development of a new single-phase field...

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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AUGUST

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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

iv

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


Machine with Salient Rotor 14


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


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


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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


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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x

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

xi

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


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


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

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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

2

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-

3

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.

5

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.

6

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

7

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

9

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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development of a new single-phase field...

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