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DESIGN OPTIMIZATION OF SINGLE-PHASE
INNER-ROTOR AND OUTER-ROTOR HYBRID
EXCITATION FLUX SWITCHING MACHINE FOR
EV APPLICATIONS
MOHAMED MUBIN AIZAT BIN MAZLAN
UNIVERSITI TUN HUSSEIN ONN MALAYSIA
i
DESIGN OPTIMIZATION OF SINGLE-PHASE INNER-ROTOR AND
OUTER-ROTOR HYBRID EXCITATION FLUX SWITCHING MACHINE
FOR EV APPLICATIONS
MOHAMED MUBIN AIZAT BIN MAZLAN
A thesis submitted in
fulfillment of the requirement for the award of the
Master of Electrical Engineering
Faculty of Electric and Electronic Engineering
Universiti Tun Hussein Onn Malaysia
MARCH, 2016
3
For my beloved mother and father,
Che Zarah Binti Mohd Zain and Mazlan bin Mamat,
my siblings,
Muizzuddin Azfar Mazlan and Murtaza Asmuin Mazlan
my friends,
and my lovely family
Thank you for your prayers, support, guidance and love
4
ACKNOWLEDGEMENT
In the name of Allah s.w.t, Most Gracious Most Merciful. I would like to
express my sincere appreciation to my supervisor, Dr. Erwan bin Sulaiman for the
support given throughout the duration of this master project.
The cooperation given by lecturer and technician, especially from Faculty of
Electrical and Electronic is also appreciated. Discussion and guidance with the
respect of their knowledge are valuable and cannot be forgotten. A lot of thank as
well to my members, laboratory mates, who willing to help in the making of
completing this project.
Furthermore, sincere thanks to my father, Mazlan Bin Mamat and my mother,
Che Zarah Binti Mohd Zain as being the source of inspiration. These
acknowledgements would be incomplete without my special thanks to my family and
members for their prayers, encouragement, love and emotional supports.
Last but not least, appreciation goes to everyone who has contributed directly
or indirectly towards the compilation of this thesis and may your charity and
goodwill will be blessed.
5
ABSTRACT
Electric Vehicle (EV) is considered as an ultimate eco-friendly car and this is highly
expected to be popularized in the future. One of the main candidates of electric
machine for an EV drive is a flux switching machine (FSM). However, since the
designed machine consists of three-phase complicated winding, the copper loss
which contributes to efficiency of the machine is expected to be increased.
Furthermore, the three-phase armature winding has a large area size of the total
system. Due to the complicated three-phase armature winding that contribute to high
copper losses, a single-phase inner-rotor and outer-rotor Hybrid Excitation Flux
Switching Machine (HEFSM) with much simpler structure and less armature coil
consumption are introduced in this research. Various characteristics of HEFSM are
investigated by analytical approaching based in finite element analysis using JMAG
software. The project implementation of this research is divided into three parts
including design, analyze and optimize. Firstly, the impact of a rotor pole number of
the proposed is investigated for inner-rotor and outer-rotor configuration in order to
determine the optimal performances of the rotor poles combinations. Then 8S-4P and
8S-8P HEFSM are chosen for optimization analysis. The combination of 8S-8P
inner-rotor HEFSM have best performance with 284Nm maximum torque, 62.98kW
maximum power and 90% efficiency. Then 8S-8P HEFSM have been compared with
three-phase 12S-14P HEFSM in term of copper loss, weight and efficiency. As
conclusion, the final design machine produce 12.45% less copper loss, 8.88% less
weight and with almost similar efficiency compared to three-phase configuration.
6
ABSTRAK
Kenderaan elektrik dianggap sebagai kereta yang mesra alam dan ini dijangka sangat
popular pada masa akan datang. Calon utama mesin elektrik untuk kegunaan
kenderaan elektrik adalah mesin pensuisan fluks. Walau bagaimanapun, oleh kerana
mesin direka terdiri daripada penggulungan tiga-fasa yang rumit, kehilangan
tembaga yang menyumbang kepada kecekapan mesin dijangka akan meningkat.
Tambahan pula, penggulungan angker tiga-fasa mempunyai saiz yang besar daripada
jumlah sistem. Disebabkan angker penggulungan tiga-fasa yang rumit menyumbang
kepada kerugian tinggi tembaga, pemutar dalam fasa tunggal dan pemutar luar
HEFSM dengan struktur lebih mudah dan kurang penggunaan gegelung angker
diperkenalkan dalam kajian ini. Dalam tesis ini, pengoptimuman reka bentuk
konfigurasi pemutar dalam dan luar rotor HEFSM dianalisis. Pelbagai ciri-ciri
HEFSM disiasat oleh analisis berdasarkan Perisian JMAG-Designer. Pelaksanaan
projek penyelidikan ini dibahagikan kepada tiga bahagian termasuk reka bentuk,
analisis dan mengoptimumkan rekaan. Pertama, kesan bilangan kutub motor yang
dicadangkan dengan lapan slot pemegun disiasat untuk konfigurasi pemutar dalam
dan luar bagi menentukan prestasi optimum untuk persembahan gabungan kutub
pemutar. Kemudian 8S-4P dan 8S-8P HEFSM dipilih untuk analisis pengoptimuman.
Gabungan 8S-8P pemutar dalam HEFSM mempunyai prestasi terbaik dengan tork
maksimum 284Nm, kuasa maksimum 62.98kW dan kecekapan 90%. Kemudian 8S-
8P HEFSM telah dibandingkan dengan tiga fasa 12S-14P HEFSM dari segi
kehilangan tembaga, berat dan kecekapan. Kesimpulannya, fasa tunggal
penggulungan menghasilkan 12.45% kurang kehilangan tembaga, 0.67%, 8.88%
kurang berat dan kecekapan hampir sama berbanding dengan tiga fasa penggulungan.
vii
CONTENTS
TITLE i
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
CONTENTS vii
LIST OF TABLES xii
LIST OF FIGURES xiii
LIST OF ABBREVIATIONS xv
LIST OF PUBLICATIONS
LIST OF AWARDS
xvi
xviii
CHAPTER 1 INTRODUCTION
1.1 Introduction 1
1.2 Problem Statement 3
1.3 Objectives 4
1.4 Scope 5
1.5 Outlines of Thesis 6
CHAPTER 2 LITERATURE REVIEW
2.1 Introduction to Flux Switching Machine 8
8
2.1.1 Permanent Magnet FSM 9
2.1.2 Field-Excitation FSM 10
2.1.3 Hybrid Excitation FSM 11
2.2 Outer-Rotor vs. Inner-Rotor Configuration 12
2.3 Reviews on Three-Phase Winding of Flux Switching 14 Machine (FSM)
2.4 Reviews on Single-Phase Winding of Flux Switching 17
Machine (FSM)
2.5 Summary 19
CHAPTER 3 METHODOLOGY
3.1 Project Methodology 20
3.2 Part 1: Design 21
3.3 Part 2: Analysis 25
3.4 Part 3: Optimize 26
3.5 Summary 29
CHAPTER 4 RESULTS
4.1 Various Rotor Pole Analysis 30
4.1.1 Inner-rotor and Outer-rotor HEFSM Various Rotor 30 Pole Analysis
4.1.2 No Load Analysis 32
4.1.2.1 Flux Linkage at Maximum DC FEC 32
Current Density, JE
4.1.2.2 Induced Voltage at Open Circuit Condition 33
4.1.2.3 Cogging Torque 34
4.1.3 Load Analysis 35
4.1.3.1 Torque and Power vs. JE at Maximum 35 Armature Coil Current Density, JA
9
4.1.4 Summary of Rotor Poles Study 37
4.2 Design Optimization Single-Phase Inner-Rotor 37 and Outer-Rotor 8S-4P and 8S-8P HEFSM
4.2.1 No Load Analysis 45
4.2.1.1 Flux Linkage at PM and Maximum 45
DC FEC Current Density, JE
4.2.1.2 Cogging Torque 46
4.2.1.3 Induced Voltage/Back EMF of PM 48
with DC FEC
4.2.2 Load Analysis 49
4.2.2.1 Torque versus FEC Current Density, JE 49
at Maximum Armature Coil Current Density, JA
4.2.2.2 Instantaneous Torque Characteristic of 52
Maximum JE and JA
4.2.2.5 Rotor Mechanical Strength 53
4.2.2.4 Torque and Power Vs. Speed 56
Characteristic
4.2.2.5 Motor Losses and Efficiencies 59
4.2.3 Summary of Optimization 64
CHAPTER 5 CONCLUSION AND RECOMMENDATION
5.1 Introduction 66
5.2 Conclusion 66
5.3 Future Work 67
REFERENCES 68
xii
LIST OF TABLES
1.1 Design Restrictions and Specifications of HEFSM 5
3.1 Material for Rotor, Stator, Armature Coil, Permanent 25
Magnet and FEC
4.1 Parameter of Inner-Rotor and Outer-Rotor HEFSM 32
4.2 Summary of Rotor Pole Study for Inner-Rotor HEFSM 37
4.3 Summary of Rotor Pole Study for Outer-Rotor HEFSM 37
4.4 Design Parameters of Initial and Final 8S-4P Inner- 42
Rotor and Outer-Rotor HEFSM
4.5 Design Parameters of Initial and Final 8S-8P Inner- 42
Rotor and Outer-Rotor HEFSM
4.6 Input Current of FEC of Initial and Final 8S-4P Inner- 50
Rotor and Outer-Rotor HEFSM
4.7 Input Current of FEC of Initial and Final 8S-4P Inner- 50
Rotor and Outer-Rotor HEFSM
4.8 Summary of Instantaneous Torque for Final Design 52
HEFSMs
4.9 Weight, Power and Torque Density of Final Design 59
HEFSM
4.10 Loss and Efficiency of Inner0Rotor and Outer-Rotor 63
8S-4P HEFSM
4.11 Loss and Efficiency of Inner0Rotor and Outer-Rotor 63
8S-8P HEFSM
4.12 Overall Performances of The Design of Single-Phase 64
8S-4P and 8S-8P Inner-Rotor and Outer-Rotor HEFSM
4.13 Comparison Single-Phase 8S-8P and Three-Phase 12S- 65
14P Inner-Rotor and Outer-Rotor Configuration
13
LIST OF FIGURES
1.1 Four Main Candidates of Electric Machine for HEV 2
Drives
2.1 Classification of Flux Switching Machine (FSM) 8
2.2 Operating Principle of Permanent Magnet Flux 9
Switching Machine (PMFSM)
2.3 Operating Principle of Field Excitation Flux Switching 10
Machine (FEFSM)
2.4 Operating Principle of Hybrid Excitation Flux 12
Switching Machine (HEFSM)
2.5 Operating Principle of Outer-rotor HEFSM 13
2.6 Example of Three-Phase FSM 16
2.7 Example of Single-Phase FSM 18
3.1 Project Implementation 20
3.2 Design and Condition Setting Proposed Inner-Rotor 21
and Outer-Rotor HEFSM
3.3 Initial Design of HEFSM 22
3.4 Direction of Permanent Magnet 23
3.5 Direction of FEC 24
3.6 The Direction of Armature Coil 25
3.7 Analysis Procedure 26
3.8 Optimization Procedure 27
3.9 Design Parameter of Inner-Rotor and Outer-Rotor 27
HEFSM
4.1 Initial Design of the IR-HEFSM Configurations 31
4.2 Initial Design of the OR-HEFSM Configurations 31
4.3 Magnetic Flux Linkage at Various Rotor Pole Numbers 33
14
4.4 Induced Voltage at Various Rotor Pole Numbers 34
4.5 Cogging Torque 35
4.6 Torque versus JE at Maximum JA 36
4.7 Power versus JE at Maximum JA 36
4.8 Comparison of Torque and Power at Various 38
Topologies
4.9 Design Parameter 38
4.10 Torque versus D1 Characteristic 39
4.11 Torque versus D2 and D3 Characteristic 39
4.12 Torque versus D5 and D6 Characteristic 40
4.13 Torque versus D7 and D8 Characteristic 40
4.14 Torque versus D9 and D10 Characteristic 41
4.15 Torque versus Cycle 41
4.16 Design of Single-Phase 8S-4P 43
4.17 Design of Single-Phase 8S-8P 44
4.18 Flux Linkage of PM with DC FEC 46
4.19 Cogging Torque 47
4.20 Induced Voltage/ Back EMF of PM with DC FEC 48
4.21 Torque versus FEC Current Density, JE at Maximum 51
Armature Coil Current Density, JA
4.22 Instantaneous Torque of the Design HEFSMs 53
4.23 Rotor Mechanical Stress Distribution at 20,000r/min 54
4.24 Torque versus Speed Characteristics 57
4.25 Power versus Speed Characteristics 58
4.26 Estimated Coil End Volume of Final Design HEFSM 59
4.27 HEFSMs Losses and Efficiencies 61
4.28 Iron Loss and Copper Loss Distributions 62
15
LIST OF ABBREVIATIONS
A Ampere
AC Alternating Current
Dy Dysprosium DC
Direct Current
EV Electric Vehicle
FEA Finite Element Analysis
FEC Field Excitation Coil
FEFSM Field Excitation Flux Switching Motor
HEFSM Hybrid Excitation Flux Switching Motor
HEV Hybrid Electric Vehicle
EV Electric Vehicle
IMs Induction Motors
IPMSMs Interior Permanent Magnet Synchronous Motors
ICE Internal Combustion Engine
JE FEC current density
JA Armature coil current density
kg Kilogram
Mm Millimeter
Nm Newton meter
Nd Neodymium
PM Permanent Magnet
PMFSM Permanent Magnet Flux Switching Motor
r/min Revolution per minute
V Volt
Wb Weber
16
LIST OF PUBLICATIONS
Journals:
(i)
Mohamed Mubin Aizat Mazlan, Erwan Sulaiman, Md Zarafi Ahmad,
Zhafir Aizat Husin and Hassan Ali Soomro, “Design Optimization of
Single-Phase Outer-Rotor 8S-8P Hybrid Excitation Flux Switching Motor
for Electric Vehicle”, Journal of Applied Mechanics and Materials, Vol.
695, pp. 761-764, Nov 2014.
(ii) Mohamed Mubin Aizat Mazlan, Erwan Sulaiman, Md Zarafi Ahmad,
Zhafir Aizat Husin, Siti Nur Umira Zakaria, “Performance Comparison of
Optimum 8S-4P and 8S-8P of Single-Phase Hybrid Excitation Flux
Switching Machine with Outer-Rotor Configuration’’, Journal of Applied
Science and Agriculture, Vol. 9, pp 112-118, Oct 2014.
Proceedings:
(i)
Mohamed Mubin Aizat Bin Mazlan, Erwan Bin Sulaiman, and Takeshi
Kosaka “Design Study of Single-Phase Outer-Rotor Hybrid Excitation Flux
Switching Machine for Hybrid Electric Vehicles”, IEEE 8th International
Power Engineering and Optimization Techniques, Mar. 2014.
(ii) Mohamed Mubin Aizat Mazlan, Zhafir Aizat Husin, Syed Muhammad
Naufal Syed Othman and Erwan Sulaiman “Design Study of Single-Phase
Inner-Rotor Hybrid Excitation Flux Switching Machine for Hybrid Electric
Vehicles”, 2nd Power and Energy Conversion Symposium (PECS 2014),
May 2014.
(iii) Mohamed Mubin Aizat Mazlan, Erwan Sulaiman, Zhafir Aizat Husin, Syed
xvii
Muhammad Naufal Syed Othman and Faisal Khan “Design Comparison of
Single Phase Outer and Inner-Rotor Hybrid Excitation Flux Switching
Motor for Hybrid Electric Vehicles”, International Conference on
Mathematics, Engineering & Industrial Applications (ICoMEIA), May
2014.
(iv) Mohamed Mubin Aizat Mazlan, Erwan Sulaiman, Md Zarafi Ahmad, Syed
Mohammad Naufal Syed Othman, “Topologies of Single-Phase Outer-
Rotor Hybrid Excitation Flux Switching Motor for In Wheel Drive
Applications”, IEEE Conference on Energy Conversion (CENCON), Oct.
2014.
(v) Mohamed Mubin Aizat Mazlan, Md Zarafi Ahmad, Syed Mohammad
Naufal Syed Othman and Erwan Sulaiman, “Design Studies and
Performance of Single-Phase HEFSM with Various Rotor Pole Number for
Hybrid Electric Vehicle Applications”, Malaysian Technical Universities
Conference on Engineering and Technology (MUCET), Nov. 2014.
(vi) Mohamed Mubin Aizat Mazlan, Erwan Sulaiman, Md Zarafi Ahmad,
Zhafir Aizat Husin, Siti Nur Umira Zakaria, “Performance Comparison of
Optimum 8S-4P and 8S-8P of Single-Phase Hybrid Excitation Flux
Switching Machine with Outer-Rotor Configuration”, International
Postgraduate Conference on Engineering and Technology Research
(IPCETR), Oct. 2014.
(vii) Mohamed Mubin Aizat Mazlan, Erwan Sulaiman, Md Zarafi Ahmad, Syed
Muhammad Naufal Syed Othman, “Design Optimization of Single-Phase
Outer-Rotor Hybrid Excitation Flux Switching Motor For Electric
Vehicles”, IEEE Student Conferences on Research and Development (IEEE
SCoRED), Dec. 2014.
xviii
LIST OF AWARDS
(i)
(ii)
(iii)
(iv)
Bronze medal “Outer-Rotor Hybrid Excitation Flux Switching Machine for
In-Wheel Drive Electric Vehicle”, UTHM Research and Innovative Festival
2013, Dec 2013.
Best paper award “Performances Comparison of 12S-10P and 12S-14P of
Field Excitation Flux Switching Motor for Hybrid Electric Vehicle”, 2nd
Power and Energy Conversion Symposium (PECS 2014), May 2014.
Best paper award “Performance Analysis of 12Slot-14Pole for HEFSM and
FEFSM with Outer-Rotor Configuration”, 2014 Malaysian Technical
Universities Conference on Engineering and Technology (MUCET 2014),
Nov. 2014.
Bronze medal ‘In-Wheel HEFSM’, Malaysian Technology Expo 2015, 12-14
Feb. 2015.
CHAPTER 1
INTRODUCTION
1.1 Introduction
With the increasing number of world population, the demand for vehicles for
personal transportation has increased dramatically in the past decades. This leads to
serious problems called ‘global warming’. One of the main causes of global warming
is Internal Combustion Engine (ICE). From the report in year 2013 [1], about 26% of
global carbon dioxide (CO2) emission in year 2013 came from the vehicles. By the
year 2020, it is expected that CO2 emission rate from vehicles will increase two times
with economic growth.
Hybrid Electric Vehicle (HEV) is considered as an ultimate eco-friendly car
and this is highly expected to be popularized in the future [2]-[4]. The important of
the basic characteristic requirements of an electric motor for HEV drive systems are
high torque at low speed, high power density, and constant power at high speed as
well as high efficiency [5].
Electric vehicles (EVs) seem like an ideal solution to deal with the energy
crisis and global warming since they have zero oil consumption and zero emissions.
EVs have several advantages over HEV such as EVs emit no tailpipe pollutants,
although the power plant producing the electricity may emit them and EV provide
quiet, smooth operation and stronger acceleration and require less maintenance than
HEV. Therefore, EV is now regarded as an ultimate eco-friendly car and is widely
expected to become more popular in the very near future [6]-[8].
Various electric motors used in HEV and EV have been designed and
successfully installed in the vehicles such as Honda Jazz, Toyota Prius, Mitsubishi
Mirage and Nissan Leaf as illustrated in Figure 1.1. Figure 1.1(a) illustrates an
2
example of Permanent Magnet Synchronous Machine (PMSMs) installed in Lexus,
Prius and Nissan Leaf. Although PMSM has the advantage of high torque density
and high efficiency, still it has the problem of PM demagnetization, mechanical
damage of rotor’s magnet and uncontrolled flux of PM [9]-[11].
(a) (b)
(c) (d)
Figure1.1: Four Main Candidates of Electric Machine for HEV Drives
(a) Permanent Magnet Synchronous Machines (b) DC motor (c) Induction Motor
(d) Switched Reluctant Motor
3
Furthermore, Figure 1.1(b) depicts an example of Direct Current (DC) motor
used in HEV and EV. Since DC motor utilizes DC supply battery, the control
principle becomes simpler that makes it widely accepted in electric propulsion
system. However, DC motor drives have major disadvantages such as low reliability
and high maintenance [12]. Thus DC motors are unsuitable for maintenance-free
drives.
At present, induction motor (IM) as shown in Figure 1.1(c), are generally
established as the most potential candidate for the electric propulsion of EV and
HEVs, due to their reliability, ruggedness, low maintenance, and low cost [13]-[14].
However, IM drives have demerits such as high loss, low efficiency and low power
factor [15]-[17].
Figure 1.1(d) shows the structure of a switched reluctant motor (SRM) which
is invented to overcome the permanent magnet motor problem. SRM has no PM and
robust rotor structure but it is not suitable for HEV and EV due to large torque
ripples and noisy [18]-[19]. Although the SRMs have been successfully installed in
HEV and EV, the drawbacks of each electric motor can further be improved and
optimized.
In order to overcome the previous motor problems, hybrid excitation flux
switching machine (HEFSM) in which all flux source are located in stator body is
introduced in this research. Proposed HEFSM that consists of permanent magnet
(PM) and field excitation coil (FEC) as main flux sources is more advantageous
compared to existing electric motor [20]-[21]. HEFSM with a robust rotor structure
similar with SRM is suitable for extreme driving condition. Additionally, an extra
advantage of locating PM and FEC at the stator core provide a simple cooling system
for this machines. In addition, the FEC can control constant PM flux to produce
variable flux capabilities, which can enhance more torque and power.
1.2 Problem Statement
Several invention of HEFSM for EV application has been proposed. Three-phase
HEFSM have been developed for various EV drives applications with strong
performance in term of high torque, high power and high speed ability. This is
4
proven by three-phase inner-rotor HEFSM [2] and outer-rotor HEFSM [21].
However, the proposed machines have problems of high torque ripple and high
induced voltage [22]-[24]. Moreover, since the designed machine consists of three-
phase complicated winding, the copper loss which contributes to efficiency of the
machine is expected to be increased. Furthermore, the three-phase winding has high
voltage supply and use big battery size and complex inverter. Therefore the three-
phase armature winding has a large area of the total system [25]. Due to complicated
three-phase armature winding that contribute to high copper losses, a single-phase
inner-rotor and outer-rotor HEFSM with much simpler structure and less armature
coil consumption are introduced in this research. It is obvious that both inner rotor
and outer-rotor configurations can be applied for normal and direct drive HEV and
EV system respectively. Moreover, single-phase also requires low voltage supply,
uses small battery size and simple inverter. Therefore the single-phase armature
winding has a small area of the total system.
The performances of the proposed machine under some restrictions and
specifications will be analyzed and evaluated. The proposed machine is expected to
provide high efficiency, high durability and less copper losses compared to the three-
phase winding of HEFSM.
1.3 Objectives of Project
The objectives of this research are:
(i) To design a single-phase inner-rotor and outer-rotor hybrid excitation flux
switching motor for electric vehicle applications.
(ii) To analyze a single-phase inner-rotor and outer-rotor hybrid excitation flux
switching motor for electric vehicle applications.
(iii) To optimize the performances of the 8S-4P and 8S-8P single-phase inner-
rotor and outer-rotor hybrid excitation flux switching motor for electric
vehicle applications.
5
1.4 Scopes of Project
The scopes of this research are divided into three parts based on the objectives. The
scopes are:
(i) The design restrictions, target specifications and parameters of the proposed
HEFSM for EV applications are listed in Table 1.1 [26]. The electrical
restrictions related with the inverter such as maximum 240V DC bus voltage
and maximum 360A inverter current are set. Assuming 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 shaft radius and the air gap of the main part of the machine design being
264mm, 70mm, 30mm and 0.8mm respectively. The target of maximum
torque and power for proposed single-phase are 111Nm and 41kW
respectively which are one third of three-phase HEFSM.
(ii) The performances of rotor poles study are investigated in order to determine
the optimal performances. The no load and load analysis such as flux linkage,
cogging torque, induced voltage and torque and power vs. JE are determined.
Table 1.1: Design Restrictions and Specifications of HEFSM [26]
Items Unit Three-Phase
HEFSM
Single-Phase
HEFSSM
Max. DC-bus voltage inverter V 650 240
Max. inverter current Arms 360 360
Max. current density in armature winding, Ja Arms/mm2 30 30
Max. current density in excitation winding, Je A/mm2 30 30
Stator outer diameter mm 264 264
Motor stack length mm 70 70
Shaft radius mm 30 30
Air gap length mm 0.80 0.80
PM weight kg 1 1
Maximum torque Nm >333 >111
Maximum power kW >123 >41
6
(iii) The motor 8S-4P and 8S-8P single-phase inner-rotor and outer-rotor
configuration are chosen from rotor pole analysis and are optimized by using
deterministic optimization method [27] and treated to all parameters until the
optimum performances are achieved. Then the outer-rotor motor is compared
to inner-rotor 8S-4P and 8S-8P HEFSM with the same design restrictions and
specifications. Finally, loss analysis, structural analysis and efficiency are
analyzed and compared for 8S-4P and 8S-8P inner-rotor and outer-rotor
configuration HEFSM.
1.5 Outlines of Thesis
This thesis deals with the design studies on single-phase inner-rotor and outer-rotor
hybrid excitation flux switching machine (HEFSM) for EV applications. The thesis
is divided into 5 chapters and the summary of each chapter are listed as follows:
(i) Chapter 1: Introduction
The first chapter gives some introduction about the research including
research background, related works on EV and some explanation regarding
inner-rotor and outer-rotor configuration used in EV. Then problems of
current three-phase winding used in EV are highlighted and the research
objectives are set to solve the problems.
(ii) Chapter 2: Literature Review
The second chapter explains some introduction and classifications of FSM
including the example of PMFSM, HEFSM and FEFSM, the operating
principle and the proposed HEFSM for HEV applications. Then the review of
single-phase for all FSM is explained.
(iii) Chapter 3: Methodology
The third chapter describes the project implementation of this research. The
project implementation is divided into three parts including design, analysis
and optimization. The design is divided into two parts that are geometry
editor and JMAG-Designer. Then the design is analyzed at no load and load
analysis such as flux linkage, cogging torque, induced voltage and torque and
power vs. maximum JE. Finally the “deterministic optimization method” is
7
used and treated to all parameters until the optimum performances are
achieved.
(iv) Chapter 4: Result
In this chapter, various combinations of slot-pole inner-rotor and outer-rotor
HEFSMs such as 8S-4P, 8S-8P, 8S-12P, 8S-16P and 8S-20P are designed and
analyzed. Among various slot-pole combinations of HEFSM, the combination
of 8S-4P and 8S-8P of inner-rotor and outer-rotor configuration has better
performance and chosen for design optimization. The design is optimized by
using deterministic optimization method and treated to all parameters until
the optimum performances are achieved. The results of the initial and final
design which met the target performances such as maximum flux linkage,
cogging torque, induced voltage, instantaneous torque characteristic, rotor
mechanical stress and motor losses and efficiency are analyzed and discussed.
(v) Chapter 5: Conclusion
The final chapter describes and concludes the summary of the research and
pointed out some future works for design improvements.
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction to Flux Switching Motor
Generally, the flux switching motor (FSM) can be categorized into three groups that
are permanent magnet flux switching motor (PMFSM), field excitation flux
switching motor (FEFSM), and hybrid excitation flux switching motor (HEFSM).
Both PMFSM and FEFSM has only PM and field excitation coil (FEC), respectively
as their main flux sources, while HEFSM combines both PM and FEC as their main
flux sources. Figure 2.1 illustrates the general classification of FSM.
Flux Switching Motor (FSM)
Permanent Magnet (PM) FSM
Field Excitation (FE) FSM
Hybrid Excitation (HE) FSM
Figure 2.1: Classification of Flux Switching Machine (FSM)
FSM consists of the rotor and stator. The rotor consist of only single structure
which is iron core thus allowing its simple construction and inherent robustness to be
retained while both field and armature windings are on the stator. The operation of
the motor is based on the principle of switching flux. The term “flux switching” is
coined to describe machines in which the stator tooth flux switches polarity
9
following the motion of a salient pole rotor [28-29]. All excitation sources are on the
stator with the armature and field allocated to alternate stator teeth.
Flux is produced in the stator of the machine by 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 of stator poles by reversing the
polarity of the current in the armature winding.
2.1.1 Permanent Magnet Flux Switching Motor
Permanent magnet flux switching motor (PMFSM) is a simple construction. The
stator consists of PM and armature windings and due to this it provides some
advantages such easy cooling and better suitability for high speed applications [30].
PMFSM is popular due to high power density, efficiency and it uses PM to generate
flux. Unfortunately, the generated flux produced is fixed and will not change-
diverged which means it is constant flux because of characteristics of the PM.
Stator Stator
PM PM
Armature Coil
Rotor Rotor
(a) (b)
Figure 2.2: Operating Principle of PMFSM (a) Flux Linkage Correspond to One
Polarity (b) Flux Linkage Switch Polarity as the Salient Pole Rotates [31]-[33]
Figure 2.2 demonstrates the general ideal of the operating principle of the
PMFSM where the red arrows indicate the flux line of PM as an instance. The flux-
10
linkage corresponds to one polarity is when the relative position of the rotor poles
and a particular stator tooth are as in Figure 2.2 (a). But in Figure 2.2 (b) the polarity
of the flux-linkage reverses as the relative position of the rotor poles and the stator
tooth changes. The salient pole rotor rotates when the flux linkage switches polarity
[31]-[33].
2.1.2 Field Excitation Flux Switching Motor
In spite of the fact that permanent magnet (PM) machines exhibit high torque density
and high efficiency, the rare earth magnet material, is expensive and the working
environmental temperature may limit its application [34]-[36].
Stator Stator
FEC FEC FEC FEC
Armature Coil
Rotor Rotor
(a) (b)
Stator Stator
FEC FEC FEC FEC
Armature Coil
Rotor Rotor
(c) (d)
Figure 2.3: Operating Principle 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
[37]-[39]
11
A Flux-switching machine with field excitation coil is recommended in order
to reduce the cost. The conventional DC winding excited synchronous machine
employs the field winding on the rotor and the slip-rings are required to supply the
field current [33].
Figure 2.3 (a) reveals the operating principle of the FEFSM and Figure 2.3 (b)
reveals the direction of the FEC fluxes into the rotor. Figure 2.3 (c) and (d) indicate
the direction of FEC fluxes into the stator which produces a complete one cycle flux.
Alike 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 Figure 2.3(a) and (b),
causes the stator flux to switch between the alternate stator teeth. The flux does not
rotate but shifts clockwise and counter clockwise with each armature-current reversal
[37]-[39].
2.1.3 Hybrid Excitation Flux Switching Motor
Hybrid Excitation Flux Switching Motor (HEFSM) is the combination of PM and
FE. HEFSM has significantly less magnet and higher torque density than those of a
conventional PMFSM.
By applying negative d-axis current, the PM flux 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 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 [40].
The operating principle of the proposed HEFSM is illustrated in Figure 2.4,
where the red and blue line indicate the flux from PM and FEC, respectively. In
Figure 2.4(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. Furthermore, in Figure 2.4(c) and
12
(d), where the FEC is in reverse polarity, only flux of PM flows into the rotor while
the flux of FEC moves around the stator outer yoke which results in less flux
excitation [41]-[42].
Stator Stator
FEC FEC
PM PM
Armature Coil
Rotor Rotor
Stator
(a) (b) Stator
FEC FEC
PM PM
Armature Coil
Rotor (c) (d)
Rotor
Figure 2.4: Operating Principle of HEFSM (a) θe=0°-More Excitation
(b) θe=180°-More Excitation (c) θe=0°-Less Excitation
(d) θe=180°-Less Excitation [41]-[42]
2.2 Outer-Rotor vs. Inner-Rotor Configurations
Most of commercial EV used single motor and transmission gears coupled to the
wheels. This system leads to the transmission losses and reduce the efficiency and
13
reliability of the motor [43]-[44]. Therefore, in-wheel direct drive mechanism is
introduced to overcome this problem. In-wheel direct drive eliminates the
mechanical transmission, differential gears and drive belts.
Rotor Rotor
Armature Coil
PM PM
FEC FEC Stator Stator
(a) (b)
Rotor Rotor
Armature Coil
PM PM
FEC FEC Stator Stator
(c) (d)
Figure 2.5: Operating Principle of Outer-rotor HEFSM (a) θe = 0º (b) θe = 180º
More Excitation, (c) θe = 0º (b) θe = 180º Less Excitation [56]-[57]
Since the in-wheel direct drive with outer-rotor configuration is more
practical for direct drive application, several invention of in-wheel mechanism for
EV application has been proposed. For example 12S-22P outer-rotor permanent-
magnet flux-switching machine (PMFSM) for electric propulsion in a lightweight
electric vehicle has been proposed [45]. The proposed machine is a highly possible
14
candidate for in-wheel direct-drives. This PMFSM has physical compactness, robust
rotor structure, higher torque and power density and high efficiency. However
PMFSM has several disadvantages of uncontrolled flux and demagnetization [46].
The operating principle of OR-HEFSM is illustrated in Figure 2.5. The single
piece of rotor that makes the motor more robust similar to SRM is shown in the
upper part, while the stator that consists of PMs, FECs, and armature coils are
located in the lower part. The PM and FEC are placed between two stator poles to
generate excitation fluxes that create the term of “hybrid excitation flux”. Figure 2.5
(a) and (b) demonstrate the flux generated by PM and FEC flow from the stator into
the rotor and from the rotor into the stator, respectively, to produce a complete one
flux cycle. The combined flux generated by PM and FEC established more excitation
fluxes that are required to produce higher torque of the motor. When the rotor rotate
clockwise, the rotor pole goes to the next stator tooth, hence switching the magnitude
and polarities of the flux linkage. The flux does not rotate but shifts clockwise and
counter clockwise in direction with each armature current reversal. According to
Figure 2.5 (c) and (d), only the PM flux flows from the stator into the rotor and from
the rotor into the stator, respectively, while the FEC flux is only circulating on its
particular winding slots. This condition establishes less excitation flux and generates
less torque [47]-[48].
2.3 Reviews on Three-Phase Winding of Flux Switching Machine (FSM)
Early examples of three-phase Flux Switching Machine (FSM), the three-phase
PMFSM, FEFSM and HEFSM are developed as shown in Figure 2.6 (a), (b) and (c),
respectively. Figure 2.6(a) shows a typical three-phase 12S-10P PMFSM, where the
salient pole stator core consists of modular U-shaped laminated segments placed next
to each other with circumferentially magnetized PMs placed in between them. For
the flux switching principles, the PM magnetization polarity is being reversed from
one magnet to another [49]-[51].
The stator armature winding consists of concentrated coils and each coil
being wound around the stator tooth formed by two adjacent laminated segments and
a magnet. The salient pole rotor is similar to that of SRMs, which is more robust and
15
suitable for high speed applications, and the difference in the number of rotor poles
and stator teeth is two. In contrast with conventional IPMSM, the slot area is reduced
when the magnets are moved from the rotor to the stator, it is easier to dissipate the
heat from the stator and the temperature rise in the magnet can be controlled by
proper cooling system.
In addition, since the flux path generated by mmf of the armature windings
and PMs are magnetically in parallel, rather than in series as in conventional
IPMSM, the influence of the armature reaction field on the working point of the PMs
is almost eliminated. As a result, the specific electric loading and the specific torque
capability of a PMFSM can be increased. In addition, a high per-unit winding
inductance can be readily achieved. Thus, such machines are eminently suitable for
constant power operation over a wide speed range, i.e., they can have a high flux-
weakening capability [52].
The 12S-10P FEFSM in Figure 2.6(b) is redesigned from the 12S-10P
PMFSM in Figure 2.6(a) in which the PM is removed from the stator and half of the
armature coil slots in the upper layer are placed with the FEC windings as explained
in [53]. The FEC are arranged with alternate DC current source polarity to produce
two flux polarities, similar with PM polarity of 12S-10P PMFSM discussed in Figure
2.6(a). However, since the isolated and unused stator teeth reduce the performance of
the machine, further investigations into improvements of the machine design of three
phase FEFSMs should be made.
Meanwhile, the HEFSM shown in Figure 2.6(c) is a 3-phase 12S-10P
PMFSM which incorporates the FEC at outer extremity of the stator [54]-[55].
However, the outer diameter of the machine is significantly enlarged for the FEC
winding, which in turn reduces torque density. In addition, the PMs in the PMFSM
can be partially replaced by the DC FEC windings and consequently, several
HEFSM topologies were developed as in [56]-[57]. Although they have no
overlapped between the armature coil and FEC, the torque capability is significantly
reduced due to less PM volume.
16
FEC PM
Rotor Rotor
Stator Armature
Coil
Stator
Armature Coil
(a) (b)
FEC PM
Rotor
Stator (c)
Armature Coil
Figure 2.6: Example of Three-Phase FSM (a) Three-Phase PMFSM
(b) Three-Phase FEFSM (c) Three-Phase HEFSM
Furthermore, it is clear that to realize the hybrid topology of Figure 2.6(c),
both PM and armature coil volume should be sacrificed, when compared with the
conventional 3-phase 12S-10P PMFSM of Figure 2.6(a), while keeping the machine
stator outer radios as constant. From the conventional PMFSM topology, it is
possible to replace some of the magnet material with DC FECs and therefore create
several HEFSM topologies without loss of armature coil. This represents the simplest
17
method of hybridizing the conventional PMFSM topology with FEC as it retains the
existing stator and rotor dimensions and structure.
Based on the overview of various three-phase FSMs that have been discussed,
three-phase FSM produce high instant power, high power density, and high power at
high speed for cruising. Three-phase FSM also produce fast torque response and high
torque at low speed for starting and climbing.
2.4 Reviews on Single-Phase Winding of Flux Switching Machine (FSM)
Although a few three-phase FSM have been designed in recent years, the
fundamental three-phase drawbacks such as high copper loss, complicated winding,
high cost and high supply voltage are yet to be overcome. Thus a single-phase FSM
have been fundamentally design. The advantages of single-phase FSM are simple
design due to single winding, less copper loss and easy to manufacture. Single-phase
FSM also less controlled circuit and simple control system compared to three-phase
Figure 2.7 illustrates the single-phase of FSMs.
Figure 2.7(a) shows a typical single-phase 6S-4P PMFSM, where the salient
pole stator ore consists of modular U-shaped laminated segments placed next to each
other with circumferentially magnetized PMs placed in between them. For the flux
switching principles, the PM magnetization polarity is being reversed from one
magnet to another [58]-[59]. The stator armature winding consists of concentrated
coils and each coil being wound around the stator tooth formed by two adjacent
laminated segments and a magnet. In the same figure, all armature coil phases have
the same winding configuration and are placed in the stator core to form 6 slots of
windings. The salient pole rotor is similar to that of SRMs, which is more robust and
suitable for high speed applications, and the difference in the number of rotor poles
and stator teeth is two. In contrast with conventional IPMSM, the slot area is reduced
when the magnets are moved from the rotor to the stator, it is easier to dissipate the
heat from the stator and the temperature rise in the magnet can be controlled by
proper cooling system. In addition, since the flux path generated by mmf of the
armature windings and PMs are magnetically in parallel, rather than in series as in
conventional IPMSM, the influence of the armature reaction field on the working
18
point of the PMs is almost eliminated. As a result, the specific electric loading and
the specific torque capability of a PMFSM can be increased. In addition, a high per-
unit winding inductance can be readily achieved. Thus, such machines are eminently
suitable for constant power operation over a wide speed range, i.e., they can have a
high flux-weakening capability [60].
Stator Stator FEC
Rotor
Rotor
PM Armature Coil
(a) (b)
Armature Coil
FEC
PM Rotor
Stator Armature
Coil
(c)
Figure 2.7: Example of Single-Phase FSM (a) Single-Phase PMFSM
(b) Single-Phase FEFSM (c) Single-Phase HEFSM
19
The concept of the FEFSM involves changing the polarity of the flux linking
with the armature winding, with respect to the rotor position. Early examples of
single-phase 4S-2P FEFSM that employs with a DC FEC on the stator, a toothed-
rotor structure and fully-pitched windings on the stator is shown in Figure 2.7(b)
[61]. From the figure, it is clear that two armature coil and FEC windings are placed
in the stator which overlapped each other. The viability of this design was
demonstrated in applications requiring high power densities and a good level of
durability [62]–[64]. The novelty of the invention was that the single-phase ac
configuration could be realized in the armature windings by deployment of DC FEC
and armature winding, to give the required flux orientation for rotation. The torque is
produced by the variable mutual inductance of the windings. The single-phase
FEFSM is very simple motor to manufacture, coupled with a power electronic
controller and it has the potential to be extremely low cost in high volume
applications. Furthermore, being an electronically commutated brushless motor, it
inherently offers longer life and very flexible and precise control of torque, speed,
and position at no additional cost.
Hybrid excitation flux switching machines (HEFSMs) are those which utilize
primary excitation by PMs as well as DC FEC as a secondary source. HEFSM is an
alternative option where the advantages of both PM machines and DC FEC
synchronous machines are combined. Figure 2.7(c) shows a single-phase 6S-4P
HEFSM in which the active parts are arranged in three layers in the stator. The inner
stator consists of the armature windings, followed by the FECs in the middle layer,
while the PMs are placed in outer stator as discussed in [65]-[66]. However, the
machine has low torque density and long end winding for the DC FECs, which
overlaps the armature windings, and increase copper loss.
2.6 Summary
In this chapter, the overview and classifications of various FSMs are discussed. The
PMFSM, FEFSM and HEFSM have their own advantages and disadvantages which
requires further investigations to extract higher performances for several
applications.
CHAPTER 3
METHODOLOGY
3.1 Project Methodology
The project implementation of this research is divided into three parts based on
objectives including design, analyze and optimize. The general process of research
methodology is illustrated in Figure 3.1. An analytical study, Finite Element
Analysis (FEA) study based on reluctant network is used to evaluate magnetic flux is
needed to design the inner-rotor and outer-rotor HEFSM. Using FEA based on
JMAG-Designer Software allows obtaining information that is not available through
an actual device test because it gives us substantially greater insight into the device's
performance. JMAG is simulation software for electromechanical design striving to
be easy to use while providing versatility to support users from conceptual design to
comprehensive analyses. JMAG can accurately capture and quickly evaluate
complex physical phenomena inside of machine.
Start
Part 1: Design
Part 2: Analyze
Part 3: Optimize
End
Figure 3.1: Project Implementation
21
3.2 Part 1: Design
The project implementation is divided into two parts that are geometry editor and
JMAG-Designer. The design process of single-phase inner-rotor and outer-rotor
HEFSM parts is demonstrated in Figure 3.2.
START
Sketch of Rotor
Sketch of
Stator
Sketch of
Armature coil
Sketch of
FEC
Sketch of Permanent
Magnet
GEOMETRY EDITOR
DESIGNER
Set materials
Set the conditions
Set the NO
circuits
Set the mesh & study
properties
Run and Simulate
YES
END
Figure 3.2: Design and Condition Setting of the Proposed Inner-Rotor
and Outer-Rotor HEFSM
In this design study, the motor are divided into two groups, namely, those
related to stator iron core and rotor iron core. On the stator iron core, it is subdivided
into three components which are the PM shape, FEC slot shape, and armature slot
shape. The rotor parameters involved are the inner rotor radius, rotor pole depth, and
rotor pole arc width. The PM slot shape parameters are the PM depth and the PM
width, while for the FEC slot parameters are FEC slot depth and FEC slot width, and
22
respectively. Finally, the armature coil parameters are armature coil slot depth and
the armature coil slot width. The initial designs are demonstrated in Figure 3.3.
Rotor
Rotor
FEC
PM Stator
PM FEC
Armature Coil
Stator Armature
Coil
(a) (b)
Figure 3.3: Initial Design of HEFSM (a) Inner-Rotor HEFSM (b) Outer-Rotor HEFSM
The selections of the initial design single-phase HEFSMs are based on the
main geometrical dimensions identical to existing three-phase HEFSM in which the
stator outer diameter, stack length and shaft are set respectively to 132mm, 70mm
and 30mm as mentioned earlier in Table 1.1 with following assumptions follows:
(i) The rotor radius is 70% for inner rotor and 83% for outer rotor of the size of
motor and both within the range of general machine split ratio [67]-[68].
(ii) The rotor pole depth is half of the rotor to give much depth for the flux to
flow while keeping the suitable distance of the rotor inner part to avoid flux
saturation and to keep the acceptable rotor mechanical strength,
simultaneously.
(iii) The rotor pole width is defined as in equation (3.1) [69].
∑ Stator Tooth Width = ∑ Rotor Tooth Width (3.1)
(iv) The PM depth and width is calculated based on the volume of 1kg permanent
magnet. The PM depth is approximately one third of stator depth and
expecting give more space for flux to flow from stator to rotor. The direction
of permanent magnet are shown in Figure 3.4.
23
Rotor
PM
FEC
(a)
Stator Armature
Coil
(b)
Figure 3.4: Direction of Permanent Magnet
(a) Inner-Rotor HEFSM (b) Outer-Rotor HEFSM
(v) The FEC depth and width is calculated based on 147mm2 area of FEC. The
area of FEC, Se is defined by equations 3.2, with the filling factor of motor, α,
and number of turn, Ne set as 0.5 and 44 respectively.
N = J eαS e
e I
(3.2)
e
Where Ne, Je (A/mm2), α, Se (mm2), and Ie (A) are number of turns, current
density, filling factor, slot area and input current, respectively. Assuming
only one water-jackets system is employed as a cooling system, the current
density threshold is set to be 30A/mm2, for FEC winding and the input
current is set 50A as the maximum input current for FEC [71]. The FEC slot
depth is one third of stator depth to give an appropriate distance between two
FEC slot areas for the flux to flow in this area. FEC for the inner-rotor and
outer-rotor HEFSM design contains two parts namely F1 and F2. Both parts
inner and outer-rotor HEFSM for FEC1 and FEC2 is illustrated in Figure 3.5.
(vi) The armature coil depth and width are calculated based on 168mm2 area of
armature coil. The area of armature coil, Sa is defined by equations 3.3, with
the filling factor of motor, α, and number of turn, Na set as 0.5 and 7
respectively.
N = J aαS a
a I
(3.3)
a
24
Where Na, Ja (A/mm2), α, Sa (mm2) and Ia (Arms) are number of turns, current
density, filling factor, slot area and input current, respectively. Assuming
only one water-jackets system is employed as a cooling system, the current
density threshold is set to be 30A/mm2, for armature coil winding and the
input current is set 360Arms as the maximum input current for FEC [71]. The
depth of armature coil is set two third of the stator in order to avoid
overlapping between armature coil winding and FEC winding. The direction
of armature coil is shown in Figure 3.6 respectively. The direction of
armature coils is in alternate direction.
F1 o
F1 F2 x x
F2 F1 o o
F1 x
xx oo
F2 o x F2 F1 F2 F2 F1
x oo F1 F1 x F2 F2 F2 F2
x o F2 x o F2 x F1 F1 o
x F1
F1 o o
F2
o F1
x x F1
F2
F1 F1 oo F2F2 xx
(a) (b)
Figure 3.5: Direction of FEC
(a) Inner-Rotor HEFSM (b) Outer-Rotor HEFSM
The design contains stator, rotor, armature coil, permanent magnet and FEC
for inner-rotor and outer-rotor HEFSM uses the different materials. Stator and rotor
use electrical steel 35H210 [69]. The armature coil and FEC use copper as their
material. The PM material used for this motor is Neomax 35AH whose residual flux
density and coercive force at 20°C are 1.2T and 932kA/m, respectively. Table 3.1
shows the material of the motor part.
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