Kevin S.

Campbell

High-Speed Induction Motor with an Integrated

Gearbox for Propulsion

Thesis submitted in partial fulfillment of the requirements for the degree of Masters in
Science (Technology).

Espoo, May 29, 2017

Supervisor: Professor Kari Tammi

Thesis Advisor: Jenni Pippuri, D.Sc. (Tech.)

Author Kevin S. Campbell
Title of thesis High-Speed Induction Motor with an Integrated Gearbox for Propulsion
Degree program Master’s Program in Mechanical Engineering
Major/minor Mechanical Engineering Code IA3027
Thesis supervisor Professor Kari Tammi
Thesis advisor Jenni Pippuri, D.Sc. (Tech.)
Date 29.05.2017 Number of pages 61 + 15 Language English

Abstract
Induction motors with a planetary gear are a viable option for the transportation
industry as they are a relatively inexpensive electric drive solution. Designing a
prototype of a high-speed induction motor with a planetary gear is the focus of this
project. This will be the proof of concept, to demonstrate a compact and cost-
efficient electric drive solution, when compared to electric drives with lower speeds
and no gearbox. Using a high-speed electric motor and gearing it down will provide
a high torque density and power. A prototype with a high power density and
efficiency will provide a competitive alternative to other electric drive solutions.

The design choices of the prototype are covered. 3D modeling software is used for
the mechanical design that integrates the planetary gear and the induction motor.
Finite Element Method (FEM) simulations are completed to determine the final
design. The geometry and properties of the induction motor are optimized using
FEM. Electromagnetics, torque, and the losses of the induction motor are analyzed.

The prototype design presented in this thesis is analyzed to determine the overall
efficiency, cost, and feasibility for the transportation industry. The design allows for
future development by ensuring easy changes and additions that can be made to the
prototype. The development of the high-speed motor should continue with the use
of models and design presented in this thesis. The design presented in this thesis is
another step towards the final prototype production. The possibilities for future
thesis topics and improvements will be discussed at the end of this thesis. One
possibility for future development is the use of additive manufacturing to build the
induction motor.

Keywords Induction motor, manufacturing, design, electric vehicle, 3D modelling,

planetary gear, FEM, Elmer.

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Acknowledgement
I would like to thank everyone involved for allowing me the fantastic opportunity to learn
more about high-speed induction motors. To Aalto University, for giving me the opportunity
to further my studies in Finland.

I want to extend my deepest gratitude towards my thesis supervisor Professor Kari Tammi
and thesis advisor D.Sc. Jenni Pippuri. Thank you very much for the assistance and time you
dedicated to me during this work. The trust and courage you provided me was invaluable.
The assistance from D.Sc. Jenni Pippuri, Jesse Mäntylä and D.Sc. Pavel Ponomarev was
crucial to the work done with Elmer. I would also like to thank the transmission donor.
Furthermore, the Henry Ford Foundation for financial support.

Finally, I would like to thank my family for all of the encouragement during my endeavors
and time away from home. I could not have done it without your unconditional love and
support. To all the friends I made during my studies, my time spend in Finland will be
unforgettable thanks to all of you.

Espoo, 29.5.2017

Kevin Campbell

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Table of Contents
Abstract .............................................................................................................................. i
Acknowledgement ............................................................................................................ iii
Table of Contents .............................................................................................................. v
Abbreviations and Symbols ............................................................................................. vii
1 Introduction ............................................................................................................... 1
1.1 Background ......................................................................................................... 1
1.2 Research Problem................................................................................................ 1
1.3 Objective ............................................................................................................. 1
1.4 Scope .................................................................................................................. 2
2 State of the Art .......................................................................................................... 3
2.1 High-Speed Induction Motors ............................................................................. 3
2.2 Planetary Gears ................................................................................................. 10
2.3 Electric Motors and Planetary Gears .................................................................. 10
3 Methods................................................................................................................... 13
3.1 Design ............................................................................................................... 13
3.1.1 Previously Developed Work ....................................................................... 13
3.1.2 Dimensions and Requirements ................................................................... 14
3.1.3 Air Gap ...................................................................................................... 14
3.1.4 Rotor .......................................................................................................... 15
3.1.5 Stator and Windings ................................................................................... 18
3.1.6 Bearings ..................................................................................................... 20
3.1.7 Frequency Converter .................................................................................. 21
3.1.8 Planetary Gear............................................................................................ 21
3.1.9 Frame ......................................................................................................... 23
3.2 Finite Element Method Simulations ................................................................... 30
3.2.1 Software..................................................................................................... 30
3.2.2 Model Definition ........................................................................................ 30
3.2.3 Solving....................................................................................................... 31
3.2.4 Results Analysis ......................................................................................... 33
4 Results ..................................................................................................................... 35
4.1 Electromagnetic Finite Element Analysis .......................................................... 35
4.1.1 Design of Stator Slots and Conductors ....................................................... 35
4.1.2 Voltage Supplied Simulations .................................................................... 41
4.1.3 Final Simulation and Losses ....................................................................... 43
4.1.4 Comparisons and Analysis ......................................................................... 46
4.2 Final Design ...................................................................................................... 47
4.3 Bill of Materials and Cost .................................................................................. 50
5 Discussion ............................................................................................................... 51
5.1 Problems ........................................................................................................... 51
5.2 Future Development .......................................................................................... 51
6 Conclusion .............................................................................................................. 55
References....................................................................................................................... 57
Appendices...................................................................................................................... 61
Appendix 1: Transmission Disassembly Figures
Appendix 2: Example SIF file
Appendix 3: Stator Drawing File

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Abbreviations and Symbols
B Magnetic flux density [T]
Is Stator phase current [A]
Js Current density in the stator windings [A/m2]
Jslot Current density in the slot [A/m2]
KCus Space factor
N Number of turns
Nslots Number of stator slots
P Power [W]
Pin Power input [W]
Pout Power output [W]
Ps Shaft Power [W]
Scs Area of conductors in stator [m2]
Sr Area of rotor surface [m2]
Sus Area of the stator slots [m2]
T Torque [Nm]
Uin Input voltage [V]
Uph Stator phase voltage [V]
ZQs Number of conductors per slot

f Frequency [Hz]
l Length of machine [m]
l’ Equivalent length of machine [m]
Number of phases
nm Rotation speed of rotor [rad/s] [rpm]
ns Synchronous speed [rad/s] [rpm]
p Number of pole pairs
rr Rotor radius [m]
s Slip

δ Air gap length [m]

Power factor
η Efficiency
σFtan Tangential stress in the air gap [Pa]

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2D Two-dimensional
3D Three-dimensional
AC Alternating Current
CAD Computer Aided Design
EV Electric Vehicle
FEM Finite Element Method
GUI Graphical User Interface
HSD Hybrid Synergy Drive
ICE Internal Combustion Engine
PSD Power Split Device
RPM Revolutions per Minute
RTV Room Temperature Vulcanization
SIF Solver Input File

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1 Introduction
1.1 Background
Electric vehicles (EV) are an immense field of research in today’s society. Electrical motors
are an integral part of this field. Induction motors convert 70-80% of all electrical energy
into mechanical energy [1]. Induction motors with an integrated planetary gear can be
utilized in the transportation industry for many reasons. These reasons include the fact that
they can be a less expensive solution when compared to internal combustion engines (ICE)
or even other electric drives. Additionally, induction motors have a simpler construction,
which provides a higher reliability.

Induction motors are the most widely used electric motors in the world. They are easily
available and can be considered the industrial workhorse. Induction motors tend to have a
lower torque density when compared to permanent magnet motors and some other electric
drive solutions [1]. This lower torque density leads to the potential of an induction motor
with an integrated gearbox that can provide a sufficient torque density for the entire system.
This could offer a viable option for the transportation industry, as an inexpensive and
efficient solution. To obtain a high power density for the electric drive, a high speed of
around 18,000 revolutions per minute (rpm) will be used. Clean, affordable, and reliable
energy for transportation is something the world will benefit from.

1.2 Research Problem

Utilizing high-speed induction motors for propulsion can have some challenging aspects.
Designing an induction motor that is optimized for size, cooling, power and torque is critical
for practical use in transportation. Induction motors are used widely in applications like
compressors. These applications have different design aspects when compared to
transportation uses, such as considerably different operation profiles. The size of a typical
induction motor can also make it less practical for transportation. These items need to be
considered to make it a viable option for transportation.

Efficiency of high-speed induction motors is one of the greatest concerns and challenges to
overcome. The efficiency of lower speed electric motors is generally higher, so making a
more efficient high-speed motor is a priority to be a good comparison to other options. This
would allow for smaller batteries, which delivers mass and cost savings. In addition,
maintaining a price that will compare to, or be better than other options is of optimum
importance to be competitive in the market today.

1.3 Objective
The objective of this project is to design a prototype of a high-speed induction motor with a
planetary gear. The goal is to develop a compact and cost-efficient electric drive solution for
the transportation industry. This prototype will be utilized to transfer electrical energy into
physical motion of a vehicle such as a bus or automobile. This project is a proof of concept,
that increasing the speed of a typical motor with a planetary gear will provide a higher torque
density. Using the designed high-speed electric motor and gearing it down will provide those
qualities. This will lead to savings related to the mass and space, both important aspects in
vehicle design. Researching high-speed induction motors, planetary gears, and integrating
the two will be completed to produce the finest prototype for research and investigation. The
steps of designing a high-speed induction motor with an integrated planetary gear are

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intricate and will be laid out in detail. Utilizing the resources available at Aalto University
and the knowledge of colleagues will aid in the final prototype design.

1.4 Scope
The research is focused on the final prototype design of a high-speed induction motor. Items
such as cost, final design, finite element method (FEM) simulations, cooling, and future
development will be covered. The mechanical design will be completed with computer aided
design (CAD) software, and the induction motor will be designed with the help of FEM
simulations. Previously, partial electromagnetic design has been completed. Some smaller
decisions will be made, such as using a solid or squirrel cage motor, winding layout, winding
insulation, winding style and the exact air gap. In addition, the method for cooling the
induction motor has to be developed.

The thesis will be broken down into six sections. The introduction, state of the art, methods,
results, discussion and conclusion. State of the art will review all of the relevant information
regarding induction motors and planetary gears. The methods section will discuss the steps
taken to finalize the design. In addition, everything required and used for the process will be
discussed. The results will cover the outcome of this project, including the simulation results,
final 3D model design and electric motor design. The discussion will review the items that
can and should be done in the future, as well as what could have been done differently for
this project. The conclusion will give a brief synopsis of everything determined in the paper.

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2 State of the Art
This section is designated to explain the working principles behind the main components
used for this thesis. This will include what research has been done with other projects relating
to induction motors and planetary gears.

2.1 High-Speed Induction Motors

This section will give a summary of high-speed induction motors. When a motor has speeds
of over 150 m/s, the motor is considered a high-speed motor [2]. Induction motors or
asynchronous motors are used in a wide variety of applications today. The working principle
behind an induction motor is widely known. There are two main parts to an induction motor,
a stator and a rotor. The rotor will produce the final torque or output of the machine. The
stator has electrical windings that will have an alternating current (AC) supplied to it. This
creates a rotating magnetic field that will rotate with the frequency of the AC supply.
According to Faraday’s law of electromagnetic induction, this field will induce a current into
the short-circuited rotor winding. This will create another electromagnetic field. This will
cause the rotor to rotate in the direction of the stator’s magnetic field. Synchronous speed is
the speed that the stator electromagnetic field rotates. Synchronous speed is defined as

60
= (1)

where is the supply frequency and is the number of pole pairs. Induction motors work at
a speed that is a little less than the synchronous speed. The difference between the
synchronous speed and the rotor rotation speed is called the slip. Slip is defined as

−
= (2)

where ns is the synchronous speed and nm is the rotation speed of the rotor. This will typically
be given as a percentage, so the final number should be multiplied by 100.

Permanent magnet motors and induction motors are some of the most common types of
motors used for electrical applications today [3]. These are used for a wide variety of reasons.
Permanent magnet motors are more common in the automotive industry. Permanent magnet
motors are more expensive and are not as mechanically rigid as induction motors. For these
reasons, the induction motor is used in this thesis.

The efficiency of electric motors is an important aspect to study. The more efficient the
motor is, the more reasonable and cost effective it could be for transportation. Reducing the
amount of electromagnetic and mechanical losses in an electric motor is one way to improve
the efficiency. Efficiency is

= (3)

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where Pout is the output power and Pin is the input power. High-speed motors have a larger
power density and loss-density, so implementation of a proper cooling system is key to
reduce the amount of losses from heat [4].

The losses in a high-speed machine are an important consideration in the design process.
Figure 1 lists most of the common types of losses to consider during the design of an
induction motor. According to [5], the power density of a high-speed machine could be three
times higher than a standard machine. With that factor, and less cooling area, the machine
needs to have adequate cooling designed into the system.

The first type of losses are electromagnetic. Winding losses are due to the resistance in the
conductors that are dispersed through the stator and rotor slots. Next, are core losses; these
are the losses that occur in core material of the machine. These can also be called iron losses,
as most of the cores are made of iron or a ferromagnetic material. The core losses are due to
a changing magnetic field. Furthermore, the core losses can be broken down into hysteresis
losses, eddy current losses, and excess losses.

In addition, some other types of electromagnetic losses are harmonic losses and eddy current
losses. Eddy currents are produced when electrically conducting machine parts are subjected
to changing magnetic fields. Harmonic losses come from the design of the rotating machine.
These come from stator and rotor slot harmonics, and the converter utilized to power the
machine. It is critical that the converter provides as sinusoidal voltage supply as possible to
reduce losses [6].

Next, are of the losses due to the mechanics of the machine. The most common types of
mechanical losses are due to friction, from items such as the bearings and gearing. The
bearings and gearbox needs to be adequately cooled and lubricated to reduce friction losses.

These losses are dissipated as heat. This is why the cooling of high-speed machines is
essential. The higher operating frequency and speeds cause higher operating temperatures,
therefore the possibly of losses from heat are higher. More information about losses can be
found in the previous thesis [7].

Figure 1: Flowchart of losses in an induction motor [5]

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The stator is the stationary part of an electric motor. Stators are usually made from thin slices
of electrical steel or iron 0.1 to 1 mm thick. Electrical steel provides a higher electric
resistivity. From [8], choosing the thinnest sheets possible will reduce eddy current losses.
The steel used is magnetic, and has good properties for electromagnetic induction. Hundreds
of these thin steel sheets or laminations will be placed together to make the final structure of
the stator, as seen in Figure 2. Each lamination has multiple slots for the electrical winding
to pass through. The shape and size of the slots should be optimized for each specific
application. This can be done, for example, using simulations with FEM software.
Additionally, determining the number of slots used in the stator is another crucial parameter.
The overall size or diameter of the stator can help determine these characteristics. The stator
yoke is the material above the stator slots. The yoke affects the flux density of the machine.
Although using electrical steel laminations are beneficial from a magnetization point of
view, they are expensive to make and are not as structurally sound as a solid piece of
material. Luckily, the stator does not rotate. Thus, there are typically low stresses and forces
during operation.

Figure 2: Stator lamination stack

The windings in an induction motor are key to the operation and efficiency of the system.
There are many different winding layouts possible. Distributed windings reduce the
harmonics and provide better efficiency values. Concentrated windings are another common
type of winding. They also have higher noise and vibrations than distributed windings [9].
Distributed windings use one conductor wire passing though many different stator slots and
multiple poles of the machine. Concentrated winding layouts use one conductor wire wound
around one tooth of the stator and only one pole of the machine. These layouts are shown in
Figure 3.

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 Figure 3: Distributed vs. concentrated windings [10]
Double layer windings are common practice for induction motors. Double layer windings
place one coil side on the top of one slot and on the bottom of another slot. Essentially, this
divides each slot into half to make double layer windings. Single layer windings use one coil
side for the whole stator slot. Multiple coil sides can be placed in each slot for double layer
windings [11]. This can be better visualized in Figure 4 and Figure 5. Double layer windings
are often used to reduce the high-frequency losses. According to [12], a well-designed multi-
layer design can have fewer losses than single-layer windings, although it is crucial for it to
be intricately designed and not randomly put together.

Fractional windings use a fractional number of slots per pole and phase; this will not be used
in the design presented. If the windings are not fractional, then they are considered integer
windings. Furthermore, short pitching can be used. Short pitching is when one slot has
conductors from two different phases; this also provides smaller end windings. The end
windings are the visible conductors seen at the end of the machine. The end windings are
used to loop the conductors to the next desired slot.

Figure 4: Single layer vs. double layer windings [13]

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 Figure 5: Double layer winding layout for 36 stator slots [11]

Using the right conductive material for the windings is important to minimize the losses, as
the material has to handle the operating temperatures. Filling the stator slots compactly with
a highly conductive material such as copper allows for higher power densities. The windings
inside the stator slots will be placed inside of an insulation material. This will provide
thermal insulation from the stator material and the thermals created from the other windings.
It is best to fill the slots with epoxy to fill the empty space and so the conductors stay
together. In addition, after the windings have been installed, a wedge can be placed at the
stator slot opening to keep them in place.

Induction motors can be connected in two different ways, star and delta configurations. Star
connected motors have one end of each coil connected at a common point; this is called the
neutral point. In delta connections, one end of each coil is connected with the start of another
coil. In star connected motors, the line current is equal to the phase current. The line voltage
is √3 times the phase voltage. In delta connections, the line voltage is equal to the phase
voltage. The line current is √3 times phase current. Star connections generally do not require
as much insulation as delta connections. In addition, star connected motors can take a lower
current to produce a higher torque [14]. However, most 3-phase induction motors are delta
connected.

Figure 6: Delta and star connections [15]

The thermal properties of the stator and rotor are one of the most critical areas of concern
when designing the induction machine for high-speeds. Designing a high-speed induction
motor is a demanding task. Many values have to be determined, and these can have a major

7
influence on the properties and performance of the motor. Typically, induction motors are
air cooled by a fan that is connected to the shaft of the spinning rotor. This will allow airflow
through the system that travels through the air gap. This allows convection to reduce and
maintain an ideal operating temperature. Conduction also occurs from the rotor to the
bearings. In addition, determining the ideal material for the rotor can reduce the thermals.
Copper, aluminum and steel provide high thermal conductivity [16].

The rotor is the rotating part of the electric machine. Multiple constructions can be used for
the rotor. For high-speed applications, solid rotors will provide the best option due to their
mechanical durability, reliability, manufacturing costs, and low level of vibrations [8]. Using
a laminated rotor would provide more electromagnetic benefits and can have a 2 - 3% higher
efficiency when compared to solid rotors [17] [18]. However, any unexpected stresses or
balancing issues would present themselves faster in a laminated type rotor. Solid rotors are
made with one large piece of ferromagnetic material. The simplest solid rotor construction
is a smooth cylinder, but this has electromagnetic properties which are not always ideal [8].
Improvements have been made on the smooth rotor in an attempt to improve performance
and electromagnetic characteristics. The other types of solid rotors are slitted, slitted with
end rings, squirrel cage, and coated smooth. These rotor constructions can be seen in Figure
7. Each one of these constructions is more difficult to manufacture and therefore, more
expensive than a solid smooth rotor. Solid slitted rotors help guide the flux into the rotor and
reduce eddy current losses. Unfortunately, slitting can also increase the air gap friction losses
[19]. This type of rotor is becoming increasingly more common for high-speed machines.

Figure 7: Solid rotor constructions: a) smooth, b) slitted, c) slitted with end rings,
d) squirrel cage, e) coated smooth [8]

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The air gap is another crucial element to the overall efficiency of an induction motor. The
air gap is a small space between the rotor and stator. This will typically be no larger than 4.0
mm. This gap serves multiple purposes. First, it allows convention of air from the rotor.
Second, it allows air to flow through the machine. This will provide cooling for the electrical
machine. This small space is also, what allows the rotor to spin without any interference.
The air gap also plays a huge role in the magnetization. The size of the air gap determines a
number of items in the motor. In order to decrease harmonics and overall losses in the rotor
is it necessary to have a sinusoidal air gap flux. Selecting the best air gap size is essential to
determining a way to minimize the overall losses in the motor. Choosing a larger air gap is
the standard for high-speed induction motors [17].

All of these components from an electrical machine that were explained above can be seen
in Figure 8.

Figure 8: Components of a typical induction motor

Rotating at high-speeds is a process that must be handled delicately. Using the proper
bearings for this application is vital to maintain proper rotating speeds without causing
problems in the future. The bearings also have a significant influence on the efficiency of
the motor due to mechanical losses that come from the high rotation speeds.

The frame of the induction motor is the part that houses all of the other components of the
machine. Furthermore, it allows for stable mounting of the system. The wiring interface is
also housed in the frame. It allows the complete package to be delivered fully assembled.

The asynchronous AC machine talked about in this thesis will require a frequency converter
for operation. The primary reason a converter is required is to convert a fixed frequency and
voltage to a variable frequency and voltage. Essentially this allows for speed control of the

9
motor. In addition, the converter will convert the incoming direct current power to
alternating current power used by the induction motor.

2.2 Planetary Gears

The idea of planetary gear trains have been used for a long time, dating back to the second
century. A planetary gear train consists of four major components. These are the sun gear,
planet gears, planet carrier and the ring gear. Typically, one of the three gears is constrained
not to rotate, which is normally the ring gear. In this case, the sun gear is the input gear and
the planet gears are the output of the system through the planet carrier. The planet gears are
connected with a planet carrier. This configuration of the gear train provides an output speed
that is reduced from the input.

These gear trains can evenly distributed the load and stress applied. The multiple points of
contact allow of the load to be shared in multiple locations. As a result, planetary gears are
very strong and reliable. The teeth of the gears are typically designed in one of two ways,
using helical gears or spur gears. Helical gears are the standard today because the two mating
gears will have a larger contact surface area when compared to spur gears.

Planetary gears can be used in multiple configurations. Depending on which gear is held
stationary will provide different results. Figure 9 shows what can occur for each specific
case.

Figure 9: Planetary gear operation [20]

The most common material for planetary gears is steel. Although, for applications with less
loads, plastics have become widely used for servomotors.

Planetary gears can be compounded to provide alternative solutions. This is most commonly
seen in transmissions. This can allow for even more variation in gear ratios. Planetary gears
are most commonly used in automatic transmissions. Typical input speeds of planetary gears
for transmissions are around 10,000 rpm. Since planetary gears can rotate at such high
speeds, vibrations can be present.

2.3 Electric Motors and Planetary Gears

Combining these two systems could potentially provide a promising alternative for electric
drive systems. This area has not been studied largely; it could provide a cheaper system with
ideally the same efficiency as a permanent magnet motor. Using a high-speed induction
motor with a planetary gear can improve the overall torque density throughout all of the

10
different operating speeds. An initial prototype design was visualized in Figure 10 from [21].
This is the basis for the mechanical design presented in this thesis.

Figure 10: Initial prototype design [21]

Utilizing electric motors with planetary gears is not necessarily a new system. They are
common in a few types of situations. First, small electric motors, such as stepper motors are
used in conjunction with small planetary gears. Second, the Toyota Prius is widely known
for using electric motors in conjunction with a planetary gear. The system used in the Prius
is called a Power-Split Device (PSD) and Hybrid Synergy Drive (HSD). However, the motors
used in the Prius are synchronous permanent magnet motors and are expensive. In addition,
this system is combined with an internal combustion engine and is not a fully electric vehicle.
This method is much more complicated and expensive when compared to using an induction
motor with a planetary gear. The application investigated in this thesis will be fully electric.

The Prius is a hybrid vehicle, and as stated, uses an electric motor with an ICE. Hybrid
electric vehicles are quite common in today’s market. One of the main benefits of hybrid
vehicles is their fuel efficiency. In addition, they also provide higher performance and lower
emissions than standard internal combustion engines. Many different drivetrain
configurations can be used in hybrid vehicles to provide different qualities. This includes
using different types of electrical motors such as induction motors, permanent magnet
motors and switched reluctance motors. The three main types are series hybrid, parallel
hybrid and series-parallel hybrid drivetrains. In series hybrid, the internal combustion engine
and electric motor are ran in line so the electric motor is the only thing providing power to
the wheels. The parallel hybrid system is when the electric motor and internal combustion
engine are directly coupled through something like a gearbox. They are both supplying
torque to the wheels. Series-parallel hybrid drivetrains are used in conjunction with a
planetary gear to allow the wheel speed to be removed from the engine speed [22]. This is
the type of system used in the Toyota Prius. This allows either one of the power sources to
be used separately or together. The PSD and HSD used in the Prius allows for five different

11
driving modes. These include, starting out, normal driving, full acceleration, deceleration
and reverse [23].

General Motors has been working with electric vehicles for a long time. From as early as
1964, they have been testing three-phase induction motors for electric vehicles. These
electric vehicles run at speeds up to 13,000 rpm and 137 horsepower [24].

Another example of electric motors used with gearing is the Chevrolet Bolt EV. This system
uses an electric permanent magnet motor in conjunction with a transmission. The electric
motor provides 97% efficiency. It utilizes a trademark bar-wound stator and a double-layer
of magnets in the rotor. The 150 kW motor, that has a maximum speed of 8810 rpm is the
only power source for the vehicle. The gear ratio in the Bolt is 7.05 [25]. This system is
similar to the system designed for this thesis. However, it does not use a planetary gear and
uses a higher gear reduction.

Many modern electric vehicles are simply direct drive and do not require any additional
gearing. For example, this system is used in all current electric vehicles designed by Tesla.
The Tesla uses a high-speed induction motor [26].

Stepper motors are often used in conjunction with planetary gears. They utilize high speeds
and low gear ratios in the gear train, which provides maximum torque. Torque is one of the
most sought after qualities in a stepper motor. This system provides similar qualities desired
for the project at hand. However, stepper motors are small, commonly use permanent magnet
motors, and are not designed to rotate continuously. They are designed to rotate to a precise
position and stop for accurate placement of the attached component.

This project will combine the ideas from some of the aforementioned systems and some new
ideas for a system that will provide high torque density at operating speeds designed for
automobiles.

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3 Methods
Taking a scientific concept to a reality can be a challenging process. This section will layout
the procedures that went into designing the prototype, from simulations to 3D modeling.

3.1 Design
The principal design choices will be explained in detail. The process to design a rotating
electrical asynchronous machine is an exacting task. The proper design process is important
to achieve the best efficiency possible. Figure 11 shows the typical design process and the
relevant values that need to be determined.

Figure 11: Design process for an asynchronous machine [4]

3.1.1 Previously Developed Work

Two theses have been completed related to this project. Partial electromagnetic simulations
were done to determine some influencing factors in the design. This work is the basis for
this thesis, and is used to determine many factors for the design. This work can be found at
[7]. Additionally, the rotor dynamics were analyzed [27]. This work shows the vibrations,
natural frequencies, critical speed, bending modes and centrifugal forces of the rotor design.

13
The goal of this thesis is to collect the previously completed work, and the work completed
in this thesis to finalize a design that will be used for prototyping and proof of concept.

3.1.2 Dimensions and Requirements

Designing this system for transportation purposes means that the system has to be capable
of highway speeds. A goal of around 100 km/h was set for this electric vehicle. In an
application of a city bus, the max speed would be 80 km/h. A tire diameter of 0.9 to 0.95 m
and a circumference of 2.8 to 3.0 m was used. 100 km/h is roughly 27 m/s. With these values,
the rotations per minute were calculated to be around 600 rpm. The final gear ratio from the
transmission to the final speed of the wheels in similar applications is between six and seven.
This provides a speed of around 4,000 rpm. With a planetary gears reduction ratio between
two and four, this leads to a speed of around 16,000 rpm, and when accounting for some
margin in the speed, a value of 18,000 rpm was determined. State-of-the-art motors are
increasing the overall top speed, the Prius has moved from a speed of 10,000 rpm to 14,000
rpm [23]. Electric motors in newer EV’s are trending to increased speeds above 18,000 rpm,
such as the EV’s made by Tesla [26].

Below is an initial design specification list for the integrated electrical motor and gear of this
project. These items have been previously determined [7]. Adjustments to these values will
be made for the final design.

∂ Machine type: Induction machine

∂ Type: Radial flux
∂ Rated power: 150 kW
∂ Maximum rotational speed: 18,000 rpm
∂ Maximum rotational speed after gear: 6,000 rpm
∂ Slip: 2%
∂ The number of poles: 4 (2 pole pairs)
∂ Rated frequency: 600 Hz
∂ Number of phases: Three
∂ Outer diameter of the stator: 250 mm
∂ Length of the stator: 80 mm
∂ Outer diameter of the rotor: 150 mm
∂ Air gap length: 0.7 mm
∂ Stator slot height: 25 mm
∂ Stator slot width: 10 mm
∂ Stator slot opening: 2 mm
∂ Number of stator slots: 36
∂ Stator yoke thickness: 36.8 mm
∂ Rotor type: Solid
∂ Winding layout: Double-layer and distributed

3.1.3 Air Gap

For a 50 Hz asynchronous machine, the air gap length can be estimated by:
.
0.18 + 0.006 ×
= (4)
1000

14
where P is power in watts. This equation is designated for machines with the number of
poles pairs greater than one. As this equation is designed for 50 Hz machines, it will not give
a perfect air gap length for this project. In addition, this equation is only designed to give a
starting point for the air gap; changes should be made after determining what qualities are
desired for the machine being designed.

Using a power of 150,000 watts, the air gap can be calculated to be 0.885 mm. When
comparing this to the air gap determined from previous simulations it shows that the size is
similar. This machine is designed for a frequency much higher than 50 Hz, so there should
be a difference between the values. However, there is no absolute way to calculate the air
gap length. Simulations are the best way to determine the air gap. The starting point for the
air gap is 0.7 mm based on the work completed in [7].

In high-speed machines, the air gap is typically larger than lower speed machines to mitigate
losses. The air gap should be designed for high-speed and high frequency operation. An air
gap of 3.0 mm is quite common for machines with similar designs as the one presented in
this thesis. After conferring with some colleagues in expert interviews, it was determined
that the air gap should be increased by a large margin. The calculated value of 0.885 mm
and simulated value of 0.7 mm are too small. The new air gap value will be 3.5 mm for the
final design. When comparing this to similar machines with higher frequencies, the air gap
was similar, as seen in [5] and [17]. The previous air gap would be in the right range for a
machine with normal frequencies and speed, for example in [17].

Increasing the air gap also has beneficial impacts on the machine. The rotor iron losses are
decreased, the mechanical stability is increased, and additional losses are reduced [28].
However, the stator winding losses and power factor are decreased.

3.1.4 Rotor
A cylindrical solid rotor was chosen for this design as it is the most suitable for high-speed
applications [4]. This is because it was determined that having a more mechanically robust
structure will be better for the development. Using a short rotor with a large diameter is
better for high-speed applications to reduce vibrations [5].

There are multiple choices to be made when designing the rotor. What material to use, should
the rotor be slitted, should the rotor be coated, should the rotor be solid or laminated, and
how to keep the rotor cool. Induction machines running at the operating speed will create a
lot of heat. It is common practice for high-speed machines with solid rotors to have slits or
machined groves in the surface of the rotor to help with cooling and magnetic inductance.
When using axially slitted rotors, the width can start at around 2.0 mm and the depth of the
slit should be half of the rotors radius [29] [30]. Increasing the depth of the slits any more
will result in a decrease of torque.

A solid rotor construction has been chosen for the purposes of this thesis. This will allow for
easy development and manufacturing in the early stages. The rotor will be milled from a
solid piece of ferromagnetic steel. Slits will also be added to the rotor for cooling and
improved magnetization. The design will made with 30 slits in the rotor. This design is
shown in Figure 12. It is recommended to have between 5 and 15 slits per pole pair [5].
Without the slitting, the magnetization characteristics of the rotor are poor. During the
process of getting electrical steel sheets cut for the stator, there will be cylindrical pieces cut

15
from the inside on the stator that can be made into a laminated rotor if desired. These pieces
will be kept in the event that a laminated rotor is designed.

Figure 12: Rotor design with 30 slits

The outer diameter of the rotor is 150 mm. The rotor shaft will input power to the planetary
gear. The size of the shaft is made to fit the chosen bearings for the system, which are
discussed in section 3.1.6. The shaft used in this design is made from the same material as
the rotor for simplicity purposes. The entire rotor and shaft is designed to be milled from a
solid piece of metal. When done on a lathe, deviations to the rotor and shaft shape can be
reduced; this will provide a cylindrical shape and reduce vibrations. The design was chosen
this way, because if made into two pieces, the two would need to be mated by welding, end
rings or something similar. This would not be ideal for the initial design; extra vibrations
could be present, and is not as structurally sound as a solid design. However, making a two-
piece rotor is possible, and would present the possibly for using a different material for the
shaft. The shaft length is 167 mm. The shaft is shown below in Figure 13. Once inserted into
the planetary gear, this leaves a 5.0 mm spacing between the end of the shaft and the inside
of the planetary gear. This also provides room for small changes in placement. The shaft has
a center hole drilled the entire length for oil to travel through and enter the planetary gear.
This is the main source of cooling for the planetary gear. Each end of the shaft has been
made to the same diameter of the bearings used to support the rotor. Small air vents have
been drilled into the shaft for airflow.

16
 Figure 13: Rotor shaft

The material used for this rotor will be ferromagnetic steel Fe52. This material has proven
to be the standard for solid rotors. This material was also utilized in a high-speed solid rotor
induction machine from [5].

The torque produced from the machine is a key characteristic. The torque provides
information on how powerful the motor is, and if it is strong enough to drive an electric
vehicle. First, the tangential stress σFtan is determined from common values of induction
motors. For our purposes σFtan = 21500 Pa [4]. Next, the required torque T was calculated.
The torque T is

= (5)

where rr is rotor radius and Sr the area of rotor surface. The area of rotor surface is

=2 (6)

where l’ is the equivalent length of the machine. Equivalent length l’ is

= +2 (7)

where is the length of the stator and is the air-gap length.

Using the equations listed above, the required Torque is 66.10 Nm. This result is similar
when compared to simulated results found previously [7].

From [27], many aspects of the rotor design have been checked and verified. First, the natural
frequencies were obtained. The first bending mode was found to be around 6,000 Hz, and
even higher for the second and third. It should be noted that the high values of the bending
modes are expected to be higher with a rotor of these dimensions. Second, the critical speed
was determined of the rotor with the addition of some bearing stiffness values. With
minimum recommended stiffness value of 50 kN/mm, the critical speed was determined to

17
be 23,000 rpm. Additionally, using a higher stiffness value of 100 kN/mm, the critical speed
was 31,000 rpm. Finally, the centrifugal force was analyzed. At the maximum rotational
speed of 18,000 rpm, the force was about 75 kN. This lead to a higher Von-Misses Stress,
with an absolute maximum value of 90 MPa. After this detailed analysis, it was believed that
the rotors characteristics are satisfactory for the operation in this induction machine. Detailed
information about these analyses can be found in [27].

3.1.5 Stator and Windings

Determining the correct dimensions of the stator is a critical component to obtaining ideal
properties of an induction motor. Determining the dimensions started with the stator and
rotor outer diameters. The stator outer diameter was known to be 250 mm so the machine
would not be too large for use in the automotive industry. The rotor outer diameter was
known to be 150 mm. The best diameter ratio from the outer to inner diameter of the stator
is 0.6 [4]. The stator outer diameter is 250 mm and with the addition of the air gap to the
rotor diameter, the stator inner diameter is 157 mm. This provides a ratio of 0.628.

Finite element simulations are used to determine the dimensions of the stator slots, stator
teeth and stator yoke. Different geometries can be simulated to identify the ideal shape of
the stator. By analyzing the magnetic flux densities and torque, the best shape can be found.
The second stage is to perform simulations with the current density supply and voltage
supply. Additionally, the motion of the motor will be included to provide the most accurate
to real life test results.

A crucial design aspect is the size of the electrical steel sheets. The thickness of the material
is determined based on availability, cost, and the magnetic and mechanical characteristics
desired. High frequency applications can make choosing a suitable material difficult.
Materials with high amounts of silicon can lead to brittleness, and materials with high
amounts of aluminum have a high Vickers hardness value and a high resistivity that can be
used for special applications [4]. Iron with small amounts of Cobalt can be used at a higher
price point, but can provide better strength [31]. Choosing the material should first be done
by checking availability, as it can be difficult to procure the desired material and thickness.
The electrical sheet will be sent to a water jet to get the exact shape of the stator cut out.

During the design of the stator, some important information from expert interviews was
determined. The wire thickness should be small, around 0.6 mm. The thickness of the
electrical steel sheet should be between 0.2 and 0.35 mm. All of the losses from the stator
and rotor should be calculated using FEM. In addition, the air gap should be large and there
should be temperature sensors in the machine. All of these items have been implemented
into the design process.

The method to calculate values of the current densities, space factors, number of turns and
the number of conductors per slot can be seen below. It should be noted that values calculated
using these equations are designed for a starting point. The values are subject to change with
multiple iterations and simulations to achieve the desired results. The shaft power Ps is

=2 (8)
60

18
where nm is the rotation speed of the rotor at 17,640 rpm assuming a 2% slip. The stator
phase current Is is calculated by:

= (9)

where m is the number of phases, the target efficiency value is 0.95, Uph is the stator phase
voltage, and cos is the target power factor at 0.8. In star connection, the phase voltage can
be calculated by:

= (10)
√3

where Uin is the voltage fed to the machine by the converter. For our purposes, it is 500 volts.
Next is the area of the conductors in the stator Scs:

= (11)

where Js is the current density in the stator conductors. The current density value is typically
between 3-8 A/mm2 [4]. The area of the stator slots Sus is:

= (12)

where KCus is the space factor for the stator winding. The previous equation can be used to
calculate the number of conductors per slot ZQs. Finally, the current density in the slot can
be calculated Jslot:

= (13)

The number of turns N in the machine can also be calculated:

= (14)
2

The motor will be 3-phase and 4-pole machine. The windings in the motor will be distributed
throughout the stator slots as shown in Figure 14. As the efficiency of the motor is one of
the most critical design aspects for this prototype, distributed windings have been chosen.
For the best possible results, the windings will be manufactured and installed by a specialized
company. The company will also install the epoxy, slot insulation and slot wedges for the
windings.

19
 Figure 14: Example winding layout [32]

3.1.6 Bearings
Bearings are a central piece in the design of an electric motor. The bearings will provide
extra strength and rigidity to the system. There are three bearings utilized for this design,
two of which are located on the rotor shaft. The inner race of the bearings will be an
interference fit with the rotor shaft. Moreover, one face of each bearing will be pushed
against the larger diameter of the shaft, and will serve as a way to locate the proper x-axis
positioning of the bearings. These two bearings are the most critical bearings in the design.
Bearings two and three in Figure 15 are on the rotor shaft, and will help provide vibration
dampening. Bearing one will be press fit onto the shaft of the planetary gear using an
interference fit.

Figure 15: Bearing location. Planetary gear on the left and rotor on the right

These are deep groove ball bearings. Ball bearings provide low friction, minimal noise
vibrations. These bearings are desirable for axial and radial load applications. However, for
this application they will only be in radial loading. The bearings chosen for this application
are ceramic bearings developed by SKF. They are specifically designed for electrical motors

20
and are resistant to electric currents, as the balls in the bearings are not made from steel or
iron [33]. Furthermore, bearings two and three had to be capable of speeds up to 18,000 rpm,
and have an inside diameter of 30 mm for the rotor shaft. SKF offers a 30 mm ceramic hybrid
bearing that have a limiting speed of 19,000 rpm. Bearing one only needs to rotate at 6,000
rpm after the gear reduction. The planetary gear has a shaft size of 35 mm, so that was the
bearing size chosen for bearing one. That ceramic bearing has a limiting speed of 17,000
rpm. This bearing will not be in direct contact with electrical currents; however, it was
chosen to utilize the same type of bearings and to ensure that it would not be affected in any
way. The outer diameter of bearings two and three is 55 mm, and of bearing one is 62 mm.
These are the dimensions used in the frame components to encase the bearings. The bearings
will use high-strength bearing locking adhesive to prevent the outer race from rotating in the
housings. It will also provide sealing.

3.1.7 Frequency Converter

The converter will be sourced from ABB. It will provide 3-phase voltage between the range
of 380 and 500 volts and an output frequency of up to 599 Hz. Many converters are available
that meet the needs of this motor. For example, ABB machinery drive model number ACS850
is a good example of a converter that will be capable of powering this machine. The
specification sheet can be seen in [34]. Using pulse-width modulation voltage supply can
reduce the low-order harmonics and improve efficiency with a coil pitch of 120 degrees [35].

3.1.8 Planetary Gear

Designing a planetary gear from scratch is not necessary; many companies make off the shelf
planetary gears. Finding the correct planetary gear however, proved a difficult task. It was
previously determined that there were some initial constraints to be met. Those constraints
are listed below:

∂ Reduction ratio of 3 or similar

∂ Capable of an input speed of 18,000 rpm
∂ Nominal torque value of 60 Nm
∂ Dimensions are smaller or similar in size to the induction motor

Initially, it was believed that Bosch Rexroth had an off the shelf solution that would meet
these requirements. After further research, that was not the case. The gears were for heavy-
duty applications. They were too large and heavy for the needs of this project. Next, Matex
Gears was found with some off the shelf solutions. It was determined that the gears with a
reduction ratio of three had a maximum input speed of 5,000 rpm. The centrifugal forces on
the sub-components were computed to determine how problematic rotating the gear system
at higher speeds would be. The centrifugal force F is

= (15)

where m is the mass of the component, v is the velocity and r is the radius. Using a radius of
0.0325 m and 0.08 kg, the planetary gears were calculated to have a centrifugal force of
79.13 N with a rotating speed of 1,666 rpm after the speed reduction. When comparing this
to the speeds that we require at 6,000 rpm, the centrifugal force was 1026.44 N. This is
almost 13 times the rated force. This demonstrated that this gear train was not usable at those
operating speeds.

21
Formerly, a few planetary gear trains from two Toyota Prius’ were found. The gear sets were
from a second and third generation Prius. This system proved to be difficult to use as the
power input and output were on the same side of the gear train system as shown in Figure
16. The second-generation gears were larger and more robust. The gear set from the second
generation was put on a lathe and some material was removed to try to remove the shaft from
the planet carrier and turn it around. This would allow the input and output to be on opposite
sides. The shaft was not designed to be removed, and if removed, the strength of the
planetary gear train would be compromised. In addition, maintaining tight tolerances would
be difficult if it was put back together. Detailed information about these gears were
previously studied during another thesis [23], and provided insight on the operation of these
planetary gears.

Figure 16: Prius planetary gears

After extensive research and communication with multiple parties, it seemed that the best
option would to utilize a planetary gear from an automatic transmission. ZF transmissions
makes many different planetary gears that seemed to meet the needs established. This
company makes multiple transmissions for many car manufacturers. Typically, these
transmissions were used in BMW’s and Audi’s. The focus was to find a broken transmission
that someone would be willing to donate to the university. An old BMW transmission was
found online. The owner was contacted and was willing to donate the transmission, as he
had no use for it anymore. The transmission model number was ZF 5HP18. The planetary
gears in this transmission had a few key qualities that made it a good candidate for the
project. First, the input and output were on opposite sides, unlike the Prius planetary gear.
Second, the front-end planetary gear had a high input speed from the ICE. Third, with the
ring gear held stationary, it provided a gear ratio of 3:1. All of these were important

22
parameters that met the initial requirements. Further information about the transmission used
can be found in [36].

After the transmission was acquired, it was dismantled piece by piece to access the front-
end planetary gear located inside. The disassembly figures can be seen in Appendix 1. The
first step was to remove the transmission oil pan. Next, the valve train system was then
removed. After that was removed, the final bolts could be removed that kept one of the clutch
pack housings in place. Bolts holding in the input shaft housing were then removed to pull
out the shaft and first clutch pack system. The broken component of the transmission was
found during this process, it was a housing for a clutch pack. All the remaining components
were then pulled out from the transmission housing, including the planetary gears. After
everything was removed, the two planetary gears were observed to determine the condition
and operating principals. The planetary gear train used can be seen in Figure 17.

Figure 17: Planetary gear system. Input on the left, and output on the right

This system proved to be an ideal choice for the design. The planetary gear was then
measured and 3D modeled using Creo Parametric 3.0. This allowed for modeling of the
entire system so the interfaces and dimensions could be used for the rest of the design.

3.1.9 Frame
The section will describe the frame or housing used to encase all of the components in the
system. A 3D model was made of the entire prototype using all of the previously developed
design constraints and dimensions. The final prototype design is shown in section 4.2. A
cylindrical design is the most practical and common design for use in the automotive
industry. A bottom surface mounting design was made for tabletop testing and storage.
Figure 18 shows this design. The next design is mounted using the face where the output
shaft is located. For prototyping, the machine will be mounted using the cylindrical design

23
like the one seen in Figure 19. This shows how it can be mounted when used in a vehicle.
The second design is the focus as it will be the most practical for use in an automobile.

Figure 18: Bottom mounting design and entire prototype

Figure 19: Cylindrical mounting design and entire prototype

24
Many iterations of the frame were designed; the figures above are early iterations, they are
shown for displaying the different mounting configurations considered.

It is important that the entire frame can handle the speeds and vibrations that will occur. It
needs to be rigid without adding too much mass. Thermally, it has to allow for airflow while
the rotor is spinning to allow heat to escape. Oil channels are included in the design for
proper cooling of the electric motor. After manufacturing, a suitable oil pump will be found
with adequate oil pressure. With the addition of an oil pump, there should be an oil drain pan
to collect all the oil so the pump can recirculate it into the system. This is not in the scope of
this thesis.

The frame includes many different components. Each component and design decision will
be explained. The main components include:

∂ Stator housing
∂ Stator guides
∂ Non-drive end housing
∂ Planetary gear support plate
∂ Drive-end housing
∂ Lifting hooks/feet

In addition, bolts, nuts, washers, spacers, bearing adhesive and gasket maker are used in the
design. This design is made for the initial prototype testing, and changes may be necessary
in the future, if unforeseen issues arise during manufacturing and testing.

The main component of the entire system is the stator housing. Everything will be bolted up
or mounted to this component. This can be seen in Figure 20. Many items have been
considered for the final design. On the front mounting face, there are twelve holes for
securing this component with the other components. Those mounting holes are on a lip. This
lip will allow adequate space so the bolt heads or nuts do not contact the rest of the housing.
On the same face, there are four holes for disassembly. When the entire system is assembled,
these holes can be used to thread in a bolt and push against the planetary support plate to
separate them, as it could be difficult otherwise with the gasket used for sealing. Inside the
stator housing is a small lip; this is used for when the stator is inserted. This will provide
accurate depth placement. In addition, while inserting the stator, stator guides are used. The
guides are used to prevent rotation upon installation, as seen in Figure 21. These guides are
bolted into place with two holes each. The stator guides are 85 mm long with two mounting
holes. The bottom face of the guide has a radius to match that of the stator housing inside
diameter. The inserting procedure will require either the stator or the housing to be heated,
and the opposite component to be cooled. After the stator has been properly installed, four
holes are drilled in the side of the stator housing to provide additional securing points using
bolts. At the bottom of the housing, are two large oil drain holes, one will be on each side of
the stator, once it is installed. Another large hole is drilled on the side for the wiring to pass
though and connect to the converter. A single small hole is also drilled on the side for a
thermocouple wire to pass through and measure the temperature of the stator during
operation. Six holes are drilled on the back face for the non-drive end housing to be bolted
on. The non-drive end housing can be seen in Figure 22. Finally, on the outside of the
housing is a strength lip, designed to provide additional support if needed to the design. If
not needed, it can be machined off to provide mass savings.

25
All of the holes that do not have bolts placed in them during operation, such as the wiring
hole and thermocouple hold will require sealing to prevent oil from escaping. The largest
outside diameter of the housing is 290 mm, and the average wall thickness of the housing is
10 mm. The stator housing will be milled from a half-meter length of aluminum rod.
Although the housing is only 140 mm long, additional length will be used for other
components. In addition, additional length is required for mounting the rod in the machine
used for the manufacturing process. Machining this out of a single piece of aluminum rod is
not the most practical; however, the large size required warrants this. If multiple components
were going to be made, casting would be the most effective way to manufacture this, but for
prototyping, this is the most practical.

Figure 20: Stator housing

Figure 21: Stator guides

The non-drive end housing has an outside diameter of 270 mm to be flush with the back
mounting face of the stator housing. There is a large ring on the back used to provide internal
guidance and locating inside the stator housing. This allows this single design aspect to have
accurate tolerances, instead of every mounting hole. The tolerances on the bearing mounting
ring and larger ring are crucial for proper rotation of the rotor. Any improper tolerances in
the rotor could cause wobble and unnecessary vibrations. Six oil cooling channels are drilled

26
though this ring for oil to be provided to the stator. The large center hole is also for oil
cooling. It will provide oil to the planetary gear, through the rotor shaft. A single hose fitting
can be seen in the center hole for the oil cooling line. The six other oil cooling holes will
also require these fittings. The smaller ring on the inside will be the mounting location for
one of the bearings. Six mounting holes and three disassembly holes are drilled in the end
housing as well.

Figure 22: Non-drive end housing

The next design component is the planetary gear support plate, as seen in Figure 23. This
component is placed in between the stator housing and the drive-end housing. On the front
face is the placement ring for the ring gear of the planetary system. Once the planetary gear
is installed, this will lock the ring gear in place and prevent it from rotating. Located on the
front and back of the plate is a locating ring just like the non-drive end housing. It will allow
proper alignment in the stator housing and the drive-end housing. In the center of the plate
is a large hole for the rotor shaft to pass though and connect to the planetary gear. Twelve
holes are drilled for mounting. These are pass-through holes. The mounting bolts will pass
though the drive-end housing, the support plate, and the stator housing. Once the nuts are
on, all three components will be squeezed together. At the bottom of the support plate is a
hole for oil to flow and drain freely between the drive-end housing and the stator housing.
The last part on the support plate is the bearing mounting ring on the back face. This is the
same design as on the non-drive end housing.

27
 Figure 23: Planetary gear support plate

The drive-end housing is shown in Figure 24. This component has many similar features to
the others, including four disassembly holes and twelve mounting holes. Inside the housing
is a bearing mounting cutout, just as the other components. The drive-end housing has the
same lip and diameter size of the stator housing. From the back view, it can be seen that the
inside is hollow to allow room for the planetary gear. On the front view, there is an extruded
feature that will allow the entire system to be mounted on a test bench. Multiple bolt patterns
can be added for easy adaptability to other test benches. An oil drain hole is also included in
the design.

Figure 24: Drive-end housing

The drive-end housing can be removed without the support plate. However, the planetary
gear would also have then be removed because the planetary gear will not be supported on

28
one end by the bearing located in the drive-end housing. This will cause a bending stress in
the rotor shaft if it is not also removed. Once they are both removed, the bolts will then be
reinserted through the stator housing and the support plate. When the support plate is
removed, the rotor should be removed as well, because the rotor would not be supported on
one side without the support plate. This will provide a way to inspect the stator.

A few features have been added for future use and testing. One of these is a bolt on hook for
lifting the system with a crane. This hook bolts on through two of the existing mounting
holes located on the drive-end housing. Figure 25 shows how this can be done. Multiple
hooks can also be used to support the system on a table by acting as feet. However, another
design for feet could be easily added by bolting it to the existing bolt patterns. In addition to
the support hook, a hole is added for a thermocouple to measure the temperature of the stator
during operation. Extra holes for additional thermocouples can be added easily. The next
design consideration was the oil drain holes. In addition to the oil, these also allow air to
escape. This allows moisture to escape which will prevent long-term corrosion.

Figure 25: Lifting hook attached to the drive-end housing

It is important to note that the tolerances and fit for many of these components have not been
exactly specified. When the product is being manufactured, the tolerances should be checked
during the machining process to ensure the desired fit. All of the mounting faces will utilize
a gasket maker compound or Room Temperature Vulcanization (RTV) silicon equivalent
for sealing. It is easy to apply and easy to remove since the prototype will most likely be
disassembled in the future for inspection or adding features. As previously stated, the
bearings will use high-strength bearing locking adhesive.

29
3.2 Finite Element Method Simulations
There are many steps to creating a proper FEM simulation. This section is dedicated to the
process required to perform these simulations. The objective of these simulations and the
tools used to execute this will be explained. The steps used to analyze the results will also
be described.

It is essential to have a plan on how to solve for the desired variables. Using FEM software
with a computer provides a much faster solution for reaching the objective. The model can
be modified to accommodate any needed changes with ease. This method is a huge time
saver when compared to other methods such as trial and error of testing real prototypes.

The simulations are a continuation of the work completed by Jesse Mäntylä. The models
were originally designed by him and were used for his work. They have been adapted to suit
the needs of this project. Further information about Elmer and the programs used can be
found in his thesis [7].

3.2.1 Software
The primary program used for the simulations was Elmer. Elmer is an open source finite
element analysis program. Elmer consists of multiple programs to produce the final model
and results. These include, ElmerGrid, ElmerGUI, ElmerSolver and ElmerPost. ElmerGrid
is designed to make and change the mesh. ElmerGUI is the graphical user interface, or the
actual program that lets you see the model. ElmerSolver is the portion that runs the code and
mathematics for each individual element in the mesh. ElmerSolver is the most important
software used for this project. ElmerPost can be used for analyzing the results from
ElmerSolver. However, Paraview will be used instead of ElmerPost. Paraview is also an
open source program that can turn data files into a visual representation. Matlab is also used
for additional data processing. GMSH was used for making the geometry and the meshing
required for ElmerSolver. Again, GMSH is an open source program.

The fact that Elmer is an open source program means that more problems and trouble areas
are likely to happen. Elmer is developed by CSC – IT Center for Science in Finland. The
open source publication was published in 2005, so Elmer is also a relatively new program.
Many issues were found throughout this process, so using the most updated version of Elmer
is vital.

The simulations were ran on a high performance computer, as the simulations require a lot
of memory and processing power to complete. The average time to complete a simulation
was eight hours.

3.2.2 Model Definition

Multiple design items went under the microscope during the process to finalize a design
ready for prototyping. The first item that was studied in this thesis was the geometry of the
stator slots using a current density supplied model. Next, the voltage, current and torque was
tested using a voltage supplied model. The last item studied was the losses of the motor. The
number of simulations required was quite high to reach the goal.

First, the model was setup using 2D simulations. This provided a simpler process to work
with. The first set of simulations were to determine the best geometry of the stator slots. The
number of stator slots, pole number and initial air gap were done previously. The air gap has

30
since changed, and the updated air gap is simulated in the later models. Each different
geometry was ran through a simulation and the corresponding magnetic flux densities were
analyzed. After all of the simulations were completed, the overall best geometry was
decided.

The next set of simulations were done using the best geometry found. This step was to ensure
that the voltages, currents and torque values of the induction motor are properly designed.

The last step is to verify the losses. The amount of losses is important from a thermal design
aspect. The core losses or iron losses were analyzed. The losses will provide information
about how efficient the motor is running, and how much energy is lost to heat.

3.2.3 Solving
The geometry was made using GMSH. Using the models from [7] as a starting point, GMSH
can be used to create GEO files needed for meshing and ElmerSolver. The models allow
different parameters of the stator and rotor to be changed with relative ease.

GMSH is also utilized to create the mesh file. The mesh density can be changed if needed.
The meshing was done in 2D, as the rest of the simulations are setup for 2D. An example of
a 2D mesh created with GMSH is shown in Figure 26. A solver input file or SIF file is also
needed for ElmerSolver. The SIF file defines the types of solvers and settings needed for
ElmerSolver. The SIF files also includes all of the parameters and material definitions of the
motor such as the speed, slip, lengths, moment of inertia, resistances and inductances. The
ElmerSolver manual was used to help define the SIF file properly [37]. There are many
different uses for ElmerSolver. The types of solvers available and the solvers used in this
thesis are explained in [38]. This explains all of the math and variables that can be solved
with ElmerSolver. The main solver used for this project was MagnetoDynamics2D, the
computation of magnetic fields in 2D. Multiple solvers were used in conjunction with this
one to form the final model definition. Different sections of the model can be broken up into
additional files, such as the rotor and stator slots, and the cage body. The parameters of the
motor can also be broken up into a separate parameters file. A detailed example of how to
create all these files and the process from start to end can be found in [39].

An example of a SIF file can be found in Appendix 2. This shows all of the different sections
of the file. All the different sections and settings used for this thesis are shown. This is only
the SIF file and does not include the rest of the files for the simulations. The other files
needed are the rotor slots file, stator slots file, geometry file, B-H curve file, cage body file,
and the cage definitions file.

31
 Figure 26: Geometry and mesh with 36 stator slots and 30 rotor bars

The B-H curve is the relationship of the magnetic field (H) and magnetic flux density (B) of
a given material. The simulations require this file to define the electrical steel being used
and the magnetic properties of the metal. It is simply a text document with two columns, of
the B and H values corresponding to each other. Every material has a different B-H curve
depending on the composition of the metal. The material is generally defined by the
thickness of the sheets and the specific total loss at 1.5 T. Figure 27 shows three different B-
H curve examples. 35PN230 would correspond to a sheet thickness of 0.35 mm and 230
W/kg specific total loss at 1.5 T. The material is also commonly written as M230-35A. The
type of material used can have a huge impact on the performance of the machine. For
example, when the silicon content increases, the core loss and saturation flux density
decrease. A decrease in saturation flux density will result in an increase of copper losses
[40].

32
 Figure 27: B-H curves of three common materials [40]

After everything previously mentioned is defined, ElmerSolver can then be run with all of
the necessary files located in the same folder. ElmerSolver can be run from the ElmerGUI
or it can be run from command line in windows and Linux. To help speed up the process an
automatization program was created in [7], and is run in command line to create the mesh
from the geometry, run ElmerGrid to get the meshing data for ElmerSolver, and start
ElmerSolver. The results will then be published in the same folder for analysis. The
simulations were done using a Linux operating system. The version of Linux was Ubuntu
14.04 LTS.

Any additional information desired about the files used and how to setup Elmer can be found
in [7] and [37], and thus is not explained in more detail in this thesis.

3.2.4 Results Analysis

Matlab and Paraview are used for all of the post-processing. After the ElmerSolver has
finished, the results are saved into a VTU file format. Paraview can use this file format.
Matlab analysis was done with a DAT file that was also saved by ElmerSolver. The DAT
file has many values in different columns. Each column corresponds to a specific variable.
A file is also saved by ElmerSolver that shows what variable is in each column. Matlab was
used to read the data and turn it into graphs. Matlab will be used to analyze the torque,
voltage and current levels of the model. The output provided from Matlab will be a visual
representation to assist with the results analysis. This will be the easiest way to determine
exactly what is happening, and allow easy comparison to other results. Paraview will be used
for analysis of the magnetic flux densities. The analysis in Paraview will be done by
measuring the magnetic flux densities at multiple intersection points of the mesh.

33
34
4 Results
The results are broken up into three main sections. The simulations results, the final
mechanical design from 3D modeling, and the cost. The geometry resulting from the
electromagnetic FEM simulations are included in the 3D modeling. This provides the
complete system design.

4.1 Electromagnetic Finite Element Analysis

The simulations done were completed in steps. The first step was to determine the best stator
slot geometry using a current supplied model. Next, simulations using a voltage-supplied
model were done. Finally, the losses of the final design were simulated. The results are
compared to other electric machines and designs.

4.1.1 Design of Stator Slots and Conductors

The geometry of the stator slots are the focus of this section. This section is based on
simulations setup in [7]. The simulations were setup using a current density supplied electric
motor. The basic operation of the simulations were not changed from [7], the geometry and
current densities were adjusted to determine the final geometry. For these simulations with
Elmer, eight different solvers were used. These solvers were:

∂ FreeMotion
∂ RigidMeshMapper
∂ CircuitsAndDynamics
∂ MagnettoDynamics2D
∂ MagnettoDynamicsCalcFields
∂ CircuitsOutput
∂ ResultOutputSolver
∂ SaveData

The setup for the current supplied model can be seen in SIF file in Appendix 2. This shows
all of the different input parameters used and how the solvers are used in the model. The
model is ran using current supplied in the stator slots and a circuit for the rotor cage windings.

Over twenty different geometries were prepared for simulations. Fifteen geometries were
analyzed in detail. Ten slots used an angled slot opening and five slots used a square slot
opening. Information about these slots can be found in Table 1. Besides the shape, the main
difference is the slot area. The slot areas ranged from 223 mm2 to 400 mm2. These areas
were calculated from the geometry files used in the simulations. Examples of a few slot
shapes can be seen in Figure 28. Every geometry had different sizes of the slots, teeth and
yoke. Changing the geometry changes the number of conductors and current density. The
actual number of conductors that would be used is shown as well, because the value needs
to be an integer. The current density of each slot was calculated using equations (8) – (14).
For these calculations, a value of 8.00 was used for Js to provide the smallest conductor area
possible at 17.32 mm2.

35
 Table 1: Slot geometry information
Slot Type Sus [mm2] ZQs Actual ZQs Jslot [A/mm2]
Angled 1 307 8.86 9 4.06
Angled 2 285 8.23 8 3.89
Angled 3 294 8.48 8 3.77
Angled 4 247 7.13 7 3.93
Angled 5 223 6.44 6 3.73
Angled 6 299 8.63 9 4.17
Angled 7 281 8.11 8 3.95
Angled 8 263 7.59 8 4.22
Angled 9 245 7.07 7 3.96
Angled 10 227 6.55 7 4.27
Square 1 244 7.04 7 3.98
Square 2 292 8.43 8 3.80
Square 3 344 9.93 10 4.03
Square 4 400 11.54 12 4.16
Square 5 460 13.28 13 3.92

Simulations were ran in Elmer to determine which shape was the overall best. First, every
geometry was ran using the same parameters, and only the slot area was different. This let
all the results be on a level playing field, so just the affect from the slot area could be
analyzed. The results were analyzed by comparing the simulated magnetic flux densities.
The magnetic flux density values received from the simulations were compared to theoretical
maximum values for standard asynchronous machines listed in Table 2. The magnetic flux
density values from the simulations can be seen in Table 3. For these simulations, the current
density in all the slots was set to a value of 4.00 A/mm2. This let the geometry be analyzed
without any other influencing factors.

Table 2: Permitted flux densities for asynchronous machines. Adapted from [3]
Placement B
Stator Yoke 1.4 - 1.7 T
Stator Teeth 1.4 - 2.1 T
Rotor Yoke 1.0 - 1.6 T
Rotor Teeth 1.5 - 2.2 T
Air Gap 0.7 - 0.9 T

36
 Table 3: Magnetic flux densities from simulations
Stator Rotor
Slot Type Air Gap Status
Yoke Teeth Yoke Teeth
Angled 1 2.2 T 1.8 T 1.0 T 1.6 T 1.1 T Bad
Angled 2 2.2 T 1.7 T 1.0 T 1.5 T 1.3 T Bad
Angled 3 2.1 T 2.1 T 1.0 T 1.5 T 0.9 T Good
Angled 4 2.0 T 2.1 T 1.0 T 1.7 T 1.1 T OK
Angled 5 2.3 T 2.2 T 1.2 T 1.6 T 1.3 T Bad
Angled 6 2.3 T 2.0 T 0.9 T 1.4 T 1.2 T Bad
Angled 7 2.3 T 2.0 T 1.0 T 1.4 T 1.2 T Bad
Angled 8 2.1 T 2.0 T 1.2 T 1.4 T 1.0 T Bad
Angled 9 2.0 T 2.1 T 1.2 T 1.5 T 1.0 T Good
Angled 10 2.0 T 2.1 T 1.2 T 1.8 T 1.1 T OK
Square 1 2.0 T 2.1 T 1.0 T 1.5 T 1.1 T Good
Square 2 2.1 T 2.0 T 0.9 T 1.4 T 1.0 T Bad
Square 3 2.2 T 2.1 T 0.9 T 1.4 T 1.1 T Bad
Square 4 2.2 T 2.1 T 0.8 T 1.3 T 0.9 T Bad
Square 5 2.2 T 2.1 T 0.7 T 1.2 T 0.9 T Bad

The three best geometries were chosen for further simulations. The three best were Angled
3, Angled 9, and Square 1 as seen in Figure 28. The actual current density was then calculated
again using equations (8) – (14). The computed current density was then input into the
simulations for further analysis of the magnetic flux densities and torque curves. The
calculations were done using one parallel subconductor.

Figure 28: Three best stator slot geometries

The torque curves for the three best shapes can be seen in Figure 29, Figure 30 and Figure
31. All of the torque curves are similar. This was expected as the number of stator slots and
the number of rotor bars affect the torque more than the slot shape. They all reach
equilibrium around 0.1 seconds with a torque of 60 Nm. Since the torque curves were similar
for all three geometries, the magnetic flux densities were analyzed to determine the overall
best.

37
Figure 29: Torque curve for angled 3 geometry

Figure 30: Torque curve for angled 9 geometry

38
 Figure 31: Torque curve for square 1 geometry

Angled 9 was the overall best geometry and can be seen in Figure 32. This shows that the
maximum magnetic flux is 2.133 T. When taking a closer look, it can be seen that the
extremely dark red is the only areas with that value. Only a few areas in the design have this
value, and they are extremely concentrated. In real life, the values would be more evenly
distributed. The values are at the intersections points of the mesh, so it cannot be as evenly
distributed. Using a finer sized meshing could potentially help this a little. The actual
calculated current density values and magnetic flux density values based on the
corresponding geometries can be seen in Table 4.

39
 Figure 32: Angled 9 magnetic flux densities [T]

Table 4: Magnetic flux densities of the best slots with corrected current densities
Slot Stator Rotor
Jslot [A/mm2] Air Gap Status
Type Yoke Teeth Yoke Teeth
Angled 3 4.26 2.1 T 2.1 T 1.0 T 1.5 T 0.9 T OK
Angled 9 3.96 2.0 T 2.1 T 1.2 T 1.5 T 0.9 T Good
Square 1 3.98 2.0 T 2.1 T 1.0 T 1.5 T 1.1 T OK

The results are the maxima values found. ParaView was used to determine the values at the
intersection points of each of the mesh areas that were created during the process. The
extreme outliers were not included because they were concentrated in one area and not
distributed; this means that in real life, the flux density would be more evenly distributed
throughout the entire stator yoke. The values given are the average maxima’s. This gives a
better approximation to real life scenarios.

If the values listed in Table 3 and Table 4 are higher than the allowed maxima’s in Table 2
it was not of much concern, as the values were mostly concentrated to specific locations.
This means that the average maxima would actually be lower.

These simulations were done with the original air gap of 0.7 mm and slot opening of 2.0
mm. After this step was completed, the design changed to the updated values that were
determined from expert interviews and conferring with the companies who will manufacture
the electric motor.

The material used for the B-H curve definition was M400-50A. This is the closest material
definition found when compared to what is planned to be used. The planned material is M90-
27A.

40
The simulations were done using a more advanced rotor design than what will be utilized
for initial prototyping. The simulations use a squirrel cage rotor as it provides better magnetic
characteristics. The rotor slots are using a copper material and the rest of the rotor is using
the properties of the ferromagnetic iron M400-50A. However, this design is more
complicated and costly. As stated before, the initial design is planned to be a solid slitted
rotor without a squirrel cage for simplicity.

4.1.2 Voltage Supplied Simulations

This section was completed using a voltage suppled electric motor, instead of a current
density supplied motor. These simulations are designed to provide a second means of
verification that a proper design is ready for prototyping and manufacturing. The solvers
used in Elmer are the same as the current density supplied model, minus the FreeMotion
solver. The model is setup to use a circuit to simulate the stator and rotor windings. This
model no longer uses a current density value for the stator slots. In addition, it no longer uses
the moment of inertia, initial speed and initial angle for the rotor. However, the model does
use the supply voltage as an input.

These simulations started with a 400 V star connected motor with the rotor and stator circuits
implemented. The rotor is modelled at an imposed speed with a slip of 2%. The results
received were not ideal; the torque and current values were too low. The reasoning for these
low values is unsure. The torque value is negative because the rotor is rotating in the opposite
direction as the previous simulations. The peak value of the phase voltage is around 320
volts. These simulations were done using Angled 9 geometry and the original air gap of 0.7
mm, slot opening of 2.0 mm, conductor area of 17.32 mm2, and 8 conductors.

Figure 33: Torque level for 400 V star connected motor

41
 Figure 34: Current levels for 400 V star connected motor

Figure 35: Voltage levels for 400 V star connected motor

Next, a simulation was started with an increased voltage of 500 volts; it also utilized the
updated geometry that is used in section 4.1.3. Unfortunately, there were many issues with
Elmer, so the voltage simulations could not be completed. At first, errors in the coding of
Elmer were found. These errors were related to the physics of the program and produced
unreliable results. This was fixed with an update of Elmer. Second, an issue with getting the
model to converge was found when the voltage was increased to 500 volts for a star
connected motor.

The process to define many of the parameters is an iterative process. Some of the values
have to be specifically decided so that other values can be calculated. These parameters
include the air gap, slot opening, space factor, phase current, and the conductor area or
diameter.

42
The simulations are setup to run in parallel. This provides a sophisticated use of the cores in
the central processing unit of the computer used. This takes a mesh and separates it into
multiple parts. Each part can then be simulated on a specific core, and then it is reassembled
once it is completed [37]. This was ran with the command ‘./run.sh’. The convergence issue
needs to be addressed first, and then the simulation needs to be properly ran with parallel
computation.

4.1.3 Final Simulation and Losses

The final step was to analyze the losses in the final design chosen. This was also done with
a current density supplied model, like in section 4.1.1. The losses will provide a better idea
of how much energy is lost to heat. An additional solver was added to model called the
FourierLossSolver to complete this step. This is shown in the SIF file in Appendix 2.

This design uses the final design with 3.5 mm air gap, 3.0 mm slot opening, and 0.6 mm
wire diameter. This resulted in a current density of 4.53 A/mm2. It is important that when
using a wire diameter of this size, double layer winding should be used with parallel branches
or paths. The final design and mesh is shown in Figure 36 using the Angled 9 geometry.

Figure 36: Final geometry design and mesh

The analysis was done just as in the previous section. The resulting magnetic flux densities
are shown in Figure 37. The values are all within the permitted range from Table 2.

43
 Figure 37: Final design magnetic flux densities [T]

The slip and toque of the design are shown in Figure 38 and Figure 39. The slip is about
1.1%. This value is in the acceptable range as the design is estimated for a slip of close to
2%. The torque reaches a steady value of 60 Nm. The curve is much smoother than the
previous designs with a smaller air gap.

Figure 38: Percentage of slip of the final design

44
 Figure 39: Torque curve of the final design

Table 5 shows the losses for the final design. These values are output from Elmer. Elmer
outputs the values in watts per meter and have to be scaled to the length of the machine of
0.08 m. The total iron losses are the summation of the hysteresis losses and dynamic eddy
current losses.
Table 5: Induction motor losses
Total hysteresis losses [kW] 0.98
Total dynamic eddy current losses [kW] 24.27

The total iron losses are 25.25 kW. The losses received are quite large. Using these values,
the efficiency of the motor can be calculated. Equation 8 is used to determine the output
power at 111.85 kW watts using a slip of 1.1% and a torque of 60 Nm. The efficiency is
calculated using equation 3, taking the power output divided by the power input. The input
power is summation of the output power and the losses, 137.10 kW. This provides an
efficiency value of 82%. These results show that the motor is not as efficient when compared
to other induction motors. Most induction motors have an efficiency value from 85-97%.
The losses need to be reduced to improve the efficiency of the motor. The efficiency was
previously estimated at 95% in section 3.1.5.

The iron losses received from Elmer are dependent upon coefficients that are predetermined
and used in the SIF file. The coefficients used are estimates, and are the best available at this
time.

45
4.1.4 Comparisons and Analysis
The overall design originated from the work done in [7]. Aspects of the design have changed
to provide improvements and manufacturability. Both designs utilize a four pole, radial flux
high-speed induction motor. The size of the stator slots, the air gap, the conductor diameter,
the slot opening and the current density in the slots have all changed. The rotor and stator
outer diameters, the number of stator slots, length of the machine, the number of rotor bars,
and the rotor bar shape remained the same. Other characteristics such as, lamination sheets
size, number of conductors, number of turns and space factor are now finalized.

When comparing this design to the Chevrolet Bolt EV [25], similarities are seen. This design
uses a speed of 6,000 rpm and the Bolt uses 4,500 to 8,810 rpm. The size of the two motors
are comparable, with a length of 125 mm, and outer diameter of around 200 mm for the Bolt.
The Bolt has a peak torque of 360 Nm and maximum battery power of 150 kW. The peak
torque for the final design in this thesis is around 90 Nm, and the shaft power is 112 kW.
The Bolt achieves 97% efficiency. With an efficiency value of 82%, the design for this
project needs improvement. Designing an electric motor with a high efficiency takes practice
and care. Although, the efficiency value is lower than desired, the design is quite far along,
but still has room for improvement.

The losses of a high-speed machine at 520Hz and 218kW are shown in Table 6 [41]. The
total losses for the design presented in thesis is 25.25 kW. The 520 Hz motor has 32.26 kW
of losses. The losses were analyzed in more detail for the 520 Hz motor. Total amount of
losses is higher, but the power of the motor is also higher. In addition, the electric, friction,
cooling and bearing losses were computed. Direct comparison is challenging, but the total
losses in the stator and rotor for the 520 Hz motor is 7.66 kW. The design presented in this
thesis has 25.25 kW of losses. This does not include the other types of losses such as fiction
losses and cooling losses. The amount of dynamic eddy current losses for this project is
large.

Table 6: Calculated losses for a high-speed 520Hz electric motor. Adapted from [41]
Electric Losses [kW] 7.7
Friction losses [kW] 4.6
Cooling losses [kW] 11.6
Bearing losses [kW] 0.7
Total stator losses [kW] 4.50
Total rotor losses [kW] 3.16

The losses presented in Table 7 correspond to a 120 kW synchronous electric generator [42].
They are used for comparison to a different type of machine with similar features. The design
uses a star connected generator with a diameter of 430 mm and 1.2 mm air gap. Eddy current
losses are much lower in the generator, again leading to the conclusion that the losses
received for this thesis are higher than desired. The frequency in this design is much lower
at 50 Hz, and the frequency affects the losses of the machine greatly. This is used to show
how the losses of a lower speed and frequency machine compare.

46
 Table 7: 2D Losses in a 50 Hz generator [42]
Loss Type Area Value [W]
Stator Winding 307.66
Damping Cage 68.40
Resistive Loss
Rotor Winding 411.83
Other Conducting Part 141.68
Stator 618.24
Hysteresis Loss
Rotor 148.25
Stator 403.45
Eddy Current Loss
Rotor 1894.16
Stator 187.80
Excess Loss
Rotor 101.85

Lamination thickness plays an important role on the amount of losses. Table 8 presents the
rotor eddy current losses for the same generator. As the lamination thickness decreases, so
does the eddy current losses.

Table 8: Rotor eddy current losses based on lamination sheet thickness [36]
Lamination Rotor eddy
Thickness [mm] current loss [W]
0.20 43.6
0.35 113.92
0.50 207.59
0.65 316.69
1.00 635.48
2.00 1894.16

The thickness used for the simulations in section 4.1.1 to 4.1.3 was 0.50 mm. The thickness
of the material is simulated by using the correct B-H curve corresponding to the material.
The desired lamination thickness is 0.27 mm. The correct B-H curve should be found and
applied to the simulations. This will reduce the amount of eddy current losses in the machine,
as the thickness of the material is almost being cut in half.

4.2 Final Design

This section provides the first look at the final design and the specifications of the motor.
Figure 40 shows what the prototype will look like. To show how the components are
assembled inside of the housing, Figure 41 shows a transparent view. Everything is
assembled using a coincident axis in the center. Hardware and the oil fittings for the stator
cooling lines are not included in the figures.

47
 Figure 40: Final prototype design

Figure 41: Transparent prototype design

48
This motor is planned to be Class A or Class B. This design uses normal starting torque with
normal to low starting current and low slip. These are the most common classes for induction
motors. The oil planned for the motor is polyester CC1105.

The lamination sheets for the stator are sourced from Veslatec. The thickness of the electrical
steel will be 0.27 mm. The updated design will be used with the new air gap of 3.5 mm, 3.0
mm slot opening and 0.6 mm conductor diameter. The final specifications of the electric
motor design is laid out in Table 9. The values used in the table are a combination of the
calculated values and simulated values. The torque is the value received from the
simulations, and the power is calculated using equation 8. A slip value of 1.1% was used,
that was received from the simulations. This table shows all of the information that can be
provided to the manufacturer along with a drawing file of the stator. A drawing file is
provided in Appendix 3.

Table 9: Final high-speed induction motor specifications

Parameter Value
Machine type Induction machine – Radial flux
Number of phases 3
The number of poles 4 (2 pole pairs)
Number of stator slots 36
Maximum rotational speed 18,000 rpm
Maximum rotational speed after gear 6,000 rpm
Rotor type Solid
Slip 1.1%
Torque 60 Nm
Rated frequency 600 Hz
Rated power 150 kW
Shaft power 112 kW
Stator current 136 Amps
Voltage 500 Volts
Phase voltage 289 Volts
Tangential stress 21500 Pa
Outer diameter of the stator 250 mm
Length of the machine 80 mm
Diameter of the rotor 150 mm
Air-gap length 3.5 mm
Stator slot height ~30 mm
Stator slot width ~10 mm
Stator slot opening 3.0 mm
Stator yoke thickness ~19 mm
Winding layout Double-layer and distributed
Number of turns 48
Number of conductors per slot 8
Conductor diameter 0.6 mm
Space factor 0.5 – 0.6
Lamination thickness 0.27 mm

49
4.3 Bill of Materials and Cost
All the components required to manufacture the prototype are listed below. A detailed
breakdown including the item, cost, manufacturer, and product number can be found in
Table 10. The prices used are not final prices as nothing has been ordered. Estimates are
entered for prices that are not known for items like the converter, stator windings, and rotor
iron. Some quotes were provided by a few companies and have exact pricing.

Table 10: Bill of materials used for the prototype design

# Item Price (€) Company Product Number
1 Aluminum Rod 300 Alumeco Aluminum Rod 300mmx600mm
2 35mm Bearing 30 SKF 6007-2RZTN9/HC5C3WT
3 Planetary Gear 0 N/A N/A
4 Aluminum Plate 0 Aalto University N/A
5 30mm Bearings 30 SKF 6006-2RZTN9/HC5C3WT
6 Rotor/Shaft Iron 150 Unknown N/A
7 Stator Laminations 3,022 Veslatec N/A
8 Stator Windings 1,000 Unknown N/A
N/A Hardware 0 Aalto University N/A
N/A Converter 500 ABB ACS850
N/A Bearing Glue 15 Würth 893603050
N/A Oil 100 Stenbacka Polyester CC1105
Total 5,147€

Figure 42: Exploded view of the prototype

Some of these items are already in possession of Aalto University or were donated for this
project. Therefore, they were given a value of zero. The corresponding BOM items can be
seen in Figure 42. Item four will be used to manufacture the planetary support plate and the
stator guides. Item one is used for manufacturing the stator housing and the end housings.
Item eight is the stator windings, which are distributed throughout the stator slots, and are
not displayed in the figure. The hardware, converter, glue and oil is not pictured.

A specific goal was not set for the price of this project. The final price at 5,147€ is reasonable
for an initial prototype.

50
5 Discussion
The design of the entire prototype has been described in detail. A few final simulations are
required, and then the project should be ready for the next step, manufacturing.
Manufacturing the prototype was the original plan for this thesis, but with unforeseen time
issues and the vast amount of simulations needed, it was not possible. This section is
designed to provide more insight to the work that went on during this thesis and the items
that can be done in the future. The mechanical design, basic rotor dynamics, electromagnetic
simulations, and iron losses have all be covered to determine the ideal geometry and setup.

5.1 Problems
During this thesis, some issues were found with the use of Elmer. Primarily, it is not a user-
friendly program to use. The simulations can be ran from ElmerGUI, but for this project,
everything was done using Terminal on Linux. Command Prompt for Windows operating
systems can also be used. There is a bit of a learning curve to using the program, but is
manageable with help from experienced users and the internet. Problems with the actual
code of Elmer were found in addition to the model convergence issues discussed in section
4.1.3. Executing all the simulations with the tool given, required a significantly large effort.
Some problems were found late in the work, and cost valuable time. Updating to the most
current code solved some issues.

After some deliberation, it was decided that more work needed to be accomplished in regards
to the design of the electric motor. The simulations completed were strictly focused on the
induction motor, and mainly the stator. The rotor design was not developed extensively
because a solid rotor should be sufficient for the initial testing. Again, this took an extensive
amount of time, and a lot more than initially planned. Completing more detailed simulations
with voltages and losses were done as well, since learning how to use Elmer had already
been done. This validated the current design even further and provided more data to ensure
the motor would be capable of the desired tasks. This thesis developed into furthering the
design of the motor and completing the mechanical design of the entire system.

A lot of time was spent finding a suitable planetary gear. As previously discussed, multiple
options were considered. No perfect solution was found. With time running out, the best
option at the time was chosen. This ended up being the planetary gear from the BMW.

Doing the work on Linux also had a learning curve because some programs were setup
differently than on Windows. This caused issues with Elmer trying to access the rights and
files needed to run program. An intensive goal was set for this project, with finishing the
design, simulations, and manufacturing the prototype. A more realistic goal should have
been set and the simulation models should have been started sooner in the project. The design
was believed to be further along and little to no simulations were planned, but that was not
the case.

5.2 Future Development

One of the most important issues to study next is the structural design of the prototype. This
includes both the design of the induction motor and mechanical design that houses the motor
and planetary gear. Although the current design has been made to provide excess strength,
thorough analysis has not been completed. The strength of the system is not of great concern,
as it is over designed for this purpose. This is ideal for prototyping because any weak points

51
could be catastrophic under load. On the other hand, the added material, adds additional
mass and cost. Extra mass can be a disadvantage when considering the fact that this is
designed for automobiles. A heavier design means the system has to work hard and more
energy will be required for movement. Weight savings is a key aspect to consider in
automobile design. In the testing phase, the system will not be used in an actual automobile,
so the mass is not so critical. After enough testing has be done, another design should be
done to improve on the mass and other flaws found. For example, the wall thickness can be
reduced, the support plate can be made thinner, or even different material choices for the
housings. The current design is made from billet aluminum, which is light, but a final design
will most likely be made from cast aluminum. This means that more intricate shapes could
be implemented for weight and cost savings. Rigidity of the system should not be
compromised at all.

During manufacturing, the tolerances of all the components should be checked. These
include how the following components fit together:

∂ Stator to the stator housing

∂ Bearings to the end housings and support plate
∂ Rotor shaft to the planetary gear
∂ Support plate to the stator housing
∂ Support plate to the drive-end housing
∂ Non-drive end housing to the stator housing

The fit is crucial to ensure the rotation of the bearings and so the rotor will not be out of
balance. The fit can be checked and tested multiple times during the process to provide the
ideal fit. Some components will require interference fits, and some will require a tight
clearance fit for disassembly. A transition fit may be the best choice for the end housings.

The planetary gear used in the system is not specifically designed for speeds up to 18,000
rpm. It is designed for an automatic transmission, and most car engines do not exceed 7,000
rpm. Assuming a small safety factor, 10,000 rpm should not be a problem for the current
gearset. Ideally, a gearset meant for higher speeds would be used. However, it proved
difficult to find a gearset that could reach these speeds with the desired torque and reduction
ratios. It is possible that one could be designed specifically for the needs of this project, and
would be a great opportunity for another thesis.

Another important aspect to study is the vibrations in the frame. With sufficient tolerances,
the system should minimize vibrations and losses. Currently, only a solid rotor has been
analyzed for vibrations and natural frequencies. A more sophisticated design with a squirrel
cage could be modeled and analyzed. The better the design, the more efficient the prototype
will be, and the more magnetic flux can be induced into the rotor. The current rotor design
should be tested for symmetry and balancing after it is made. If improperly balanced during
the manufacturing process, the rotor will cause excessive vibrations therefore harming the
bearings and possibly more components.

Since the electrical sheets are available from the stator lamination cuts, a laminated squirrel
cage rotor should be considered. This design will typically provide the most electromagnetic
benefits while reducing the losses. The design is much more complex than a solid rotor. The

52
strength of the rotor can also be of concern, as rotating hundreds of these steel sheets at high
speeds could be difficult to balance, potentially leading to catastrophic failure.

Oil cooling has a large influence on the design of this system. Proper design of the cooling
has not been analyzed. Computational fluid dynamics of the oil flow and airflow can be done
to investigate the cooling properties of the system. However, this may not be necessary for
initial testing. The prototype can be made with the current oil cooling design. A proper oil
pump, fittings and cooling lines need to be obtained. This is easy to implement after the
system is assembled. Measuring the temperature of the stator can be analyzed with the
thermocouple, this will provide information if the motor is running too hot. Additional oil
cooling lines and holes can be implemented without too much difficulty. If needed, extra
holes can be drilled into the stator for the oil to pass through. The amount of oil flow needed
can be tested by adjusting the flow rate on the pump. The amount of oil entering the system
should be the same amount of oil draining from the system. This will provide a constant oil
level. A rising oil level is of concern, because if the oil level rises and hits the rotor, it will
inhibit the speed of the rotor and cause extra losses. A heat exchanger or something similar
will cool the exiting oil before re-entering the system. This will require airflow through the
heat exchanger, easily accessible at a proper test bench with a fan. Cooling ducts can also be
added on the outside of the frame as shown in [30].

The design used to send oil to the planetary gear should be verified with real world testing.
The bearing in the non-drive end housing needs to be sealed properly so the oil will flow
from the input fitting into the hole in the rotor shaft. Sealing the bearing in the drive-end
housing might also be required. The bearing glue will help with this however, SKF makes
bearing seals that could be utilized as well. The planetary gear might require more oil flow
than the stator oil cooling channels. The oil cooling channels design might have to change
slightly if the end windings in the stator are larger than expected, as the ring on the non-drive
end leaves some space for the end windings, but it is unknown exactly how much will be
needed until the stator is made. The ring can be seen in Figure 22.

With the proper design of the oil cooling, thermal analysis of the entire machine can be done.
Again, computational fluid dynamics can be used, or this can be tested in the real life. Real
life testing may be easier, and if the system is not ran at full speed then the thermals are not
of great concern. Multiple thermocouples will provide temperature verification. The
efficiency can be measured once the motor is running by comparing the power input versus
the power output.

Close to a hundred simulations were completed for this project. The design process for
induction motors is iterative. This means that a lot more time could be spent adapting small
changes into the design for benefits. The windings, electromagnetics and voltages could all
be analyzed further to minimize losses, and improve the overall performance. Little
geometry changes to the stator slots, air gap and stator slot openings can have a great
influence on the machine. However, this is almost a never-ending process. The goal was to
provide a good design with satisfactory characteristics. Incorporating small changes will
sometimes only provide marginally better results and may not be worth the additional time
required.

An interesting future development idea is to use 3D printing or additive manufacturing for

the electric motor materials such as the stator and rotor. The stator would be the best initial

53
choice, as it does not rotate and incur many stresses. Printing methods such as selective laser
sintering, or stereolithography are commonly used to print metals. These methods can
provide material densities similar to the more common materials used for electric motors
[43]. The thermal properties and electromagnetic properties of the metal used can be
analyzed for this concept. In addition, as the material is fused together by a laser, so the
mechanical and structural properties should be tested, especially if used for the rotor.

The bearings used are designed specifically for electric motors. The bearings are made from
ceramic to provide resistance to eddy currents and magnetic induction [33]. Steel bearings
are generally more susceptible to magnetic induction. Steel bearings could be tested to
compare the difference. The ceramic bearings are more expensive and may not even be
needed for this prototype, but are used to reduce any unnecessary losses.

In addition to the cost of the bearings, the cost of other components can be considered. The
cost for the initial prototype is not of the greatest concern. In the future, reducing the amount
of material used, the type of materials used, and the companies for producing the stator can
be evaluated for areas of cost savings.

The overall efficiency and performance of the entire system is a key factor. Some items may
need to be sacrificed on to improve others. As long as the final design works, is cost effective
and efficient then the concept can be proved. Providing the required specifications to be
competitive is probably the most important aspect to consider. If the design has benefits over
other products on the market, then there is a place for this in the transportation industry, or
possibly even other industries.

To summarize, below is a list of final items that need to be finished before the motor should
be ordered:

∂ Voltage simulations
o Fix convergence issues
o Check voltage, current and torque levels
∂ Double layer winding definitions should be checked
∂ End winding parameters should be checked
∂ Correct BH curve used in the simulations
∂ Reduces the overall losses (Correct BH curve and simulation coefficients)

This is a list of items that should be done after the motor is ordered and during
manufacturing:

∂ Tolerances should be checked

∂ Proper oil cooling design
∂ Verify converter will work

54
6 Conclusion
The objective of this thesis was to develop a final design for prototyping a high-speed
induction motor with an integrated planetary gear. Many iterations of the design were
completed to deliver a great foundation for manufacturing, proof of concept, and testing.
The design was completed using FEM simulations and 3D modeling. Each iteration of the
design and was analyzed in detail.

The project goal is to develop a compact and cost efficient electric drive solution for the
transportation industry. The basic operating principals of an induction motor and the
integration with a planetary gear were explained in detail. This concept is compared to
similar systems that use electric motors in conjunction with a planetary gear.

Starting with previous designs, the mechanical design was further developed with the use of
Creo Parametric modeling software. This includes the most important design features and
things to consider when making a prototype of an induction motor. The method to integrate
the induction motor and planetary gear is also explained. Items such as thermals, cost and
manufacturability were covered.

To aid in the demanding process of designing an induction motor, FEM Simulations with
Elmer were used. This extensive process required close to a hundred simulations of different
types to determine a final design. The geometry of the stator slots, magnetic flux densities,
currents, voltages, torque levels and losses were put into extreme scrutiny. Paraview and
Matlab provided a visual representation of what each change to the design did, and how it
affected the motor specifications.

Many other parts of this design can be researched in more detail in the future. Designing an
induction motor with an integrated planetary gear is a challenging task. Much more time
could be spent developing this design and concept. However, the most important task should
be to test the proof of concept. Every change made can affect other aspects of the prototype
and the final operating principals. A different planetary gear may be required for high-speed
tests of above 10,000 rpm. A few small items need to be finalized, and then the design is at
a stage where the next step is to order and manufacture the components.

55
56
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59
60
Appendices
Appendix 1: Transmission Disassembly Figures. 4 Pages.
Appendix 2: Example SIF file. 9 Pages.
Appendix 3: Stator Drawing File. 1 Page.

61
 Appendix 1 (1/4)

Appendix 1: Transmission Disassembly Figures

Donated automatic transmission

Transmission oil pan - first step for disassembly

Appendix 1 (2/4)

Transmission valve train

Transmission valve train channels

 Appendix 1 (3/4)

Transmission input shaft

Broken component - clutch pack housing

Appendix 1 (4/4)

Transmission inside – large bolts to remove clutch packs

Entire disassembled transmission. Input from right to left

 Appendix 2 (1/9)

Appendix 2: Example SIF file

!Made for Master's Thesis of Jesse Mäntylä, Aalto University, Department of Mechanical
Engineering 05/2016
!Modified by Kevin Campbell 05/2017

$ w_mech_rpm = 18000 ![rpm] Synchronous rotation speed

$ w_mech = w_mech_rpm*2*pi/60 ![rad/s] Synchronous angular velocity
$ pp = 2 !Pole pairs
$ w_elec = w_mech*pp ![rad/s] Electrical angular velocity
$ r_inner = 0.075 ![m] Rotor radius
$ r_outer = 0.0785 ![m] Rotor radius with air gap
$ J_stator = 4.53e6 !Current density in the slot
$ L_rot = 0.08 !Length of the motor
$ area_bar = 0.000047
$ SLIP = 0.98 !Rotor slip
$ Imom = 0.03 !Moment of Inertia of the rotor
$ InitialSpeed = w_mech*SLIP !Tnitial rotor speed [rad/s]
$ InitialAngle = 0 !Initial rotor angle [rad]

!Circuit module, cage windings

$ R_b2b = 0.000016 ![Ohm] bar-2-bar end ring rotor resistance
$ L_b2b = 0.000000007 ![H] bar-2-bar end ring rotor inductance

$ Circuits = 1
$ results1 = "results_9"

!!!!!!HEADER!!!!!!
Header
CHECK KEYWORDS Warn
Mesh DB "." "Angled_9"
Include Path "bar_sections"
Results Directory ""
End

Simulation
Max Output Level = 3 !Message level max. 10.

Coordinate System = Cartesian 2D

Coordinate Mapping(3) = 1 2 3
Coordinate Scaling= 0.001

Simulation Type = Transient

Steady State Max Iterations = 1
Output Intervals = 1
Timestepping Method = BDF
BDF Order = 1
Timestep Sizes =$ 1/(w_elec/2/pi)/90
Timestep Intervals = 8000
Appendix 2 (2/9)

imom = Real $Imom

Circuit Model Depth = Real $ L_rot

loadtorque1 = Real 375

loadtorqueAngle1 = Real 30
loadtorque2 = Real 375
loadtorqueAngle2 = Real 70
loadtorque3 = Real 375
loadtorqueAngle3 = Real 80
loadtorque4 = Real 375
loadtorqueAngle4 = Real 90
End

!!!!!!SOLVERS!!!!!!
!Mesh deforming
Solver 1
Equation = Motion
Procedure = "FreeMotion" "FreeMotion"
Exec Solver = Always !Before Timestep
End

Solver 2
Equation = MeshDeform2
Procedure = "RigidMeshMapper" "RigidMeshMapper"
Exec Solver = Before Timestep
End

!Cirquit equations
Solver 3
Equation = Circuits
Variable = X
Procedure = "CircuitsAndDynamics" "CircuitsAndDynamics"! "Circuits2D"
"CircuitsAndDynamics"
Exec Solver = Always
End

!Magnetic vector potential A

Solver 4
Equation = MgDyn2D
Procedure = "MagnetoDynamics2D" "MagnetoDynamics2D"
Exec Solver = Always
Variable = A
Apply Mortar BCs = Logical True

Steady State Convergence Tolerance = 1e-05

Nonlinear System Convergence Tolerance = 1e-5

Nonlinear System Max Iterations = 40
 Appendix 2 (3/9)

Nonlinear System Min Iterations = 1

Nonlinear System Relaxation Factor = 1.0
Nonlinear System Newton After Iterations = 3

Newton-Raphson Iteration = Logical True

Export Lagrange Multiplier = Logical True

Linear System Normalize Guess = Logical True

Linear System Abort Not Converged = True
Linear System Solver = Iterative
Linear System Iterative Method = GCR
Linear System GCR Restart = 1000
Bicgstabl Polynomial Degree = 4
Linear System Preconditioning = Ilu2
Linear System Max Iterations = 1500
Linear System Residual Output = Integer 10
Linear System Convergence Tolerance = 2.0e-10 ! 2.0e-6
End

!Other fields from potential A, automatically flux density B [T]

Solver 5
Equation = MagDynCalc
Procedure = "MagnetoDynamics" "MagnetoDynamicsCalcFields"
Potential Variable = "A"
Exec Solver = Always ! After Timestep

Calculate Current Density = Logical True

Calculate Electric Field = Logical True
Calculate Magnetic Field Strength = Logical True
Calculate Magnetic Vector Potential = Logical True

!GNF Torque calculation, a new feature

Calculate Nodal Forces = Logical True
Calculate Magnetic Torque = Logical True

!Iterative
Linear System Solver = "Iterative"
Linear System Preconditioning = ILU2
Linear System Residual Output = 10
Linear System Max Iterations = 100
Linear System Iterative Method = BicgstabL
Linear System Convergence Tolerance = 1.0e-8
Linear System Symmetric = True
End

Solver 6
Exec Solver = Always
Equation = CircOutput
Procedure = "CircuitsAndDynamics" "CircuitsOutput"
Appendix 2 (4/9)

End

!VTU Format
Solver 7
Exec Solver = After Simulation! After Timestep
Equation = ResultOutput
Procedure = "ResultOutputSolve" "ResultOutputSolver"
Vtu Format = True
Output Directory = $ results1
Single Precision = True!Default = false
Save Geometry Ids = True
End

!Save scalars
Solver 8
Exec Solver = After Timestep
Output Directory = $ results1
Filename = scalars.dat
Procedure = "SaveData" "SaveScalars"
End

Solver 9
Equation = "Fourier"
Exec Solver = Before Saving
Procedure = "FourierLoss" "FourierLossSolver"
Target Variable = "A"

Fourier Start Cycles = Integer 1

Fourier Integrate Cycles = Integer 6
!k - number of harmonic components calculated, must be high enough to capture slotting
effect
Fourier Series Components = Integer 12

Frequency = Real 600.0

Fourier Loss Filename = File "Loss.dat"

Harmonic Loss Linear Exponent = Real 1.7 !b1
Harmonic Loss Quadratic Exponent = Real 2.0 !b2

Linear System Symmetric = True

Linear System Solver = "Iterative"
Linear System Residual Output = 100
Linear System Max Iterations = 5000
Linear System Iterative Method = GCR
Linear System Convergence Tolerance = 1.0e-4
End

!!!!!!EQUATIONS!!!!!!
Equation 1
 Appendix 2 (5/9)

Active Solvers(3) = 3 4 5
End

Equation 2
Active Solvers(4) = 3 4 5 9
End

!!!!!!INITIAL CONDITIONS, CIRCUIT MODEL!!!!!!

Initial Condition 1
Rotor Velo = Real $InitialSpeed
End

Initial Condition 2
Rotor Angle = Real $InitialAngle
End

!!!!!!BOUNDARY CONDITIONS!!!!!!
Boundary Condition 1
Name = "BC_outer"
Target Boundaries(1) = 2
A = Real 0
End

!Mortar
Boundary Condition 2
Name = "BC_rotation"
Target Boundaries(1) = 1
Discontinuous Boundary = Logical True
Mortar BC = Integer 4
Anti Rotational Projector = Logical True
Galerkin Projector = Logical True
End

!!!!!!BODY FORCES!!!!!!
!Rotation of the rotor

Body Force 1
Name = "Rotation"
Mesh Rotate 3 = Variable Rotor Angle
Real MATC "360*tx(0)/(2*pi)"
End

Body Force 2
Name = "Current_U1"
Current Density = Variable Time
Real MATC "J_stator*sin(w_elec*tx(0)+(2*pi)*0)"
End

Body Force 3
Appendix 2 (6/9)

Name = "Current_U2"
Current Density = Variable Time
Real MATC "-J_stator*sin(w_elec*tx(0)+(2*pi)*0)"
End

Body Force 4
Name = "Current_V1"
Current Density = Variable Time
Real MATC "J_stator*sin(w_elec*tx(0)+(2*pi)/3)"
End

Body Force 5
Name = "Current_V2"
Current Density = Variable Time
Real MATC "-J_stator*sin(w_elec*tx(0)+(2*pi)/3)"
End

Body Force 6
Name = "Current_W1"
Current Density = Variable Time
Real MATC "J_stator*sin(w_elec*tx(0)-(2*pi)/3)"
End

Body Force 7
Name = "Current_W2"
Current Density = Variable Time
Real MATC "-J_stator*sin(w_elec*tx(0)-(2*pi)/3)"
End

!!!!!!BODIES!!!!!!
Body 1
Name = "U1"
Target Bodies(1) = 5
Equation = 1
Material =1
Body Force =2
End

Body 2
Name = "U2"
Target Bodies(1) = 8
Equation = 1
Material =1
Body Force =3
End

Body 3
Name = "V1"
Target Bodies(1) = 9
 Appendix 2 (7/9)

Equation = 1
Material =1
Body Force =4
End

Body 4
Name = "V2"
Target Bodies(1) = 6
Equation = 1
Material =1
Body Force =5
End

Body 5
Name = "W1"
Target Bodies(1) = 7
Equation = 1
Material =1
Body Force =6
End

Body 6
Name = "W2"
Target Bodies(1) = 10
Equation = 1
Material =1
Body Force =7
End

Body 7
Name = "Stator"
Target Bodies(1) = 2
Equation = 2
Material = 2
End

Body 8
Name = "Rotor"
Target Bodies(1) = 12
Equation = 2
Material = 2
Body Force = 1
Torque Groups(1) = Integer 1
End

Body 9
Name = "Stator_air_gap"
Target Bodies(1) = 4
Equation = 1
Appendix 2 (8/9)

Material = 1
End

Body 10
Name = "Rotor_air_gap"
Target Bodies(1) = 11
Equation = 1
Material = 1
Body Force = 1
r outer = Real $ r_outer
r inner = Real $ r_inner
End

Body 11
Name = "Wedge"
Target Bodies(1) = 3
Equation = 1
Material = 3
End

Body 12
Name = "Shaft"
Target Bodies(1) = 1
Equation = 1
Material = 1
Body Force = 1
Torque Groups(1) = Integer 1
End

Include "cage_body30"

!!!!!!!Components!!!!!!
include "cage.definitions.30"

!!!!!!MATERIALS!!!!!!
Material 1
Name = "Air"
Relative Permeability = 1
Relative Permittivity = 1
Electric Conductivity = 0
End

Material 2
Name = "Iron"
Include el_steel_M400_50A
Relative Permittivity = Real 1

!C1
 Appendix 2 (9/9)

Harmonic Loss Linear Coefficient = Variable "Frequency"

Real
0.0 250.0
10000.0 250.0
End

!C2
Harmonic Loss Quadratic Coefficient = Variable "Frequency"
Real
0.0 0.8
10000.0 0.8
End
End

Material 3
Name= "Wedge"
Relative Permeability = 1
Relative Permittivity = 1
End

Material 4
Name = "Copper"
Relative Permeability = 1
Electric Conductivity = 59.59e6 ![S/m]
Relative Permittivity = 1
End
 Appendix 3 (1/1)

Appendix 3: Stator Drawing File