energies
Article
Performance Analysis of Permanent Magnet Motors
for Electric Vehicles (EV) Traction Considering
Driving Cycles
Thanh Anh Huynh 1
1
2
*
ID
and Min-Fu Hsieh 2, *
ID
Department of Systems and Naval Mechatronic Engineering, National Cheng Kung University,
Tainan 70101, Taiwan; hthanhanh86@gmail.com
Department of Electrical Engineering, National Cheng Kung University, Tainan 70101, Taiwan
Correspondence: mfhsieh@mail.ncku.edu.tw; Tel.: +866-06-275-7575 (ext. 62366)
Received: 1 May 2018; Accepted: 25 May 2018; Published: 29 May 2018
Abstract: This paper evaluates the electromagnetic and thermal performance of several traction
motors for electric vehicles (EVs). Two different driving cycles are employed for the evaluation of the
motors, one for urban and the other for highway driving. The electromagnetic performance to be
assessed includes maximum motor torque output for vehicle acceleration and the flux weakening
capability for wide operating range under current and voltage limits. Thermal analysis is performed
to evaluate the health status of the magnets and windings for the prescribed driving cycles. Two types
of traction motors are investigated: two interior permanent magnet motors and one permanent
magnet-assisted synchronous reluctance motor. The analysis results demonstrate the benefits and
disadvantages of these motors for EV traction and provide suggestions for traction motor design.
Finally, experiments are conducted to validate the analysis.
Keywords: Electric vehicles; IPMSM; SynRM; PMa-SynRM; driving cycle
1. Introduction
Electric vehicles (EVs) have become more and more attractive in recent years, as they are
considered as the most viable solution to help protect the environment and to achieve high energy
efficiency for transportation [1]. In EVs, traction motors are the key component for propulsion,
which requires high torque and power density, wide speed range, high efficiency, high reliability,
low noise, and reasonable cost. Interior permanent magnet synchronous machines (IPMSMs) have
emerged as the brightest candidates, which have been widely used for EV (or hybrid EV) tractions,
such as Toyota Prius and Nissan Leaf. These electric motors may be designed with different rotor
topologies, where rare-earth magnet is often employed to achieve high performance [2]. However,
the material cost of rare-earth magnet is high and the supply is mainly controlled by few countries
owning the mineral resources. Some EVs adopt propulsion solutions without rare earth permanent
magnet (PM), such as Tesla Model S, which uses copper rotor induction motors (IMs). However,
the starting current of IMs can be high and this is disadvantageous for battery duration [3]. In response
to the demands for rare-earth-free or less-rare-earth traction motors, PM-assisted synchronous
reluctance motors (PMa-SynRMs) can be an excellent candidate [4]. The PMa-SynRM is often designed
with ferrite magnets or small amount of rare-earth magnets in the rotor core. The weaker or less PM
can be potentially demagnetized during high performance operation (e.g., high armature reaction or
flux weakening). Also, the rotor should be well designed in order to gain as much reluctance torque as
possible in order to compensate the loss in electromagnetic torque due to less amount of PM used [4,5].
On the other hand, the EVs require high torque for starting at zero speed, acceleration, climbing,
and high power for cruising at highway speeds [6]. Therefore, traction motors are usually designed
Energies 2018, 11, 1385; doi:10.3390/en11061385
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Energies 2018, 11, 1385
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to produce peak torque or power that is several times the rated values. However, for frequent urban
or suburban driving, traction motors can be mostly operated in low torque, low power, and low
efficiency conditions. This would lead to energy waste and the cruise range reduces. To investigate
the effect of driving conditions on design of traction motors, some established driving cycles could
be employed to test the vehicles. Degano and Carraro [7,8], based on the torque profiles of selected
driving cycles, determined some representative operating points of traction motors for PMa-SynRM
global optimization. Nguyen and Wang [6,9] proposed a method to calculate the losses and to
optimize the design of a surface-mounted PM motors (SPMSM), according to a selected driving
cycle. Sarigiannidis [10,11] evaluated the energy consumption, optimized the design, and compared
the performance of a fractional-slot concentrated-winding SPMSM and IPMSM based on the New
European Drive Cycle (NEDC). Yang [12] determined the target torque and the speed curve based
on a driving scenario and the design for an axial-flux permanent magnet (AFPM) was optimized to
minimize energy consumption. Most of these studies focused on evaluating and minimizing the losses
and energy consumption of traction motors. However, the evaluation of traction motor designs by
employing driving cycle test results has not been comprehensively studied. The performance of an
IPMSM was evaluated using a driving cycle [13]; however, the thermal issue was not considered for
the traction motor to satisfy the driving cycle. Thermal imaging was employed in diagnosis of faults
that are related to temperature rise for industrial induction motors [14,15]. The thermal problem can
be even more crucial for traction motors with high performance operations, and therefore, the thermal
analysis is considered to be critical. The design factors of tractions motors should involve flux linkages,
inductances, torque generation, and thermal condition. More study is also required for EV tractions
while using PMa-SynRM.
This paper compares two IPMSMs and one PMa-SynRM (all using rare-earth magnet) that are
based on two standard driving cycles: the Urban Dynamometer Driving Schedule (UDDS) and
Highway Fuel Economy Driving Schedule (HWFET) [16]. These driving cycles are employed to
comprehensively test the traction motor performance in terms of torque, efficiency, and thermal
condition. The torque–speed envelope is derived under the current and voltage limits that the inverter
can supply. Thermal analysis is performed to check the temperature of the magnets and windings
under various loading conditions. Based on the analysis, the benefits and the disadvantages of the
IPMSMs and PMa-SynRM for EV tractions can be fully elaborated. Some suggestions regarding the
design of EV traction motors are provided. Finally, experiments are conducted to verify the analysis.
2. Target Traction Motors and EV
As previously mentioned, two IPMSMs and one PMa-SynRM with rare-earth magnet are
investigated. Among these motors, the PMa-SynRM is a less-magnet option with a dominant reluctance
torque. This would make its torque performance at high speed different to that of the IPMSMs,
whose electromagnetic torque dominates. For fair comparison, some design constraints for the motors
are listed, as follows:
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
output power: greater or equal to 10 kW (this makes a total power of 20 kW for the EVs.
Explained later);
torque density: greater or equal to 30 Nm/L;
maximum current density: 16–17 Arms /mm2 ;
outer stator diameter: 160 mm;
air gap: 0.5 mm;
number of slots: 36;
winding configuration: distributed winding; and,
efficiency: greater or equal to 95%.
Figure 1a shows the design of the IPMSM with double-layers PM. This rotor design can reduce
the torque ripple due to the harmonics that are induced by the flux barriers/magnets with the stator
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teeth. The reluctance torque can also be improved although the electromagnetic torque (hereafter
called
torque) may
may be
be slightly
slightly reduced.
reduced.The
Thegreater
greaternumber
numberofofmagnet
magnetpoles
polesusually
usuallygenerates
generatesa
called PM
PM torque)
ahigher
highertorque
torquefor
forthe
thesame
samecurrent
currentlevel;
level;however,
however,ititalso
alsorequires
requiresmore
moreroom
roomfor
foreach
eachpole.
pole.
Figure 1.
1. Traction
(a) double-layers
double-layers interior
interior
Figure
Traction motors
motors using
using rare-earth
rare-earth permanent
permanent magnet
magnet (PM):
(PM): (a)
permanent magnet
magnet synchronous
synchronous machines
machines (IPMSM).
(IPMSM). Rotor
Rotor material:
material: 50CS1300.
50CS1300. Stator
permanent
Stator material:
material:
25CS1500HF; (b)
material:
25CS1500HF;
and,and,
(c)
25CS1500HF;
(b) V-shaped
V-shaped IPMSM.
IPMSM. Rotor
Rotor material:
material:35CS550.
35CS550.Stator
Stator
material:
25CS1500HF;
PM-assisted
synchronous
reluctance
motors
(PMa-SynRM).
Rotor
material:
50CS1300.
Stator
material:
(c) PM-assisted synchronous reluctance motors (PMa-SynRM). Rotor material: 50CS1300. Stator
◦ C, H
25CS1500HF.
Permanent
magnet: magnet:
NdFeB-N35H,
Br = 1.2TB@r =201.2T
°C, @
Hc20
= 915
kA/m.
AllkA/m.
of the All
cases
are
material:
25CS1500HF.
Permanent
NdFeB-N35H,
of the
c = 915
distributed
windings.windings.
cases
are distributed
The V-shaped IPMSM that is shown in Figure 1b is known to possess the advantages of flux
The V-shaped IPMSM that is shown in Figure 1b is known to possess the advantages of flux
weakening capability [17]. The PM position and dimension for the V-shaped design are also arranged
weakening capability [17]. The PM position and dimension for the V-shaped design are also arranged
to satisfy the constraints given previously. The iron loss of the V-shaped design is expected to be
to satisfy the constraints given previously. The iron loss of the V-shaped design is expected to be
greater than that of the double-layers one because the harmonics in the air gap flux density
greater than that of the double-layers one because the harmonics in the air gap flux density distribution
distribution may increase the stator core loss.
may increase the stator core loss.
Figure 1c shows the design of the PMa-SynRM using rare earth PM with each piece having the
Figure 1c shows the design of the PMa-SynRM using rare earth PM with each piece having the
same dimension. This PMa-SynRM adopts five flux barriers per pole to reduce the torque ripple and
same dimension. This PMa-SynRM adopts five flux barriers per pole to reduce the torque ripple and
to increase the reluctance torque. Only four of the barriers are filled with PMs (except the outermost
to increase the reluctance torque. Only four of the barriers are filled with PMs (except the outermost
one) for each pole, as seen in Figure 1c.
one) for each pole, as seen in Figure 1c.
Using thin electrical steel laminations for motor core would reduce iron losses and enhance
Using thin electrical steel laminations for motor core would reduce iron losses and enhance
traction motor efficiency [18,19]. However, thin laminations are usually expensive [18]. Therefore, as
traction motor efficiency [18,19]. However, thin laminations are usually expensive [18]. Therefore,
a compromise between loss reduction and material cost, thin laminations can be used for the stator
as a compromise between loss reduction and material cost, thin laminations can be used for the stator
(with alternating flux) and common laminations (e.g., thicker with a possible higher saturation flux
(with alternating flux) and common laminations (e.g., thicker with a possible higher saturation flux
density) are for the rotor. This may improve the efficiency by 2% to 2.5%, as demonstrated in [19].
density) are for the rotor. This may improve the efficiency by 2% to 2.5%, as demonstrated in [19].
This idea is adopted here. In Figure 1, thin laminations (20CS1500HF) are employed for the stator due
This idea is adopted here. In Figure 1, thin laminations (20CS1500HF) are employed for the stator due
to the alternating flux that generates significant iron losses and other materials (50CS1300 or 35CS550)
to the alternating flux that generates significant iron losses and other materials (50CS1300 or 35CS550)
are utilized in the rotors. Note that all of the laminations are produced by China Steel Corporation in
are utilized in the rotors. Note that all of the laminations are produced by China Steel Corporation
Taiwan. The Neodymium Iron Boron (NdFeB) magnet used for all the three motors is N35H with a
in Taiwan. The Neodymium Iron Boron (NdFeB) magnet used for all the three motors is N35H with
remanence (Br) and coercive force (Hc) of 1.2 T and 915 kA/m, respectively.
a remanence (Br ) and coercive force (Hc ) of 1.2 T and 915 kA/m, respectively.
The main specifications and parameters of the motors are given in Table 1. As can be seen, the
The main specifications and parameters of the motors are given in Table 1. As can be seen,
PMa-SynRM is axially longer than the other two. All of the motors are designed to meet the
the PMa-SynRM is axially longer than the other two. All of the motors are designed to meet the
prescribed minimum requirements. Note that the design processes are not the focus in this paper,
prescribed minimum requirements. Note that the design processes are not the focus in this paper,
and thus will not be detailed here.
and thus will not be detailed here.
As shown in Figure 2, two traction motors, one in the front, and the other the rear drivetrains,
As shown in Figure 2, two traction motors, one in the front, and the other the rear drivetrains,
are employed to a light-duty vehicle and each is connected to the front or rear axles via a differential.
are employed to a light-duty vehicle and each is connected to the front or rear axles via a differential.
With the driving independence of the front and rear wheels, this offers advantages, such as fault
With the driving independence of the front and rear wheels, this offers advantages, such as fault
tolerance, excellent safety, and enhanced steering ability with an appropriate distribution of driving
tolerance, excellent safety, and enhanced steering ability with an appropriate distribution of driving
torque to the front and rear wheels according to operating conditions. This also helps to improve the
torque to the front and rear wheels according to operating conditions. This also helps to improve
stability of the vehicle by precisely distributing the braking torque to the front and rear wheels upon
the detection of a wheel slip or wheel lock [20]. Table 2 lists the parameters of the target EV. The
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the stability
of the
by precisely
the braking
torque
front and rear
wheels
analysis
process
forvehicle
the traction
motors distributing
while considering
driving
cyclestoisthe
summarized
in the
flow
upon
the
detection
of
a
wheel
slip
or
wheel
lock
[20].
Table
2
lists
the
parameters
of
the
target
EV.
chart shown in Figure 3.
The analysis process for the traction motors while considering driving cycles is summarized in the
Table 1. Motor specifications.
flow chart shown in Figure 3.
Parameter (Unit)
Double Layers
Table 1. Motor specifications.
Max. power (kW)
10
Max.
torque (Nm)
56Layers
Parameter
(Unit)
Double
Max. speed (rpm)
7000
Max. power (kW)
10
Rated
power
6.6
Max.
torque(kW)
(Nm)
56
Rated
torque
30
Max.
speed(Nm)
(rpm)
7000
power (kW)
6.6
Base speed @Rated
maximum
torque (rpm)
≥1800
Rated torque (Nm)
30
Base speed
@ rated torque (rpm)
≥2100
Base speed @ maximum torque (rpm)
≥1800
No.@ofrated
slotstorque (rpm)
36
Base speed
≥2100
No.No.
of poles
8
of slots
36
poles
84
No.No.
of of
turns
of turns
4
Max.No.
current
(A)
110
Max. current (A)
110
Outer rotor diameter (mm)
94
Outer rotor diameter (mm)
94
Stack
length
(mm)
86
Stack
length
(mm)
86
Coil
pitch
Coil
pitch
4
3)
3
7740
PM
amount
per
pole
(mm
PM amount per pole (mm )
7740
8.3
Current
density
ratedtorque
torque (A/mm
(A/mm22))
Current
density
@@
rated
8.3
V-Shaped
10
56
V-Shaped
7000
10
6.6
56
30
7000
6.6
≥1800
30
≥2100
≥1800
36
≥2100
368
85
5100
100
109
109
9090
33
8100
8100
8.3
8.3
Figure
of light-duty
light-duty vehicle.
vehicle.
Figure 2.
2. Schematic
Schematic of
of aa front
front and
and rear
rear drives
drives of
Table 2. Vehicle specifications.
Table 2. Vehicle specifications.
Parameter (Unit)
Parameter
(Unit) (m)
Radius
of wheels
Radius
of wheels
(m)
Vehicle
mass (kg)
Vehicle
mass
(kg)
Mass correction coefficient
Mass correction coefficient
Gravitational
acceleration (m/s2)
Gravitational acceleration (m/s2 )
Rolling
resistancecoefficient
coefficient
Rolling resistance
3 ) 3)
Airmass
massdensity
density
(kg/m
Air
(kg/m
Aerodynamic
drag
coefficient
Aerodynamic drag coefficient
2)
Vehicle frontal
(m(m
2)
Vehicle
frontalarea
area
Differential gear ratio
Differential
gear
ratio (V)
Battery
pack nominal
voltage
Battery pack nominal voltage (V)
Value
Value
0.265
0.265
950
950
1.04
1.04
9.8
9.8
0.011
0.011
1.225
1.225
0.4
0.4
2.14
2.14
7
7
310
310
PMa-SynRM
10
65
PMa-SynRM
7000
10
65 6.6
700030
6.6
≥1500
30
≥2100
≥1500
36
≥2100
36 4
4 6
6 80
80
94
94
120120
9 9
5760
5760
8.3 8.3
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Figure
cycle.
Figure 3.
3. The
The analysis
analysis process
process for
for traction
traction motors
motors with
with driving
driving cycle.
3. Theoretical Background
3. Theoretical Background
To satisfy the required performance of the EV shown in Table 2 and Figure 2, the designed
To satisfy the required performance of the EV shown in Table 2 and Figure 2, the designed motors
motors
should possess
capabilities
terms of flux-weakening
peak
torque
output
should possess
excellentexcellent
capabilities
in terms in
of flux-weakening
and peak and
torque
output
under
the
under
the
inverter
current
and
voltage
limits.
Thus,
the
first
constraint
is
the
maximum
current
and
inverter current and voltage limits. Thus, the first constraint is the maximum current and the maximum
the maximum voltage for the IPMSMs and PMa-SynRM, which can be given by [21]:
voltage for the IPMSMs and PMa-SynRM, which can be given by [21]:
I s q Id 2  Iq 2  I s _ max
Is = Id 2 + Iq 2 ≤ Is_max
(1)
(1)
q
2
V V
2
Vs _ max
I d+ λ
m )2 + LqLI q I 2 ≤ DC
d
√ DC
Vs_max
= p p ( L L
I
m
q
q
d d
3s3ωs
(2)
(2)


where
are armature
armature current
current and
and the
the maximum
maximum current
current provided
provided by
by the
the inverter,
inverter,
where IIss and
and IIs_max
s_max are
respectively; IIdd and
and IIqq are
are dd- and
and q-axis
q-axis currents,
currents, respectively;
respectively; L
Ldd and
and LLqq are
are dd- and
and q-axis
q-axis inductances,
inductances,
respectively;
respectively;
p
is
number
of
pole
pair;
λ
is
PM
flux
linkage;
ω
is
rotor
speed;
V
is
m
s
s_max
respectively; p is number of pole pair; λm is PM flux linkage; ωs is rotor speed; Vs_max is maximum
maximum
phase voltage;
isbattery
batteryvoltage
voltageapplied
appliedto
tothe
theinverter.
inverter.
DCis
phase
voltage; and,
and, V
VDC
The induced
back electromotive
The
induced back
electromotive force
force at
at the
the maximum
maximum speed
speed is
is determined
determined by:
by:
VVDC
√
E=
≤ DC
E pλ
pmmω
s_max
s _ max 
33
(3)
(3)
where E
ismaximum
maximumrotor
rotorspeed.
speed.
E is the induced back
back electromotive
electromotive force
force (BEMF)
(BEMF) and
and ω
ωs_max
s_max is
To maximize
constant-power speed
speed range
range that
that is
is required
required by
by
To
maximize the
the flux
flux weakening
weakening capability
capability and
and constant-power
the traction motor, the
the following
following ideal
ideal condition
condition should
should be
be satisfied
satisfied [21]:
[21]:
 LLd IIs
λmm =
d s
(4)
(4)
 LLqqIIss
λmm =
(5)
(5)
for IPMSM and
for IPMSM and
for PMa-SynRM [22]. However, this is only an ideal condition. Practically, the stator flux linkage
should be carefully designed with a limit, so that PM would not be demagnetized. If the design cannot
Energies 2018, 11, 1385
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for PMa-SynRM [22]. However, this is only an ideal condition. Practically, the stator flux linkage
should be carefully designed with a limit, so that PM would not be demagnetized. If the design
cannot fully meet the conditions in Equations (4) or (5), a reasonable high constant power speed range
can still be achieved if the values of both sides are as close as possible. Note that the conventional
d-q-axis definitions with respect to PM flux linkage are different for IPMSMs and PMa-SynRMs [21,22],
since the IPMSM is essentially a PM motor, while the PMa-SynRM is basically a SynRM with enhanced
performance using PMs. Note that the definitions of d- and q-axis for the two types of motors are
indicated in Figure 1, and these are used for all of the analysis and results that are presented.
Traction motors should be maintained at high efficiency for a speed range that is as wide as
possible. This may be achieved by employing the maximum torque per ampere (MTPA) control at low
speed for peak torque and the flux weakening control at high speed. For a wider speed range, a lower
back EMF is needed (i.e., lower λm ), and this indicates an increase of d-axis inductance and reluctance
torque referring to Equation (4) for IPMSMs [22]. For the two types of motors, the output torque can
be calculated by [6]:
T = 32p λd Id , Iq Iq − λq Id , Iq Id
λ ( I ,Iq )−λd ( Id =0,Iq )
Id Iq −
= 23 p λd Id = 0, Iq Iq + d d
Id
3
= 2 p λm Iq Iq + Ld Id , Iq − Lq Id , Iq Id Iq
λq ( Id ,Iq )
Id Iq
Iq
(6)
where λd and λq are, respectively, d- and q-axis flux linkage, p is number of pole pair, Id and Iq are,
respectively, d- and q-axis currents excitations.
The flux linkages of the motors can be defined by:
λm Iq = λd Id = 0, Iq
(7)
λd Id , Iq = Ld Id , Iq Id + λm Iq
λq Id , Iq = Lq Id , Iq Iq
(8)
(9)
It can be seen from Equations (1)–(6) that a small value of pλm is preferred for low induced BEMF
at high speed. In contrast, a large value is desirable for high torque and high efficiency. Therefore,
the PMa-SynRMs may require higher total electric loading than that for IPMSMs to achieve the same
torque that is required.
4. Performance Evaluation of Traction Motors
The design characteristics of the two types of motors under no-load and load conditions are
evaluated using finite element analysis (FEA). The PM flux linkage at no-load is given in Figure 4.
As can be seen in Figure 4a, the PM flux linkage of the V-shaped IPMSM is higher than that of
the double-layer one. This is due to a higher amount of PM that is used in the V-shaped design.
However, the total torque of the two IPMSMs is designed to be equivalent at the same current
density by using full coil pitch windings on the double-layer IPMSM and the short-pitch windings
for the V-shaped one. Figure 4b shows the PM flux linkage at no-load of the PMa-SynRM, which is
apparently smaller than that of the IPMSM. The major torque of IPMSMs is contributed by PM flux.
This is different for PMa-SynRM, whose torque mainly comes from the flux linkage that is produced
by current excitation. Thus, using large amount of PM does not help improve the output torque
of the PMa-SynRM, but increase the material cost [5]. Therefore, the PM volume in PMa-SynRM
should be kept small, but the risk of demagnetization should be avoided by maintaining the required
performance [5].
Inductance variation plays a critical role in the speed range of the IPMSM and PMa-SynRM,
as indicated in Equations (4) and (5). Therefore, accurate calculation of the inductance variation in the
entire operating range is necessary, especially when saturation occurs. Figures 5–7 show the inductance
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inductance
for entire
the double-layer
IPMSM
smaller
than that
the V-shaped
one. This
might be
variation
for the
operating range.
Asiscan
be observed,
theof
variation
of the d-axis
inductance
for
inductance for the double-layer IPMSM is smaller than that of the V-shaped one. This might be
partially
causedIPMSM
by the iron
bridges
in that
the V-shaped
rotor that
additional
flux paths.
This
the
double-layer
is smaller
than
of the V-shaped
one.creates
This might
be partially
caused
by
partially caused by the iron bridges in the V-shaped rotor that creates additional flux paths. This
leads
to
a
higher
saliency
ratio
and
a
wider
speed
range
for
the
double-layer
case,
where
the
saliency
the iron bridges in the V-shaped rotor that creates additional flux paths. This leads to a higher saliency
leads to a higher saliency ratio and a wider speed range for the double-layer case, where the saliency
ratioand
S isadefined
as: range for the double-layer case, where the saliency ratio S is defined as:
ratio
wider speed
ratio S is defined as:
S  Lq Ld
(10)
SS=
(10)
 Lqq /L
Ldd
(10)
for IPMSM, or
forIPMSM,
IPMSM,or
or
for
L
(11)
SS= LLd /L
(11)
S  Ld Lqqq
(11)
for
high saliency
saliencyratio
ratioofofthe
thePMa-SynRM.
PMa-SynRM.
forPMa-SynRM.
PMa-SynRM.The
Theinductance
inductancevariation
variation in
in Figure 7 shows aa high
for PMa-SynRM. The inductance variation in Figure 7 shows a high saliency ratio of the PMa-SynRM.
This
indicates
that
the
high
reluctance
torque
can
help
to
maintain
the
operation
at
high
speed
forthe
the
This indicates that the high reluctance torque can help
operation at high speed for
This indicates that the high reluctance torque can help to maintain the operation at high speed for the
PMa-SynRM.
PMa-SynRM.
PMa-SynRM.
Figure 4. Comparison of PM flux linkage of IPMSM and PMa-SynRM: (a) IPMSM and (b) PMaFigure
PM
flux
linkage
of IPMSM
and and
PMa-SynRM:
(a) IPMSM
and (b)
PMa-SynRM.
Figure4.4.Comparison
Comparisonofof
PM
flux
linkage
of IPMSM
PMa-SynRM:
(a) IPMSM
and
(b) PMaSynRM. Reference angle starts from q-axis.
Reference
angle
starts
from
q-axis.
SynRM. Reference angle starts from q-axis.
Figure 5. d-q-axis inductance of double-layer PM IPMSM: (a) Ld, (b) Lq.
Figure5.5.d-q-axis
d-q-axis inductance
inductance of
of double-layer
double-layer PM
PM IPMSM:
IPMSM: (a)
Figure
(a) LLdd,,(b)
(b)LLq.q .
Energies 2018, 11, 1385
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8 of 24
6. d-q-axis inductance of V-shaped PM IPMSM: (a) Ld, (b) Lq.
FigureFigure
6. d-q-axis
inductance of V-shaped PM IPMSM: (a) Ld , (b) Lq .
Figure 6. d-q-axis inductance of V-shaped PM IPMSM: (a) Ld, (b) Lq.
Figure
PMa-SynRM:(a)
(a)LdL, d(b)
, (b)LqL. q.
Figure7.7.d-q-axis
d-q-axisinductance
inductance of PMa-SynRM:
Figure 7. d-q-axis inductance of PMa-SynRM: (a) Ld , (b) Lq .
Figure
8 showsthe
theflux
fluxlinkage
linkage characteristics
characteristics of
different
Figure
8 shows
of the
the IPMSM
IPMSM(double-layer)
(double-layer)with
with
different
current
excitations
andphase
phaseangles
anglesthat
that were
were calculated
calculated using
based
onon
thethe
PMPM
current
excitations
and
usingEquations
Equations(7)–(9)
(7)–(9)
based
Figureflux
8 shows
the
flux
linkage
characteristics
of
the
IPMSM
(double-layer)
with
different
current
linkage
and
inductance
previously
obtained.
It
is
observed
that
the
IPMSM
can
be
potentially
flux linkage and inductance previously obtained. It is observed that the IPMSM can be potentially
excitations
and
phase
angles
that
were
calculated
using
Equations
(7)–(9)
based
on
the
PM
flux
linkage
demagnetizedwith
withhigh
highcurrent
current excitation
excitation and
and deep
armature
demagnetized
deep flux
flux weakening.
weakening.Therefore,
Therefore,thethe
armature
current,
current
angle,
torquefor
forMTPA
MTPA
control, and
and
flux
weakening
should
bebe
carefully
and inductance
previously
obtained.
It
is observed
that
the
IPMSMoperations
can be potentially
demagnetized
current,
current
angle,
torque
control,
flux
weakening
operations
should
carefully
analyzed excitation
order to achieve
sufficient
and safe speedTherefore,
and 10 showcurrent,
the calculated
with high
current
and deep
flux weakening.
the9 9armature
current angle,
analyzed
in in
order
to achieve
a asufficient
and
safe speed range.
range.Figures
Figures
and 10 show
the calculated
armature current, current angle, and torque characteristics of the IPMSM for wide speed range. At
armature
current,
current
angle,
and torque characteristics
of
the IPMSM
for wide analyzed
speed range.
torque for
MTPA
control,
and
flux
weakening
operations
should
be
carefully
inAt
order to
the armature current below 54.8 A, the IPMSM cannot achieve the maximum speed (7000 rpm), as
the
armature
current
below
54.8
A,
the
IPMSM
cannot
achieve
the
maximum
speed
(7000
rpm),
as
achieve a sufficient
and10.
safe
range.
Figures
and 10
show
the calculated
armature
shown in Figure
Thisspeed
is because
the low
armature9 current
cannot
sufficiently
weaken the
PM flux current,
shown in Figure 10. This is because the low armature current cannot sufficiently weaken the PM flux
to extend
operating
speed withinof
thethe
voltage
limit. for
The wide
PM flux
can berange.
effectively
for current
current angle,
and the
torque
characteristics
IPMSM
speed
At weakened
the armature
to extend
the operating
speed than
within
the
The
flux can be effectively weakened for
the
armature
current
greater
54.8
A voltage
(current limit.
density
9.7PM
A(7000
rms/mm 2), for the cases beyond which
below 54.8
A,
the
IPMSM
cannot
achieve
the
maximum
speed
rpm),
as
shown
in
Figure
10. This is
2), for the cases beyond which
theaarmature
current
54.8 with
A (current
density
9.7 Beyond
Arms/mmthe
wide speed
rangegreater
can bethan
reached
the voltage
limit.
base speed, the armature
becauseathe
low
armature
current
cannot
sufficiently
weaken
the PM
fluxuntil
to extend
the operating
wide
speed
range can
bethe
reached
voltage
limit. for
Beyond
the base
speed,
armature
current
is maintained
and
currentwith
phasethe
angle
is increased
flux weakening
thethe
maximum
speed within
the
voltage
limit.
The
PM
flux
can
be
effectively
weakened
for
the
armature
current
is
maintained
and
the
current
phase
angle
is
increased
for
flux
weakening
until
the
maximum
speed. Note that the base speed depends on the voltage or the power limit. High armature current current
2 ), for
speed.
Note
speed
depends
the
voltage
or
power
limit.
High
armature
would
also
leadthe
to abase
low
base speed.
Figure
10
shows
thatthe
thethe
IPMSM
hits
the voltage
limit
at a current
base
greater than
54.8
Athat
(current
density
9.7 A
/mm
cases
beyond
which
a wide
speed range
rmson
would
also
lead
to
a
low
base
speed.
Figure
10
shows
that
the
IPMSM
hits
the
voltage
limit
at
base
speed
of
2500
rpm
(achievable
base
speed),
an
armature
current
of
54.8
A,
and
a
current
density
of
can be reached with the voltage limit. Beyond the base speed, the armature current isamaintained
2 without
9.7 A
/mmrpm
force cooling.
Nevertheless,
the speed
range of
of 54.8
the IPMSM
be enhanced
if of
speed
ofrms2500
(achievable
base speed),
an armature
current
A, andcan
a current
density
and the current
phase
angle so
is that
increased
for flux
weakening
until the
maximum
speed. Note that the
2 without
cooling
is usedforce
more current
can be input
to improve
torque
at high
speed.
9.7 better
Arms/mm
cooling.
Nevertheless,
the speed
rangethe
of the
IPMSM
can
be enhanced if
base speed
depends
the
voltage
the
power
limit.
armature
current
would
also lead to
Contrarily,
the
PMa-SynRM
can
achieve
theinput
maximum
speed
(7000
rpm)
armature
better
cooling
ison
used
so
that moreor
current
can be
toHigh
improve
the
torque
atwith
highlow
speed.
(lower
than10
40shows
A) for the
MTPA
and
flux
as shown
in
Figures
11 and
a low basecurrent
speed.
Figure
that
IPMSM
hits the operations,
voltage
limit
at a with
base
speed
of 2500 rpm
Contrarily,
the
PMa-SynRM
canthe
achieve
theweakening
maximum
speed (7000
rpm)
low
armature
2 without
12.
This
is due
toan
the
low
linkage,
which
be a
easily
weakened
withofa9.7
small
armature
current
(lower
than
40
A)
forPM
theflux
MTPA
and
weakening
operations,
as shown
in Figures
11 and
(achievable
base
speed),
armature
current
of flux
54.8
A,can
and
current
density
Arms
/mm
current.
Therefore,
the
torque-speed
curve can
be can
extended
under
voltage limit
toa asmall
high armature
speed.
12.
This
is
due
to
the
low
PM
flux
linkage,
which
be
easily
weakened
with
force cooling.
Nevertheless, the speed range of the IPMSM can be enhanced if better cooling is used so
However, the base speed reduces at maximum torque where the voltage saturates due to the high
current.
Therefore, the torque-speed curve can be extended under voltage limit to a high speed.
that more
current
can be input to improve the torque at high speed.
However, the base speed reduces at maximum torque where the voltage saturates due to the high
Contrarily, the PMa-SynRM can achieve the maximum speed (7000 rpm) with low armature
current (lower than 40 A) for the MTPA and flux weakening operations, as shown in Figures 11 and 12.
This is due to the low PM flux linkage, which can be easily weakened with a small armature current.
Therefore, the torque-speed curve can be extended under voltage limit to a high speed. However,
the base speed reduces at maximum torque where the voltage saturates due to the high current and
winding resistance. The high current weakens the PM flux and it increases the reluctance torque,
leading to speed extension under the voltage limit.
Energies 2018, 11, x FOR PEER REVIEW
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9 of 24
9 of 24
current2018,
and11,
winding
resistance. The high current weakens the PM flux and it increases the reluctance
Energies
1385
9 of 24
current and winding resistance. The high current weakens the PM flux and it increases the reluctance
torque, leading to speed extension under the voltage limit.
torque, leading to speed extension under the voltage limit.
Figure 8. Flux linkage variations on (a) d- and (b) q-axis of IPMSM with respect to current and current
Figure
Fluxlinkage
linkagevariations
variations
d- and
(b) q-axis
of IPMSM
with respect
to current
and
Figure 8. Flux
onon
(a) (a)
d- and
(b) q-axis
of IPMSM
with respect
to current
and current
angle.
current
angle. angle.
Figure 9. (a) Current and (b) current angle variation of IPMSM with speed.
Figure 9.
9. (a)
(a) Current
Current and
and (b)
(b) current
current angle
angle variation
variation of
of IPMSM
IPMSM with
with speed.
speed.
Figure
Energies 2018, 11, 1385
Energies 2018, 11, x FOR PEER REVIEW
Energies 2018, 11, x FOR PEER REVIEW
Figure 10. (a) Torque-current angle and (b) torque-speed curves of IPMSM.
Figure
torque-speedcurves
curvesofofIPMSM.
IPMSM.
Figure10.
10.(a)
(a)Torque-current
Torque-current angle
angle and (b) torque-speed
Figure 11. (a) Current and (b) current angle variations of PMa-SynRM with speed.
Figure 11. (a) Current and (b) current angle variations of PMa-SynRM with speed.
Figure 11. (a) Current and (b) current angle variations of PMa-SynRM with speed.
10 of 24
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10 of 24
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11 of 24
Figure 12. The torque-speed curves of PMa-SynRM.
Figure 12. The torque-speed curves of PMa-SynRM.
5. Driving Cycle Applications
5. Driving Cycle Applications
The combination of UDDS and HWFET driving cycles is used to evaluate the traction motor
The combination of UDDS and HWFET driving cycles is used to evaluate the traction motor
performance based on the vehicle specifications, including the battery and the drivetrain properties,
performance based on the vehicle specifications, including the battery and the drivetrain properties,
as shown in Table 2. The combined UDDS and HWFET is converted into traction motor speed, as
as shown in Table 2. The combined UDDS and HWFET is converted into traction motor speed,
shown in Figure 13a. The UDDS is suitable for urban lightweight vehicles with 23 start-stop cycles
as shown in Figure 13a. The UDDS is suitable for urban lightweight vehicles with 23 start-stop cycles
and a maximum speed of 91.2 km/h. There are two phases of speed: a “cold start” phase of 505 s for
and a maximum speed of 91.2 km/h. There are two phases of speed: a “cold start” phase of 505 s
a distance of 5.78 km with 41.2 km/h average speed, and a “transient phase” of 864 s in the total
for a distance of 5.78 km with 41.2 km/h average speed, and a “transient phase” of 864 s in the total
duration of 1369 s. The HWFET is used to test the thermal condition of the traction motors without
duration of 1369 s. The HWFET is used to test the thermal condition of the traction motors without
stop cycles. It is suitable for highway driving with an average speed of 77 km/h and a peak speed of
stop cycles. It is suitable for highway driving with an average speed of 77 km/h and a peak speed of
97 km/h in a total duration of 765 s and 16.45 km route [16].
97 km/h in a total duration of 765 s and 16.45 km route [16].
The torque of the traction motor should be generated and delivered to satisfy the vehicle
The torque of the traction motor should be generated and delivered to satisfy the vehicle dynamics
dynamics during the operation of the prescribed driving cycles, i.e., short-term overload (peak)
during the operation of the prescribed driving cycles, i.e., short-term overload (peak) torque output
torque output for acceleration/climbing, and the effective energy utilization in the medium- and highfor acceleration/climbing, and the effective energy utilization in the medium- and high-speed ranges.
speed ranges. Therefore, the root-mean-square (RMS) torque is defined to relate the operating
Therefore, the root-mean-square (RMS) torque is defined to relate the operating condition to the
condition to the thermal limits of the traction motors in the driving cycle, as given by [8]:
thermal limits of the traction motors in the driving cycle, as given by [8]:
t
v 1 2 2
Trms u
(12)
ZTt2 (t )dt
ut
1 t1
u cycle
2
Trms = t
T (t)dt
(12)
tcycle
t
where tcycle is the time period of the entire driving cycle
1 and T(t) is the instantaneous torque.
Figure 13 shows the motor speed, load torque, and power in the motor mode, and the
where
tcycle is the
time period
the entire
driving cycle
andand
T(t) is
the instantaneous
torque.
regenerative
braking
mode of
over
the combined
UDDS
HYFET
driving cycles,
where the
Figure
13
shows
the
motor
speed,
load
torque,
and
power
in
the
motor
mode,
and
the
regenerative
maximum speed is 97 km/h. It can be seen that for the target vehicle, the driving cycle requires a
braking
mode
overand
thepeak
combined
and HYFET60
driving
cycles,
where
the maximum
speedthe
is
maximum
torque
powerUDDS
of approximately
Nm and
20 kW,
respectively.
However,
97
km/h.
It
can
be
seen
that
for
the
target
vehicle,
the
driving
cycle
requires
a
maximum
torque
and
RMS torque is about 29.5 Nm and the average power is only 5.4 kW for the whole cycle. Note that
peak
powerand
of power
approximately
60 Nm by
and
kW, respectively.
However,
the RMS
torque
isshared
about
the torque
that is required
the20vehicle
calculated above
is assumed
to be
evenly
29.5
Nm
and
the
average
power
is
only
5.4
kW
for
the
whole
cycle.
Note
that
the
torque
and
power
by the front and rear motors, as seen in Figure 2. Therefore, the motor specifications in Table 1 satisfy
that
required
byprescribed
the vehicledriving
calculated
above
is assumed
to be evenlyofshared
by the and
frontPMaand
this is
vehicle
if the
cycles
are used.
The performance
the IPMSMs
rear
motors,
as seen
in Figure
2. on
Therefore,
theand
motor
specifications
in Table
satisfy
this vehicle
if
SynRM
will be
evaluated
based
the torque
power
that is required
for 1the
prescribed
driving
the
prescribed
driving
cycles
are
used.
The
performance
of
the
IPMSMs
and
PMa-SynRM
will
be
cycles. Note that, practically, this lightweight vehicle may not be suitable for highway driving.
evaluated
on make
the torque
andreference
power that
is required
the prescribed
driving in
cycles.
Note that,
However, based
it would
a useful
if the
highwayfor
driving
can be included
the analysis
for
practically,
this
lightweight
vehicle
may
not
be
suitable
for
highway
driving.
However,
it
would
make
design considerations of traction motors.
a useful reference if the highway driving can be included in the analysis for design considerations of
traction motors.
Energies 2018, 11, 1385
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Energies 2018, 11, x FOR PEER REVIEW
12 of 24
Figure 13. Motor (a) speed; (b) torque; and, (c) power over the driving cycles.
Figure 13. Motor (a) speed; (b) torque; and, (c) power over the driving cycles.
6. Comparison of Motor Performance in Driving Cycles
6. Comparison of Motor Performance in Driving Cycles
Again, the FEA (JMAG software) is used for simulation of the motor electromagnetic
Again, the FEA
(JMAG
software)
used for simulation
of the motor
performance.
Figure
14 shows
theistorque-speed
curves of
IPMSMelectromagnetic
(double-layer) performance.
and PMaFigure
14 shows
the
torque-speed
curves ofconditions,
the IPMSMwhere
(double-layer)
and PMa-SynRM
the
peak
SynRM
under
the
peak and continuous
the maximum
torque of the under
IPMSM
and
is 57 Nm and
68 the
Nm,
respectively.
Theofrated
conditions
the motors isshould
and PMa-SynRM
continuous conditions,
where
maximum
torque
the IPMSM
and of
PMa-SynRM
57 Nmbeand
determined
usingThe
thermal
analysis,
which
discussed
later.
this stage,
theanalysis,
rated
68 Nm,
respectively.
rated
conditions
ofwill
the be
motors
should
beNevertheless,
determined at
using
thermal
torque
types oflater.
motors
is preliminarily
determined
byrated
the root-mean-square
torqueofthat
was is
which
will of
beboth
discussed
Nevertheless,
at this
stage, the
torque of both types
motors
calculated
from
the
driving
cycles
using
Equation
(12),
which
is
29.5
Nm.
Then,
beyond
the
rated
preliminarily determined by the root-mean-square torque that was calculated from the driving cycles
torque
in Figure
the speed
increases
bythe
increasing
the current
angles
weakening
using
Equation
(12),14,
which
is 29.5gradually
Nm. Then,
beyond
rated torque
in Figure
14,for
theflux
speed
gradually
with the same current amplitude. Thus, the two IPMSMs have similar characteristics.
increases by increasing the current angles for flux weakening with the same current amplitude. Thus,
the two IPMSMs have similar characteristics.
Energies 2018, 11, 1385
Energies 2018, 11, x FOR PEER REVIEW
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13 of 24
Figure 14. Torque distribution profiles for (a) IPMSMs and (b) PMa-SynRMs over the driving cycles.
Figure 14. Torque distribution profiles for (a) IPMSMs and (b) PMa-SynRMs over the driving cycles.
It can be seen in Figure 14, that, under the UDDS and HWFET driving cycles, some operating
It are
canhigher
be seen
in Figure
14,conditions
that, under
and HWFET
driving cycles,
some
operating
points
than
the rated
of the
bothUDDS
the IPMSM
and PMa-SynRM.
For the
PMa-SynRM,
points
are
higher
than
the
rated
conditions
of
both
the
IPMSM
and
PMa-SynRM.
For
the
PMa-SynRM,
some operating points are even out of the maximum capability. This appears that the 10 kW PMasome operating
points
even
outoperation
of the maximum
capability.
appears
thatEven
the 10
SynRM
is insufficient
forare
high
speed
of the vehicles
due to This
the small
torque.
for kW
the
PMa-SynRM
is
insufficient
for
high
speed
operation
of
the
vehicles
due
to
the
small
torque.
Even
for
IPMSM, the rated power is slightly too low for high speed driving. It should be noted that operation
thehighway
IPMSM, the
rated
powerlasts
is slightly
too low
for high
speed
It should be
that operation
in
mode
usually
for a long
period
so that
thedriving.
rated condition
of noted
the traction
motors
in
highway
mode
usually
lasts
for
a
long
period
so
that
the
rated
condition
of
the
traction
motors
should cover this driving cycle. From the previous results, it is found that the PMa-SynRM seems
to
should
cover
Fromsuch
the previous
it isitsfound
that
the PMa-SynRM
seems
to
be
suitable
forthis
lowdriving
speed cycle.
operation,
as urban results,
bus, since
output
power
drops at high
speed.
be contrast,
suitable for
speed
operation,
as urban
output power
drops at high
speed.
In
thelow
IPMSM
can
be easilysuch
improved
for bus,
highsince
speeditsoperation
by improving
the cooling
In
contrast,
the
IPMSM
can
be
easily
improved
for
high
speed
operation
by
improving
the
cooling
capability or modifying the design (no forced cooling so far). This accounts for the importance of
capability
or modifying
the design
coolinglater.
so far).
This
the importance
of
thermal
design
and analysis,
which (no
willforced
be discussed
Note
thataccounts
the datafor
sampling
time is one
thermalfor
design
analysis, which
be discussed
later. (i.e.,
Noteallthat
the dots
datain
sampling
time is one
second
all ofand
the operating
pointswill
of both
driving cycles
of the
Figure 14).
second
for
all
of
the
operating
points
of
both
driving
cycles
(i.e.,
all
of
the
dots
in
Figure
14).
Figure 15a,b shows the efficiency map of the double-layers and the V-shaped IPMSMs. The
Figure
15a,b shows
map
oftwo
the double-layers
and
theand
V-shaped
IPMSMs. Theand
highest
highest
efficiency
(dark the
redefficiency
regions) for
the
cases is beyond
96%
95%, respectively,
this
efficiency
(dark
red
regions)
for
the
two
cases
is
beyond
96%
and
95%,
respectively,
and
this
is
within
is within a speed range of 2000 rpm to 4000 rpm and a torque lower than 30 Nm. The double-layers
a speed range
of 2000 higher
rpm to efficiency
4000 rpm and
torqueoperating
lower than
30 Nm.
has
IPMSM
has a slightly
for aawider
range
thanThe
the double-layers
V-shaped one.IPMSM
This could
a slightly
for a wider for
operating
range than
the V-shaped
one.
This could
be due to
be
due to higher
a higherefficiency
total Ampere-turns
the V-shaped
IPMSM.
For the two
IPMSMs,
the operating
a
higher
total
Ampere-turns
for
the
V-shaped
IPMSM.
For
the
two
IPMSMs,
the
operating
points
for the
the
points for the UDDS driving cycle (blue dots) mostly locate around 2000 rpm to 4000 rpm, where
UDDS
driving
cycle
(blue
dots)
mostly
locate
around
2000
rpm
to
4000
rpm,
where
the
high
efficiency
high efficiency region is. Meanwhile, the operating points for the HWFET driving cycle (green dots)
region
is. Meanwhile,
the operating
points
for the
HWFET
driving
cycle
withinThis
the
fall
within
the lower efficiency
regions,
ranging
from
5000 rpm
to 7000
rpm(green
for thedots)
two fall
IPMSMs.
lower
efficiency
regions,
ranging
from
5000
rpm
to
7000
rpm
for
the
two
IPMSMs.
This
may
be
caused
may be caused by a large part of the armature current that is used to weaken the flux at high speed
by a large
part
of the
armatureiscurrent
that(Figure
is used 8).
to weaken
the flux
high speed where
deep
flux
where
deep
flux
weakening
required
Contrarily,
the at
PMa-SynRM
achieves
higher
weakening
is
required
(Figure
8).
Contrarily,
the
PMa-SynRM
achieves
higher
efficiency
at
high
speed
efficiency at high speed due to the reduced armature current, as shown in Figure 15c. Therefore, it is
due to the
armature
as shown
in Figure 15c.
Therefore,
it is suitable
forofthe
HWFET
suitable
forreduced
the HWFET
and current,
the higher
speed operating
points
of the UDDS
in terms
efficiency.
and the
higher speed
operating
of 2000
the UDDS
in terms
of efficiency.
Thethe
maximum
efficiency
The
maximum
efficiency
is 95%points
beyond
rpm and
it is maintained
until
maximum
speed.
is
95%
beyond
2000
rpm
and
it
is
maintained
until
the
maximum
speed.
However,
this
PMa-SynRM
However, this PMa-SynRM requires a redesign or decent forced cooling in order to fully cover the
operating points of the driving cycles. Again, the data sampling time is also one second here.
Energies 2018, 11, 1385
14 of 24
requires a redesign or decent forced cooling in order to fully cover the operating points of the driving
cycles.
Again,
sampling
Energies
2018,the
11, xdata
FOR PEER
REVIEWtime is also one second here.
14 of 24
Figure 15. Efficiency map of IPMSMs and PMa-SynRM over the driving cycles: (a) double layers
Figure 15. Efficiency map of IPMSMs and PMa-SynRM over the driving cycles: (a) double layers
magnet IPMSM, (b) v-shaped magnets IPMSM, and (c) PMa-SynRM.
magnet IPMSM, (b) v-shaped magnets IPMSM, and (c) PMa-SynRM.
7. Thermal Analysis with Driving Cycle
7. Thermal Analysis with Driving Cycle
Thermal analysis (using MotorCAD) for the IPMSMs and PMa-SynRM is conducted for the
prescribedanalysis
driving (using
cycles. MotorCAD)
This would be
for the and
design
of traction motors
since the
Thermal
forcritical
the IPMSMs
PMa-SynRM
is conducted
for the
performance
be limited
by thermal
conditions.
First,
the operating
range
of the
traction
motors
prescribed
drivingcan
cycles.
This would
be critical
for the
design
of traction
motors
since
the performance
forlimited
the driving
cycles under
prescribed
limits
(PM:of
130
winding:
140 °C)
can be
by thermal
conditions.
First,temperature
the operating
range
the°C;
traction
motors
forwithout
the driving
forced
cooling
is
investigated.
As
shown
in
Figure
13b,
the
output
torque
of
the
traction
motors
◦
◦
cycles under prescribed temperature limits (PM: 130 C; winding: 140 C) without forcedvaries
cooling is
significantly within a driving cycle. Therefore, to represent the equivalent effect, the root-meaninvestigated. As shown in Figure 13b, the output torque of the traction motors varies significantly
square torque within a cycle is taken, as calculated by Equation (12). (29.5 Nm, as previously
within a driving cycle. Therefore, to represent the equivalent effect, the root-mean-square torque
discussed).
within a cycle is taken, as calculated by Equation (12). (29.5 Nm, as previously discussed).
Energies 2018, 11, 1385
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15 of 24
15 of 24
Figure 16 shows the torque-speed profiles under a series of temperature limits in the winding and
Figure 16 shows the torque-speed profiles under a series of temperature limits in the winding
magnet until the maximum limits (PM: 130 ◦ C; winding: 140 ◦ C) for the double-layer IPMSM. It can be
and magnet until the maximum limits (PM: 130 °C; winding: 140 °C) for the double-layer IPMSM. It
seen
that
the effective
torque oftorque
this motor
achieve
30 Nm 30
under
the temperature
limitslimits
of 140of◦ C
can
be seen
that the effective
of thiscan
motor
can achieve
Nm under
the temperature
◦
for140
winding
130 C
for130
PM.
thatNote
the PM
is N35SH,
maximum
operating
°C forand
winding
and
°CNote
for PM.
thatused
the PM
used is whose
N35SH,product
whose product
maximum
◦ C. Similarly, as shown in Figure 17, the effective torque for the V-shaped IPMSM
temperature
is
150
operating temperature is 150 °C. Similarly, as shown in Figure 17, the effective torque for the V◦ C. Therefore, the PM of
canshaped
also achieve
30can
Nm,
with
a slightly
less with
peak amagnet
of 124 temperature
IPMSM
also
achieve
30 Nm,
slightlytemperature
less peak magnet
of 124 °C.
theTherefore,
V-shapedthe
IPMSM
is
safer
than
that
of
the
double-layer
one,
despite
a
slightly
lower
rated
torque.
PM of the V-shaped IPMSM is safer than that of the double-layer one, despite a slightly
Thelower
analysis
that the results
double-layer
andthe
V-shaped
IPMSMs
can both operate
theboth
rated
ratedresults
torque.show
The analysis
show that
double-layer
and V-shaped
IPMSMsatcan
condition
forcedcondition
cooling. However,
water cooling.
cooling should
still water
be employed
fully satisfy
operatewithout
at the rated
without forced
However,
coolingtoshould
still bethe
employed
to fully satisfy
the UDDS,
andcycles.
particularly HWFET driving cycles.
UDDS,
and particularly
HWFET
driving
The
thermal
analysis
for
the
PMa-SynRM
withoutforced
forcedcooling
coolingisisshown
shownininFigure
Figure18,
18,where
wherethe
The thermal analysis for the PMa-SynRM without
the motor
to reach
the torque,
as calculated
by Equation
Water
cooling
may
help
reducethe
motor
fails tofails
reach
the torque,
as calculated
by Equation
(12).(12).
Water
cooling
may
help
toto
reduce
the winding
and magnet
temperature
fitrequirement
into the requirement
of the
driving
cycles
for the
winding
and magnet
temperature
and to fitand
intotothe
of the driving
cycles
for the
PMa-SynRM.
PMa-SynRM.
Nevertheless,
the magnet
ofbePMa-SynRM
be redesigned to avoid
Nevertheless,
the magnet
of PMa-SynRM
should
redesigned toshould
avoid demagnetization.
demagnetization.
Figure 19 shows the temperature rise of the winding, stator, and PM of all the three motor in
Figure
19 shows theconditions
temperaturefor
rise
the winding,
andthe
PMwinding
of all the three
motor inof
thethe
the peak
and continuous
a of
period.
As canstator,
be seen,
temperature
peak and continuous conditions for a period. As can be seen, the winding temperature of the PMaPMa-SynRM is higher than that of the IPMSMs although their current densities are almost the same
SynRM is higher than that of the IPMSMs although their current densities are almost the same
(around 16.5 Arms /mm22 for peak torque). This is because the phase resistance of the PMa-SynRM
(around 16.5 Arms/mm for peak torque). This is because the phase resistance of the PMa-SynRM is
is double that of the IPMSMs. Therefore, the PMa-SynRM can only operate about 4 min at the peak
double that of the IPMSMs. Therefore, the PMa-SynRM can only operate about 4 min at the peak
condition and about 26 min at the rated condition, while the IPMSM can achieve 8 and 40 min,
condition and about 26 min at the rated condition, while the IPMSM can achieve 8 and 40 min,
respectively.
of the
the PMa-SynRM
PMa-SynRMleads
leadstotothe
thehigh
highmagnet
magnet
respectively.Also,
Also,the
thehigh
highwinding
winding temperature
temperature of
temperature,
as
shown
in
Figure
18.
The
above
analysis
can
also
be
verified
by
the
simulation
results
temperature, as shown in Figure 18. The above analysis can also be verified by the simulation results
with
the
driving
cycles,
as
shown
in
Figure
20,
where
the
winding
temperature
of
the
PMa-SynRM
with the driving cycles, as shown in Figure 20, where the winding temperature of the PMa-SynRM is is
higher
than
that
ofof
IPMSM,
can operate
operatemore
moresafely
safelythan
thanthe
thePMa-SynRM
PMa-SynRM
higher
than
that
IPMSM,and
andtherefore,
therefore,the
theIPMSMs
IPMSMs can
forfor
thethe
driving
cycles.
driving
cycles.
Figure 16. The temperature distribution profiles for (a) winding and (b) magnet of double-layer
Figure 16. The temperature distribution profiles for (a) winding and (b) magnet of double-layer IPMSM.
IPMSM.
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Figure 17. The temperature distribution profiles for (a) winding and (b) PM of V-shaped IPMSM.
Figure
17.17.The
for (a)
(a) winding
windingand
and(b)
(b)PM
PMofofV-shaped
V-shaped
IPMSM.
Figure
Thetemperature
temperaturedistribution
distribution profiles
profiles for
IPMSM.
Figure 18. The temperature distribution profiles for (a) winding and (b) PM of PMa-SynRM.
Figure 18. The temperature distribution profiles for (a) winding and (b) PM of PMa-SynRM.
Figure 18. The temperature distribution profiles for (a) winding and (b) PM of PMa-SynRM.
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Figure 19. The temperature rise for winding and magnet: (a) peak; and, (b) rated/continuous
Figure 19. The temperature rise for winding and magnet: (a) peak; and, (b) rated/continuous
Figure
19. The temperature rise for winding and magnet: (a) peak; and, (b) rated/continuous operations.
operations.
operations.
Figure 20. The temperature rise for winding and magnet: (a) UDDS, and (b) HWFET.
Figure20.
20.The
Thetemperature
temperaturerise
rise for
for winding
winding and
HWFET.
Figure
and magnet:
magnet:(a)
(a)UDDS,
UDDS,and
and(b)(b)
HWFET.
Energies 2018, 11, 1385
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8. Discussions
According to the previous analysis, the benefits and drawbacks of the IPMSMs and PMa-SynRM
for EV application are summarized as below:
-
-
-
-
The IPMSMs possess the benefit of high PM flux linkage, low armature current, and current angle
to reach the maximum torque. Meanwhile, the torque of PMa-SynRM is almost derived from the
armature current. Therefore, a higher armature current and current angle are applied in order to
generate the maximum torque for PMa-SynRM.
The PMa-SynRM can achieve very high speed at low armature current because the reluctance
torque and saliency ratio are higher than that of IPMSMs. In addition, the PMa-SynRM has
a higher efficiency at high speed than that of IPMSMs. This is the advantage of PMa-SynRM for
high speed application.
To produce the same power as the IPMSMs, the PMa-SynRM should be designed with a higher
motor volume than that of the IPMSM. Moreover, higher electrical loading is needed for the
PMa-SynRM, and this can lead to temperature rise that limits the operating range.
The IPMSMs are more advantageous in urban driving because of their higher performance and
efficiency at lower speed.
The PMa-SynRM is more suitable than the IPMSM in the highway driving cycle in terms of
efficiency. However, the design should be improved by slightly increasing the PM amount so that
the winding temperature can be brought down and the torque at high speed can be enhanced.
This indicates a better design would lie between the two types of motors that are presented in
this paper in terms of PM amount that is employed or sharing between the PM and reluctance
torques. Moreover, better cooling may be necessary.
9. Experiments
The three motors were fabricated, as shown in Figure 21. The experimental results are shown
in Figures 22 and 23. In Figure 22, the BEMF (peak value) comparison shows that the simulations
and experiments agree well for the three motors. Figure 23 shows the torque and power versus speed
curves for the three motors at the prescribed rated conditions. It can be observed that the motors can
be achieved the 30 Nm rated torque and 6.6 kW rated power. However, the power for the PMa-SynRM
cannot maintain beyond 2100 rpm, while that for the IPMSMs can. Figure 24 shows the efficiency
versus speed curves of the three motors at the rated condition. Note that the three motors were
tested at different times for different projects so the measured speed ranges varied. The measured
maximum efficiency for the double-layers IPMSM, V-shaped IPMSM and PMa-SynRM are 96.7%,
95.6%, and 93%, respectively. The largest error between the simulations and the experiments for
the three motors is about 2.5% (based on the simulations). This indicates that the simulations and
experiments agree well. The error can be attributed to some factors that are not considered in the
simulations (e.g., mechanical losses). Figure 25 shows the peak torque of the IPMSMs and PMa-SynRM
at their own base speeds (Table 1), where all of the motors can achieve the maximum torque with the
maximum current excitation. The comparison in Figure 25 also shows that the FEA and experiments
agree well.
Unlike the thermal imaging method that is presented in [14,15], this paper employed the
thermocouples for temperature measurement of the double-layers IPMSM when considering facility
availability, as the test setup shown in Figure 26. To ensure the safety in the experiments, only a light
load is applied in simulation and measurement with a 34 Arms current, 1800 rpm speed, and 15 Nm
torque for 10 min operation. Figure 27 shows the simulation model and some sample temperatures in
different parts of the motor. Figure 28 shows the comparison between the measurement and simulation
for the motor housing within 10 min operation. Both cases agree well. Although the above experiments
are limited by the laboratory facilities, the accuracy of the simulations is still properly validated. Thus,
the simulations that are presented in this paper should be sufficiently reliable.
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2018, 11,
11, xx FOR
FOR PEER
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24
Figure
21.
Figure 21.
21. Prototypes
Prototypes of
of IPMSMs
IPMSMs and
and PMa-SynRM:
PMa-SynRM: (a)
Figure
Prototypes
of
IPMSMs
and
PMa-SynRM:
(a) stator
stator of
of double-layers
double-layers IPMSM
IPMSM with
with winding,
winding,
(b)
stator
of
V-Shaped
IPMSM
without
winding,
(c)
stator
of
PMa-SynRM
with
winding,
(d)
rotor
of
(b) stator
stator of
of V-Shaped
V-ShapedIPMSM
IPMSM without
without winding,
winding, (c)
(c) stator
stator of
of PMa-SynRM
PMa-SynRM with
with winding,
winding, (d)
(d) rotor
rotor of
of
(b)
double-layers
IPMSM
with
PM,
(e)
rotor
of
V-shaped
IPMSM
without
PM,
and
(f)
rotor
of
PMadouble-layers
(e)(e)
rotor
of V-shaped
IPMSM
without
PM, and
rotor
PMa-SynRM
double-layersIPMSM
IPMSMwith
withPM,
PM,
rotor
of V-shaped
IPMSM
without
PM,(f)and
(f)ofrotor
of PMaSynRM
PM.
without
PM.
SynRM without
without
PM.
Figure
Figure 22.
22. Comparison
Comparison of
of back
back electromotive
electromotive force
force (BEMF)
(BEMF) of
of IPMSMs
IPMSMs and
and PMa-SynRM.
PMa-SynRM.
Figure 22. Comparison of back electromotive force (BEMF) of IPMSMs and PMa-SynRM.
Energies 2018, 11, 1385
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Figure 23. Torque-power vs speed curve at rated condition: (a) double layers IPMSM, (b) V-Shaped
Figure 23. Torque-power vs speed curve at rated condition: (a) double layers IPMSM, (b) V-Shaped
IPMSM, and (c) PMa-SynRM.
IPMSM, and (c) PMa-SynRM.
Energies 2018, 11, 1385
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Figure 24. Efficiency vs speed curve at rated condition: (a) double layers IPMSM, (b) V-Shaped
Figure 24. Efficiency vs speed curve at rated condition: (a) double layers IPMSM, (b) V-Shaped IPMSM,
IPMSM, and (c) PMa-SynRM.
and (c) PMa-SynRM.
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Figure 25. Torque comparison of IPMSMs and PMa-SynRM.
Figure 25. Torque comparison of IPMSMs and PMa-SynRM.
Figure 25. Torque comparison of IPMSMs and PMa-SynRM.
Figure 25. Torque comparison of IPMSMs and PMa-SynRM.
Figure 26. Temperature measurement setup for the double layer IPMSM.
Figure 26. Temperature measurement setup for the double layer IPMSM.
Figure
26. 26.
Temperature
forthe
thedouble
double
layer
IPMSM.
Figure
Temperaturemeasurement
measurement setup
setup for
layer
IPMSM.
Figure 27. Thermal simulation model and temperature for the double layer IPMSM.
Figure 27. Thermal simulation model and temperature for the double layer IPMSM.
Figure 27. Thermal simulation model and temperature for the double layer IPMSM.
Figure 27. Thermal simulation model and temperature for the double layer IPMSM.
Energies 2018, 11, 1385
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Figure
Figure28.
28.Temperature
TemperatureMeasurement
Measurement of
of double
double layer
layer IPMSM.
IPMSM.
10. Conclusions
10. Conclusions
This paper has investigated the characteristics of IPMSMs and PMa-SynRM in terms of
This paper has investigated the characteristics of IPMSMs and PMa-SynRM in terms of
electromagnetic and thermal performance via driving cycles for EV applications. It is found that the
electromagnetic and thermal performance via driving cycles for EV applications. It is found that
PMa-SynRM has an advantage in high speed operation for its high efficiency, despite insufficient
the PMa-SynRM has an advantage in high speed operation for its high efficiency, despite insufficient
torque. Instead, the IPMSMs possess better efficiency at low speed for the urban driving cycle. The
torque. Instead, the IPMSMs possess better efficiency at low speed for the urban driving cycle.
thermal analysis showed that the IPMSMs possess better performance than the PMa-SynRM subject
The thermal analysis showed that the IPMSMs possess better performance than the PMa-SynRM subject
to temperature limits. In addition, the analysis results show that the operating range of the motors
to temperature limits. In addition, the analysis results show that the operating range of the motors can
can be limited if proper cooling is not employed. Therefore, to achieve the same required
be limited if proper cooling is not employed. Therefore, to achieve the same required performance,
performance, the traction motors should be designed differently, according to the conditions with or
the traction motors should be designed differently, according to the conditions with or without cooling
without cooling systems and the cooling capacity. The analysis in this paper has demonstrated the
systems and the cooling capacity. The analysis in this paper has demonstrated the advantages and
advantages and disadvantages of the IPMSMs and PMa-SynRM for EV tractions and the suitability
disadvantages of the IPMSMs and PMa-SynRM for EV tractions and the suitability of these motors for
of these motors for specific driving cycles. Suggestions have also been provided for the design
specific driving cycles. Suggestions have also been provided for the design improvement of traction
improvement of traction motors for future study. Three prototypes were fabricated and the
motors for future study. Three prototypes were fabricated and the measurement validates the analysis
measurement validates the analysis in this paper.
in this paper.
Author
Huynhand
conceived
and the
conducted
research
andpaper.
wrote the
paper.
Min-Fu
Author Contributions:
Contributions: Thanh
T.A.H.Anh
conceived
conducted
researchthe
and
wrote the
M.-F.H.
suggested
Hsieh
suggested
theguided
research
topic,
Thanh
Anh Huynh
to complete
thefinalize
researchthe
and
helped
edit and
the research
topic,
T.A.H.
to guided
complete
the research
and helped
edit and
paper.
M.-F.H.
also
provided
laboratory
space
and
facilities
for the
thislaboratory
study.
finalize
thethe
paper.
Min-Fu
Hsieh
also
provided
space and facilities for this study.
This work
work was
was in
in part
partsupported
supportedby
byTaiwan’s
Taiwan’s Ministry
Ministry of
of Science
Scienceand
andTechnology
Technology under
under
Acknowledgments: This
Acknowledgments:
contracts MOST 106-2622-8-006-001 and 106-2218-E-006-023. The authors would like to thank Jian-Shin Lai,
contracts MOST 106-2622-8-006-001 and 106-2218-E-006-023. The authors would like to thank Jian-Shin Lai, PingPing-Yuan Wang and the lab-mates for the assistance in experiments.
Yuan Wang and the lab-mates for the assistance in experiments.
Conflicts of Interest: The authors declare no conflict of interest.
Conflicts of Interest: The authors declare no conflict of interest.
References
References
1.
1.
2.
2.
3.
3.
4.
4.
5.
5.
Ruiwu, C.; Chris, M.; Ming, C. Quantitative Comparison of Flux-Switching Permanent-Magnet Motors
Ruiwu, C.; Chris, M.; Ming, C. Quantitative Comparison of Flux-Switching Permanent-Magnet Motors
with Interior Permanent Magnet Motor for EV, HEV, and PHEV Applications. IEEE Trans. Magn. 2012, 48,
with Interior Permanent Magnet Motor for EV, HEV, and PHEV Applications. IEEE Trans. Magn. 2012, 48,
2374–2384. [CrossRef]
2374–2384,
doi:10.1109/TMAG.2012.2190614.
Won, H.; Hong,
Y.K.; Lee, W.; Choi, M. Roles of coercivity and remanent flux density of permanent magnet
Won,
H.;
Hong,
Y.K.; Lee,
W.; Choi,
M. Roles motor
of coercivity
andperformance
remanent flux
permanent
magnet
in interior permanent
magnet
synchronous
(IPMSM)
fordensity
electricofvehicle
applications.
in
interior
permanent
magnet
synchronous
motor
(IPMSM)
performance
for
electric
vehicle
applications.
AIP Adv. 2018, 8. [CrossRef]
AIP
Adv. Z.;
2018,
8, doi:10.1063/1.5007789.
Mounir,
Mohamed,
B.; Demba, D. Electric Motor Drive Selection Issues for HEV Propulsion Systems:
Mounir,
Z.;
Mohamed,
Demba,
Electric
Motor
Selection Issues
for HEV Propulsion Systems: A
A Comparative Study. B.;
IEEE
Trans. D.
Veh.
Technol.
2006,Drive
55, 1756–1764.
[CrossRef]
Comparative
Study.
IEEE
Trans.
Veh.
Technol.
2006,
55,
1756–1764,
doi:10.1109/TVT.2006.878719.
Wu, W.; Zhu, X.; Quan, L.; Du, Y.; Xiang, Z.; Zhu, X. Design and Analysis of a Hybrid Permanent Magnet
Wu,
W.; Zhu,
X.; Quan, L.;
Du, Y.; Xiang,
Zhu, X. Design
and Analysis
of and
a Hybrid
Permanent
Magnet
Assisted
Synchronous
Reluctance
MotorZ.;Considering
Magnetic
Saliency
PM Usage.
IEEE
Trans.
Assisted
Synchronous
Reluctance
Motor
Considering
Magnetic
Saliency
and
PM
Usage.
IEEE
Trans.
Appl.
Appl. Supercond. 2018, 28, 1–6. [CrossRef]
Supercond.
2018,
28, 1–6,
Huynh, T.A.;
Hsieh,
M.-F.doi:10.1109/TASC.2017.2775584.
Comparative Study of PM-Assisted SynRM and IPMSM on Constant Power Speed
Huynh,
T.A.;
Hsieh,
M.-F. Comparative
Study2017,
of PM-Assisted
SynRM and IPMSM on Constant Power
Range for EV Applications.
IEEE Trans. Magn.
53, 1–6. [CrossRef]
Speed Range for EV Applications. IEEE Trans. Magn. 2017, 53, 1–6, doi:10.1109/TMAG.2017.2707125.
Energies 2018, 11, 1385
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
24 of 24
Wang, J.; Yuan, X.; Kais, A. Design Optimization of a Surface-Mounted Permanent-Magnet Motor with
Concentrated Windings for Electric Vehicle Applications. IEEE Trans. Veh. Technol. 2013, 62, 1053–1064.
[CrossRef]
Degano, M.; Carraro, E.; Bianchi, N. Robust Optimization of a Traction PMASR Motor according to a Given
Driving Cycles. In Proceedings of the IEEE International Conference on Electrical Machines (ICEM), Berlin,
Germany, 2–5 September 2014; pp. 270–276. [CrossRef]
Carraro, E.; Morandin, M.; Bianchi, N. Traction PMASR Motor Optimization according to a Given Driving
Cycle. IEEE Trans. Ind. Appl. 2016, 52, 209–216. [CrossRef]
Nguyen, P.H.; Hoang, E.; Gabsi, M. Performance Synthesis of Permanent-Magnet Synchronous Machines
during the Driving Cycle of a Hybrid Electric Vehicle. IEEE Trans. Veh. Technol. 2011, 60, 1991–1997.
[CrossRef]
Sarigiannidis, A.G.; Beniakar, M.E.; Kladas, A.G. Fast Adaptive Evolutionary PM Traction Motor
Optimization Based on Electric Vehicle Drive Cycle. IEEE Trans. Veh. Technol. 2017, 66, 5762–5774. [CrossRef]
Sarigiannidis, A.G.; Beniakar, M.E.; Kakosimos, P.E.; Kladas, A.G. Performance Evaluation and Thermal
Analysis of Interior Permanent Magnet Traction Motor over a Wide Load Range. In Proceedings of the
IEEE International Conference on Electrical Machines (ICEM), Lausanne, Switzerland, 4–7 September 2016;
pp. 2662–2668. [CrossRef]
Yang, Y.P.; Shih, G.Y. Optimal Design of an Axial-Flux Permanent-Magnet Motor for an Electric Vehicle
Based on Driving Scenarios. Energies 2016, 9, 285. [CrossRef]
Gu, W.; Zhu, X.-Y.; Li, Q.; Yi, D. Design and Optimization of Permanent Magnet Brushless Machines for
Electric Vehicle Applications. Energies 2015, 8, 13996–14008. [CrossRef]
Glowacz, A.; Glowacz, Z. Diagnosis of the three-phase induction motor using thermal imaging.
Infrared Phys. Technol. 2017, 81, 7–16. [CrossRef]
Glowacz, A.; Glowacz, Z. Diagnostics of stator faults of the single-phase induction motor using thermal
images, MoASoS and selected classifiers. Measurement 2016, 93, 86–93. [CrossRef]
United States Environmental Protection Agency, EPA Emission Standards for Light-Duty Vehicles and Trucks.
Available online: https://www.epa.gov/emission-standards-reference-guide/epa-emission-standardslight-duty-vehicles-and-trucks (accessed on 30 April 2018).
Liu, X.; Chen, H.; Zhao, J.; Belahcen, A. Research on the Performances and Parameters of Interior PMSM
Used for Electric Vehicles. IEEE Trans. Ind. Electron. 2016, 63, 3533–3545. [CrossRef]
Liu, C.T.; Chung, H.Y.; Lin, S.Y. On the electromagnetic steel selections and performance impact assessments
of synchronous reluctance motors. IEEE Trans. Ind. Appl. 2017, 53, 2569–2577. [CrossRef]
Huynh, T.A.; Hsieh, M.-F. Performance Evaluation of Interior Permanent Magnet Motors Using Thin
Electrical Steels. IEEJ J. Ind. Appl. 2017, 6, 422–428. [CrossRef]
Yuan, X.; Wang, J. Torque Distribution Strategy for a Front- and Rear-Wheel-Driven Electric Vehicle.
IEEE Trans. Veh. Technol. 2012, 61, 3365–3374. [CrossRef]
Soong, W.L.; Ertugrul, N. Field weakening performance of interior permanent magnet motors. IEEE Trans.
Ind. Appl. 2002, 38, 1251–1258. [CrossRef]
Guglielmi, P.; Boazzo, B.; Armando, E.; Pellegrino, G.; Vagati, A. Permanent-magnet minimization in
PM-assisted synchronous reluctance motors for wide speed range. IEEE Trans. Ind. Appl. 2013, 49, 31–41.
[CrossRef]
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