DEVELOPMENT OF A NEW SINGLE-PHASE FIELD EXCITATION … · armature and Field Excitation Coil (FEC)...
Transcript of DEVELOPMENT OF A NEW SINGLE-PHASE FIELD EXCITATION … · armature and Field Excitation Coil (FEC)...
DEVELOPMENT OF A NEW SINGLE-PHASE FIELD
EXCITATION FLUX SWITCHING MOTOR
TOPOLOGY WITH SEGMENTAL ROTOR
MOHD FAIROZ BIN OMAR
UNIVERSITI TUN HUSSEIN ONN MALAYSIA
DEVELOPMENT OF A NEW SINGLE-PHASE FIELD EXCITATION FLUX
SWITCHING MOTOR TOPOLOGY WITH SEGMENTAL ROTOR
MOHD FAIROZ BIN OMAR
A thesis submitted in
fulfillment of the requirement for the award of the
Degree of Master of Electrical Engineering
Faculty of Electrical & Electronic Engineering
Universiti Tun Hussein Onn Malaysia
JULY, 2016
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DEDICATION
For my beloved mother and father
Hajah Maznah Ali and Haji Omar Ismail,
My wife and my sons,
Suriani Othman, Muhammad Yusuff and Muhammad Luqman
My siblings and my friends
Thank you for your love, guidance and support
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ACKNOWLEDGEMENT
Firstly, in the name of ALLAH, the most gracious and the most merciful.
Alhamdulillah, all praises to Allah Almighty for His grace and His blessings given to
me for the completion of my master’s studies successfully.
Secondly, I acknowledge, with many thanks, to Ministry of Higher Education
(MoHE) and Universiti Tun Hussein Onn Malaysia (UTHM) for awarding me
scholarship for my master’s program. I am much honoured to be the recipient for this
award. Receiving this scholarship motivates me to maintain a peaceful life and
providing me confidence and willingness to achieve my goals.
Thirdly, I 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 humor 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 would also like to thank my lovely wife, Suriani Othman, whose dedication,
love and persistent confidence in me, has taken the load off my shoulder. Thank you
also to my sons Muhammad Yusuff and Muhammad Luqman who brightened the lives
of our family. I would also like to thank my parents and family members for their
moral support towards the completion of my study. A sincere thanks to my beloved
father Haji Omar Ismail and also to my beloved mother, Hajah Maznah Ali.
Moreover, 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 fellow friends during my study in UTHM. Life would never have been that existing
and joyful without you all. Finally, I would like to thank everybody who was important
to the successful realization of this thesis, as well as expressing my apology that I could
not mention personally one by one.
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ABSTRACT
Diverse topology of three-phase and single-phase Field Excitation Flux Switching
Machines (FEFSMs) that have been developed recently have several advantages such
as variable flux capability and the single piece structure of rotor suitable for high-speed
applications. However, a salient rotor structure has led to a longer flux path resulting
in high flux leakage and higher rotor weight. Meanwhile, overlap windings between
armature and Field Excitation Coil (FEC) have caused the problems of high end coil
increased size of motor and high copper losses. Therefore, a new topology of single-
phase non-overlap windings 12S-6P FEFSM segmented rotor with the advantages of
less weight and non-overlap between armature coil and FEC windings is presented.
The design, flux linkage, back-EMF, cogging torque, average torque, speed, and power
of this new topology are investigated by JMAG-Designer via a 2D-FEA. As a results
the proposed motor has achieved torque and power of 0.91Nm and 293W, respectively.
To prove the simulation result based on 2D-FEA, experimental test is performed and
the armature back-EMF was observed with FE current of 4A is supplied. Finally, at
the speed of 500 rpm and 3000 rpm, the back-EMF is 2.75 V and 16.13 V, respectively.
The simulation results showed reasonable agreement with the experimental results,
approximately difference range from 4.9% to 7.4%.
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ABSTRAK
Pelbagai topologi motor fasa tunggal dan tiga fasa Motor Penukaran Fluk Pengujaan
Medan (FEFSMs) yang telah dibangunkan kebelakangan ini mempunyai beberapa
kelebihan seperti keupayaan fluk yang variasi, dan bahagian pemutar tunggal yang
kukuh sesuai digunakan pada aplikasi yang memerlukan tork, kuasa dan kelajuan
tinggi. Walau bagaimanapun, struktur pemutar menonjol telah membawa kepada
laluan fluk menjadi panjang telah menyebabkan kadar fluk bocor tinggi dan berat rotor
meningkat. Sementara itu, pertindihan antara gegelung angker dan medan pengujaan
(FE) menyebabkan hujung gegelung dan saiz motor meningkat serta kehilangan
tembaga yang tinggi. Oleh itu, satu topologi fasa tunggal 12S-6P FEFSM dengan
pemutar bersegmen baru dengan pelbagai kelebihan seperti gegelung angker dan FEC
tidak bertindih, lebih ringan dan kehilangan tembaga yang rendah telah diperkenalkan.
Rekabentuk, hubungan fluk, voltan teraruh (EMF), tork penugalan, tork purata,
kelajuan dan kuasa bagi topologi baru ini disiasat dengan menggunakan perisian
JMAG-Designer melalui kaedah Analisis Unsur Terhingga dua dimensi (2D-FEA).
Hasil analisis ke atas motor yang dicadangkan mendapati tork dan kuasa masing-
masing mencapai sebanyak 0.91Nm dan 293W. Keputusan yang diperolehi ke atas
motor yang dicadangkan adalamendapati Untuk membuktikan ujian simulasi pada
2D-FEA, ujian secara eksperimen telah dilakukan dan EMF pada gegelung angker
telah dicerap dengan arus FE sebanyak 4A telah dibekalkan. Akhir sekali, pada
kelajuan 500 rpm dan 3000 rpm, masing-masing voltan teraruh (EMF) adalah 2.75 V
dan 16.13 V. Keputusan simulasi menunjukkan perbandingan yang munasabah dengan
keputusan eksperimen, dianggarkan julat peratus perbezaan dari 4.9% hingga 7.4%.
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TABLE OF CONTENTS
TITLE i
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF SYMBOLS AND ABBREVATIONS xiv
LIST OF APPENDICES xvi
CHAPTER 1 INTRODUCTION 1
1.1 Research Background 1
1.2 Problem Statements 4
1.3 Objectives of the research 4
1.4 Scopes of the Research 5
1.5 Thesis Outlines 6
1.6 Chapter Summary 7
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CHAPTER 2 LITERATURE REVIEW ON FEFSM 8
2.1 Introduction 8
2.2 Introduction to Electric Motor 8
2.3 Flux Switching Motor (FSM) 10
2.3.1 Field Excitation Flux Switching
Machines 13
2.3.2 Field Excitation Flux Switching
Machine with Salient Rotor 14
2.3.3 Field Excitation Flux Switching
Machine with Segmental Rotor 16
2.4 Overview of Design and Analysis of FEFSMs 21
2.5 Overview of Development, Test, and Validation
of The Performances of Prototype Electric
Motor 25
2.6 Chapter Summary 31
CHAPTER 3 RESEARCH METHODOLOGY 32
3.1 Introduction 32
3.2 Design Various Rotor Pole of Single-Phase
Non-overlap Windings FEFSM with Segmental
Rotor. 33
3.2.1 Geometry Editor 34
3.2.2 JMAG-Designer 38
3.3 Analyse Performances of the Proposed Single-
Phase Non-overlap Windings 12S-6P FEFSM
with Segmental Rotor 39
3.3.1 No-load Analysis 41
3.3.2 Load Analysis 41
3.4 Prototype Fabrication and Results Comparison 42
3.4.1 Prototype Fabrication 43
3.4.2 Experiment Setup for Result
Comparison 48
3.5 Chapter Summary 49
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CHAPTER 4 RESULTS AND DISCUSSIONS 50
4.1 Introduction 50
4.2 Result of Design Various Rotor Pole of Single-
Phase Non-Overlap Windings FEFSM with
Segmental Rotor 50
4.2.1 Result of Armature Coil Arrangement
Test 52
4.2.2 Result of Flux Strengthening 53
4.2.3 Result of Back-EMF 53
4.2.4 Result of Cogging Torque 54
4.2.5 Results of Maximum Torque and Power 55
4.3 Result of Analyse Performances of the
Proposed Single-Phase Non-overlap Windings
12S-6P FEFSM with Segmental Rotor 56
4.3.1 Result of No-load Analysis 56
4.3.2 Result of Load Analysis 58
4.4 Prototype Fabrication 61
4.5 Result Comparison 71
4.6 Chapter Summary 74
CHAPTER 5 CONCLUSIONS AND FUTURE WORKS 75
5.1 Conclusions 75
5.2 Future Works 76
REFERENCES 77
APPENDICES 864
VITA 124
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LIST OF TABLES
1.1 1-Ø Induction motor specifications 3
2.1 The main parameters of FEFSM with salient rotor 16
2.2 Performances of FEFSM with salient rotor 16
2.3 The main parameters of FEFSM with segmental rotor 20
2.4 Performances of FEFSM with segmental rotor 20
3.1 Design parameters of single phase FEFSM with
segmental rotor 37
3.2 Material selection for rotor, stator, armature coil, and
FEC 39
3.3 Condition setting for Rotor, Armature Coil, FEC1,
and FEC2 39
3.4 The link of FEM Coil corresponding to its circuit 39
3.5 Part and materials type of 12S-6P FEFSM with segmental
rotor 46
4.1 Specifications of silicon electrical steel 35A250 and
35H210 63
4.2 Details and specifications of prototype 70
4.3 The percentage difference of back-EMF 73
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LIST OF FIGURES
1.1 Basic principle of FSM 59
1.2 The structure of single-phase induction motor 3
2.1 The Classification of the main types of Electric
Motors 9
2.2 Classification of Flux Switching Motors 11
2.3 Various types of FSMs 12
2.4 Principle operation of FEFSM 14
2.5 Examples of FEFSM with salient rotor 15
2.6 Basic segmental rotor structure with FE only 17
2.7 FEFSM with segmental rotor operating principles
under FE excitation 18
2.8 Examples of FEFSM with segmental rotor 19
2.9 Design implementation of the proposed FEFSM 21
2.10 Example of Permanent Magnet Spherical Motor
(PMSM) 3D drawing based on Solidworks 26
2.11 Example of 3D structure and prototype of the Hybrid
Excited Flux-Switching Machine 27
2.12 B-H properties of various magnet types 28
2.13 Experimental scheme of 3-phase FEFSM 29
2.14 Experimental set up of 3-phase PM brushless motor 29
2.15 Back-EMF versus speed at various field excitation 30
2.16 Output torque versus armature current at various field
excitations current 31
3.1 Overall research methodology 32
3.2 Work flow of various designs of FEFSM’s rotor pole
with segmental rotor 34
3.3 Stator structure 35
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3.4 Segmental rotor structure 36
3.5 Dimension of rotor pole 37
3.6 Completion of geometry editor section with various
rotor poles of single-phase FEFSM with segmental
rotor 38
3.7 Flow chart of no load and load analysis 40
3.8 Block diagram of prototype fabrication and result
comparison 42
3.9 Work flow for designing FEFSM prototype in 3D 44
3.10 Example of 2D sketch and 3D drawing of stator part 44
3.11 Work flow for fabrication of single-phase 12S-6P
FEFSM with segmental rotor 45
3.12 Wire configuration inside the slot area 47
3.13 Jig with separator used for winding process 47
3.14 Block diagram for motor measurement systems 48
3.15 Experimental setup for single-phase 12-6P FEFSM
with segmental rotor 49
4.1 Various slot-pole of FEFSM (a) 12S-3P, (b) 12S-6P,
(c) 12S-9P and (d) 12S-15P 51
4.2 The flux linkage at armature coils 52
4.3 Maximum flux at various FEC current density, JE 53
4.4 Back-EMF 54
4.5 Cogging torque 55
4.6 Maximum torque and power for various pole
configurations 56
4.7 Flux distribution 57
4.8 Illustration of flux line at four typical mechanical
rotor position 58
4.9 Graph flux total for 12S-6P FEFSM with segmental
rotor 59
4.10 Torque versus JE at various JA for12S-6P FEFSM
with segmental rotor 60
4.11 Graph torque and power versus speed characteristics 61
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4.12 Single-phase non-overlap windings FEFSM 12S-6P in
3D view 62
4.13 Parts which have been fabricated from milling
machine 64
4.14 Shaft lock position at shaft set in 3D view by
Solidworks 64
4.15 Samples of stator and rotor 65
4.16 Lamination of stator and rotor core 66
4.17 Two pieces of winding separator 66
4.18 Complete coil windings process 67
4.19 Photos of triangular shape area and high end coil 68
4.20 Length of one coil 69
4.21 The prototype of single phase 12S-6P FEFSM with
Segmental rotor that has been assembled 70
4.22 Experimental set up 71
4.23 Comparison of back-EMF at various speeds 72
4.24 Comparison of maximum back-EMF at various
speeds 73
Error! Bookmark not defined.
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LIST OF SYMBOLS AND ABBREVATIONS
ctpN - Number of periods.
- Efficiency
cteN - Electrical angle of rotation for each period of cogging
torque
exc - Flux linkage due to field excitation
- Electrical angular position of rotor
r - Rotational speed
- Flux
F - Magnetomotive force
- Reluctance
B - Magnetic flux density
- Stack length
cP - Copper loss
iP - Iron loss
N - Number of turns
- Copper resistivity
AJ - Armature current density
EJ - Field current density
rN - Number of rotor poles
sN - Number of stator slots
k - Natural number
q - Number of phases
ef - Electrical frequency
mf - Mechanical rotation frequency
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- Filling factor
S - Slot area
EI - Field current
AI - Armature current
T - Torque
FSM - Flux Switching Motor
PM - Permanent Magnet
FEC - Field Excitation Coil
HE - Hybrid Excitation
FE - Field Excitation
FEA - Finite Element Analysis
CAD - Computer Aided Design
CNC - Computer Numerical Control
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LIST OF APPENDICES
APPENDIX TITLE PAGE
A List of Publications 84
B List of Awards 86
C AC Machine Assignments Standard by
Dissectible Machines System (62-005)
87
D Table D: Lists of 12S-6P FEFSM with
Segmental Rotor Part in 3D view by
Solidworks 109
E Prototype fabrication process 110
F Technical drawing of single-phase 12S-6P
FEFSM with segmental rotor
112
1CHAPTER 1
INTRODUCTION
1.1 Research Background
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 [1]. 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 [2]. Generally,
FSM can be categorised into three groups: permanent magnet flux switching motor
(PMFSM), field excitation flux switching motor (FEFSM), and hybrid excitation flux
switching motor (HEFSM). Both PMFSM and FEFSM have only PM and field
excitation coil (FEC), respectively, as their main flux sources, while HEFSM combines
both PM and FEC as its main flux source.
Figure 1.1 illustrates the basic operation of FEFSM. Considering Figure 1.1
(a), the excitation of the field and armature windings at positive current creates a flux
vector in the north-westerly direction and north-easterly direction, respectively. The
combined flux generated by the two coils caused a flux moving vertically upwards and
the rotor aligned itself with a pair of vertical stator. Additionally, Figure 1.1 (b)
illustrates the current in the armature winding is reversed, while the FEC winding
continues being excited in the same direction by the effect of the 180° flux shifting
from west-south. The result from the 180° shifting makes the rotor tends to align with
the stator poles based on the flux movement in a westerly direction through horizontal
stator poles. Therefore, each reversal of current directions in the armature causes the
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stator flux vector to switch between horizontal and vertical directions, hence
introducing the name FSM [3], [4].
The viability of this design has been demonstrated in applications requiring
high power densities and a good level of durability. The single-phase AC motor can
be realised with the connection of the FE coil windings to the DC supply and armature
windings to the AC supply to achieve the orientation of flux in allowing the rotor
rotation [5], [6], [7]. In more recent studies some researchers have developed the use
of a segmental rotor construction for switched reluctance motors (SRMs) and two-
phase FSMs, which gives significant gains 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 in conveying the field flux to adjacent stator
armature coils as the rotor rotates [8], [9], [10]. As each coil arrangement is around a
single tooth, this design gives shorter end-windings than the salient rotor structure,
which requires fully-pitched coils. There are significant gains with this arrangement
as it uses less conductor materials and may improve the overall motor efficiency.
Hence, this motor has the ability and capability suitable for use in industrial
and commercial applications that require low torque and high speed. An example is a
conventional fan (table or stand fan), blower, exhaust fan and compressor motors.
Currently, most of the commercial applications use induction motors (IMs). Figure 1.2
and Table 1.1 show the example of structure and specifications of single-phase
induction motors used in conventional fan, respectively [11]. An induction motor's
rotor can be either wound type or squirrel-cage type. For the wound type, the winding
(a) (b)
Figure 1.1: Basic principle of FSM
F+
F- A+
A- F+
F-
A+
A-
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is located on the rotor and stator while for squirrel-cage type the winding is placed
only on stator. However, IMs have the disadvantage of having the active part located
on the rotor, thus affecting the cooling process and the rotor not being robust [12].
Therefore, the FEFSM with segmental rotor using different windings
techniques of induction motor is introduced, where both field excitation coil (FEC)
and armature coil windings are placed on the stator. This has led to advantages such
as the following; all brushes are eliminated, whilst complete control is maintained over
the field excitation flux. The concept of the FEFSM with segmental involves changing
the polarity of the flux linking the armature winding by the motion of the rotor [13],
[14].
In this research, a single-phase flux switching motor using a segmental rotor is
proposed. This research also describes the principle operation of single-phase non-
overlap windings FEFSM 12S-6P with segmental rotor, discusses the prototype
fabrication, and compares the back-EMF result of the prototype experimentally.
Figure 1.2: The structure of single-phase induction motor
Table 1.1: 1-Ø Induction motor specifications
Items Parameters
Voltage input (Volt) 240
Frequency (Hz) 50
Power (W) 60
Torque (Nm) 0.4
Range of speed (rpm) 1455-1465
Outer diameter of stator (mm) 75
Outer diameter of rotor (mm) 44.5
Length of air gap (mm) 0.25
Weight (kg) 0.91
Stator
Rotor
Case
Armature coil
4
1.2 Problem Statements
Based on previous literature, single-phase 8S-4P and 12S-6P FEFSMs with salient
rotor is suitable for high-speed applications since it has a strong single rotor structure
[5], [15], [16], [17]. However, a salient rotor structure has led to a longer flux path
resulting in high flux leakage and higher rotor weight. In addition, the overlapped
windings between armature and FEC creates the problem of high end coil, which
increases the size of the motor.
Therefore, various segmental rotor poles of single-phase non-overlap windings
FEFSM with segmental rotor between armature coil and FE coil should be analyzed
to create shorter flux path and reduce the coil end problem thus improving their flux
linkage, back-EMF, cogging torque, average torque and power versus speed
characteristics.
Moreover, the result comparison of back-EMF between simulation and
experiment should be carried out to validate the prototype of single-phase non-overlap
windings FEFSM with segmental rotor.
1.3 Objectives of the research
The objectives of this research are:
(i) To design various rotor pole of single-phase non-overlap windings
FEFSM with segmental rotor.
(ii) To analyse the flux linkage, back-EMF, cogging torque, average torque
and power versus speed characteristics of the proposed single-phase
non-overlap windings FEFSM with segmental rotor.
(iii) To validate the back-EMF of the prototype of single-phase non-overlap
windings 12S-6P FEFSM with segmental rotor.
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1.4 Scopes of the Research
Commercial FEA package, JMAG-Designer version 14.1, released by Japan Research
Institute (JRI) is used as 2D-FEA solver for this design. The electrical restrictions
related with the inverter such as maximum 240V DC inverter current and maximum
11.09A inverter current are set. Assuming the air coolant system is employed as the
cooling system for the machine, the limit of the current density is set to a maximum of
30Arms/mm2 for armature windings and 30A/mm2 for FE windings, respectively. In
various rotor poles studies, the design of the machine is focused only on 4 designs,
12S-3P, 12S-6P, 12S-9P, and 12S-15P. The stator outer diameter, the stator inner
diameter, the back inner width of stator, tooth width of stator, the motor stack length,
the rotor outer diameter, the shaft of rotor and the air gap having dimensions 75 mm,
45 mm, 5 mm, 20.3 mm, 44.5mm, 15 mm and 0.25 mm, respectively will be kept
constant for all designs. The materials used for stator and rotor are silicon electric steel
35A250, while armature and FEC winding are copper.
Therefore, design 2D and 3D part sketches during the prototype process of the
proposed single-phase 12S-6P FEFSM with segmental rotor should be done with
Solidworks 2014 software. In addition, coil winding is set to 88 turns for both FEC
and armature coil windings. While, the silicon electric steel 35A250 is cut into 58
pieces. To perform the back-EMF test by experimental, motor measuring system that
has been calibrated must be provided and connected to the motor test. The limit of DC
power supply and speed of DC motor (prime mover) are set to 4A and 3,000rpm,
respectively.
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1.5 Thesis Outlines
This thesis deals with the development of FEFSM with 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, which includes the background of
FSM and explanation regarding toothed and segmental rotor. Problems of
existing motors employing segmental rotor, research objectives and research
scope are discussed in this chapter.
(b) Literature review
This chapter defines the overview and classifications of various FSMs. Among
the three types of FSM - Permanent Magnet Flux Switching Machine
(PMFSM), Field Excitation Flux Switching Machine (FEFSM) and Hybrid
Excitation Flux Switching Machine (HEFSM), FEFSM is the best type to be
considered as it does not use PM. In addition, a variety of designs of FEFSM
with performance have been clearly explained. Besides, the analysis and all the
formulas used to design FSM have been described. The final section describes
the overviews of development, testing, and validation of the performance of
prototype that has been done by previous researchers.
(c) Research Methodology
The project implementation has been divided into three stages including the
designs of various rotor poles study of single-phase FEFSM with segmental
rotor, analysis of performance for single-phase FEFSM with segmental rotor
using 2D-FEA with JMAG Designer and prototype fabrication and results
comparison. Stage 1 is divided into two parts that are geometry editor and
JMAG Designer, while stage 2 is divided into two parts that are no-load and
load analysis by 2D FEA. Finally, stage 3 has three phases, which are designing
a FEFSM in 3D, fabrication of single-phase 12S-6P FEFSM with segmental
rotor, and experimentation and validation of prototype back-EMF.
(d) Results and Discussions
This chapter defines the design, performance analyses, and development,
testing, and validation of the performance of the FEFSM prototype. The 12S-
6P is the best design and is selected for future 2D-FEA load-analysis and
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development of the prototype. Based on 2D-FEA by JMAG, the flux linkage,
maximum torque, and power is 0.041Wb, 0.9Nm, and 293W, respectively. In
the fabrication, there are four types of methods that have been used for the
fabrication of prototype single-phase 12S-6P using CNC machines, 3D printer,
and coil windings manually. Materials used in the prototype are silicon electric
steel 35A250, aluminum, stainless steel, ABS plastic, and copper wire. The
experimental test shows the speed of 500rpm and 3,000rpm for the back-EMF
are 2.75V and 16.13V, respectively. The average percentage difference
between the experimental and JMAG simulation is 6.2%.
(e) Conclusions and Future works
The final chapter describes and concludes the research and suggestions for
future works are described in this chapter.
1.6 Chapter Summary
This chapter briefly describes the type of motors used on the existing system fan and
identifying motor weaknesses. The single-phase non-overlap windings FEFSM with
segmental rotor is introduced to overcome the drawbacks of single-phase overlap
windings FEFSM with salient rotor. In addition, the objectives and scope of the
research are also briefly described in this chapter to explain the implementation of this
research.
2CHAPTER 2
LITERATURE REVIEW ON FEFSM
2.1 Introduction
This chapter defines the overview and classifications of various FSMs. Among the
three types of FSM are PMFSM, FEFSM and HEFSM. FEFSM is the best type to be
considered and will be emphasised more due to its does not use PM. Besides, the
analysis and all the formulas used to design FSM have been described. The final
section describes the overviews of development, testing, and validation of the
performance of prototype that has been done by previous researchers.
2.2 Introduction to Electric Motor
An electric motor is an electromechanical device that converts electrical energy into
mechanical energy. Most electric motors operate through the interaction of magnetic
fields and current-carrying conductors to generate force. The reverse the process,
which is producing electrical energy from mechanical energy, is done by generators
such as an alternator or a dynamo. Some electric motors can also be used as generators,
for example, a traction motor on a vehicle may perform both tasks. Electric motors and
generators are commonly referred to as electric machines.
Electric motors can be divided into two types; alternating current (AC) electric
motors and direct current (DC) electric motors. The DC electric motors will not work
if supplied with AC supply, and vice versa. DC motors use batteries with DC supply
as it has an advantage of simple control principle. However, usage of the commutator
and brush, makes them less reliable and unsuitable for maintenance-free drives. The
speed control of DC and AC motors are also different. For DC motors, the speed is
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controlled by varying the current in the DC windings, while the speed of AC motors
is influenced by the frequency.
There are three types of AC motors, which are asynchronous motor or
Induction Motor (IM), synchronous motor (SM), and switched reluctance motor
(SRM). IM is divided into two, squirrel cage and wound cage. Most industrial uses IM
since the motor is durable and inexpensive. SM can be classified as permanent magnet
SM (PMSM), field excitation SM (FESM), hybrid excitation SM (HESM) and flux
switching motor (FSM). FSM can be further classified as permanent magnet FSM
(PMFSM), field excitation FSM (FEFSM), and hybrid excitation FSM (HEFSM).
Figure 2.1 illustrates the classification of the main types of electric motors [18].
Induction motor (IM) action involves induced currents in coils on the rotating
armature. IMs use shortened wire loops on a rotating armature and obtain their torque
from currents induced in these loops by the changing magnetic field produced in the
stator (stationary) coils. The induced voltage in the coil shown drives current and
results in a clockwise torque. Note that this simplified motor will turn once it is started
in motion, but has no starting torque. Various techniques were used to produce some
asymmetry in the fields to give the motor a starting torque [19], [20].
Figure 2.1: The Classification of the main types of Electric Motors
The switched reluctance motor (SRM) is an electric motor that runs by
reluctance torque. SRM is a kind of motor relying on the working principle of magneto
10
resistive effect, and initial motor performance is imperfect [21]. With the growth of
high-functioning and high power electronic devices as well as the diverse
implementations of intelligent control, SRM has been actively developed [22]. Unlike
common DC motor types, power is delivered to windings in the stator (case) rather
than the rotor [23]. This greatly simplifies mechanical design as power does not have
to be delivered to a moving part, but it complicates the electrical design as some sort
of switching system that needs to be used to deliver power to the different windings.
With modern electronic devices this is not a problem, and the SRM is a popular design
for modern motors. Its main drawback is torque ripple.
Synchronous motors (SMs) are naturally constant-speed motors. They operate
in synchronism with line frequency and are commonly used where precise constant
speed is required. The SM is an electric motor that is driven by AC power consisting
of two basic components: a stator and rotor. Typically, a capacitor connected to one of
the motor's coil is necessary for rotation in the appropriate direction. The outside
stationary stator contains copper wound coils that are supplied with an AC current to
produce a rotating magnetic field. The magnetised rotor is attached to the output shaft
and creates torque due to the stator rotating field. The motor's synchronous speed is
determined by the number of pair poles and is a ratio of the input (line) frequency. In
the mid-1950s, the concept of FSM was founded and first published [24]. FSM is a
new category of SMs.
2.3 Flux Switching Motor (FSM)
Generally, FSM can be categorised into three groups: permanent magnet flux
switching motor (PMFSM), field excitation flux switching motor (FEFSM), and
hybrid excitation flux switching motor (HEFSM). Both PMFSM and FEFSM have
only PM and field excitation coil (FEC), respectively, as their main flux sources, while
HEFSM combines both PM and FEC as its main flux source. Figure 2.2 illustrates the
general classification of FSMs.
11
FSM consists of the rotor and stator. The rotor consist of a single structure,
which is an iron core, thus allowing its simple construction and inherent robustness to
be retained while both field and armature windings are on the stator. These contribute
to major advantages where 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. The term “flux switching” is coined to describe motors in which the
stator tooth flux switches polarity following the motion of a salient pole rotor [25]. All
excitation sources are on the stator with the armature and field allocated to alternate
stator teeth. Figure 2.3 illustrates the various types of FSMs [26], [27].
Flux is produced in the stator of the motor by a permanent magnet or by DC
current flowing in the field winding. The orientation of the field flux is then simply
switched from one set of stator poles to another by reversing the polarity of the current
in the armature winding. As a result of preliminary studies, the FEFSM were selected
and used for detailed analysis. This is because FEFSM does not use PM as a source to
produce flux and indirectly contributes to a reduction in the cost of construction of a
motor without reducing any ability of the motor [28], [29], [30].
Figure 2.2: Classification of Flux Switching Motors
12
Figure 2.3: Various types of FSMs [26], [27]
(a) C-core PMFSM (b) E-core PMFSM
(c) FEFSM with segmental rotor (d) FEFSM with salient rotor
(e) Outer rotor HEFSM (f) HEFSM with non-overlap windings
Stator
Rotor
PM
Armature coil
Stator
Rotor
Armature coil
FE coil
PM
Armature coil
Stator
Rotor
FE coil
13
2.3.1 Field Excitation Flux Switching Machines
Among several classes of FSMs, the FEFSMs offer numerous advantages such as
magnet-less machine, low cost, simple construction, and variable flux control
capabilities that are suitable for various performances. The concept of the FEFSMs
involves changing the polarity of the DC Field Excitation Coil (FEC) flux linking with
the armature coil flux, with respect to the rotor position. To form the FEFSMs, the PM
excitation on the stator of conventional PMFSMs is replaced by DC FEC windings for
their main flux sources [13]. Figure 2.4 shows the operating principle of the FEFSM
in which a field flux path is generated by MMF of FEC at two different rotor positions
when the FECs are energised with DC current. The line with arrows depicts the field
flux path.
The direction of the FEC fluxes into the rotor is demonstrated in Figure 2.4 (a)
and Figure 2.4 (b) while the direction of FEC fluxes into the stator is represented in
Figure 2.4 (c) and Figure 2.4 (d), correspondingly to produce a complete one cycle
flux. The flux linkage of FEC switches its polarity by following the movement of the
salient pole rotor, which creates the word “flux switching”. Each reversal of armature
current shown by the transition between Figure 2.4 (a) and Figure 2.4 (b), causes the
stator flux to switch between the alternate stator teeth. The flux does not rotate but
shifts clockwise and counterclockwise with each armature-current reversal. With the
rotor inertia and appropriate timing of the armature current reversal, the reluctance
rotor can rotate continuously at a speed controlled by the armature current frequency.
The armature winding requires an alternating current reversing in polarity in
synchronism with the rotor position.
This FEFSM can be divided into two types, namely Field Excitation Flux
Switching Machine with Salient Rotor and Filed Excitation Flux Switching Machine
with Segmental Rotor. Both rotors have same characteristics but different designs.
14
2.3.2 Field Excitation Flux Switching Machine with Salient Rotor
The previous FEFSM with salient rotor configurations and dimensions are illustrated
in Figure 2.5 and Table 2.1, respectively. Figure 2.5(a) shows the single-phase 12S-6P
FEFSM [16]. The single-phase FEFSM can be considered a very simple machine to
manufacture; it requires two power electronic controllers for armature coil and DC
FEC. Thus, it has the potential to be extremely low cost, although only in high-volume
applications. Furthermore, being an electronically commutated brushless machine,
FEFSM inherently offers longer life, and very flexible and precise control of torque,
speed, and position at no additional cost. However, the single-phase FEFSMs suffer
with problems of low starting torque, large torque ripple, fixed rotating direction, and
overlapped windings between armature coil and DC FEC [27].
Figure 2.4: Principle operation 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
Stator
FEC
Stator
FEC
Stator
Rotor Rotor
Armature Coil
(a) (b)
FEC FEC FEC
Stator
Rotor
FEC
Rotor
FEC
Armature Coil
(c) (d)
15
In addition, three-phase FEFSM with salient rotor has also been introduced to
be used in HEV applications as shown in Figure 2.5(b) and Figure 2.5(c) [13], [28],
[31]. Table 2.2 shows a summary of performance for each type of FEFSM with salient
rotor. The table clearly shows that the combination of 12S-10P FEFSM salient rotor is
ranked highest, followed by a three-phase 12S-14P FEFSM salient rotor, and the
lowest is a single-phase 12S-6P FEFSM with salient rotor. This evaluation is based
from these three parameters: back-EMF, torque, and power. Although the three-phase
12S-10P FEFSM produced the back-EMF 290V, the torque and power of this machine
is the highest, with 212.9Nm and 127.3kW, respectively. Compared with the three-
phase 12S-14P and single-phase 12S-6P FEFSM with salient rotor, their torque and
power is less than the three-phase 12S-10P with salient rotor. For the three-phase 12S-
14P, the torque is 164.1Nm and power is 61.5kW. While for single-phase 12S-6P, the
torque and power is 38.2Nm and 31.6kW, respectively.
(a) Single-phase 12S-6P (b) Three-phase 12S-10P
Figure 2.5: Examples of FEFSM with salient rotor [13], [16], [28], [31]
Stator
Rotor
Armature coil FE coil
(c) Three-phase 12S-14P
Stator Rotor
Armature coil FE coil
Armature coil
16
2.3.3 Field Excitation Flux Switching Machine with Segmental Rotor
The discussion of flux switching machine in the previous sections was with rotors with
toothed or slotted structure. With a complete loop coil-turn arrangement, a standard
configuration in electrical machines with multi-turn windings, the windings are
longpitched, if not fully-pitched, and invariably overlap. In [32], Mecrow et al
suggested a structure of producing mutual coupling of single-tooth coils using a
segmental rotor for switched reluctance motor configurations.
This configuration maintains the production of higher torque densities by the
principle of the changing mutual inductance [33], [34], but has a further advantage of
reduced copper usage and power loss due to resulting shorter end-windings. Use of a
segmental rotor as applied to flux switching machines, turns the structure for field-
winding excitation proposed by Pollock et al [3] and presented in the previous section,
into one with single-tooth windings. Thus, for flux switching machines employing a
segmental rotor, there is, firstly, the attraction of achieving higher torque densities due
Table 2.1: The main parameters of FEFSM with salient rotor [13], [16], [28], [31]
Items 12S-6P 12S-10P 12S-14P
Number of phase 1 3 3
Rated speed (r/min) 1,000 3,000 1,200
Max. DC-bus voltage inverter (V) 360 650 650
Max. current density in armature winding, JA 10 21 30
Max. current density in excitation winding, JE 10 21 30
Stator outer diameter (mm) 90 264 264
Motor stack length (mm) 25 70 70
Air gap length 0.5 0.8 0.8
Table 2.2: Performances of FEFSM with salient rotor [13], [16], [28], [31]
Items 12S-6P 12S-10P 12S-14P
Back-EMF(V) 50.4 290 100
Maximum Torque (Nm) 38.2 212.9 164.1
Maximum Power (kW) 31.6 127.3 61.5
17
to operating with bipolar flux and secondly, a reduction of copper losses and material
due to shorter end-windings.
The basic structure employing a segmented rotor is shown in Figure 2.6 and is
modelled from the basic principle reported in [3]. For the two rotor positions shown in
the figure, 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.
Figure 2.7 illustrates in a simplified rectilinear arrangement how a segmental
rotor can achieve flux switching for a concept of four stator teeth and two rotor
segments, with field excitation only applied to coils winding round teeth F1 and F2.
For the different rotor positions shown, coupling between adjacent coils on the teeth
is through segments. The motion of the rotor not only varies flux in the armature teeth
A1 and A2, but also changes its polarity. This results in coils winding round teeth A1
and A2 experiencing a bipolar AC magnetic field, with EMF being induced. Armature
tooth flux switches polarity at two points in a cycle by two distinct presentations of the
rotor segment.
The first presentation for flux to switch polarity is when the trailing edge of
one segment and the leading edge of the next segment have equal overlap over the
armature tooth, while the second presentation is when a segment is centered with the
armature tooth, as illustrated in Figure 2.7 (b) and Figure 2.7 (d). Even though the flux
linkage of the armature winding is zero at these positions, there is considerably higher
flux density at the tip and the root of the armature tooth for position (b) than for
position (d).
Figure 2.6: Basic segmental rotor structure with FE only [35]
(a) Armature at positive (b) Armature at negative
18
Stator
Rotor Rotor
Stator
Rotor Rotor
Stator
Rotor Rotor
Flux FEC winding Armature winding
Figure 2.7: FEFSM with segmental rotor operating principles under FE excitation
(a) Rotor segments at initial position
(b) Rotor segments at one-fourth (1/4) of cycle
(c) Rotor segments at half (1/2) of cycle
(d) Rotor segments at three- fourths (3/4) of cycle
Legend: Stator
Rotor
F1+ F1- F2- F2+
1+
A1- A1+ A1+ A1-
F1+ F1- F2+ F2-
A1- A1+ A1+ A1-
A1- A1+ A1- A1+
F1+ F1- F2- F2+
A1+ A1- A1- A1+
F1+ F1- F2- F2+
19
Figure 2.8 shows the cross sectional views of two topogies of three phase
FEFSM with segmental rotor reported in [35], [36], [37]. From figure, clearly shows
both the FEC and the armature coils are non-overlapped, and it can reduce the usage
of copper and rate of copper loss [38]. From Figure 2.8 (a), the machine have 12 slot
of armature, 12 slot of FECs, and six poles of rotor and the FECs are allocated
uniformly in the middle of each armature coil slot. Eight stator slots and four rotor
poles of FEFSM with segmental rotor is shown in Figure 2.8 (b).
It is clear from the figure that four pole magnetic field is established when
direct current is applied to the FEC winding in four of the slots. The other four slots
hold an armature winding that is also pitched over two stator teeth. A set of four stator
poles carrying flux and the position of the rotor is decided by direction of the current
in the armature winding.
The limits on the segment span are set by the minimum separation required to
prevent any appreciable flux crossing to adjacent segments and the segment pitch,
which is controlled by the number of segments employed. Table 2.3 shows the main
parameters of FEFSM with segmental rotor. Normally, for three-phase, the DC-bus
maximum voltage inverter is set to 650V. The estimated speed rate most commonly
used is from 500r/min to 1,200r/min. The maximum FEC current desity, JE and
armature current density, JA is 30A/mm2 and 30Arms/mm2, respectively. In addition,
from the proposed earlier design [36], [37], the highest parameter for outer stator
diameter, motor stack length, and air gap length is 150mm, 150mm, and 0.5mm,
respectively.
(a) Three-phase 24S-10P (b) Three-phase 12S-8P
Figure 2.8: Examples of FEFSM with segmental rotor [35], [36], [37]
Stator
Rotor
20
Table 2.4 shows the summary performance of previous analysis of FEFSM
with segmental rotor. The table shows that the three-phase 12S-8P FEFSM with
segmental rotor has advantages of high torque 25Nm, followed by three-phase 12S-
10P FEFSM with segmental rotor. In terms of the back-EMF voltage, only 12S-8P
FEFSMs with segmental rotor design is found, which is it achieved 38V. If viewed in
terms of power, the 12S-8P FEFSM segmental rotor design is better because based on
the theory, the power is proportional to the torque and speed.
Although the design of the three-phase 12S-8P is said to have better
performance, but the combination between rotor teeth and stator teeth that are not
balanced can interfere flux path. Which is a combination of less segmented rotor will
increase the width of the rotor teeth. This causes a flow of flux from the stator to the
segmented rotor becomes larger and easier. In addition, the use of a 8 segmented rotor
teeth is found to have led to the design of complex design and increase the weight of
the rotor as well as the fabrication process will becomes more complicated compared
with the use of a less segmented rotor teeth. From the aspect of application, previous
FEFSM segmented rotor developed only focused on applications requiring torque,
power and high speed such as HEV applications and this prompted the researchers to
conduct studies related to FEFSM three-phase only.
Table 2.3: The main parameters of FEFSM with segmental rotor [35], [36], [37]
Items 24S-10P 12S-8P
Number of phase 3 3
Rated speed (r/min) 1,200 500
Max. DC-bus voltage inverter (V) 650 650
Max. current density in armature winding, JA 30 14
Max. current density in excitation winding, JE 30 14
Stator outer diameter (mm) 150 150
Motor stack length (mm) 150 150
Air gap length 0.3 0.3
Table 2.4: Performances of FEFSM with segmental rotor [35], [36], [37]
Items 24S-10P 12S-8P
Back-EMF(V) NA 38
Maximum Torque (Nm) 21.0 25.0
Maximum Power (kW) NA NA
21
Therefore, the design FEFSM segmented rotor should be diversified to a
single-phase motor and a combination stator and rotor is calculated by using the
Formula (2.1). This indirectly enables it to be used in applications characterized by
torque, low-speed power and as a fan, blower, compressor air conditioner, washing
machine, blender, vacuum cleaner and other home appliances. In practice, significant
benefits of short end-windings appear with the 12S-6P configurations if a single-phase
topology is pursued.
2.4 Overview of Design and Analysis of FEFSMs
For design and performance analysis (2D-FEA), a commercial FEA package, JMAG-
Designer ver.12.0, released by Japan Research Institute (JRI) is used. Initially, the
rotor, stator, armature coil, and FEC of the proposed FEFSM is drawn by using
Geometry Editor followed by the setup of materials, conditions, circuits, and properties
of the machine, which are set in JMAG Designer. The electrical steel 35H210 is used
for rotor and stator body. The design developments of both parts are established in
Figure 2.9 [31].
(a) Geometry Editor (b) JMAG-Designer
Figure 2.9: Design implementation of the proposed FEFSM [31]
22
For the calculation of the combination of slot and pole motor of FEFSM,
Equation (2.1) is used. Where Nr is represented as the number of rotors, Ns is the
number of stator slot, k is the integer from 1 to 5, and q is the number of phases.
Meanwhile, Equations (2.2) and (2.3) are used to estimate the number of windings on
the armature coils and the FECs, respectively. From the equation, N refers to the total
winding, J is the current density, α is filling factor, S is the total area of the slot, and I
is current. The symbols A and E in each equation indicate the use of armature and FE,
respectively.
q
kNN sr
21 (2.1)
A
AA
AI
SJN
(2.2)
E
EE
EI
SJN
(2.3)
The value of input current of armature coils, IA is calculated by using Equation
(2.4). Then, Equation (2.5) is used to calculate the input current of FE coils, IE [31],
[39].
A
AA
AN
SJI
2 (2.4)
Where,
IA = Input current of armature coil
JA = Armature coil current density (set to maximum of 30 A/mm2)
α = Armature coil filling factor (set to 0.5)
SA = Armature coil slot area
NA = Number of turns of armature coil
E
EE
EN
SJI
(2.5)
Where,
IE = Input current of FE coil
JE = FEC current density (set to maximum of 30 A/mm2)
α = FEC filling factor (set to 0.5)
SE = FEC slot area
NE = Number of turns of FEC
23
According to the principle of FSM, the general relationship between the
electrical frequency and the mechanical rotation frequency can be expressed as,
mre fNf (2.6)
From Equation (2.6), it is clear that the electrical frequency, fe is directly
proportional to the number of rotor poles, Nr and the mechanical rotation frequency,
fm is double that of the electrical frequency of conventional interior permanent magnet
synchronous motor (IPMSM), when the FSMs use the same number of poles [40].
After calculating all parameters, process simulation is run to perform further analysis.
Information such as the back-EMF, flux characteristics, and torque are obtained
directly from the simulation process.
Any changes in the magnetic environment of a coil of wire causes a voltage
(EMF) to be induced in the coil. The voltage will be generated when any change is
produced. The change could be produced by changing the magnetic field strength,
moving a magnet towards or away from the coil, moving the coil into or out of the
magnetic field, and rotating the coil relative to the magnet.
Faraday’s Law summarises the ways voltage can be generated. This law states
that if flux passes through a turn of a coil of wire, a voltage will be induced in the turn
directly proportional to the negative of the rate of change in the flux with respect to
time, as in Equation (2.7).
dt
dEind
(2.7)
Where Eind is the voltage induced in the turn of the coil and ɸ is the flux passing
through the turn. If a coil has N turns and if the same flux passes through all of them,
then the voltage induced across coil the whole coil is given by Equation (2.8)
dt
dNEind
(2.8)
Where Eind is the voltage induced in the turn of the coil, ɸ is the flux passing
through the turn, and N is the number of turns of wire in coil [41].
When back-EMF is generated by a change in magnetic flux according to
Faraday's Law, the polarity of the back-EMF is such that it produces a current whose
2.4)
24
magnetic field opposes the change, which produces it. The induced magnetic field
inside any loop of wire always acts to keep the magnetic flux, B in the loop constantly.
If the B field is increasing, the induced field acts in opposition to it. If it is decreasing,
the induced field acts in the direction of the applied field to try to keep it constant [42].
Cogging torque does not add to electro-magnetic output torque, it only affects
in torque pulsations, which correspond to undesirable vibration and acoustic noise.
The number of periods, Nctp of the cogging torque waveform over a rotation of one
stator tooth pitch is given by
],[ rs
rctp
NNHCF
NN (2.9)
Where the denominator is defined as the highest common factor (HCF)
between Ns and Nr, while Nr being the number of poles of the rotor. Using the index
Np, the electrical angle of rotation, θcog for each period of the cogging torque and the
number of periods of cogging torque, Ncte per electrical cycle are therefore
sctp
cogNN
360 (2.10)
and
r
sctp
cteN
NNN (2.11)
respectively.
Therefore, all of the above equations can be simplifed as,
NN
NN
rs
r
cte
360360
360
Hence,
NNN
Nsr
s
cte (2.12)
The electromagnetic torque, Te developed in an electrical machine generally
consists of a reluctance torque component, Trel and an excitation torque component,
Texc, and maybe expressed in a polyphase arrangement as [35]
77
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