameter, and the air gap of the main part of the machine design being 150 mm, 70

mm, 60 mm, and 0.3 mm respectively, are identical with those existing FEFSM and

PMFSM using segmental rotor. The materials used for stator, rotor, PM, armature

coil, and FEC are illustrated in Table 1.2. Commercial FEA package, JMAG-

Designer ver.13.0, released by Japan Research Institute (JRI) is used as 2D-FEA

solver for this design.

5

Table 1.1: Design restrictions and specification of HEFSM [15]

Items 12S-8P HEFSM

Max. DC-bus voltage inverter (V) 415

Max. inverter current (A) 100

Max. current density in armature winding, JA (Arms/mm2) 30

Max. current density in excitation winding, JE (A/mm2) 30

Stator outer diameter (mm) 150

Stator yoke depth (mm) 11

Stator tooth width (mm) 12.5

Rotor diameter (mm) 90

Segment span (degrees) 40°

Segment separation (degrees) 5°

Air gap length (mm) 0.3

Number of turns per field tooth coil 44

Number of turns per armature tooth coil 44

Table 1.2: Material selection for stator, rotor, armature coil, and FEC [16]

Parts Material use

Stator 35H210

Rotor 35H210

Armature coil Copper

FEC Copper

PM NEOMAX35AH

6

1.5 Thesis Outline

This thesis deals with the design, investigation, and optimisation of a new structure

(HEFSM) employing segmental rotor. Basically, this thesis is divided into five

chapters and the summary of each chapter is given below.

(a) Introduction

The first chapter introduces the research including the background of FSM

and explanation regarding toothed and segmental rotor. Problems of existing

motors employing segmental rotor, research objectives, research scope, and

methodology are discussed in this chapter.

(b) Literature Review

This chapter explains the literature of electrical motor and classification of

electrical motor including flux switching motors. The study design and

analysis of toothed and segmental rotor are also explained in this chapter.

Finally, the optimisation process is also discussed in this chapter.

(c) Methodology

This chapter describes the project implementation of this research. The

project implementation is divided into three parts including design, analyses,

and optimisation. The design is divided into two parts, which are geometry

editor and JMAG-Designer. Then, the design is analysed at no load and load

conditions such as flux linkage, cogging torque, induced voltage and torque,

and power vs. maximum Je. Finally, the “deterministic optimisation method”

is used and treated to all parameters until the optimum performances are

achieved.

(d) Results

This chapter describes performances of PMFSM, FEFSM, and proposed

HEFSM using segmental rotor. This chapter is divided into three parts:

design and investigation results, performance analysis, and optimisation.

Initially, the design and performance of proposed design HEFSM I was

analysed at load and no load conditions on the basis of 2-D FEA. The initial

design of HEFSM was then improved by relocating the PM position and by

using optimisation technique to achieve adequate and target results. An

alternate structure of HEFSM with segmental rotor was proposed by reducing

the number of FEC coil slots and PMs. Finally, the proposed design HEFSM

7

II was optimised and achieved the target values such as maximum torque and

power with smooth flux distribution around the stator and rotor segments.

(e) Conclusion

The final chapter describes and concludes the research and the comparison of

analysis of the research with previous work. Suggestions for future work are

described in this chapter.

1.6 Summary of the Chapter

In this chapter, the introduction about FSM has been explained including

tooth rotor structure and segmental rotor machines. The problems and

drawbacks of existing motors employing segmental rotor, research scope, and

research methodology have been discussed.

2CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

A motor or an electrical motor is a device that has brought about one of the biggest

advancements in the fields of engineering and technology ever since the invention of

electricity. An electric motor is an electro-mechanical device that converts electrical

energy into mechanical energy. The very basic operating principle of an electrical

motor lies on the fact that force is experienced in the direction perpendicular to

magnetic field and the current, when field and electric current are made to interact

with each other. Electric motors are always associated with involving rotating coils,

which are driven by the magnetic force. This force is produced by a reaction between

magnetic field and magnetic current. Equation (2.1) and Equation (2.2) show the

voltage and torque of DC motor respectively. Ever since the invention of motors, a

lot of advancements have been taken place in this field of engineering and it has

become a subject of extreme importance for modern engineers [17-18].

(2.1)

(2.2)

where E is the voltage applied, Eb is the back EMF produce, Ia and Ra are the

armature current and resistance respectively, T is the torque produced, ka is constant,

and ɸ is the flux produced.

9

AC electric motor can also be classified as induction motors (IMs),

synchronous motors (SMs), and switch reluctance motors (SRMs), as illustrated in

Figure 2.1. IMs are well-suited to applications requiring variable speed operation. It

is made up of the stator, or stationary winding, and the rotor. It is called “IMs”

because the rotor voltage is induced in the rotor windings instead of physically

connected by wires [19-20]. Additionally, it is built without the main DC field circuit

at all. The distinguishing feature of IMs is that no DC field current is required to run

the motor. It operates on the basis of interaction of induced rotor currents and the air

gap field [21].

The first reference to the term SRMs was made by Nasarin in 1969 and the

term became popular from 1980s onwards, through the efforts of the first commercial

exploiters of the technology, Switched Reluctance Drives Ltd. SRMs do not contain

any permanent magnets and the operation of stators is the same as brushless DC

motors while the rotors consist only of laminated iron. The operation of the SRM

where the salient poles tend to align to minimise reluctance in normal operation leads

to high normal forces acting on the stator structure. Harmonics of these normal

forces will resonate at the natural frequency resonant modes of the stator structure,

thus producing acoustic noise [23].

10

Electrical

Motor

DC Motors AC Motors

Induction

Motor (IM)

Field Excitation (FE)

SRM

Hybrid excitation

(HE) SRM

Permanent magnet

(PM) SRM

Synchronous

Motor (SM)

Switched Reluctance

Motor (SRM)

Flux Switching Motor

(FSM)

Figure 2.1: The classification of the main types of electric motors [22]

On the other hand, SMs are AC motors that have a field circuit supplied by an

external DC source. The stator has electromagnets, resulting in the creation of a

magnetic field, which rotates in time with the oscillations of the line current. The

rotation period of SM is equal to an integral number of AC cycles. Equation (2.3)

and equation (2.4) show the speed and voltage of synchronous motors [23].

(2.3)

(2.4)

where S is the speed of rotor, f is the frequency, P is the number of poles, I is

the current, and ɸ is the flux.

SMs can be classified as permanent magnet synchronous motors (PMSMs),

field excitation synchronous motors (FESMs), hybrid excitation synchronous motors

(HESM), and flux switching motor (FSM). The rotor of PMSM contains PM, the

11

rotor for FESM has field excitation (FE) winding, while the rotor for HESM is the

combination of both PM and FE, and FSM is a type of SM that contains robust rotor

structure without PM and FE winding [24].

2.2 Permanent Magnet Synchronous Motor (PMSM)

A permanent magnet synchronous motor (PMSM) is a motor that uses permanent

magnets to produce an air gap magnetic field rather than using electromagnets. These

motors have significant advantages, attracting the interest of researchers and

industries for applications such as traction, automobiles, robotics, and aerospace

technology. Permanent magnet synchronous machines have been applied to servo

drives for a long time, and nowadays, there are quite a number of large permanent

magnet synchronous machines available for industrial use. In wind generators, the

development is currently in the direction of permanent magnet machines. In

principle, vector control is required for controlling the PMSMs [25].

The basic idea of the vector control algorithm is to decompose stator currents

into a magnetic field-generating part and a torque-generating part. Both components

can be controlled separately after decomposition. The structure of the motor

controller (vector control controller) is almost the same as a separately excited DC

motor, which simplifies the control of a PMSM The vector control of the PMSM is

derived from its dynamic model. Considering the currents as inputs, the three

currents and torque are shown in equations (2.5), (2.6), (2.7), and (2.8) respectively

[26]. Figure 2.2 shows the structure of interior PMSM.

(2.5)

(2.6)

(2.7)

(2.8)

Where α is the angle between the rotor field and stator current phases, ωr is the

electrical rotor speed.

12

PMs

Figure 2.2 Interior permanent magnet synchronous motor [26]

2.3 Field Excitation Synchronous Motor (FESM)

Synchronous motor drives are well-suited for rolling mill applications, where good

performance is required both at zero and high speed in field weakening. Synchronous

machines are used mainly in large drives, for example rolling mill drives in steel

factories. Especially in applications, where a widespeed range is needed, electrically

excited synchronous motor drives are preferred due to their large field weakening

range. During the past decade, a new control method called DTC (Direct Torque

Control) has been developed for electrical machines. DTC has been first applied to

asynchronous motor drives. According to the experience of Pyrhonen, DTC control

method is applicable to synchronous motor drives as well. With a nominal stator flux

linkage, the excitation control has an important role of current balancing reactive

power control, because stator currents are not controlled in DTC, but the reactive

power balance is defined totally by the excitation control. In the field weakening

range, the excitation control defines the static and dynamic limits for the DTC

controlled synchronous motor drive performance. [27].

In rolling mill applications, high torque is required in the whole speed range.

In the case of an inverter drive, this means over dimensioning of the stator inverter,

because large torque requires more current when the flux is reduced. The load angle

gets high in the field weakening range, and the torque producing stator current

component is mainly on the d-axis. To keep the drive stable, we must compensate the

large d-axis stator current component with a high excitation current. Thus, the

13

excitation current may be the limiting factor for the maximal torque, and the

maximal stator current cannot be used. Figure 2.3 shows the diagram of a field

excitation synchronous motor [28].

Figure 2.3: Field excitation synchronous motor [28]

2.4 Hybrid Excitation Synchronous Motor (HESM)

The hybrid excitation synchronous motor (HESM) combines the advantages of the

two abovementioned machines. Therefore, HESM is of great significance for it

widens the flux regulation range, which is a crucial requirement in many applications

such as electrical propulsion and generation systems. Researchers have proposed

several structures of HESM. Spooner and Khatab presented a variety of hybrid

configurations of AC and DC machines [29], such as the hybrid excitation

synchronous machines that combine permanent-magnet (PM) excitation with wound

field excitation, as shown in Figure 2.4. The goal behind using two excitation field

sources is to combine advantages of PM excited machines and wound field

synchronous machines. Wound field excitation is used to control excitation flux in

the air gap, which improves flux weakening capability. Hybrid excitation allows the

design of machines with a relatively low armature magnetic reaction by controlling

excitation flux and at the same time, the extension of the speed operation range.

Furthermore, it improves efficiency in the most frequently used operating zones of

the traction motor. Machines with a relatively low armature magnetic reaction have

better power factor, which implies a lower power rating for the power converters

connected to them. From the design’s point of view, hybrid excitation offers an

Rotor Pole

Stator Pole

DC Source

14

additional degree of freedom and improves energy efficiency of the traction motor.

The degree of freedom is the hybridisation ratio α of the hybrid excitation machines.

It is the ratio of the PM excitation flux Φa to the maximum value of the total

excitation flux Φe max [30].

Figure 2.4: Field excitation synchronous motor [30]

2.5 Flux Switching Motor (FSM)

Flux switching machines in general are typified by having all excitation sources on

the stator, providing simpler cooling options in principle, leaving the rotor to carry

neither windings nor magnets and essentially providing the brush gear and slip rings.

Another obvious advantage of this arrangement is the simplicity of the rotor, which

allows easy manufacture and attainment of relatively high speeds in operation. The

induced voltage v, in the armature system of a rotating electrical machine is

predicted by Faraday’s law at a specified mechanical angular speed wr, the change of

flux linkages dɸ, with position ɵ.as in equation 2.9 [31].

(2.9)

The theory of flux switching machine (FSM) was first founded and published

in the mid-1950s. Firstly, a permanent magnet flux switching machine (PMFSM), i.e.

permanent magnet (PM) single-phase limited angle actuator, or more well-known as

PMs Excitation coils

15

Laws relay, which have four stator slots and four rotor poles, was developed. Later, it

was extended to a single-phase generator, having four stator slots, with four or six

rotor poles. Over the past ten years so many novels and new FSM topologies have

been developed for various applications, ranging from low-cost domestic appliances,

automotive, wind power, aerospace, and others [32-33].

Generally, according to rotor structure, FSMs can be categorised into two

classes, which are FSMs using toothed rotor structure and FSMs using segmental

rotor structure.

2.5.1 FSM Using Toothed Rotor Structure

The basic and common arrangement of the flux switching machine using a toothed-

rotor is based on the principle of Rauch’s flux switch alternator, as shown in Figure

2.5 [34]. The fundamental principle is illustrated in rectilinear representation in

Figure 2.6, showing an elementary cell that contains a PM, FEC, armature winding,

and a toothed-rotor [35].

The operating principle and definition of flux switching can be described either

by changing flux in the stator or changing flux in the rotor. Figure 2.6 explains the

operating principle of E-Core HEFSM in three different conditions. In Figure 2.6(a),

both fluxes of PM and FEC flow from stator to rotor pole P2 and return back to the

stator by rotor pole P1. At this stage, it is obvious that rotor pole P2 received the flux

from the stator. Meanwhile, in Figure 2.6(b), when the rotor moves to the left side

approximately by half electric cycles, both fluxes from the stator flow to rotor pole

P3 in between FEC winding on the right side. It is clear that the stator flux switches

its polarity through rotor pole P3, as receiving flux while rotor pole P2 brings the

flux back to the stator to form a complete flux cycle. Finally, Figure 2.6(c) depicts

the condition where rotor pole P3 is in similar condition with rotor pole P2 in Figure

2.6(a) to form one electric cycle. At this stage, the flux from the stator flows through

stator teeth between PM and armature coil to rotor pole P3 while rotor pole P2 brings

the flux to the stator, simultaneously. Since the direction of both PM and FEC fluxes

are in the same polarity, both fluxes are combined and move together into the rotor,

hence producing more fluxes with a so-called hybrid excitation flux [35].

16

Based on this concept, a rotary elementary single-phase concept has been

discussed in [36], while a practical single phase concept of four U-stator cores, four

magnets, and a four-tooth rotor has been credited with industrial application [37].

More extensive developments and applications on these structures have been

published on multiphase arrangements. Figure 2.7 illustrates the main line of

evolution of the flux switching structure of three-phase toothed rotor [38]. FSMs

using toothed rotor are further divided into three categories, which are PM FSMs,

field excitation FSMs, and hybrid excitation FSMs.

Figure 2.5: A simplified flux-switch alternator scheme [34]

(a) (b)

17

Figure 2.6: Principle Operation of E-Core HEFSM [35]

(a)

(b)

(c)

18

Figure 2.7: Three-phase structure of FSM toothed rotor [38]

2.5.1.1 Permanent Magnet Flux Switching Motor (PMFSM)

Permanent magnet flux switching motor (PMFSM) is simple in construction with

robust toothed rotor structure as shown in Figure 2.8. The stator consists of PM and

armature windings. Due to this it provides some advantages such as easy cooling of

all active parts and better suitability for high-speed applications [39]. PMFSM is

popular due to its high-power density and efficiency. PMFSM uses PMs to generate

flux. The generated flux produced is fixed and will not change-diverged, which

means flux is constant [40-42].

However, in proportion of HEV becoming popular, the increase of the usage

of rare-earth magnet results in the increase of the price. This caused serious concern

about high cost [5]. The general operating principle of the PMFSM is illustrated in

Figure 2.9, where the black arrows show the flux line of PM. From the figure, when

the relative position of the rotor poles and a particular stator tooth are as in Figure

2.9(a), the flux-linkage corresponds to one polarity. However, the polarity of the

flux-linkage reverses as the relative position of the rotor poles and the stator tooth

changes as shown in Figure 2.9(b), i.e., the flux linkage switches polarity as the

salient pole rotor rotates [43].

19

Figure 2.8: 12S-10P PMFSM with toothed rotor [5]

Figure 2.9: Operation principle of PMFSM (a) Flux linkage correspond to one

polarity (b) Flux linkage switch polarity as the salient pole rotates [44]

2.5.1.2 Field Excitation Flux Switching Motor (FEFSM).

Field Excitation Flux Switching Motor (FEFSM) is distinct from PMFSM. Instead of

PM it uses FE to generate flux as shown in Figure 2.10. The stator is composed of

laminated iron core, armature coils, and DC field excitation coils (FECs) as the only

field mmf source. The rotor is only made of laminated iron core similar with SRM.

The external DC source is applied to produce the magnetic field by making sure that

current is flowing through to the winding [45-46]. Although the construction of

(a) (b)

Rotor

Armature coil

20

FEFSM is not as simple as PMFSM because of the use of external DC source, the

main advantages of FEFSM are that it can control the flux and there is no use of rare-

earth magnet, resulting in cost reduction [47].

The operating principle of the FEFSM is illustrated in Figure 2.11. Figure

2.11 (a) and (b) show the direction of the FEC fluxes into the rotor while Figure 2.11

(c) and (d) illustrate the direction of FEC fluxes into the stator, which produces a

complete one-cycle flux. Similar with PMFSM, the flux linkage of FEC switches its

polarity by following the movement of salient pole rotor which creates the term “flux

switching”. Each reversal of armature current shown by the transition between

Figures 2.11(a) and (b), causes the stator flux to switch between the alternate stator

teeth [5].

Figure 2.10: 18S-14P FEFSM with toothed rotor [48]

21

(a) (b)

(c) (d)

Armature coil

Armature coil

Figure 2.11: Operation principles of FEFSM (a) θe=0° and (b) θe=180° flux moves

from stator to rotor (c) θe=0° and (d) θe=180° flux moves from rotor to stator [49]

2.5.1.3 Hybrid Excitation Flux Switching Motor (HEFSM)

Hybrid Excitation Flux Switching Motor (HEFSM) is the combination of PM and

FEC, where PM is used as the primary source of excitation and FEC as the secondary

source of excitation as shown in Figure 2.12. HEFSM requires significantly less

magnet and has higher torque density compared with a conventional PMFSM. To

easily adjust the main flux, which is fixed in PMFSM, HEFSM was developed to

improve the starting/low-speed torque and high-speed flux-weakening capabilities,

which are required for HEV [50-51].

22

By applying negative d-axis current, the PM flux can be counteracted but

with the disadvantage of copper loss, which reduces the efficiency and power

capability, and also possible irreversible demagnetisation of the PMs. Thus, HEFSM

is an alternative option where the advantages of both PM machines and DC FEC

synchronous machines are combined. As such, HEFSMs have the potential to

improve flux weakening performance, power and torque density, variable flux

capability, and efficiency, which have been researched extensively over many years

[52-53].

The operating principle of the proposed HEFSM is illustrated in Fig. 2.13,

where the red and blue lines indicate the flux from PM and FEC, respectively. In Fig.

2.13(a) and (b), since the direction of both PM and FEC fluxes are in the same

polarity, both fluxes are combined and move together into the rotor, hence producing

more fluxes with a so-called hybrid excitation flux.

Figure 2.12. (a) 6S-4P HEFSM (b) 12S-10P inner FE HEFSM [54]

(a

) (b

)

(a) (b)

23

Figure 2.13: The operating principle of the proposed HEFSM (a) θe=0° - more

excitation (b) θe=180° - more excitation (c) θe=0° - less excitation (d) θe=180° - less

excitation [54].

Furthermore in Fig. 2.13(c) and (d), where the FEC is in reverse polarity, only

the flux of the PM flows into the rotor while the flux of the FEC moves around the

stator outer yoke, which results in less flux excitation. An advantage of the DC FEC

is that the flux of the PM can easily be controlled with variable flux control

capabilities as well as under field weakening and or field strengthening excitation.

Overview of various FSMs, design and performance features, various machine

topologies, variable flux capability as well as their relationships with doubly-salient

PM machines and flux reversal PM machines have also been discussed in [54].

(a) (b)

(c) (d)

24

2.5.2 FSM Using Segmental Rotor Structure

In the previous sections, the discussion of flux switching machine was on rotors with

toothed or salient structure rotor. With a complete loop coil-turn arrangement, a

standard configuration in electrical machines with multi-turn windings, the windings

are long-pitched, if not fully-pitched, and invariably overlap. For switched reluctance

motor configurations, an arrangement has been suggested for producing mutual

coupling of single-tooth coils using a segmental rotor. This configuration maintains

the production of higher torque densities by the principle of the changing mutual

inductance, and has a further advantage of reduced copper usage and power loss due

to shorter end-windings. Meanwhile, the use of a segmental rotor as applied to flux

switching machines has been proposed by another researcher for field-winding

excitation into one with single-tooth windings [56]. Thus, for flux switching

machines employing a segmental rotor, there is, firstly, the attraction of achieving

higher torque densities due to operating with bipolar flux and secondly, a reduction

of copper losses and material due to shorter end-windings.

Figure 2.14 and Figure 2.15 show the basic principle of FSMs using a

segmented rotor with field excitation winding and with PM, respectively. For the two

rotor positions shown in the figures, while the field flux F1 and F2 are unchanged,

there is a change of polarity of the armature flux linkages on A1 and A2 as the rotor

segments S1 as S2 rotate. It is easy to follow that the scheme can be implemented

with PM excitation by replacing the field winding on F1 and F2 with radially acting

PMs on the field teeth structures, as shown in Figure 2.15. In practice, significant

benefits of short endings appear with the 8/4-configuration if a single-phase topology

is sought, whilst the 12/6 is another possible configuration with significantly shorter

end-windings [57].