ABSTRACT
Interior Permanent Magnet (IPM) motor is widely used for many industrial applications
and has relatively high torque ripple generated by reluctance torque. Since the
configuration of the stator has great influence on reluctance torque, different stator
configuration is necessary to improve the torque performance of IPM motor. Natural
variable modeling and performance comparison of Interior Permanent Magnet Motor
with Concentrated winding (CW), Short pitched and Full pitched distributed winding
(DW) is presented in this project report. Three phase Interior Permanent Magnet Motor
with identical rotor dimensions, air gap length, series turn number, stator outer radius,
and axial length was studied with different stator winding configuration. Basic
parameters and machine performance, such as inductances, copper losses, power density,
efficiency at high and low speed, torque ripple, rotor speed with load torque, phase
currents, electromagnetic torque, controllability and demagnetization tolerance are
compared. As a means of supplementing analysis of the IPM motor, winding function
theory (WFT) is used to analyze the motor. Winding function theory has enjoyed success
with induction, synchronous, and even switched reluctance machines in the past. It is
shown that this method is capable of analyzing IPM motor with different stator
configuration and the simulations were carried out by using Embedded MATLAB
function. It was observed that, the concentrated winding IPM motor has a lower copper
loss of 0.3 kw and 3.7 kw at low and high speed respectively and 133 Nm high peak
torque developed, pull out power of 58 kw, torque ripple of 96 Nm, average torque of
142 Nm, demagnetization tolerance of 60%, amplitude of the fundamental winding is
26.45 and efficiency of 89. the short pitched distributed winding IPM motor has a lower
copper loss of 0.35 kw and 3.6 kw at low and high speed respectively and 116 Nm high
peak torque developed, pull out power of 57 kw, torque ripple of 71 Nm, average torque
of 185 Nm, demagnetization tolerance of 78%, amplitude of the fundamental winding is
27.53 and efficiency of 87. As for full pitched distributed winding IPM motor has a lower
copper loss of 0.35 kw and 3.6 kw at low and high speed respectively and 116 Nm high
peak torque developed, pull out power of 56 kw, torque ripple of 71 Nm, average torque
of 185 Nm, demagnetization tolerance of 78%, amplitude of the fundamental winding is
29.3 and efficiency of 88.
TABLE OF CONTENTS
TITLE PAGE ……………………………………………………………………………..i
CERTIFICATION ………………………………………………………………………..ii
DEDICATION ……………………………………………………………………………iii
ACKNOWLEDGEMENT …………………….…………………………………………iv
ABSTRACT …………………………………………………………….………………..v
TABLE OF CONTENTS ……………………………………………………..………..vii
LIST OF FIGURES & DIAGRAMS ……………………………………………………x
LIST OF TABLES …………………………………………………………….……….viii
CHAPTER ONE
1.0 Introduction………………….……………………………………………….1
1.1 Overview ………….…………………………………………………………1
1.2 Research Objectives …………………………………………………………6
1.3 Thesis Outline ………………………………………………………………..6
1.4 Study limitation ………………………………………………………………7
CHAPTER TWO
2.0 Literature Review …. ………………………………………………………..8
2.1 Introduction ………………………………………………………………….8
2.2 Permanent Magnet Materials …………………………………………………8
2.3 IPM Machine Technology …………………………………………………… 9
2.4 Winding Function Theory ………………………………………….…….…15
2.5 Why Winding Function Theory ………………………………………… ..17
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CHAPTER THREE
3.0 Analysis of IPM Motor with Winding Function Theory..………………….18
3.1 Introduction ………………………………………………………………..18
3.2 Winding Function Theory and its Modifications …………………….…….18
3.2.1 Basic Winding Function Theory …………………………………18
3.2.2 WFT for machines with salient air gaps …………………………22
3.2.3 WFT Applied to magnetic devices ………………………………28
3.2.4 Verification of a single phase per rotor ………………………….30
3.2.5 Matlab Program for Solving Machine Equations ………………..33
3.2.6 Torque calculated from inductance ………………………………39
3.3 Clock diagram of IPM motor ………………………………………………41
3.4 Total Harmonic Distortion (THD)………………………………………….41
3.5 Winding factor (kw)……..………………….………………………….……42
3.6 Slot-fill factor ………………………………………………………….……45
3.7 The Voltage Equations ……………………………….…………………….45
3.8 Solution of Equation (3.52) ……………………………………………….48
3.9 Torque Ripple ………………………………………………………………49
3.10 Losses in IPM motor ………………………………………………………49
3.10.1 Core Loss ……………………………………………………….50
3.10.2 Magnet Loss ……………………………………………………..50
3.10.3 Stator Winding Loss …………………………………………….51
3.10.4 Mechanical Losses ………………………………………………51
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CHAPTER FOUR
4.0 Dynamic Simulation in MATLAB Simulink ………………………………52
4.1 Simulation Tools ……………………………………………………………52
4.2 Simulink Simulation of IPM with Short pitched, Full pitched & Concentration
Winding using Embedded MATLAB Function Blocks ……………………52
4.3 Simulation Results …………………………………………………………52
4.4 Discussions …………………………………………………………………66
CHAPTER FIVE
5.0 Conclusion and Recommendation …………………………………………69
5.1 References …………………………………………………………………70
Appendix 1……………………………………………………………………………77
Appendix 2……………………………………………………………………………78
Appendix 3……………………………………………………………………………80
Appendix 4……………………………………………………………………………82
Appendix 5……………………………………………………………………………83
Appendix 6 ……………………………………………………………………………84
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CHAPTER ONE
1.0 Introduction
1.1 Overview
Over the years, the application of electric motors has replaced vast numbers of
mechanical rotating devices. From tiny motors used in wristwatches, to very large motors
used for ship propulsion and wind turbines. There are numerous types of electric motors
available for present-day applications, of which the AC types are most commonly used in
high performance applications due to its increased efficiency and excellent dynamic
performance [1]. The classifications of common types of AC motors are shown in Figure
1.1[2].
Figure 1.1: Classification of AC machine types
The Induction, Surface Permanent Magnet (SPM), Inset Permanent Magnet Machine, and
Interior Permanent Magnet (IPM) machine types have already been applied to present
day drive systems. Induction, SPM and inset PM machines usually have a lower power
rating compared to the IPM machine and are most commonly applied as an Integrated
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Motor Assist (IMA) system, where the main driver of the vehicle is the internal
combustion engine while the electric motor assists. On the other hand, the IPM machine
itself produces up to 73kW or more of power and can be driven in full electric mode,
producing zero emissions. [2]
This project report will focus on the IPM machine type, which is generally preferred due
to three main reasons: Firstly, the buried magnets make the rotor structurally stronger,
which make it more capable of withstanding higher speeds. Secondly, the additional
useful reluctance torque, resulting from the salient pole structure, thus giving the motor
greater field-weakening capabilities. Additionally, this saliency allows sensorless control,
properties which the SPM does not offer [3]. Lastly, the possibility of changing the
geometry of buried magnets in the rotor makes it possible to employ flux concentration,
and provides the possibility of saliency ratio optimisation [4].
With the availability of high energy permanent magnet materials and advanced power
electronics, the fields in which IPM machines can be applied to are rapidly broadening.
They include aerospace, nautical, automobile, rail transportation, medical, generation and
industrial process automation [5]. Common magnet geometries include single-piece/pole,
rectangular shaped magnet design (Figure 1.2a), segmented magnet design (Figure 1.2b),
v-shaped magnet design (Figure 1.2c), and the multi-barrier design (Figure 1.2d) [6].
Each of these designs has its advantages and disadvantages: The single-piece/pole
magnet design, for example, is the easiest to manufacture, but has larger magnet losses
compared to the other designs due to the larger magnet pole surface [7]. The segmented
magnet design has lower magnet losses and better field-weakening capability but requires
more magnet pieces. It also results in decreased magnet flux density due to the leakage
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flux in the iron bridges [8]. The v-shaped magnet design provides flux concentration but
also requires more magnet pieces compared to the single-piece/pole design.
(a) rectangular single-piece/pole magnets (b) segmented magnets
(c) v-shaped magnets (d) multi-barrier magnets
Figure 1.2: Various IPM rotor geometries
The multi-barrier magnet design creates a very high saliency ratio, but consequently
results in an increased amount of structural stress on the rotor steel [6]. In practice, there
is no single rotor that can satisfy all applications. The pros and cons of each design as
well as more specific magnet type and shape have to be altered to meet desired
specifications. As magnets are very brittle, there are also practical limits to the
manufacturability of the magnets.
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Before the 21st century, the majority of IPM machines were designed with distributed
stator windings (DW). The use of concentrated winding (CW) was not popular due to a
poor torque to magnetomotive force (MMF) ratio. However in the early 21st century,
Cros and Viarouge [9], Magnussen and Sadarangani [10] proved that by an appropriate
choice of slot and pole combination, the winding factor can be significantly increased,
thus increasing output torque. Additionally it was also shown that with appropriate slot
and pole combination, cogging torque can also be reduced.
Stator windings can either be single-layer or double-layer. The choice depends on the
desired machine performance characteristics. Single-layer CW creates high selfinductance
and low mutual-inductance which leads to better fault-tolerant capability. On
the other hand, double-layer CW has lower airgap MMF harmonic components, thereby
resulting in smaller torque ripples and lower magnet eddy current losses [11]. The
winding layouts for single-layer and double-layer DW are shown in (Figure1.3a) and
(Figure 1.3b), while the layouts for single-layer and double-layer CW are shown in
(Figure1.3c) and (Figure 1.3d) respectively [12].
Finally, the study is primarily concerned with the natural variable modeling and
performance comparison of Interior permanent magnet (IPM) motors with a short pitched
distributed winding, full-pitched distributed winding and concentrated winding. An
Interior permanent magnet (IPM) motor has many advantages such as high power
density, efficiency and wide speed operation. These merits make it particularly suitable
for automotive and other applications where space and energy savings are critical.
However, IPM motor has relatively high torque ripple generated by reluctance torque
which results in noise and vibration [13].
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(a) Single-layer distributed windings (b) Double-layer distributed windings
(c) Single-layer concentrated windings (d) Double-layer concentrated windings
Figure 1.3: Various stator winding layouts
Torque ripple in IPM motor is often a major concern in applications where speed and
position accuracy are great important. Since the component configuration such as a stator
has great impact on reluctance torque, different stator configuration is necessary to
improve the performance of IPM motor [14]. Most previous works to obtain optimal
design for torque ripple reduction have been restricted to size optimization in which
design parameters are known in priori and fixed throughout the optimization process
[15]. The size design variables include slot opening, depth of rotor yoke, angle of one
pole magnet, thickness of permanent magnet and so on.
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1.2 Research Objectives
The general objective of this project report is firstly to present a feasibility study on the
IPM motor with different stator configuration. Subsequently to carryout a natural variable
modeling and performance comparison on a three phase IPM motor with short pitched
distributed winding, full-pitched distributed winding and concentrated winding. Despite
the fact that the machines are now widely in use, there has been considerable interest in a
three phase Interior Permanent Magnet Motor. Finally, the study will help clarify the
advantages and disadvantages of implementing the different stator configuration in IPM
motor, as well as its prospects in industrial applications requiring high efficiency.
1.3. Thesis Outline
In order to conduct the stated project objectives, this project report is outlined as
following:
Chapter I covers overview and some backgrounds on interior permanent magnet motor.
In this chapter the main objectives and motivations of this project, thesis outline and
study limitation are introduced.
Chapter II, this chapter gives the literature reviews on Interior Permanent Magnet
machine technology, permanent magnet materials, winding function theory and why
winding function theory.
Chapter III gives the analysis of Interior Permanent Magnet Motor with winding function
theory and its modifications which include basic winding function theory, winding
function theory for machines with salient air gaps, winding function theory applied to
magnetic devices, verification of a single phase per rotor and Torque calculated from
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inductance. It also include the clock diagram of IPM motor, Total Harmonic Distortion
(THD), winding factor (kw), Slot-fill Factor, the Voltage Equations, Torque Ripple and
Losses in IPM motor which includes the core loss, magnet loss, stator winding loss and
mechanical losses
Chapter IV is a set performance, simulation and results.
Chapter V is a Conclusions and Recommendations.
1.4 Study Limitations
A major limitation encountered in this project report thesis occurred during the modeling
of the different stator configuration of the machines and only the first harmonics was
used since third harmonic would be eliminated if the motor is connected in star.
Eventually, certain assumptions deemed necessary.
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