Comparison of Two FSCW PM Machines for
Integrated Traction Motor/Generator
Gurakuq Dajaku, Sachar Spas, Xhevat Dajaku, and Dieter Gerling, IEEE
s
concentrated windings offers the advantage of short and
less complex end-winding, high slot filling factor, low
cogging torque, greater fault tolerance, and low
manufacturing costs [1, 2]. Further, FSCW offers also
different possible combinations of numbers of rotor poles
and stator slots [3]. Thus, depending on the slot/pole
combination, there exist several winding topologies with
high winding factor for the fundamental wave (up to 97%),
that is a necessary and a desired parameter for high torque
capability machines. On the other side, FSCW are
characterized with high space harmonic contents in their
magneto motive force (MMF) distribution. Except the
fundamental harmonic which is responsible for machine
torque and effective power, the rest of sub- and high MMF
winding harmonics induce negative effect on the machine
such as, significant rotor losses (rotor core and permanent
magnets) [4-6], rotor heating, noise and vibrations problems
[7-9], and so on. Therefore, as results of space MMF
harmonic problems, the all manufacturer until now are
Abstract- This paper presents a comparative study of two
different FSCW PM machines for application as integrated
motor-generator in hybrid vehicles. The first machine design
contains the conventional concentrated winding with q=0.5
that is recently used in many hybrid systems for commercial
vehicles, whereas the second machine use the new 18-teeth/10poles concentrated winding with the optimized magneto
motive force. Design and analysis of considered machines is
based on their performances which included evaluation of
electromagnetic torque and torque ripples, Ohmic losses,
magnet losses, field weakening capability, noise analysis, and
temperature behaviour. Using 2D and 3D finite elements the
both machine types are investigated and compared under the
same geometrical and electromagnetic constrains. Considering
the main electromagnetic and thermal aspects, the new
machine show high power capability and efficiency, low
torque ripple, low magnet losses, noiseless design, and
thermally robust.
Index Terms-- Concentrated winding, permanent magnet
machines, MMF harmonics, magnet losses, optimization.
I
I. INTRODUCTION
N THE last time, many automobile manufacturer and
also some automotive suppliers have developed different
hybrid systems based on integrated motor/generator
principle, where depending on the application and the mode
of operation, calling them as Integrated Starter Generator
(ISG), Integrated Motor Assist (IMA), or Integrated Motor
Generator (IMG). Fig. 1 show different actual traction
machines provided from different manufactures that already
exists in the marked. In hybrid electric vehicle (HEV)
applications they perform several important functions, such
as, start-stop, recuperation, power boosting, and power
generation. In order to save space, the electric machine is
integrated into the drivetrain between clutch and
transmission. Usually it is a short axis, large diameter
permanent magnet (PM) synchronous motor with fractional
slots concentrated winding (FSCW). The use of
G. Dajaku is Senior Scientist with FEAAM GmbH, Germany (e-mail:
gurakuq.dajaku@unibw.de).
S. Spas is with FEAAM GmbH (e-mail: sachar.spas@unibw.de).
Xh. Dajaku is with Universitaet der Bundeswehr Muenchen, Institute
for Electrical Drives, Germany (e-mail: xhevat.dajaku@unibw.de).
D. Gerling is Full Professor at the Universitaet der Bundeswehr
Muenchen, Institute for Electrical Drives, Germany (e-mail:
dieter.gerling@unibw.de).
978-1-4799-7940-0/15/$31.00 ©2015 IEEE
a)
b)
c)
d)
Fig.1. Different FSCW traction PM machine [21, 22], a). Integrated Motor
Generator (IMG) from Bosch, b). DynaStart from ZF-Sachs, c)Integrated
Motor Assist (IMA) from Honda, d). PM generator from Toyota Prius
2010.
187
using the conventional 3-teeth/2-poles concentrated
winding with q=0.5 for their PM traction machines. This
assumption can be confirmed also from the different
machines types presented in Fig. 1. All these machines are
designed with the same 3-teeth/2-poles FSCW, while the
main difference exists only on the number of pole pairs, as
well as, on the rotor topology and design.
The MMF analysis presented in [4] show low winding
factor (about 86%) for the conventional 3-teeth/2-poles
winding compared with the others FSCWs (up to 97%). On
the other side, it is the single winding type that operates
with the first MMF harmonics, while the rest use the high
harmonics as operating wave. Thus, referred to the
fundamental wave, the conventional winding has only high
harmonics in the MMF spectrum, while the others FSCW
includes the both sub- and high harmonics. Concerning the
rotor losses and also the noise problems, many
investigations show that, the amount of sub- and high
harmonics contents, and also their location with respect to
fundamental wave are the main responsible factors for the
machine performances [2 to 9]. It is important to point out
that, for low rotor losses and noiseless machines it is
required to have a stator windings with low harmonic
contents, none sub harmonics, and also with high
harmonics located far away from the working wave. Thus,
considering all these conditions, the conventional 3-teeth/2poles winding overcomes the rest of the FSCW, and at the
moment it is the only one winding type that until now is
being used for different traction PM machines.
The actual traction machines with the conventional
winding even already are in application in different hybrid
systems, they still to have several problems concerning the
rotor losses and rotor heating, especially in the high power
and high speed region. Fig. 2 illustrates the torque-speed
requirements for a standard traction machine, and also the
area related with existing problems in the conventional
designs. Thus, to overcome the existing problems, this
paper propose a new integrated motor/generator design as
an alternative solution. The new PM machine use an
optimized 18-teeth/10-poles FSCW which is characterized
with low winding factor for the fundamental wave,
however, also with low harmonic contents compared with
the conventional 3-teeth/2-poles winding. The main
motivation of this work was to show the opportunity and
potentials of the new winding for traction PM machines as
integrated motor/generator. Thus, during the following
analysis two machine types with the conventional and also
the new winding are designed and investigated under the
same electromagnetic and geometrical constrains. From the
analysis and comparison of the electromagnetic and thermal
results, valuable and positive conclusions are obtained,
which wake up the interests to consider the new winding
type as an alternative solution for the actual problems on
the conventional designs!
II. CONSIDERED CONCENTRATED WINDING TYPES
A. Conventional 3-teeth/2-poles Winding
Fig. 3a) illustrate the winding layout for the
conventional 3-teeth/2-poles concentrated winding, where
each phase comprises one coil, and with “+A+B+C” coil
(phase) sequence. For high poles machine, the standard
phase sequence is repeated p-time. In many literatures this
winding type is called often also as FSCW with q=0.5 (with
q is the number of coils/phase/pole). For the “+A+B+C”
basic winding version, the MMF distribution and also its
space harmonics are given in Fig. 3b), however eq. (1)
describe the MMF using the Fourier series function.
∞
2N w ⋅ ˆi ν
Θ 3T / 2P (φS , t) = ∑
ξ w ⋅ cos ( ωt − νφS )
πν
ν =1,2,4,5,...
(1)
⎛ π⎞
ν
ξ w , = sin ⎜ ν ⎟
⎝ 3⎠
In the above eq.(1), ν ξ w is the winding factor, i the phase
current, ω the angular frequency, Nw the number of turns
per phase, and ν the MMF harmonic order.
From the Fig. 3b), the conventional winding contains all
harmonic order except the multiple of 3rd, e.g. the 1st, 2nd,
4th, 5th, and so on. For the PM machines, usually the first
harmonic is used as working wave (torque component),
whereas the rest of all high space harmonics induce
parasitic effects in the machine, such as torque ripple,
losses, noises, and thermal problems.
Torque [Nm]
required torque
B. New 18-teeth/10-poles Winding
Several new techniques and methods are developed in
the past to improve the MMF winding characteristics, or to
reduce their effects on the machine parameters. These
techniques are based, either on the winding design such as
using,
1. multi-layer FSCW [10, 11],
2. coils with different turns per coil side [12],
delivered torque
Area characterized with high rotor
losses and temperature problems
nb
nmax
Fig. 2. Requirements for torque-speed. and regions characterized with
high rotor losses and temperature problems in the actual PM traction
machine.
188
a)
MMF [ p.u. ]
MMF [ p.u. ]
a)
1
0
-1
0
1
2
3
4
theta [rad. degree]
b)
5
6
-1
1
2
3
4
theta [rad. degree]
5
6
1
MMF [ p.u. ]
MMF [ p.u. ]
0
0
b)
1
0.5
0
0
1
0.5
0
0
2
4
6
8
10
harmonic order
Fig. 3. a). Conventional 3-teeth/2-poles FSCW, b). MMF-characteristics.
5
10
15
20
harmonic order
Fig. 4. a). New 18-teeth/10-poles FSCW, b). MMF-characteristics.
combination, the resulting (total) MMF winding
distribution can be calculated from the sum of the
corresponding MMFs for the first and the second winding
system, as is described in eqs. (2) to (4).
3. stator shifting concept [13-15], or
4. dual multiphase FSCW [16],
or, on the modification of the stator core structure by
applying
(2)
Θ18T /10P (φS , t) = Θ1 (φS , t) + Θ 2 (φS , t)
m 2N w1 ⋅ ˆi ν
⋅ ξ w1 ⋅ cos ( ωt − νφS + δ1 ) (3)
Θ1 (φS , t) = ∑ ⋅
πν
ν 2
m 2N ⋅ ˆi
Θ2 (φS ,t) = ∑ ⋅ w2 ⋅ ν ξw2 ⋅ cos ( ωt −ν( φS +αw ) +δ2 ) (4)
πν
ν 2
1. magnetic flux-barriers in stator yoke [17], or
2. magnetic flux-barriers in teeth locations [18].
Fig. 4a) illustrate the winding layout for the new
18-teeth/10-poles concentrated winding that is developed
according to the dual multiphase FSCW concept [16]. It
consists of two different winding systems which are
integrated in the same stator core and are shifted in space
and time to each other. The winding layout for the first
winding system is similar with the 12-teeth/10-poles
single-layer winding (yellow winding), whereas for the
second system, it is similar with the 12-teeth/10-poles
double-layer winding (index 1 and 2 denotes the first and
the second winding system, respectively). Further,
concerning the machine supply, it offers several options for
connecting the phase windings to the power source device.
The six-phase windings can be fed by a six-phase inverter,
or alternatively, using the star&delta winding combination
it can be supplied also with a three-phase conventional
inverter.
The MMF distribution and the corresponding space
harmonics for the new winding type are presented in Fig.
4b), that shows high quality MMF distribution and also low
harmonic contents. According to the dual winding
with the corresponding winding factors,
⎛ π⎞
⎛ 7 ⎞
⎛ 1 ⎞
ν
ξw1 = sin ⎜ ν ⎟ , ν ξw2 = cos ⎜ ν π ⎟ ⋅ sin ⎜ ν π ⎟
18
18
⎝
⎠
⎝
⎠
⎝ 18 ⎠
(5)
In the above equation. (3) to (4), with α w is denoted the
mechanical shift angle between the two winding systems,
and Nw1, Nw2 are the number of turns per phase for the first
and the second winding, respectively.
C. Comparison of MMF Characterisitcs
In following, the MMF characteristics for the both
winding types are analyzed for the five pole-pairs machine
case (same operating wave condition).
For the
conventional winding, to achieve the corresponding number
of poles, the basic winding layout shown in Fig. 3a) is
repeated five-time in the circumferential direction. Thus,
189
for the five-poles condition, the conventional and the new
winding are called as 5*(3T/2P) and 18T/10P, respectively.
The following Fig. 5 and also Table-1 compares the
respective results for the MMF distribution, space
harmonics, and the winding factors. From these results it
can be concluded here that, with the new winding, the
harmonic contents is reduced for the factor two, and also
the existing high harmonics are locate far away from the
fundamental wave compared with the conventional design.
As well discussed earlier, these two specifics are very
important for rotor loss and also noise problems reduction.
On the other side, the winding factor for the fundamental
wave is for about 12% lower. Since, by the electric
machines the lower winding factor is directly related with
the Ohmic losses, at the first point of view, the new
winding design shows to represent drawbacks concerning
the winding losses. But, as will be shown from this
analysis, considering only the winding factor parameter
isn’t always the right way for selection or rejection any
FSCW for a specific application. However, depending on
the requirements and also on the operation conditions of the
machine, for a proper decision, the all machine parameters
should be considered and analyzed carefully, such as the
winding factor (Ohmic losses), rotor losses, thermal and
also the noise aspect. Thus, the main motivation of this
work was to investigate in details the main performances of
the new FSCW considering the all aspects mentioned
above, and to show its chances and potentials for traction
PM machine applications.
III. TRACTION MACHINE DESIGNS
Two different PM machines for application as an
integrated motor/generator are designed and their main
performances are investigated and compared. For the first
design, the conventional 3-teeth/2-poles winding shown in
Fig. 3a) is used, while for the second machine, the new 18teeth/10-poles winding presented in Fig. 4b) is considered.
The requirements for the electric motor concerning to the
machine geometry data, materials, as well as, the maximum
power and speed, continuous power, and the battery DC
voltage, are summarized in Table II. For a proper
comparison, the both machines are designed and
investigated under the same electrical and geometrical
constrains (voltage, current and volume). Further, the same
materials for the machine components, same rotor
dimensions, and also the same magnet volume is selected
for the both machines; The main difference is only on the
stator core geometry and in the winding type. Additionally,
since the studied machines have different winding types,
the number of turns per phase for the both winding
configuration is defined under the condition that the both
machines should generate the same torque for the same
excitation load current.
Fig. 6 shows the geometries of the investigated
machines. Two dimensional (2D) and three-dimensional
(3D) finite elements (FE) tools are used to determine the
main machine parameters and performances. The
simulation results presented in following are performed for
250Arms maximal load current. For simplicity, the 20-poles
conventional and the new machines are called as 30T/20P
and 36T/20P, respectively.
MMF [ p.u. ]
5*(3T/2P)
1
0
-1
0
1
MMF [ p.u. ]
a)
2
3
4
theta [rad. degree]
5
2
3
4
theta [rad. degree]
5
6
18T/10P
1
0
-1
0
1
6
5*(3T/2P)
18T/10P
MMF [ p.u. ]
1
0.8
TABLE II: MAIN ELECTROMECHANICAL AND GEOMETRY DATA
Active length
63 mm
Outer stator diameter
300 mm
Outer rotor diameter
240 mm
Gap length
1 mm
Number of rotor poles
20
Fig. 5: MMF distribution and the corresponding MMF spectrum for the
conventional and the new winding topology.
Iron Core material
STEEL 330-35AP
Magnet material
VACODYM 854 AP
TABLE-I: Winding factors
Maximal Torque
270 Nm
b)
0.6
0.4
0.2
0
0
5
10
15
Harmonic Order
20
ν
ξw
5th
10th
13th
20th
Maximal current
250A
ν
ξw ,3T / 2P
86.6%
86.6%
0%
86.6%
Maximal speed
6000 rpm
ν
ξ w ,18T /10P
76%
0%
76%
0%
DC Voltage
300V
190
IV. COMPARISON OF RESULTS
320
A. Electromagnetic Torque
a)
T [Nm]
240
The torque results vs. rotor position presented in Fig.
7a) shows high torque ripples for the conventional design
(16%). Thus, for reducing the torque ripples under the 5%
limit, the first machine design need to be skewed, that
increase the manufacturing costs of the machine, and also
reduce the effective torque. In contrast, due to low torque
ripples for the proposed 36T/20P design, none skewing is
required. Furthermore, the new machine overcomes the
conventional design also on the field weakening region,
Fig. 7b). As results of low MMF harmonic contents, the
harmonic inductance amount for the new winding is lower
compared with the conventional winding, and according to
analysis performed in [20], this leads to field weakening
improvement for the 36T/20P machine.
Conv. 30T/20P
New 36T/20P
160
80
0
0
60
120
180
240
300
rotor position [ el. degree ]
300
Conv. 30T/20P
New 36T/20P
250
B. Magnet Losses
200
T [Nm]
b)
360
150
100
The high harmonics in the air-gap MMF distribution
rotate at different speeds to that of the rotor magnets and
induce significant eddy currents in the magnets. To take
into account the correct path of the eddy currents in the
magnet regions, the loss calculations is performed using 3D
FE analysis. Fig. 8 compares the losses distribution for one
operation point (maximal rotor speed), while Fig. 9 shows
the magnet losses vs. rotor speed for the maximal load
current and non-segmented magnets. From the both results
it can be concluded that, with the new motor design the
magnet losses are reduced significantly compared with the
reference machine (factor ten). Thus, none magnet
segmentation is required for the new machine. On the other
side, for the 30T/20P machine, the magnet segmentation
with very short magnet pieces (5mm) is required to reduce
the magnet losses at the same level with the proposed
design, Fig. 10.
50
0
0
2000
4000
6000
8000
speed [rpm]
Fig. 7: a).Electromagnetic torque vs. rotor position, b). Field weakening
capability.
30T/20P Design
[W/m³]
3.81e+8
36T/20P Design
a)
4.30e+3
b)
Fig. 6: Investigated PM machines, a). Conventional 30-teeth/20-poles
design (30T/20P), b). New 36-teeth/20-poles design (36T/20P).
Fig. 8: Magnet loss distribution for 250Arms and 6000rpm.
191
10
30T/20P Design
Magnet losses [kW]
Conv. 30T/20P
8
36T/20P Design
New 36T/20P
6
4
2
0
0
2000
4000
6000
8000
speed [rpm]
Fig. 9: Magnet losses vs. rotor speed for non-segmented magnets.
Fig. 11: Geometrical coil shape approach.
TABLE-III: Winding resistances and Joule losses for 250Arms current
Machine type
30-teeth/20-poles
Phase resistance
RWinding = 11,8mΩ
Joule losses
36-teeth/20-poles
RWinding ,I = 5, 2mΩ
RWinding ,II = 22,5mΩ
2,21 kW
2,38 kW
2
30T20P
36T20P
B [T]
1
Fig. 10: Segmentation effect on the eddy current losses in permanent
magnets for the 30T/20P machine.
0
-1
-2
0
50
a)
C. Ohmic Losses
100
theta [degree]
150
1.5
B [T]
Fig. 11 illustrate the geometrical approach used for
determination of winding resistances, while Table III
presents the derived results for the phase resistances and
also the corresponding Joule losses. Thus, even the winding
factor for the 36T/20P design is for 12% lower than for the
30T/20P design (76% vs. 86.6%), the Ohmic losses are
only for 7.5% higher. This effect can be justified
considering the shorter end-winding length and also the low
saturation due to low harmonic contents in the new
machine. Further, for the same active length for the both
machines, the total length for the 36T/20P design is reduced
for about 6% as results of shorter end-winding.
30T20P
36T20P
1
0.5
0
F [ N/m² ]
10
D. Noise Excitation Magnetic Forces
The radial force density distribution on the stator bore,
which results from the air-gap magnetic field under no-load
(open-circuit), as well as on-load conditions, is the main
cause of electromagnetically induced noise and vibrations.
Fig. 12 gives the simulation results for the air-gap fluxdensity and the resulting magnetic radial forces for the
maximal excitation load current. Considering the radial
force harmonics (modes) in Fig. 12.b), it can be shown that
except the mode zero (m = 0) the lowest mode for the
0
x 10
5
25
30
35
30T20P
36T20P
5
0
3
F [ N/m² ]
15
20
Space Harmonics
5
-5
0
b)
10
50
x 10
100
theta [degree]
150
5
30T20P
36T20P
2
1
0
0
5
10
15
20
Space Harmonics
25
30
35
Fig. 12: a). Air-gap flux density, b). Radial force density.
192
30T/20P design is the mode-10, while for the 36T/20P is
the mode-16 (the amplitude of mode-4 is too low and it can
be completely cancelled by a proper rotor design).
According to [7 to 9], in relation to acoustic behavior of the
electric machines, the significant radial force modes are
those of low order, i. e m = 0, 1, 2, 3. Thus, for the both
machine designs only mode-0 can be critical for the noise
excitations, while the high order modes usually doesn’t
meet the resonance frequency of the stator structure within
the speed range of the machines. However, considering the
mode-0 alone, it is well known that only the frequency
components of this mode are responsible of the noise and
vibrations. Therefore, to evaluate the frequency
components for the mode-0, the both machines are
investigated in time domain. From Fig. 13, the 30T/20P
design contains several mode-0 time harmonics that can be
responsible for the noise problems, while the proposed
deign it has a very smooth mode-0 response.
F [ N/m² ]
2.6
x 10
5
30T20P
36T20P
2.5
2.4
2.3
2.2
0
5
10
time [ms]
15
20
F [ N/m² ]
15000
30T20P
36T20P
10000
5000
0
10
20
30
xp f
R
40
50
[ Hz ]
Fig. 13: Mod -0 in time domain for 250Arms load current..
350
E. Temperature Results
300
T [ °C ]
During the thermal analysis, the both machines are
assumed to be mounted inside the water cooled jacked with
80°C coolant temperature. In the FE model the coolant
convention coefficient between the fluid and the stator
frame is taken to be 2000 W/(Km²). Further, in order to
simplify the FE model, the stator slot is modeled with a
homogeneous copper section with a thin insolation area
around it. The equivalent thermal conductivity for the
insolation slot area is taken to be 0.08 W/(Km) [23]. Fig. 14
gives the temperature behaviors in the rotor magnets and
also in the stator slot for the maximal speed and power
condition. As results of rotor loss reduction, and also higher
number of stator slots, the proposed machine is thermally
robust also for the maximal load condition. Otherwise, the
high rotor losses and the resulting high rotor temperature
are the main factors that limit the operating capability of the
conventional machine at high speed and power range.
a)
250
200
Conv. 30T/20P
150
New 36T/20P
100
50
0
0
50
100
150
time [s]
200
250
300
200
250
300
600
Conv. 30T/20P
b)
V. CONCLUSIONS
T [ °C ]
500
New 36T/20P
400
300
200
This paper deals with a detailed analysis of two
different FSCW traction PM machines. From the obtained
results, the following can be concluded:
30-Teeth/20-Poles Design; The conventional 30T/20P
machine is characterized with high torque ripple, high
magnet losses, noise and vibration excitation forces, and
rotor temperature problems. As results of high MMF
harmonic contents, at high power&speed region this
machine type can’t fulfill the requirements. Stator/rotor
skewing is required to reduce torque ripples. Additionally,
magnet segmentation with very short magnet pieces (5mm)
is needed to reduce the magnet losses and high rotor
temperatures. On the other side, the existing time-harmonic
components of mode-0 are critical for the noise and
vibration problems.
36-Teeth/20-Poles Design; An alternative machine
design with 36-teeth/20-poles is presented to solve the
existing ISG problems. The new winding is characterized
100
0
0
50
100
150
time [s]
Fig. 14: Temperature results for 250Arms and 6000rpm, a). Winding
temperature, b). Magnet temperature.
with low winding factor (76%), however with low
harmonic contents (factor two). Even the lower winding
factor, the Ohmic losses are only for 7% higher compared
with the reference machine. This is as results of shorter
end-winding length, low saturation due to high harmonics,
and non-required skewing. Further,
ƒ The total machine length is for 6%shorter,
ƒ Smooth torque response => none skewing is required,
ƒ Noiseless design => mode-0 is constant, and other
modes are of the high order,
193
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[20] G. Dajaku, D. Gerling, “Analysis of Different PM Machines with
Concentrated Windings and Flux Barriers in Stator Core”, 21-th
International Conference on Electrical Machines (ICEM’2014),
02.-05. September 2014, Berlin, Germany.
[21] T.A. Burress, et Al., “Evaluation of the 2010 Toyota Prius Hybrid
Synergy Drive System”, U.S. Department of Energy Vehicle
Technology, March 2011.
[22] http://www.bosch-presse.de; http://www.zf.com/media;
http://www.autoblog.com.
[23] D. A. Staton, A. Boglietti, A. Cavagnino, “Solving the more
difficult aspects of electric motor thermal analysis”. IEEE
International Electric Machines and Drives Conference, 2003,
IEMD’03, Vol. 2, pp. 1-4, June 2003.
ƒ
Low magnet losses (factor ten) => none segmentation
is required
ƒ Thermally robust; low rotor losses due to the low
MMF harmonic contents, and
ƒ Higher cooling capability; 20% more available cooling
surface for the stator winding.
Thus, considering the main merits of the proposed new
machine design, it can be concluded here that, for the
FSCWs, the winding factor (or low winding factor) isn’t
always the main criteria to select or to reject a winding for a
specific application. However, for a proper decision it is
required to consider carefully the all winding parameters
and their resulting effects on the machine performances. It
is shown from this analysis that, a FSCW with low winding
factor but with low harmonic contents overcomes the
existing PM machines in ISG applications.
VI. REFERENCES
[1]
G. Heins, D. Ionel, M. Thiele, “Winding Factors and Magnetic
Fields in Permanent Magnet Brushless Machines with Concentrated
Windings and Modular Stator Cores”; Energy Conversion Congress
and Exposition (ECCE), pp. 5048 – 5055, 15.-19. September 2013.
[2] A.M.
El-Refaie,
"Fractional-Slot
Concentrated-Windings
Synchronous Permanent Magnet Machines: Opportunities and
Challenges," IEEE Transactions on Industrial Electronics, Jan.
2010.
[3] D. Ishak, Z. Q. Zhu: “Comparison of PM Brushless Motors, Having
Either All Teeth or Alternate Teeth Wound”, IEEE Transactions on
Energy Conversion, Vol. 21, No. 1, March 2006, pp. 95-103.
[4] Magnussen F., Sadarangani Ch.: “Winding factors and Joule losses
of permanent magnet machines with concentrated windings”. 2003
IEEE International Electric Machines & Drives Conference
(IEMDC 2003), 01-04.06 Madison Wisconsin, USA.
[5] E. Farnasiero, N. Bianchi and S. Bolognani.: “Slot Harmonic Impact
on Rotor Losses in Fractional-Slot Permanent-Magnet Machines”,
IEEE Transactions on Industrial Electronics, Vol. 59, No. 6, pp.
2557-2564, June 2012.
[6] J. Li, D. W. Choi, D. H. Son, Y. H. Cho, “Effects of MMF
Harmonics on Rotor Eddy-Current Losses for Inner-Rotor
Fractional Slot Axial Flux Permanent Magnet Synchronous
Machines”, IEEE Transactions on Magnetics, Vol. 48, No. 2, pp.
839-842, February 2012.
[7] G. Dajaku, D. Gerling: “Magnetic Radial Force Density of the PM
Machine with 12teeth/10-poles Winding Topology,” IEEE
International Electric Machines and Drives Conference,
IEMDC2009, Florida USA, May 3-6, 2009, pp.157-164.
[8] M. Boesing, K. A. Kasper, R. W. Doncker: “Vibration Excitation in
an Electric Traction Motor for a Hybrid Electric Vehicle,” 37th
International Congress and Exposition on Noise Control
Engineering, Inter-Noise 2008, 26-29 October 2008, ShanghaiChina.
[9] Z. Q. Zhu, Z.P. Xia, L. J. Wu, G.W. Jewell: “Analytical modelling
and finite element computation of radial vibration force in fractional
slot permanent magnet brushless machines,” IEEE International
Electric Machines and Drives Conference, IEMDC2009, Florida
USA, May 3-6, 2009, pp.157-164.
[10] M. V. Cistelecan, F. J. T. E. Ferreira, “Three phase toothconcentrated multiple-layer fractional windings with low space
harmonic content”, IEEE on Energy Conversion Congress and
Exposition (ECCE) 2010.
[11] H. Kometani, Y. Asao, K. Adachi, “Dynamo-electric Machine”, US
Patent 6,166,471, Dec. 26, 2000.
[12] G. Dajaku, D. Gerling, “Eddy Current Loss Minimization in Rotor
Magnets of PM Machines using High-Efficiency 12-teeth/10-poles
Winding Topology”, International Conference on Electrical
Machines and Systems (ICEMS-2011), 20.-23. August 2011,
Beijing, China.
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