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Abstract—Forced induction uses otherwise wasted
exhaust gases to improve the volumetric efficiency of an
engine allowing for higher thermodynamic efficiency. As the
fuel economy and greenhouse gas emission standards are
projected to be much more stringent globally, the use of a
forced induction engine in passenger cars and light duty
trucks has become a new trend in automotive industry. The
aerodynamic matching of an exhaust driven turbocharger is
a compromise of transient response at low exhaust energy
levels and power targets on the high. The trend towards
highly boosted downsized engines results in larger
aerodynamic matches compromising responsiveness on the
low side, known as turbo lag. The electrification of forced
induction system (electric forced induction system (EFIS))
has emerged as a feasible solution and it also possesses
numerous benefits depending on its topologies. This paper
provides a comprehensive study on EFIS by investigating
system level topologies, performance, various types of high-
speed machines, power electronics, and control techniques.
The advantages and disadvantages of existing electric forced
induction system are summarized and the new challenges
and opportunities are also introduced.
Index Terms— electrically assisted turbocharger; forced
induction system; high-speed machine; hybrid electric
vehicles; turbocharger;
I. INTRODUCTION
The use of an internal combustion engine (ICE) using
liquid-transportation fuel will presumably continue to
hold a major role over the next few decades [1]. However,
there are still significant challenges of improving fuel
efficiency and reducing emissions considering the rapid
growth of environmental concerns. According to the most
recent research report from the U.S. Environmental
Protection Agency (EPA), transportation is the second
largest source (34%) of carbon dioxide (CO2) emission in
the U.S. followed by the electricity generation (40%). Out
of the transportation sector, light duty vehicles (passenger
cars and light duty trucks) are responsible for almost 60%
and medium and heavy duty vehicles take up 23% [2]. It
clearly indicates that the improvement of fuel economy
and the reduction of CO2 emission in road vehicles can
have a significant impact on the conservation of the
global environment.
Recently, the regulatory authorities around the world
have established unprecedentedly high fuel economy and
CO2 emission standards. For instance, the U.S. and
Canada are targeting 56.2 miles per gallon (mpg) by 2025,
which is 50% higher than that of 2015. The EU
introduced the 56.9 mpg target by 2020 as well as South
Korea. Japan has already exceeded its 2020 statutory
target as of 2013 and achieved 45.9 mpg, which is the
highest among other countries [3]. China, India, Mexico,
and Brazil also proposed or established new fuel
economy and greenhouse gas (GHG) emission standards.
Over the past few years, the automotive industry has
introduced a number of new technologies to meet these
new regulations such as integration of light-weight
material, idle stop and go, energy regenerative braking
systems, engine downsizing with a forced induction
system (FIS) and hybrid or battery electric vehicles [4-5].
Amongst these recent technologies, the engine
downsizing with a FIS is gaining popularity as a viable
solution. Compared to a conventional non-electric forced
induction system (NFIS), the newly introduced electric
forced induction system (EFIS) has several benefits
including
• improved transient response (reduced turbo lag),
• improved engine output power,
• energy regenerative capability,
• applicable to fuel cell vehicles.
This paper reviews NFIS and EFIS in terms of power
level, operating speed range, performance, types of high-
speed machines, topologies, mechanical and electrical
issues. It begins with the overview of the fundamental
NFIS and EFIS followed by the investigation and
comparison of various high-speed machines. As high-
speed electric machine technologies are becoming more
mature than ever, there are new techniques applicable to
EFIS that have not yet been discussed in the previous
EFIS research papers. This paper also introduces
challenges and opportunities in EFIS technology from
both electrical and mechanical engineering perspectives.
Overview of Electric Turbocharger and Supercharger
for Downsized Internal Combustion Engines
Woongkul Lee, Student Member, IEEE, Erik Schubert, Yingjie Li, Student Member, IEEE,
Silong Li, Student Member, IEEE, Dheeraj Bobba, Student Member, IEEE, and
Bulent Sarlioglu1, Senior Member, IEEE
Electrical and Computer Engineering
Wisconsin Electric Machines and Power Electronics Consortium (WEMPEC)
University of Wisconsin – Madison
Madison, WI, USA
1sarlioglu@wisc.edu
II. OVERVIEW OF NON-ELECTRIC AND ELECTRIC FORCED
INDUCTION SYSTEM
A. The Advantages of Air Pressure Boosting
The internal combustion engine indicated power can
be estimated by
Pengine = ρim ηv ηth ηcomb
mf
˙
ma
˙ Qfuel_LHV N
Ve
nR (1)
the air density is
ρim = pim
RspecificTa (2)
and the engine swept volume can be calculated by
Ve = n Ac L (3)
where
Pengine
engine indicated power,
𝜌im
air density in the intake manifold,
𝜂v
volumetric efficiency,
𝜂th
thermal efficiency
𝜂comb
combustion efficiency,
mf
˙
fuel mass flow rate,
ma
˙
air mass flow rate,
Qfuel_LHV
mass specific lower heating value of the fuel,
N
crankshaft rotational speed,
Ve
engine swept volume,
nR
number of crank revolution per power stroke,
N
number of cylinders,
Ac
cylinder area,
L
stroke length,
pim
intake manifold air pressure,
Rspecific
specific gas constant for dry air,
Ta
absolute air temperature.
In the past, FIS was mainly utilized in high-
performance gasoline engine or diesel engine vehicles for
the purpose of boosting the engine power in (1) by
compressing inlet air to increase air pressure and density
in (2). More recently, automotive manufacturers are
paying more attention to the use of FIS with a downsized
engine or a hybrid electric vehicle for improving the fuel
economy while reducing the GHG emission. In general,
the downsized ICE with a turbocharger performs more
efficiently with lower fuel consumption and emission [6-
8]. A turbocharger compresses the inlet air charge (which
increases air pressure and volumetric efficiency in (2)) by
deriving energy from the exhaust gas, which is otherwise
wasted. It helps to downsize ICE by reducing the cylinder
area, Ac and stroke length, L or the number of cylinders, n
in (3), while producing engine output power similar to
that of a higher displacement naturally aspirated (NA)
engine.
A typical family car engine with 2.0-liter displacement
volume has the peak engine torque of 220 Nm and brake
mean effective pressure (BMEP) value of 13.5 bar as
shown in Fig. 1. If the swept volume of this engine is
reduced by 40% (1.2-liter), the engine will deliver the
torque of 132 Nm at the similar BMEP of 13.5 bar. To
restore the initial torque of 220 Nm, the BMEP should be
increased by 70% (23 bar) using FIS [9].
Turbocharger market has been growing rapidly and
sales of turbocharged vehicles are expected to grow up to
47% by 2020 [10]. Ford Motor Company has been
investing in the development of Gasoline Turbocharged
Direct Injection (GTDI) engine technology with
Department of Energy (DOE) since 2010 [11]. The new
type of engine marketed as EcoBoost achieves 25% total
fuel economy improvement while satisfying the GHG
emission standard. General Motors has also been
developing a downsized engine with turbocharger called
ECOTEC since 2000 [12]. Nissan Motor unveiled a 3-
cylinder 1.2-liter engine with a supercharger, which can
deliver the output power equivalent to that of a 1.5-liter
engine [13]. Volkswagen released a 4-cylinder 1.4-liter
turbocharged engine to replace its conventional 4-
cylinder 2.0-liter naturally aspirated engine and improved
fuel economy by 13% [14].
B. Non-Electric Forced Induction System (NFIS)
In general, an NFIS can be classified into two types
depending on the energy source for driving a compressor:
an exhaust driven turbocharger and a crank driven
supercharger. A conventional single stage turbocharger
consists of a turbine and a compressor directly coupled
together through a shaft as shown in Fig. 2 (a). Since
exhaust gas from an ICE is the only energy source to
drive the turbine and the coupled compressor, this
topology suffers from the slow mechanical response and
low efficiency especially when the engine speed is low
[4]. Also, a wastegate valve must be employed to prevent
turbine over-speed, which results in a potential waste of
energy. To solve these issues, several different
approaches have been introduced such as multiple staged
turbochargers (regulated two-stage turbocharger in Fig. 2
(c)), twin charger (combination of a turbocharger and a
supercharger in Fig. 2 (d)), sequential turbocharger (in
Fig. 2 (e)), low inertia rotating components, variable
geometry turbine (VGT), active control turbocharger
(ACT), control of valve timings and fuel injection and
adopting external energy sources to enhance air supply
[5].
A supercharger is directly connected to a crankshaft of
an ICE with a belt or chain so that the engine becomes
the energy source for driving the compressor as shown in
Fig. 1. Torque restoration with turbocharging for downsized engine
(NA-naturally aspirated) [9].
Fig. 2 (b). Typically, the supercharger can be classified
into three different types depending on the methods of
gas transfer or compression: Roots, twin screw, and
centrifugal. Roots and twin screw superchargers are
positive displacement compressors and tend to have
better volumetric efficiency at lower speeds compared to
centrifugal compressors which rely on mass flow
acceleration. The advantages and disadvantages of NFIS
are summarized and compared in Table I.
C. Electric Forced Induction System (EFIS)
The electrification of NFIS can be realized in 5 different
topologies as shown in Fig. 3 (a), (b), (c), (d) and (e).
Since the main advantages of EFIS are to improve
transient performance and minimize the lagging effect,
there is no practical reason to electrify roots and twin
screw superchargers, which have relatively high boost
performance in low engine RPM as shown in Table I.
Nevertheless, the centrifugal supercharger can be
electrified and the topology is equivalent to the electric
compressor as illustrated in Fig. 3 (b). The characteristics,
advantages, and disadvantages are summarized in Table
II. In order to improve the transient response of the
conventional turbocharger using an electric machine, the
torque/inertia ratio (or angular acceleration,
) of EFIS
must be higher than that of the conventional NFIS as
shown in (4)
TEFIS_net
JEFIS > TNFIS_net
JNFIS (4)
where
TEFIS_net
EFIS net torque,
TNFIS_net
NFIS net torque,
JEFIS
EFIS total inertia,
JNFIS
NFIS total inertia.
TABLE I
THE COMPARISON OF NON-ELEC TRIC FORCED IND UCTION SYSTEM TOPOLOGIES
Single-stage
Turbocharger
Mechanical Supercharger
Regulated
Two-stage
Turbocharger
Twincharger
Parallel
Sequential
Turbocharger
Type
Centrifugal
Roots
Twin screw
Centrifugal
Centrifugal
Centrifugal
Centrifugal
Energy source
Exhaust gas
Engine
Exhaust gas
Exhaust gas /
Engine
Exhaust gas
Power boost with RPM
Non-linear
Linear
Linear
Non-linear
Linear
Linear
Linear
Response time
Slow (turbo lag)
Fast
Fast
Slow
Fast
Fast
Fast
Low RPM boost
Low
High
High
Low
High
High
High
High RPM boost
High
Low
Low
High
High
High
High
Internal compression
Yes
No
Yes
Yes
Yes
Yes
Yes
Efficiency
High
Low
Low
Low
High
Medium
High
Cost
Lowest
Low
High
Medium
High
High
High
Electrification
Fig. 3 (a), (b), (c)
N/A
N/A
Fig. 3 (b)
Fig. 3 (d), (e)
Fig. 3 (d), (e)
Fig. 3 (d), (e)
(a)
(b)
(c)
(d)
(e)
Fig. 2. Schematic layout of the non-electric forced induction system (NFIS) topologies (black line – air flow path with valve, blue line – engine inlet
air flow, red line – exhaust gas flow). (a) Single-stage turbocharger. (b) Mechanical supercharger. (c) Regulated two-stage turbocharger (d) Low-
pressure turbocharger with high-pressure mechanically driven supercharger with bypass (twincharger-Volkswagen). (e) Parallel sequential
turbocharging.
Minimizing the inertia of the overall system and
maximizing output torque are the challenges in EFIS and
5 different topologies are characterized based on this
equation.
1. Electrically assisted turbocharger (EAT)
The electrically assisted turbocharger (EAT) is shown
in Fig. 3 (a). A high-speed electric machine is
interconnected between the turbine and the compressor.
When the engine speed is low, the electric machine
functions as a motor providing additional torque to the
compressor generating higher boost pressure with a faster
transient response. When the engine speed is high, the
electric machine generates power, which can be
transmitted to energy storage. It can also prevent the
turbine to exceed its speed limitation. However, this
might also cause high backpressure effect to the ICE,
which can negate the energy recovered from exhaust gas
[15].
In this topology, the characteristics of the electric
machine are important especially inertia and output
torque since the electric motor is directly coupled with
the turbine and the compressor. The increased output
torque from the electric motor, TEM_EAT should exceed the
additional inertia of the electric motor, JEM to the system
[5] as below
TT_EAT + TEM_EAT – TC_EAT – TMech_load_EAT
JTC+EM >
TT_conv – TC_conv – TMech_load_conv
JTC_conv (5)
where
TT_EAT
EAT turbine output torque,
TEM_EAT
EAT electric machine output torque,
TC_EAT
EAT compressor load torque,
TMech_load_EAT
EAT mechanical load torque,
JTC+EM
turbine, compressor and electric
machine inertia,
TT_conv
conventional turbocharger turbine
output torque,
TC_ conv
conventional turbocharger compressor
load torque,
TMech_load_onv
conventional turbocharger mechanical
load torque,
JTC_conv
conventional turbocharger inertia.
Typically, the additional rotor inertia of the electric
machine should be limited from 1/3 to a maximum 1/2 of
the mass moment inertia of the turbocharger to efficiently
assist the turbocharger [16]. The angular acceleration of
the free electric machine should be an order of magnitude
larger than that of the baseline turbocharger to
significantly improve the transient response [16]. The
advantages of this topology are improved low RPM
boosting, electric machine rotor position self-sensing
capability [17], motoring and generating capabilities, and
the necessity of electric components with relatively low
power output which, in turn, means low cost.
The main challenge of this topology is to minimize the
high-temperature effect on the electric machine,
especially when the machine is placed inside the
turbocharger. Induction machines, switched reluctance
machines, or flux-switching permanent magnet machines
can be used for this topology since they are more
advantageous than surface permanent magnet machines
in terms of high-temperature operation and thermal
management. There are some other topological
approaches to mitigate this issue as well.
For instance, BMW utilized clutches to connect and
disconnect the electric machine to the shaft of the
(a)
(b)
(c)
(d)
(e)
Fig. 3. Schematic layout of electric forced induction system (EFIS) topologies (black line (thin) – power flow, black line (thick) – air flow path with
valve, blue line – engine inlet air flow, red line – exhaust gas flow). (a) Electrically assisted turbocharger (EAT). (b) Electric compressor (EC). (c)
Electrically split turbocharger (EST). (d) Turbocharger with an additional electrically driven compressor - upstream (TEDC). (e) Turbocharger with
an additional electrically driven compressor - downstream (TEDC).
turbocharger so that the machine can be placed outside of
the turbocharger [18]. G+L innotec introduced large
airgap permanent magnet machine, which can also be
placed outside of the turbocharger [19]. The inner
diameter of the stator is equivalent to the outer diameter
of the compressor and the outer diameter of the rotor is
equivalent to the output diameter of the shaft. The airgap
is also used as inlet air path so that it has multiple
benefits in cooling, low inertia, and less temperature
effect.
2. Electric compressor(EC)
The electric compressor (EC) is illustrated in Fig. 3 (b).
The energy for driving the compressor is solely provided
from electric energy storage so that it has more flexibility
in terms of control. In addition, the compressor can be
driven at its optimal operating point ensuring high
efficiency. The electric components are required to have
high power output compared to other topologies. This
topology does not have the capability of energy
generation itself but the regenerative braking system or
integrated starter generator (ISG) can be combined to
provide electrical energy to the energy storage [5]. The
torque/inertia ratio can be fulfilled if an electric machine
with high power density and low inertia is utilized as
shown below
TEM_EC – TC_EC – TMech_load_EC
JC+EM >
TT_conv – TC_conv – TMech_load_conv
JTC_conv (6)
where
TEM_EC
ET electric machine output torque,
TC_EC
ET compressor load torque,
TMech_load_EC
ET mechanical load torque,
JC+EM
compressor and electric machine inertia.
3. Electrically split turbocharger (EST)
The third topology is called electrically split
turbocharger (EST) as shown in Fig. 3 (c). In this
topology, the mechanical energy from exhaust gas is not
directly delivered to the compressor but converted to
electrical energy initially using a generator. The stored
energy is utilized to drive the compressor for boosting.
The advantages of this topology is the ability to drive the
compressor at a different speed than the turbine. The
other advantages of this topology are less temperature
effect due to the separation of the turbine and the
compressor and no additional inertia from the turbine and
the turbine shaft as shown below
TEM_EST – TC_EST – TMech_load_EST
JC+EM >
TT_conv – TC_conv – TMech_load_conv
JTC_conv (7)
where
TEM_EST
EST electric machine output torque,
TC_EST
EST compressor load torque,
TMech_load_EST
EST mechanical load torque,
JC+EM
compressor and electric machine inertia.
Splitting the turbine and the compressor is also beneficial
in terms of installation so that the airflow path can be
optimized. However, this topology requires high power
TABLE II
THE COMPARISON OF ELECTR IC FORCED INDUCTION SYSTEM TOPOLOGIES
Type
EAT
EC
EST
TEDC (up and downstream)
Energy source
Exhaust gas /
Energy storage
Energy storage
Exhaust gas /
Energy storage
Exhaust gas /
Energy storage
Motor / inverter rating
Low
High
High
Low
Temperature effect
High
Low
Low
Low
Size
Medium
Small
Large
Large
Electric turbo
compounding
Yes
No
Yes
No
Turbine and electrically-
driven compressor
coupling
Yes
No
No
No
Advantages
- Compact size
- Low rating motor
and inverter
- No wastegate valve
- Compact size
- No additional
inertia
- Control flexibility
- Installation
flexibility
- No backpressure
- No additional
inertia
- Control flexibility
- Installation
flexibility
- No wastegate valve
Upstream
Downstream
- Easy installation
- No additional
inertia
- Low power motor
and inverter
- Steady-state
performance
improvement
- Fastest transient
response
- Easy installation
- Low power motor
and inverter
- Steady-state
performance
improvement
Disadvantages
- Additional cooling
- Additional shaft
inertia
- Backpressure
(surge limit)
- High rating motor
and inverter
- Low system
efficiency
- Backpressure
(surge limit)
- High rating motor
and inverter
- Extra space
required
- Backpressure
(surge limit)
- Extra energy
conversion loss
- Not the fastest
transient response
- Extra space
required
- Low system
efficiency
- Extra space
required
- Low system
efficiency
electric motor, generator, and inverters to satisfy
torque/inertia ratio in (7), which will increase the overall
system cost.
4. Turbocharger with an additional electrically driven
compressor (TEDC) – upstream and downstream
The last topology is the turbocharger with an
additional electrically driven compressor (TEDC) as
shown in Fig. 3 (d) and (e). Depending on the location of
the electrically driven compressor, TEDC can be
classified into upstream and downstream TEDCs. In this
topology, the electric machine operates independently
from the exhaust gas driven turbine and the electrically
driven compressor is designed to increase air pressure at
low engine speed. Therefore, this topology significantly
improves the transient response when the engine speed is
low since the electric motor operation is not affected by
the inertia of the turbine nor the shaft. However, the
electric energy needs to be produced from an ISG
powered by the engine shaft or regenerative braking
system [5].
The main advantage of this topology is the fastest
transient response when the ICE speed is low [5]. In
general, downstream TEDC has a faster transient
response than upstream TEDC since the latter has a larger
volume to pressurize. The other advantage is that this
topology requires minimal modifications to the
conventional NFIS for the electrification.
III. PERFORMANCE EVALUATION OF ELECTRIC FORCED
INDUCTION SYSTEM
The improvements of transient response, steady-state
performance, and fuel efficiency are the prime
advantages of EFIS. Investigating these characteristics is
one way of evaluating the performance of EFIS in
comparison with the conventional NFIS. It is also
important to consider the characteristics of ICEs such as
fuel type (diesel or gasoline), size, number of cylinders,
fuel injection systems and engine control techniques.
In general, a diesel engine tends to burn leaner (high
air-to-fuel ratio,
) than its stoichiometric ratio (
diesel =
14.5), since it becomes more fuel-efficient and generates
higher power with fewer pollutants. Since compression-
ignition (CI) provides high combustion pressure, the
boost pressure from the FIS is relatively low. Therefore,
the FIS for a diesel engine is generally larger than the
counterpart of a gasoline engine to increase the intake
airflow.
On the other hand, gasoline engine generally operates
near or lower than its stoichiometric ratio (
gasoline =
14.7). Therefore, the high boost pressure is more
important than high intake air flow to improve the
efficiency and performance of the engine. Nevertheless,
the surge limit and detonation (pre-ignition) are potential
issues with the FIS for the gasoline engine. The general
characteristics of diesel and gasoline engines are
summarized in Table III.
The transient response analysis is a typical figure-of-
merit for assessing the performance of NFIS and EFIS,
which can be conducted by measuring and comparing
turbo lag. The definition of turbo lag is the amount of
time delay required to reach the commanded engine
output power or torque due to the insufficient exhaust gas
at low engine speed. For the conventional NFIS, it takes a
few seconds to accelerate the turbine and the compressor,
and the acceleration time from angular velocity 1 to 2
is given by
tacceleration = JTC
2
1
d
PT – PC – PMech_load (8)
where
JTC
turbocharger inertia,
angular velocity,
PT
turbocharger turbine power,
PC
turbocharger compressor power,
PMech_load
turbocharger mechanical load power,
tacceleration
acceleration time.
The acceleration time determines how fast the engine
intake manifold pressure can be built up and the shorter
acceleration time helps to minimize the turbo lag.
Typically, the transient response can be significantly
improved in EFIS, but it primarily depends on the amount
of electrical power available in the vehicle electrical
system and the electric machine. It also varies with the
topology of NFIS and EFIS.
The fast transient response and high low engine speed
torque are highly preferable in downsized ICEs [20], and
some recent development efforts of EFIS revealed the
superior performance of EFIS over the conventional
NFIS.
Extensive modeling and design validations were
conducted in [21-23] to quantify the temporary turbo
boost that can be obtained with EFIS. The time to boost,
defined as the time taken by the engine/turbo system to
reach desired boost level with reference to the steady
state torque at a given speed is studied and shown to be
reduced by up to 90% compared to NFIS [21]. Studies
comparing NFIS and EFIS by Mitsubishi Heavy
Industries showed that the e-assisted EFIS can improve
the transient response time by 33% as well as the steady
state torque by 17% at low engine speeds [22]. In [16],
the transient response of a baseline diesel engine is
improved by up to 26% using EAT. The comprehensive
comparison of transient responses with baseline
turbocharger, EAT, EST, and TEDC showed that TEDC
TABLE III
THE COMPARISON OF DIESEL AND GA SOLINE ENGINE S WITH
FORCED IND UCTION SYSTEMS
Diesel
Gasoline
Ignition
Compression
Spark
Engine speed [rpm]
2000 – 4000
3000 – 7000
Compression ratio
15 – 20
8 – 10
Exhaust gas
temperature [C]
400 – 600
500 – 800
Air-to-fuel ratio
20 – 60
12 – 13
Boost pressure [psi]
5 – 8
10 – 15
FIS Design
considerations
- High airflow
- Surge limit
- Back pressure
- High boost pressure
- Surge limit
- High temperature
- Detonation (knock)
has the fastest boost pressure build-up with 67% transient
response improvement [5]. EAT and EST feature the
similar transient improvement, which is about 20%. In
[23], the utilization of EAT in hybrid electric vehicle
(HEV) is simulated and it shows 4% reduction in
acceleration time compared with HEV with a
conventional turbocharger. Reducing the turbo lag with
EFIS does not improve the overall fuel economy
significantly in both ICE and HEV but the energy
regeneration with EAT can potentially provide fuel
saving in HEV [23]. The use of EFIS in HEVs can be
more advantageous since some of the HEVs are equipped
with the higher than the typical battery voltage of 12V.
The use of 24V or 48V battery can significantly reduce
the current rating of the electric motor, which improves
the overall efficiency of the motor and the motor drive
system.
IV. HIGH-SPEED ELECTRIC MACHINES
A high-speed electric machine technology simplifies a
machine drive system by eliminating essential
mechanical components required in a conventional
electro-mechanical drive system [24] and also reduces the
dimension of the machines [25]. Fewer mechanical
components improve the system reliability and the
reduction of size and weight is valued in numerous
applications such as aerospace, aircraft, and hybrid or
purely electric vehicles. In these applications, space is
limited and weight is highly related to the performance
and efficiency. The turbocharger/supercharger systems
benefit from having high-speed electric machines.
Nevertheless, designing and manufacturing of high-
speed machines are challenging and there are several
constraints that need to be carefully considered. In this
chapter, 4 different machine types that can be utilized in
the EFIS with the target output power from 0.5 kW to 30
kW and the minimum speed of 50 krpm are introduced.
Figure 4 shows high-speed machine types plotted
nominal power against speed. Permanent magnet,
switched reluctance, and induction machine are in the
target range and flux-switching machine, which is not
included in Fig. 4, will also be discussed. It needs to be
mentioned that the interior permanent magnet (IPM)
machine is not discussed in the high-speed electric
machine realm, because their mechanical integrity is not
high enough for very high speed conditions. The cavity
and bridges in the rotor laminations of an IPM machine
have tendencies to deform under high centrifugal forces
and mechanical stress. As a result, IPM machine is not
popular in high-speed machine application. The
characteristics, advantages, and disadvantages of
aforementioned four machines are compared and
summarized in Table IV. The machine types, ratings,
topologies and manufacturers of EFIS, which have been
reported in previous literature are summarized in Table V.
A. Induction Machine (IM)
The induction machine is one of the most mature
electric machine topologies, and it has been widely used
in the high-speed operation. The rotor of a high-speed
induction machine can be either laminated or solid
construction, depending on the operating speed. When the
tip speed is lower than a threshold speed, laminated rotor
is used which has the benefits of reduced eddy current
loss and improved efficiency compared to solid rotor
design [26]. The bar shape design in the rotor lamination
is critical to the rotor dynamic response, which influences
the performance of the turbocharger. For very high-speed
conditions, the rotor of an induction machine can be
designed as solid rotor instead of the caged rotor as
presented in [27]. One of the challenges is to design the
appropriate stator leakage reactance which influences the
peak torque and efficiency of the induction machine.
Design and analysis of induction machine are well
understood. However, due to the eddy current loss in the
rotor conductor, the induction machine has generally
lower efficiency than other electric machines especially
the PM machines. It should also be noted that the
manufacturing cost of the rotor for ultra-high-speed
induction machine is extremely expensive (possibly
higher than SPM and SRM). Induction machine is
generally considered to have lower torque ripple and less
vibration, which is good for turbocharger applications.
B. Surface Permanent Magnet Machine (SPM) /
Brushless DC Machine (BLDC)
The surface permanent magnet (SPM) and brushless
DC (BLDC) machines are good candidates for high-speed
operations. Both machines have permanent magnets
Fig. 4. High-speed machines nominal power vs. speed for different machine types (highlighted region – EFIS operating range) [24].
mounted on the surface of the rotor. The SPM machine
uses sinusoidal current excitation, while the BLDC
machine uses rectangular current excitation. Typically,
these two machines have high torque density and high
efficiency due the utilization of strong permanent
magnets. There are many turbocharger applications that
implement high-speed SPM and BLDC machines as
presented in [22], [28-31] due to the benefits of high
torque density, small size and weight.
One of the main challenges in the design process is the
thermal regulation of the machine, particularly for the
rotor part. This is because the permanent magnets
generate eddy current loss that increases the operating
temperature, which brings thermal demagnetization risks
to the permanent magnets. The other challenge is the
magnet containment issue at very high-speed conditions.
The permanent magnets are subject to large centrifugal
forces, and retaining sleeves are needed to protect the
magnets.
C. Switched Reluctance Machine (SRM)
The machines with passive rotor geometry, such as
switched reluctance machine (SRM), have an inherent
advantage for high speed operation due to their ability to
withstand higher centrifugal forces [32-34]. Due to the
absence of permanent magnets, the high temperature
operation capability and performance stability of SRM is
superior to PM machines. The SRM has inherent fault
tolerant capability because each of the phases can be
operated separately, this means that the machine can still
produce partial torque even if some of the phases are at
failure. There are a number of industrial
turbochargers/superchargers that implement SRM as
reported in [34-36].
The power electronic drives for SRM is different than
the conventional sinusoidal inverter. The performance of
SRM is sensitive to the variation of airgap length. Torque
ripple for SRM is usually very large, so the induced
vibration and noise are also much higher than induction
and PM machines at high-speed conditions. However, the
high torque ripple property of SRM may not be a
particular concern for turbocharger application due to its
high rotational speed which smooths out the ripple
torque. SRM machine has very good temperature
variation withstand capability because the absence of
permanent magnet materials, so it is suitable for high
temperature environment of the turbocharger application.
D. Flux-Switching Permanent Magnet Machine
(FSPM)
The flux-switching permanent magnet machine has
been developed rapidly over the past decades, and there
are many suitable applications including those for high-
speed operations. The FSPM machine has robust rotor as
that of the switched reluctance machine. The permanent
magnets are in the stator instead of in the rotor.
Therefore, permanent magnet containment issue does not
exist at high-speed condition. The cooling of the
permanent magnets is much easier since they are closer to
the cooling surface. Conventional sinusoidal inverter is
used for the FSPM machine, and the control is almost the
same as a SPM machine [37]. Conventional FSPM
machines are focused primarily on topologies with
number of poles equal or larger than 10 [38]. Novel low-
pole FSPM machine with only 4 rotor poles is recently
developed that is amenable for high-speed operation, due
to the notable reduction of high frequency losses such as
iron loss and magnet eddy current loss as shown in Fig. 5
[39-40].
The construction of FSPM machine is more
complicated than other electric machines due to the
highly segmented stator structure. Because of the doubly
salient structure, the torque ripple could be higher than
that of the SPM/BLDC machine. The efficiency of FSPM
machine can be higher than IM and SRM under high-
speed conditions. The FSPM machine is suitable for
turbocharger application in the aspects of high torque
density enabled by the permanent magnets in the
TABLE IV
THE COMPARISON OF ELECTR IC MACHINES FO R ELECTRIC FORCED INDUCTION SYSTEM
Type
Induction machine
Surface permanent magnet
machine / Brushless DC
machine
Switched reluctance
machine
Flux-switching
permanent magnet
machine
Machine design
Temperature effect
- Copper or aluminum loss
in rotor
- Hot shutdown issue
- Demagnetization
- Torque reduction
- High copper loss
- High core losses
- Hot shutdown issue
- Demagnetization
- Torque reduction
Advantages
- No permanent magnet
- Robust
- Inexpensive
- High power density
- High efficiency
- No permanent magnet
- Robust and simple rotor
structure
- Low rotor inertia
- Fault tolerance
- Robust and simple rotor
structure
- Easier magnet cooling
- Low rotor inertia
Disadvantages
- High rotor loss
- Rotor cooling required
- Lower power factor
- Lower efficiency
- Magnet retention
- High rotor inertia
- High magnet eddy
current loss
(if concentrated winding
is used)
- High inverter rating
- Control complexity
- High torque ripple
- High acoustic noise
- May require high
fundamental frequency
- Medium torque ripple
- Medium acoustic noise
machine, and high temperature withstand capability due
to easier dissipation of heat generated by the stator
windings and permanent magnets, which are directly in
contact with the cooling surface such as water jackets.
Fig. 5. Novel 6/4 flux-switching permanent magnet machine with dual
stator structure [39].
TABLE V
SUMMARY OF HIGH-SPEED MACHINES FOR ELECTRIC FORCED
INDUCTION SYSTEMS [19], [22], [28], [41-48]
Machine
Power
[kW]
Speed
[krpm]
Voltage
[V]
Topology
Manufacturer
IM
1.4
250
12
EAT
Honeywell
2.8
120
48
EAT
Honeywell
2.5
120
280
EAT
EcoMotor
SPM
2
140
12
EAT
MHI
2
140
12
EC
MHI
2
150
12
EAT
IHI
1.5
160
12
EAT
G+L innotec
2
280
12
EAT
EcoMotor
5
150
48
EAT
EcoMotor
15
150
300
EAT
EcoMotor
2
150
12
EST
Aeristech
14
150
48
EST
Aeristech
BLDC
-
-
24
EAT
Turbodyne
2.5
60
12
TEDC
BorgWarner
5
70
48
TEDC
BorgWarner
2
80
48
TEDC
MMT
7
-
12/24
EC
Duryea
SRM
2
70
12
TEDC
Valeo / CPT
7
70
48
TEDC
Valeo / CPT
V. CHALLENGES AND OPPORTUNITIES
A. Electrical Issues
The fundamental frequency of an electric machine
used in the electric turbocharger ranges from 1 to 8 kHz
depending on the rated speed and the number of the pole.
The fundamental frequency of surface permanent magnet
(SPM) or brushless DC (BLDC) motor can be estimated
from (9). In the case of the induction machine, the
fundamental frequency can be calculated from (10) and
that of the flux-switching permanent magnet (FSPM)
from (11) where n and s are the speed of motor and slip
respectively and P is a number of poles.
ffund =nP
120
(9)
ffund _ind =nP(1-s)
120
(10)
ffund _FSPM =nP
60
(11)
fratio = fsamp
ffund (12)
In (12), fswitch and ffund are the sampling frequency and the
fundamental frequency of an electric motor respectively.
fratio ³10.31
(13)
With a conventional PI controller, the minimum
frequency ratio, fratio is about 10.31 considering current
regulation performance, transient response and digital
execution time delay as shown in (13) [17], [49-50].
It indicates that the switching frequency of a motor
drive can exceed 20 kHz, which imposes various issues in
power switching devices and motor drives such as high
switching loss, heat dissipation, and electromagnetic
interference (EMI). The state-of-the-art power switching
devices such as gallium nitride (GaN) and silicon carbide
(SiC) can shed light on these issues due to their superior
device characteristics compared to conventional silicon
MOSFET or IGBT [51-54].
The use of position sensor is avoided in high-speed
SPM and BLDC machine drives since it tends to increase
the failure probability and an axial extension of the
machine [55]. Instead, self-sensing (sensorless) control
technique is widely used to detect a rotor position and it
is also applicable for an electrically assisted turbocharger
[17], [55]. In the case of IM and SRM, since there is
almost no back-EMF, a sensor feedback is required to
close the loop on speed. In addition, time delay
compensation control is essential in high-speed machine
operation especially when high switching frequency
PWM based full-digital current regulator is used [49],
[55]. When fratio is lower than 10.31, the minimum time
delay of one-and-a-half cycle from space-vector PWM
updated at each sampling point can have a critical impact
on the operating performance [49].
B. Mechanical Issues
1. Rotor mechanical stress
Rotor mechanical stress is a major design constraint for
the high-speed electric machines in EFIS. For SPM
machines, the stress is highest in the pre-stressed
constraining sleeve, which holds the magnets in place.
For IM, SRM, and FSPM machines, their rotors tend to
be more compliant than sleeved PM rotors and the base
of the rotor teeth has the maximum mechanical stress [56].
Therefore, the proper analysis should be done through
FEA or analytical methods to ensure the stress is
acceptable at maximum operating speed.
2. Bearings
Bearings are a fundamental mechanical component of
high-speed electric machines in EFIS. The choice of the
bearing can affect the mean time before failure of the
system as the bearings are often the first parts of the
system to wear out. Ball bearings rated for high-speed are
a common and practical choice for high-speed electric
machine design. The lifetime of ball bearings depends on
the lubrication and the load [57]. Other more advanced
bearings are oil film, airfoil/gas, and magnetic bearings.
These advanced types of bearings have very low
frictional losses when operating correctly. Magnetic
bearings have been used often in high-speed electric
machine research in recent years [58-60]. Magnetic
bearings offer the possibility of no friction losses except
for windage, but the magnetic control system must have
the correct gains and control strategy to avoid unwanted
vibration effects.
3. Temperature effect
Thermal issues are another important challenge for the
high-speed electric machines. In general, the size of an
electric machine operating at high-speed is smaller than a
low-speed electric machine with the same power rating
[57]. The small size has numerous benefits in EFIS, but it
also poses several thermal management issues. In general,
high-speed electric machines need to have lower losses
than low-speed machines with equivalent power ratings,
or alternatively, they should be equipped with a more
effective cooling system. High-speed electric machines
often run at temperatures near the critical temperatures
for some of the components [4]. High-speed permanent
magnet machines also have thermally sensitive parts
including permanent magnets and/or a carbon fiber rotor
sleeve.
In addition to the heat generation from losses of the
electric machines, a significant heat source is the hot
turbine of the turbocharger. Especially in EAT, the
electric machine is directly connected to the electric
machine via the shaft and typically placed between the
turbine and compressor. The electric machine can be
cooled by oil or water from the engine cooling system [4],
[61]. However, during hot shutdown of the engine, the
flow of coolant will cease and the temperature of the
electric machine can rise as the heat from the turbine is
gradually dissipated and partly transferred to the electric
machine. The electric machine and overall system should
be designed in such a way that the electric machine
components do not reach a critical temperature during hot
shutdown where the components could be damaged.
When the electric machines operate at very high
temperature, the characteristics and performance will
vary. The resistivity of conductors such as copper and
aluminum will increase with temperature. As a
consequence, the losses in the rotor-bars of IMs and the
stator winding are higher compared to low temperature.
The rotor-bars of IMs are usually made of aluminum
instead of copper for weight reduction. However, the
temperature coefficient of resistivity of aluminum is
higher than copper, which makes the high-temperature
loss more challenging. In addition, the rotor-bars of high-
speed IMs are usually buried in the rotor surface.
Therefore, the cooling of rotor-bars becomes challenging
as well.
The property of magnet materials changes significantly
during temperature variation. The remanence of magnet
materials decreases with increasing temperature [62-64].
Therefore, the torque production capability of both SPM
machines and FSPM machines decreases with increasing
temperature. Selection of the magnet material type is also
important. If the machine is designed to operate at very
high temperature, SmCo magnet is a better choice
compared to NdFeB magnet, since it not only has higher
Curie temperature, but is also less sensitive to
temperature variation.
As temperature increases, both the eddy current loss
and the hysteresis loss in the core materials will decrease,
which make the total core losses in all types of high-
speed electric machines lower at higher temperature [65-
69]. However, the saturation magnetization of electrical
steels typically slightly decreases with increasing
temperature, which means that the maximum flux density
in the core material will reduce with an increasing
temperature. As a result, the maximum output torque of
the machine at a constant current will slightly reduce.
Fortunately, this reduction is typically small in the
normal operating temperature range of electric machines
[65-66].
VI. CONCLUSIONS
This paper reviews non-electric and electric forced
induction system (NFIS and EFIS) with regard to
topologies, performance, electric machines. The existing
NFIS and EFIS topologies are analyzed and compared in
terms of their advantages and disadvantages. To better
understand the performance of each EFIS topology
compared to NFIS, transient response and steady-state
performance are investigated in detail. As the high-speed
machine technology improves, new types of machine
designs, inverter topologies, power devices, and control
techniques applicable for EFIS are introduced and studied.
In addition to the conventional high-speed machine
designs (IM, SPM, BLDC, and SRM), the newly
introduced FSPM machine is presented as a viable option
for EFIS application. The pros and cons of each machine
design are summarized and possible electrical and
mechanical issues are introduced.
ACKNOWLEDGEMENT
The authors wish to acknowledge the motivation
provided by Wisconsin Electric Machines and Power
Electronics Consortium (WEMPEC) of University of
Wisconsin - Madison.
REFERENCES
[1] S. Chu and A. Majumdar, “Opportunities and challenges
for a sustainable energy future,” nature, vol. 488, no.
7411, pp. 294–303, 2012.
[2] L. Hockstad and M. Weitz, “Inventory of U.S.
Greenhouse Gas Emission and Sinks,” U.S.
Environmental Protection Agency (EPA), Washington,
DC, Apr. 2015.
[3] Global PV standards chart library [Online]. Available:
http://www.theicct.org/global-pv-standards-chart-library
[4] J. R. Bumby, E. S. Spooner, J. Carter, H. Tennant, G.
Ganio Mego, G. Dellora, W. Gstrein, H. Sutter, and J.
Wagner, “Electrical machines for use in electrically
assisted turbochargers,” in Proc. IEEE Power Electron.,
Machines and Drives, 2004, pp. 344-349.
[5] G. Tavcar, F. Bizjan, and T. Katrasnik, “Methods for
improving transient response of diesel engines –
influences of different electrically assisted turbocharging
topologies,” in Trans. Journal of Automobile Engineering,
vol. 225, no. 9, pp. 1167-1185, Sep. 2011.
[6] A. Jain and C. Naegele, P. M. Lassus, and C. Onder
“Modeling and control of a hybrid electric vehicle with an
electrically assisted turbocharger,” in Trans. Vehicular
Technology, Feb. 2016.
[7] M. Karabektas, “The effects of turbocharger on the
performance and exhaust emissions of a diesel engine
fuelled with biodiesel,” in Trans. Renewable Energy, vol.
34, no. 4, pp. 989-993, Apr. 2009.
[8] N. Terdich, “Impact of electrically assisted turbocharging
on the transient response of an off-highway diesel
engine,” Ph.D. dissertation, Mechanical Engineering,
Imperial College London, London, U.K., 2014.
[9] D. Cieslar, “Control for transient response of
turbocharged engiens,” Ph.D. dissertation, Department of
Engineering, University of Cambridge, Cambridge, U.K.,
2013.
[10] Honeywell’s 2015 Turbocharger Forecast Signals
Increased Expectations of Turbo Technology as Global
Penetration Nears 50 Percent by 2020 [Online].
Available: https://turbo.honeywell.com/whats-new-in-
turbo/press-release/honeywells-2015-turbocharger-
forecast-signals-increased-expectations-of-turbo-
technology-as-global-penetration-nears-50-percent-by-
2020/
[11] C. E. Weaver, “Advanced gasoline turbocharged direct
injection (GTDI) engine development,” Department of
Energy (DOE) vehicle technologies program review, May
2011.
[12] New modular Ecotec engines are more adaptable effi
cient [Online] Available: http://media.gm.com/media/us
/en/gm/news.detail.html/content/Pages/news/us/en/2014/
mar/ecotec/english/0319-ecotec-overview.html
[13] Reducing is evolving: downsized engine combines lo
w fuel consumption & power [Online]. Available: htt
p://www.nissan-global.com/EN/TECHNOLOGY/MAGA
ZINE/downsizing.html
[14] The 1.4-liter solution for 2016 fuel economy [Online].
Available: http://articles.sae.org/7268/
[15] R. Dijkstra, M. Boot, R. Eichhorn, D. Smeulders, J.
Lennblad, and A. Serrarens, “Experimental analysis of
engine exhaust waste energy recovery using power
turbine technology for light duty application,” SAE Int. J.
Engines 5(4):1729-1739, 2012, doi:10.4271/2012-01-
1749.
[16] T. Katrašnik, F. Trenc, V. Medica, and S. Markič “An
analysis of turbocharged diesel engine dynamic response
improvement by electric assisting systems,” ASME. J.
Eng. Gas Turbines Power., vol. 127, no. 4, pp. 918-926,
Jul. 2004.
[17] S. Kim and J. Seok, “Comprehensive PM motor controller
design for electrically assisted turbo-charger systems,” in
Proc. IEEE Energy Convers. Congr. Expo., 2013, pp.
860-866.
[18] T. Kresse and S. Rubbert, “Loading device for internal-
combustion engine, has turbine shaft and compressor
shaft of electrical machine, which are propelled as driving
motor or generator operated electrical machine over
machine shaft,” DE Patent 102010011027 A1, Sep. 15,
2011.
[19] H. Gödeke, K. Prevedel, “Hybrid turbocharger with
innovative electric motor”, MTZ worldwide, 75(3), pp.
26-31, 2014.
[20] K. H. Bauer, C. Balis, G. Donkin, and P. Davies, “The
next generation of gasoline turbo technology,” 33rd
International Vienna Motor Symposium, Vienna, 2012.
[21] C. Balis, C. Middlemass, and S. M. Shahed, “Design and
development of E-turbo for SUV and light truck
applications,” Diesel Engine Emissions Reduction
Conference (DEER), Newport, RI, August, 2003.
[22] S. Ibaraki, Y. Yamashita, K. Sumida, H. Ogita, and Y.
Jinnai, “Development of the “hybrid turbo,” an
electrically assisted turbocharger,” Mitsubishi Heavy
Industries Technical Review, vol. 43, no. 3, Sep. 2006.
[23] A. Jain, T. Nuesch, C. Nagele, P. Lassus, and C. Onder,
“Modeling and Control of a Hybrid Electric Vehicle with
an Electrically Assisted Turbocharger,” IEEE Trans. Veh.
Technol., pp. 1–1, 2016.
[24] R. R. Moghaddam, “High speed operation of electrical
machines, a review on technology, benefits and
challenges,” in Proc. IEEE Energy Convers. Congr.
Expo., 2014, pp. 5539-5546.
[25] D. Han, Y. Li, and B. Sarlioglu, “Analysis of SiC based
power electronics inverters for high speed machines,” in
Proc. IEEE Appl. Power Electron. Conf. Expo., 2015, pp.
304-310.
[26] D. Gerada, A. Mebarki, N. Brown, K. Bradley, and C.
Gerada, “Design aspects of high-speed high-power-
density laminated-rotor induction machines,” IEEE Trans.
Ind. Electron. vol. 58, no. 9, September, 2011.
[27] J. R. Bumby, E. Spooner, and M. Jagiela, “Solid rotor
induction machines for use in electrically-assisted
turbochargers,” The 3rd IET International Conference on
Power Electronics, Machines and Drives, pp. 341-345,
2006.
[28] Y. Yamashita, S. Ibaraki, K. Sumida, M. Ebisu, B. An,
and H. Ogita, “Development of electric supercharger to
facilitate the downsizing of automobile engines,”
Mitsubishi Heavy Industries Technical Review, vol. 47,
no. 4, Dec. 2010.
[29] S. Tavernier and S. Equoy, “Design and characterization
of an E-booster driven by a high speed brushless DC
motor,” SAE International, January 2013.
[30] K. Shiraishi and V. Krishnam, “Electro-assist turbo for
marine turbocharged diesel engines,” Proceedings of
ASME Turbo Expo, Dusseldorf, Germany, June 16-20,
2014.
[31] T. Noguchi, Y. Takata, Y. Yamashita, and S. Ibaraki,
“160,000-r/min, 2.7-kW electric drive of supercharger for
automobiles,” International Conference on Power
Electronics and Drives Systems, pp. 1380-1385, 2005.
[32] T. Fukao, A. Chiba, and M. Matsui, “Test results on a
super-high-speed amorphous-iron reluctance motor,”
IEEE Transactions on Industry Applications, vol. 25, no.
1, pp. 119–125, Jan 1989.
[33] M. Besharati, K. R. Pullen, J. D. Widmer, G. Atkinson,
and V. Pickert, “Investigation of the mechanical
constraints on the design of a super- high-speed switched
reluctance motor for automotive traction,” in Power
Electronics, Machines and Drives (PEMD 2014), 7th IET
International Conference, April 2014, pp. 1–6.
[34] J. Kunz, S. Cheng, Y. Duan, J. R. Mayor, R. Harley, and
T. Habetler, “Design of a 750,000 rpm switched
reluctance motor for micro machining,” in Energy
Conversion Congress and Exposition (ECCE), 2010
IEEE, Sept 2010, pp. 3986–3992.
[35] N. Chayopitak, R. Pupadubsin, S. Karukanan, and P.
Champa, “Design of a 1.5 kW high speed switched
reluctance motor for electric supercharger with optimal
performance assessment,” 15th International Conference
on Electrical Machines and Systems (ICEMS), pp. 1-5,
2012.
[36] M. Michon, S. D. Calverley, and K. Atallah, “Operating
strategies of switched reluctance machines for exhaust gas
energy recovery systems,” IEEE Trans. Ind. Appl. vol. 48,
no. 5, September/October, 2012.
[37] A. S. Thomas, Z. Q. Zhu, and G. W. Jewell, “Comparison
of flux switching and surface mounted permanent magnet
generators for high-speed applications,” IET Electrical
Systems in Transportation, vol. 1, no. 3, pp. 111-116,
2011.
[38] Z. Zhu and J. Chen, "Advanced flux-switching permanent
magnet brushless machines," IEEE Trans. Magn., vol. 46,
no. 6, pp. 1447-1453, 2010.
[39] Y. Li, D. Bobba, and B. Sarlioglu, “A novel 6/4 flux-
switching permanent magnet machine designed for high-
speed operations,” IEEE Trans. Magn. vol. 52, no. 8,
August, 2016.
[40] D. Bobba, Y. Li, and B. Sarlioglu, “Harmonic analysis of
low stator slot and rotor pole combination FSPM machine
topology for high speed,” IEEE Trans. Magn., vol. 51, no.
11, 2015.
[41] W. E. Woollenweber and E. M. Halimi, “Motor-generator
assisted turbocharging systems for use with internal
combustion engines and control method therefor,” U.S.
Patent 5906098 A, May 25, 1999.
[42] S. Arnold, C. Balis, P. Barthelet, E. Poix, T. Samad, G.
Hampson, and S. M. Shahed, “Garrett electric boosting
systems (EBS) program federal grant DE-FC05-
00OR22809,” Honeywell Turbo Technologies, Jun. 22,
2005.
[43] P. Hofbauer, “Method of controlling an electrically
assisted turbocharger,” U.S. Patent 20110022289 A1, Jan.
27, 2011.
[44] M. Shimizu, “Turbocharger with electric motor,” U.S.
Patent 8 882 478 B2, Nov. 11, 2014.
[45] N. gill, “Driving clean technology,” Cleantech Forum
Europe, Apr. 2012.
[46] H. Breitbach, D. Metz, S. Weiske, and G. Spinner,
“Application and design of the eBooster from
BorgWarner,” BorgWarner Knowledge Library, 2015.
[47] S. Biwersi, S. Taverier, and S. Equoy, “Electric
compressor with high-speed brushless DC motor,” MTZ
worldwide, 73, pp. 50-53, 2012.
[48] P. Menegazzi, Y. Wu, and V. Thomas, “Design of an
electric supercharger for downsized engines,” MTZ
worldwide, 74, pp. 36-41, 2013.
[49] B. Bae and S. Sul, “A compensation method for time
delay of full-digital synchronous frame current regulator
of PWM AC drives,” IEEE Trans. Ind. Applicat., vol. 39,
no. 3, pp. 802-810, May-June 2003.
[50] J. Yim, S. Sul, B. Bae, N. R. Patel, and S. Hiti, “Modified
current control schemes for high-performance permanent-
magnet AC drives with low sampling to operating
frequency ratio,” IEEE Trans. Ind. Applicat., vol. 45, no.
2, pp. 763-771, March-April 2009.
[51] A. Tuysuz, R. Bosshard, and J. W. Kolar, “Performance
comparison of a GaN GIT and a Si IGBT for high-speed
drive applications,” in Proc. IEEE Power Electron. Conf.,
2014, pp. 1904-1911.
[52] A. F. Pinkos and Y. Guo, “Automotive design challenges
for wide-band-gap devices used in high temperature
capable, scalable power vehicle electronics,” in Proc.
IEEE Energytech, 2013, pp. 1-5.
[53] W. Lee, D. Han, and B. Sarlioglu, “GaN-based single
phase brushless dc motor drive for high-speed
applications,” in Proc. IEEE Annu. Conf. Ind. Electron.
Soc., 2014, pp. 1499-1505.
[54] D. Lusignani, D. Barater, G. Franceschini, G. Buticchi,
M. Galea, and C. Gerada, “A high-speed electric drive for
the more electric engine,” in Proc. IEEE Energy Convers.
Congr. Expo., 2015, pp. 4004-4011.
[55] J. Kim, I, Jeong, K. Nam, J. Yang, and T. Hwang,
“Sensorless control of PMSM in a high-speed region
considering iron loss,” IEEE Trans. Ind. Electron., vol.
62, no. 10, pp. 6151–6159, Oct. 2015.
[56] E. Sulaiman, T. Kosaka, and N. Matsui, “Parameter
optimization study and performance analysis of 6S-8P
permanent magnet flux switching machine with field
excitation for high speed hybrid electric vehicles,” in
European Conf. on Power Electron. and Appl., 2011.
[57] S. Li, Y. Li, W. Choi, and B. Sarlioglu, “High-Speed
Electric Machines: Challenges and Design
Considerations,” IEEE Trans. Transportation
Electrification, vol. 2, no. 1, pp. 2–13, Mar. 2016.
[58] Z. Guan, F. Zhang, and J. W. Ahn, “High speed direct
current compensation control for 8/10 bearingless SRM,”
in IEEE Int. Symposium on Industrial Electronics, 2012,
pp. 1934–1939.
[59] C. Wildmann, T. Nussbaumer, and J. W. Kolar, “10
Mrpm spinning ball motor: Preparing the next generation
of ultra-high speed drive systems,” in Int. Power
Electronics Conf., 2010, pp. 278–283.
[60] K. V. Rodrigues, J. F. Pradurat, N. Barras, and E. Thibaut,
“Design of high-speed induction motors and associate
inverter for direct drive of centrifugal machines,” in
Electrical Machines, Int. Conf. on, 2008.
[61] W. Hippen, F. Laimboeck, and T. Garrard, “Cooling an
electrically controlled turbocharger,” U.S. Patent 7 946
118 B2, May 24, 2011.
[62] T. Sebastian, “Temperature effects on torque production
and efficiency of PM motors using NdFeB magnets,”
IEEE Trans. Ind. Appl., vol. 3, no. 2, pp. 353–357, 1995.
[63] Available_online, “The effect of temperature variation
s on the magnetic performance of permanent magnets
,” MMG Canada Ltd. http://www.mmgca.com/apps/M
MG-magtempvar.pdf.
[64] K. Bertsche, J.-F. Ostiguy, and W. B. Foster,
“Temperature considerations in the design of a permanent
magnet storage ring,” in Proc. Particle Accelerator Conf.,
1995, vol. 2, pp. 1381–1383.
[65] I. Bogdanov, S. Kozub, P. Shcherbakov, L. Tkachenko, E.
Fischer, F. Klos, G. Moritz, and C. Muehle, “Study of
electrical steel magnetic properties for fast cycling
magnets of SIS100 and SIS300 rings,” in Proc. of EPAC,
2004, pp. 1741–1743.
[66] M. Morishita, N. Takahashi, D. Miyagi, and M. Nakano,
“Examination of magnetic properties of several magnetic
materials at high temperature,” Prz. Elektrotechniczny
(Electrical Rev., vol. 87, no. 9, pp. 106–110, 2011.
[67] A. Krings, S. A. Mousavi, O. Wallmark, and J. Soulard,
“Temperature influence of NiFe steel laminations on the
characteristics of small slotless permanent magnet
machines,” IEEE Trans. Magn., vol. 49, no. 7, pp. 4064–
4067, Jul. 2013.
[68] M. Nakaoka, A. Fukuma, H. Nakaya, D. Miyagi, M.
Nakano, and N. Takahashi, “Examination of temperature
characteristics of magnetic properties using a single sheet
tester,” IEEJ Trans. Fundam. Mater., vol. 125, no. 1, pp.
63–68, 2005.
[69] N. Takahashi, M. Morishita, D. Miyagi, and M. Nakano,
“Examination of magnetic properties of magnetic
materials at high temperature using a ring specimen,”
IEEE Trans. Magn., vol. 47, no. 10, pp. 4352–4355, Oct.
2011.
