Energy and Power Engineering, 2013, 5, 446-454
http://dx.doi.org/10.4236/epe.2013.57048 Published Online September 2013 (http://www.scirp.org/journal/epe)
Development of High Torque and High Power Density
Hybrid Excitation Flux Switching Motor for Traction
Drive in Hybrid Electric Vehicles
Erwan Sulaiman1,2*, Takashi Kosaka2
1MyEV, Department of Electrical Power Engineering, University Tun Hussein Onn Malaysia, Johor, Malaysia
2Department of Electrical & Computer Science Engineering, Nagoya Institute of Technology, Nagoya, Japan
Received February 15, 2012; revised January 2, 2013; accepted January 9, 2013
Copyright © 2013 Erwan Sulaiman, Takashi Kosaka. This is an open access article distributed under the Creative Commons Attribu-
tion License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
ABSTRACT
This paper presents design feasibility study and development of a new hybrid excitation flux switching motor (HEFSM)
as a contender for traction drives in hybrid electric vehicles (HEVs). Initially, the motor general construction, the basic
working principle and the design concept of the proposed HEFSM are outlined. Then, the initial drive performances of
the proposed HEFSM are evaluated based on 2D-FEA, in which the design restrictions, specifications and target per-
formances are similar with conventional interior permanent magnet synchronous motor (IPMSM) used in HEV. Since
the initial results fail to achieve the target performances, deterministic design optimization approach is used to treat
several design parameters. After several cycles of optimization, the proposed motor makes it possible to obtain the tar-
get torque and power of 333 Nm and 123 kW, respectively. In addition, due to definite advantage of robust rotor struc-
ture of HEFSM, rotor mechanical stress prediction at maximum speed of 12,400 r/min is much lower than the me-
chanical stress in conventional IPMSM. Finally, the maximum torque and power density of the final design HEFSM are
approximately 11.41 Nm/kg and 5.55 kW/kg, respectively, which is 19.98% and 58.12% more than the torque and
power density in existing IPMSM for Lexus RX400h.
Keywords: Hybrid Excitation Flux Switching Machine (HEFSM); Field Excitation Coil (FEC); Permanent Magnet
(PM); Hybrid Electric Vehicle (HEV)
1. Introduction
Hybrid excitation machine (HEM) which consists of
permanent magnet (PM) and field excitation coil (FEC)
as their combined flux sources, has several unique fea-
tures that can be applied in HEV drive system. In general
HEM can be classified into four categories based on the
location of PM and FEC such as 1) both PM and FEC are
located at rotor side [1-3], 2) the PM is in the rotor while
the FEC is in the stator [4], 3) the PM is in the rotor
while the FEC is in the machine end [5,6], and 4) both
PM and FEC are located in the stator [7-9]. All HEMs
mentioned in the first three consist of a PM in the rotor
and can be categorized as “hybrid rotor-PM with FEC
machines” while the final machine can be referred as
“hybrid stator-PM with FEC machines”. Based on its
principles of operation, in which the fluxes sources are
generated in stator side and moved into the rotor, the
fourth machine is also known as “hybrid excitation flux
switching machine” (HEFSM) which is getting more
popular recently [10,11]. With all active parts located on
the stator, HEFSM has the advantages of 1) robust rotor
structure which is becoming more suitable to be applied
for high-speed drive applications, 2) due to the fact that
the all major heats are accumulated in stator part, a sim-
ple cooling system can be applied compared with a com-
plex water jacket system used in IPMSM for Lexus
RX400h, and 3) the additional FEC can be used to con-
trol flux with variable flux capabilities.
Various combinations of stator slot and rotor pole for
HEFSM have been developed for high speed applications.
For example, 12Slot-10Pole HEFSM has been proposed
such as in [12,13]. However, the machine in [12] has a
separated PM and C-type stator core that makes it diffi-
cult to manufacture, and the design is not yet optimized
*Corresponding author.
C
opyright © 2013 SciRes. EPE

E. SULAIMAN, T. KOSAKA 447
for HEV applications while the machine in [13] has a
limitation of torque and power production in high current
density condition. This is due to insufficient stator yoke
width between FEC and armature coil slots resulting in
magnetic saturation and negative torque production. To
reduce the supply frequency of inverter, 6Slot-5Pole
HEFSM has been proposed by the authors. Although the
proposed machine has met the target performances, the
problem of unbalanced pulling force due to odd number
of poles is difficult to overcome [14]. In addition, some
researchers have proposed 6Slot-8Pole machines but
these types of machines have problems of high torque
ripple and back-emf waveforms, which are usual con-
cerns for this type of eight pole machine [15,16].
In this paper, design feasibility and optimization stud-
ies are conducted to 12Slot-10Pole HEFSM in effort to
achieve the target performances for HEV applications.
Figure 1 illustrates the cross-sectional view of the main
machine part of the initial HEFSM. The motor is com-
posed of 12 PMs and 12 FECs distributed uniformly in
the midst of each armature coil while the three-phase
armature coils are accommodated in the 12 slots for each
1/4 stator body periodically. In this motor, the PMs and
FECs produce six north poles interspersed between six
south poles. The flux paths caused by both PM and mmf
of FEC under open circuit condition are demonstrated in
Figure 2. The term, “flux switching”, is created based on
the changes in polarity of each flux in each stator tooth,
depending on the motion of the rotor. When the rotor
rotates, the fluxes generated by PM and FEC link with
the armature coil flux alternately. For the rotor rotation
through 1/10 of a revolution, the flux linkage of the ar-
mature coil has one periodic cycle and thus, the fre-
quency of back-emf induced in the armature coil be-
comes ten times of the mechanical rotational frequency.
2. Design Requirements, Restrictions and
Specifications for HEV Applications
The design requirements, restrictions and specifications
of the proposed HEFSM for HEV applications are simi-
lar with IPMSM for Lexus RX400h listed in Table 1
[17]. The electrical restrictions related with the inverter
such as maximum 650 V DC bus voltage and maximum
360 V inverter current are set. The limit of the armature
coil current density, Ja and the FEC current density, Je is
set to 30 Arms/mm2 and 30 A/mm2, respectively. The
weight of the PM is 1.1kg similar with PM volume in
IPMSM. The target torque of 333 Nm with reduction
gear ration of 2.478 is set, hence, realizing the maximum
axle torque via reduction gear of 825 Nm. The maximum
operating speed is set to 12,400 r/min and the target
power is set to be more than 123 kW. As the proposed
HEFSM consists of very simple structure with concen-
trated winding in all coils, the target motor weight to be
Stator
Rotor
FEC
Armature Coil
Shaft PM
Figure 1. 12Slot-10Pole HEFSM.
FEC flux
PM flux
Figure 2. Flux paths of PM and FEC in 12Slot-10Pole
HEFSM.
Table 1. HEFSM design restrictions and specifications.
Items IPMSMHEFSM
Maximum DC-bus voltage inverter (V) 650 650
Maximum inverter current (Arms) 360 360
Maximum Ja (Arms/mm2)a 31 30
Maximum Je (A/mm2)b NA 30
Stator outer diameter (mm) 264 264
Motor stack length (mm) 70 70
Shaft radius (mm) 30 30
Air gap length (mm) 0.8 0.8
PM weight (kg) 1.1 1.1
Maximum speed (r/min) 12,400 12,400
Maximum torque (Nm) 333 333
Reduction gear ratio 2.478 2.478
Max. axle torque via reduction gear (Nm) 825 825
Maximum power (kW) 123 >123
Power density (kW/kg) 3.5 >3.5
Ja = current density in armature coil; Je = current density in FEC.

E. SULAIMAN, T. KOSAKA 448
designed is set to be less than 35 kg, resulting in that the
proposed machine promises to achieve the maximum
power density of more than 3.5 kW/kg. Commercial FEA
package, JMAG-Studio ver.10.0, released by Japanese
Research Institute (JRI) is used as 2D-FEA solver in this
design.
3. Initial Performances of the Proposed
HEFSM Based on 2D-FEA
Initially, performances of the proposed HEFSM in open
circuit condition such as back-emf and cogging torque
are analyzed as shown in Figures 3 and 4. In Figure 3,
the amplitude of the fundamental component in which
the induced voltage is generated from the flux of PM
only is 123.6 V. The back-emf is slightly sinusoidal
which results a small amount of cogging torque of
approximately 1.06 Nm peak-to-peak. However, when Je
is set to 15 A/mm2, the induced voltage is slightly
distorted and the amplitude is increased to 263.2 V which
is more than double of that under no FEC current. This is
due to the field strengthening effect by the additional
FEC. For load analysis, performances of the machine at
maximum Ja and Je are analyzed. The torque and power
obtained at base speed 5731.4 r/min are 175.9 Nm and
105.6 kW, respectively, which is less than the target
value. To investigate this issue, the torque versus Je at
various Ja is plotted as depicted in Figure 5. It is obvious
that the torque is increased with increasing Je up to
certain Je and begins to decrease when higher Je is
applied as shown in red circle. For instance, at Ja of 30
Arms/mm2, the maximum torque of 181.66 Nm is ob-
tained when Je is set to 20 A/mm2. However, the torque
starts to reduce when Je is set higher than this value. For
Ja of 20 Arms/mm2 and 25 Arms/mm2, the maximum torque
obtained are 152.72 Nm and 170.94 Nm respectively,
when Je is set to 15 A/mm2. The torque also starts to
reduce when Je is set higher than this value. Similarly,
the same phenomenon occurs at the condition of Ja of 5
Arms/mm2, 10 Arms/mm2 and 15 Arms/mm2 where the
torque starts to reduce when Je is set higher than 10
A/mm2.
To explain this phenomenon, further investigation is
examined on the flux density distribution at three condi-
tions 1) before maximum torque, 2) at maximum torque,
and 3) after maximum torque. For example, at maximum
Ja of 30 Arms/mm2, flux distribution at Je of 10 A/mm2, 20
A/mm2 and 30 A/mm2 are investigated as shown in Fig-
ure 6. It can be seen that for low Je of 10 A/mm2, the flux
can easily flow to the direction according to its principle
as shown in Figure 6(a). Nevertheless, the flux flow to
the left part starts to saturate between armature coil upper
slot and FEC lower slot marked in blue circle when Je is
set to 20 A/mm2 as shown in Figure 6(b). In this case,
some of the flux from FEC which flow to the right side
-300
-200
-100
0
100
200
300
0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00
emf [V]
t [ms]
J
e
=30A/mm
2
J
e
=15A/mm
2
J
e
=0A/mm
2
Figure 3. Back-emf at 3000 r/min.
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
0612 18 24 30 36
T [Nm]
rotor [°]
Figure 4. Cogging torque of the original design HEFSM.
0
50
100
150
200
0510 15 20 25 30 35 40
T [Nm]
J
e
[A/mm
2
]
J
a
=30A/mm
2
J
a
=25A/mm
2
J
a
=20A/mm
2
J
a
=15A/mm
2
J
a
=10A/mm
2
J
a
=5A / mm
2
35 40
J
e
[A/mm
2
]
Figure 5. Torque versus Je at various Ja.
cancelled the flux from PM as shown in red circle which
results in reducing the torque production. Hence, for the
maximum Je of 30 A/mm2 where much FEC flux is gen-
erated, the flux flow to the left part is totally saturated
between armature coil upper slot and FEC lower slot
marked in blue circle. Therefore, much higher flux from
the stator outer yoke passes the FEC pitch move towards
the PM in the right side. This flux also cancelled the PM
flux and some of the flux is forces to flow into the rotor
side producing much negative torque as shown in Figure
6(c), hence reducing the torque production. Thus, one of
the methods that can be used to overcome this problem is
by investigating the suitable length between armature
coil upper slot and FEC lower slot to avoid flux satura-
tion.

E. SULAIMAN, T. KOSAKA 449
FEC
PM
FEC 2.5T-
2.0T-
1.5T-
1.0T-
0.5T-
0.0T-
(a)
FEC
PM
FEC 2.5T-
2.0T-
1.5T-
1.0T-
0.5T-
0.0T-
(b)
FEC
PM
FEC 2.5T-
2.0T-
1.5T-
1.0T-
0.5T-
0.0T-
(c)
Figure 6. Flux vector diagram of various Je at maximum Ja
of 30 Arms/mm2 (a) Je = 10 A/mm2, T = 153.4 Nm (b) Je = 20
A/mm2, Tmax = 181.7 Nm (c) Je = 30 A/mm2, T = 175.9 Nm.
4. Design Methodology for Improvements
To make a simple design, the shape of armature coil slot
and air gap between the inner and outer PM are redesign,
so that design free parameters of D1 to D10 can be defined
as illustrated in Figure 7. The first step is carried out by
updating the rotor parameters, D1, D2 and D3 while
keeping D4 to D10 as constant. As the torque increases
with the increase in rotor radius, D1 which is considered
as the dominant parameter that can improve the torque is
firstly treated. In this condition, D4, D6, D8, D9 and D10
are simply shifted to the new position by following the
movement of D1, while D5 and D7 are kept constant.
Then, by selecting D1 at its maximum performance, both
rotor pole width D2 and rotor pole depth D3 are varied.
Once the maximum performance from the combination
of D2 and D3 is determined, the second step is carried out
by changing the FEC slot parameters D4, D5 and D6 while
keeping the other parameters constant. Then, by using
the combination of D4 to D6 that bring out the maximum
performance at the second step, the third step is carried
out by varying the armature coil slot parameters D7 and
D8 with keeping other parameters constant. The neces-
sary armature coil slot area, Sa is determined by varying
armature coil depth, D7 and armature coil width, D8 to
accommodate natural number of turns, Na for armature
coil. Furthermore, to ensure the PM is not demagnetized
at temperatures as high as 180˚C, D9 and D10 are adjusted
with keeping the same PM volume. The method of
changing D1 to D10 is treated repeatedly until the target
performances are achieved.
All design parameters are adjusted with keeping air
gap length of 0.8 mm constant under maximum Ja and Je.
In addition, at the final design, the corners circled in
Figure 7 are designed as a curve to ensure all flux at the
edge of the shape flow more smoothly, hence increases
the performance of the machine. For the rotor inner pole,
the curve designed not only increased the flux flows but
also increase the rotor mechanical strength of the ma-
chine, make it more robust to work in high speed condi-
tion. Finally, after few cycle of optimization, the machine
satisfied the target requirements and performances for
HEV applications. The cross sectional views of the final
design HEFSM is depicted in Figure 8, while details of
final parameters are listed in Table 2. The differences
between the initial and the final design HEFSM are 1)
Table 2. Initial and final design parameters.
Details InitialFinal
PM volume (kg) 1.1 1.1
D1Rotor radius (mm) 80.2 88.2
D2Rotor pole width (mm) 12.5 9.5
D3Rotor pole depth (mm) 12.2 23.2
D4Permanent magnet height (mm) 24.0 15.0
D5FEC slot pitch (mm) 7.4 20.0
D6Stator outer core thickness (mm) 7.4 8.0
D7Armature coil width (mm) 8.0 6.0
D8Armature coil depth (mm) 19.1 32.71
D9Distance between air gap and PM (mm) 2.0 0.5
D10 Distance between FEC and PM (mm) 4.0 0.5
NaNo. of turns of armature coil 7 9
T Torque (Nm) 175.86334.5
N Speed (r/min) 5731.43701.2
P Power (kW) 105.55129.6
pfPower factor 0.3680.452

E. SULAIMAN, T. KOSAKA 450
D
2
Air gap (0.8 mm)
D
1
D
3
D
8
D
7
D
6
D
5
D
4
D
10
D
9
ShaftRotor Air
Armature
coil
FE C
PM
Stat or
Figure 7. Design parameter defined as D1 to D10.
2.5T-
2.0T-
1.5T-
1.0T-
0.5T-
0.0T-
PM
FE C
FE C
Rotor
Shaf t
264 mm
60 mm
ag = 0.8mm
176.4 mm
Sta tor
Ar mature
Coil
FE C
PM
(a)
PM
FE C FE C
2.5T-
2.0T-
1.5T-
1.0T-
0.5T-
0.0T-
Figure 8. Final Design HEFSM.
the rotor radius of the final design is longer than the ini-
tial rotor radius which gives more torque as had been
expected, 2) the armature coil width of the final design is
less than the initial design, but has high armature coil
depth which results in more number of turns, 3) the FEC
slot area is reduced approximately 40% from the initial
design to cover some volume of stator yoke used for ar-
mature coil, 4) the final design has less PM depth with
high PM width to keep the same PM volume of 1.1 kg, 5)
the final design has no gap between armature coil upper
slot and FEC lower slot which solved the flux saturation
problem, 6) the stator outer core thickness is higher than
the initial design to allow more flux to flow smoothly,
and 7) the final design has a stator yoke with a straight “I
shape” that makes the flux flow more easily into the rotor.
As a proof, Figure 9 illustrates the flux distribution of
the final design HEFSM for Je of 20 A/mm2 and 30
A/mm2 with maximum Ja of 30 Arms/mm2. As the gap
between armature coil upper slot and FEC lower slot in
the final design HEFSM is expanded and considered
(b)
Figure 9. Flux vector diagram of various Je at maximum Ja
of 30 Arms/mm2 (a) Je = 20 A/mm2, T = 280.4 Nm (b) Je = 30
A/mm2, T = 334.4 Nm.
negligible, the magnetic saturation caused by higher FEC
current is relaxed. Thus, the improved design maintains
the same torque for both current density conditions and
enables to extract higher power factor.
5. Results and Performances of the Final
Design HEFSM
5.1. Flux Path at Open Circuit Condition
The open circuit field distribution for PM and FEC of the
final design HEFSM are investigated based on 2D-FEA
as illustrated in Figure 10. Figure 10(a) illustrates the

E. SULAIMAN, T. KOSAKA 451
flux path due to mmf of PM only, while Figure 10(b)
represents the combination of flux line from both PM and
mmf of FEC at maximum FEC density, Je of 30 A/mm2.
In Figure 10(a), it is obvious that almost 100% flux of
PM flow in the stator iron around the FEC. This yields
negligible cogging torque and almost no back-emf at
open-circuit condition under the maximum speed opera-
tion, which makes it easy to protect the switching devices
when the inverter is shut down due to some failures. In
contrast, from Figure 10(b), a large amount of fluxes
flow to the rotor side by field strengthening excitation,
resulting in the maximum torque production with the aid
of hybrid excitation.
Furthermore, Figures 11 and 12 illustrate the compa-
rison between back-emf and cogging torque of the initial
and final design at 3000 r/min, respectively. It is clear
that, the back emf of the final design is more sinusoidal
and much less by approximately 36% of the initial design.
The final cogging torque is also reduced by more than
50% of the initial design.
(a)
(b)
Figure 10. Flux path of the final design HEFSM at open
circuit condition (a) PM only (b) PM and maximum FEC
current density of 30 A/mm2.
-150
-100
-50
0
50
100
150
0.00 0.25 0.50 0.751.00 1.25 1.50 1.75 2.00
emf [V]
t [ms]
Initial
Final
Figure 11. Back-emf.
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
0.06.012.0 18.0 24.0 30.0 36.0
T [Nm]
rotor [°]
Final Initial
Figure 12. Cogging torque.
5.2. Torque and Power Factor versus Je
Characteristics
The torque and power factor versus Je characteristics are
plotted in Figures 13 and 14, respectively. From the plot,
it is obvious that increasing Ja will increase the torque but
will reduce the power factor. To equilibrate this situation,
Je is increased so that the power factor can be improved
and kept constant even if Ja is very high. The plots
clearly show that maximum torque of 334.4 NM is ob-
tained when Ja and Je are set to 30 A/mm2 as their maxi-
mum with the power factor of 0.452. However, for low Ja
of less than 15 Arms/mm2, the torque are slightly reduced
with the increasing of Je of more than 20 A/mm2. This
situation occurs due to excessive FEC flux that generates
negative torque thus reducing the performances, similar
with the original HEFSM discussed previously. The
comparison between the torque and power factor versus
Je under maximum Ja for the initial and final design
HEFSM is depicted Figure 15. The torque and power
factor of the final design HEFSM increased approxi-
mately 50% and 23%, respectively compared with the
original design.
5.3. Torque and Power versus Speed
Characteristics
The torque versus speed characteristics of the IPMSM
and the final design HEFSM are plotted in Figure 16.

E. SULAIMAN, T. KOSAKA 452
0
50
100
150
200
250
300
350
0510 15 2025 30 3540
T [Nm]
J
e
[A/mm
2
]
J
a
=30 A/ mm
2
J
a
=25 A/ mm
2
J
a
=20 A/ mm
2
J
a
=15 A/ mm
2
J
a
=10 A/ mm
2
J
a
=5A/mm
2
35 40
J
e
[A/mm
2
]
Figure 13. Torque vs Je.
0.0
0.2
0.4
0.6
0.8
1.0
0510 15 20 25 30 35 40
p
f
J
e
[A/mm
2
]
J
a
=5A/mm
2
J
a
=10A/mm
2
J
a
=15A/mm
2
J
a
=20A/mm
2
J
a
=25A/mm
2
J
a
=30A/mm
2
35 40
J
e
[A/mm
2
]
Figure 14. Power factor vs Je.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0
50
100
150
200
250
300
350
0510 15 20 25 30
Je[A/mm2]
pf
T [Nm]
Torque - Original
Torque - Final
pf -Original
pf -Final
Figure 15. Torque and power factor vs Je.
0
50
100
150
200
250
300
350
01,550 3,100 4,650 6,200 7,750 9,30010,85012,40
0
T [Nm]
speed [r/min]
HEFSM
IPMSM
[1]
[2]
[5]
[4]
[3]
[8]
[7] [6]
9,300 10,850 12,400
speed [r/min]
Figure 16. Torque vs speed characteristics.
The maximum torque obtained for IPMSM and HEFSM
are 333 Nm and 334.4 Nm, respectively. It is obvious
that the HEFSM has better torque condition and pro-
duced much higher torque capability in high speed region.
Meanwhile, Figure 17 illustrates the power versus speed
characteristics of the IPMSM and the final design
HEFSM. From the graph, 1) at maximum torque, the
power achieved for IPMSM and the final design HEFSM
is 72.1 kW and 129.6 kW, at the speed of approximately
2100 r/min and 3701 r/min, respectively, 2) the maxi-
mum power obtained is 123 kW for IPMSM and 162.8
kW for HEFSM 3) the average power of the IPMSM and
the HEFSM at normal driving mode of 3000 - 6000 r/min
are 113.7 kW and 133.7 kW, respectively, which proves
that the HEFSM has better performance than IPMSM in
frequent driving condition. The total weight of the final
design HEFSM including stator iron, rotor iron, PM, ar-
mature coil, FEC, and estimation of both coil ends is 29.3
kg, which is 16.2% less than the estimated of 35 kg for
IPMSM. Thus, the maximum torque density and maxi-
mum power density are 11.41 Nm/kg and 5.55 kW/kg,
respectively, which is much higher than the target re-
quirements for HEV applications. The maximum torque
and power density of the final design HEFSM are in-
creased approximately by 20.0% and 36.9%, respectively
compared to 9.51 Nm/kg and 3.51 kW/kg of existing
IPMSM.
5.4. Motor Loss and Efficiency
The motor loss and efficiency are calculated considering
iron losses in all laminated cores, and copper losses in
armature coil and FEC. The detailed loss and motor effi-
ciency of the final design HEFSM at maximum torque,
maximum power, and frequent operating point under
light load driving condition noted as No. 1 to No. 8 in
Figure 16 are illustrated in Figure 18. At high torque
operating points No. 1, the efficiency is slightly degraded
due to increase in copper loss while at high-speed oper-
ating point No. 2, the motor efficiency is degraded due to
increase in iron loss. Furthermore, at frequent driving
operation No. 3 to No. 8 under low load condition, the
proposed machine achieves relatively high efficiency of
more than 93%.
0
20
40
60
80
100
120
140
160
180
01,550 3,100 4,650 6,200 7,750 9,30010,85012,40
0
P [kW]
speed [r/mi
n
HE FSM
IPMSM
9,300 10,850 12,400
speed [r/min]
Figure 17. Power versus speed characteristics.

E. SULAIMAN, T. KOSAKA 453
5.5. Rotor Mechanical Strength
The mechanical stress prediction of rotor structure is
calculated by centrifugal force analysis based on 2D-
FEA as depicted in Figure 19. The maximum stress at
12,400 r/min reaches 46 MPa and 28 MPa for the origin-
nal and final design, respectively, which is much smaller
than allowable maximum stress of 300 MPa in conven-
tional electromagnetic steel. This is a great advantage of
the final design HEFSM that makes it more applicable
and suitable to operate in high-speed application compare
to conventional IPMSM.
6. Conclusion
In this paper, design feasibility studies and performance
analysis of 12Slot-10Pole HEFSM for traction drive in
the target HEV have been presented. The design refine-
ment has been clearly demonstrated and finally achieved
84%
88%
92%
96%
100%
12345678
Motor Efficiency
Po Pi Pc
Motor Efficiency
100%
Figure 18. Motor efficiency.
45.99 MPa
50.0-
37.5-
25.0-
12.5-
0.0-
(a)
28.05MPa
50.0-
37.5-
25.0-
12.5-
0.0-
(b)
Figure 19. Principal stress distributions of rotor at 12,400
r/min (a) initial design (b) final design.
the target performances. In addition, the rotor mechanical
stress predicted is good enough for the machine to run in
high-speed region. Finally, the power density of the final
design HEFSM has been increased of more than one
third when compared with existing IPMSM for LEXUS
RX400h. As conclusion, the goal of this research to get
maximum performances for HEV applications has been
successfully achieved.
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