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It is predicted that the maximum speed of EV traction motors will increase in the future due to reductions in size and weight. The high-speed motors are required to have high mechanical strength of the rotor for high-speed rotation, in addition to satisfying the required output and high efficiency in the wide operation area. Therefore, it is necessary to evaluate the advantages and disadvantages of motors in terms of both electrical and mechanical points of view. In this research, three motor types, PMSM, SRM, and IM, which targeted the output power of 85 kW and the maximum speed of 52,000 min−1, are designed for use with EV traction motors, and the study clarifies which the type of motor is most suitable for application in high-speed motors of EVs in terms of their mechanical and electrical characteristics.
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Citation: Aiso, K.; Akatsu, K.
Performance Comparison of
High-Speed Motors for Electric
Vehicle. World Electr. Veh. J. 2022,13,
57. https://doi.org/10.3390/
wevj13040057
Academic Editor: Ziqiang Zhu
Received: 28 February 2022
Accepted: 21 March 2022
Published: 23 March 2022
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4.0/).
Article
Performance Comparison of High-Speed Motors for
Electric Vehicle
Kohei Aiso 1, * and Kan Akatsu 2
1Shibaura Institute of Technology, Tokyo 135-8548, Japan
2Department of Mathematics, Physics, Electrical Engineering and Computer Science,
Yokohama National University, Yokohama 240-8501, Japan; akatsu-kan-py@ynu.ac.jp
*Correspondence: k-aiso@shibaura-it.ac.jp
Abstract:
It is predicted that the maximum speed of EV traction motors will increase in the future
due to reductions in size and weight. The high-speed motors are required to have high mechanical
strength of the rotor for high-speed rotation, in addition to satisfying the required output and high
efficiency in the wide operation area. Therefore, it is necessary to evaluate the advantages and
disadvantages of motors in terms of both electrical and mechanical points of view. In this research,
three motor types, PMSM, SRM, and IM, which targeted the output power of 85 kW and the maximum
speed of 52,000 min
1
, are designed for use with EV traction motors, and the study clarifies which
the type of motor is most suitable for application in high-speed motors of EVs in terms of their
mechanical and electrical characteristics.
Keywords:
electric vehicle; high-speed motor; permanent magnet synchronous motor; switched
reluctance motor; induction motor
1. Introduction
Electric vehicles (EVs) have become popular as an energy-saving countermeasure. EV
traction motors are required to have high efficiency, high power density, low manufacturing
costs, and downsized volume. Recently, downsized motors in particular have been needed
to improve electric power consumption levels and retain space where the motor is housed.
One of the methods used to downsize motor volume is to increase the motor speed [
1
]. The
output power of motors is defined by the product of the torque and the rotation speed.
Downsizing can be realized by increasing the rotation speed while obtaining the same
output power. For high-speed drives, motors need to achieve adequate mechanical and
electrical performances (i.e., high mechanical strength of the rotor and a reduction in loss).
Permanent magnet synchronous motors (PMSMs), which use rare earth magnets,
are widely used as traction motors since they can obtain high torque density and high
efficiency [
2
,
3
]. However, PMSMs have several disadvantages such as high manufacturing
costs and low mechanical strength due to the rare earth permanent magnets used in the
rotor. These magnets are broken by centrifugal force, since high Mises stress is concentrated
to these magnets in high-speed drive. Although interior permanent magnet synchronous
motors (IPMSMs) prevent these magnets from breaking, high Mises stress is generated at
the edge of the flux barrier via high-speed rotation. Therefore, the advanced optimization
of the detailed rotor shape is required in the design process to reduce the Mises stress [
4
].
Meanwhile, surface permanent magnet synchronous motors (SPMSMs) can reduce the
Mises stress more effectively compared with IPMSMs, and the rotor can be reinforced
by using reinforcing materials such as carbon fiber and titanium alloy [
5
,
6
]. However, it
requires a complex and high-cost structure. Additionally, it needs to energize the d-axis
current by the flux weakening control in the high-speed region since the back electromotive
force increases due to the magnet of rotor, which results in the generation of copper loss.
Moreover, the efficiency of PMSMs is generally decreased in the high-speed region due
World Electr. Veh. J. 2022,13, 57. https://doi.org/10.3390/wevj13040057 https://www.mdpi.com/journal/wevj
World Electr. Veh. J. 2022,13, 57 2 of 17
to the eddy current loss of the magnet, and both a retaining sleeve in the rotor and a
segmentation magnet are required [7].
Switched reluctance motors (SRMs) have been put forward as candidate automotive
motors. SRMs have a salient pole structure in the stator and the rotor and only consist
of the laminated core and the winding. Therefore, SRMs have a robust structure and can
reduce the Mises stress generated in the rotor (as they have no magnets). They are suitable
for use in the high-speed region compared with PMSMs since SRMs not only have high
mechanical strength but also no back electromotive force that is caused by magnets in
a rotor. However, the torque density of SRMs is lower than that of PMSMs. Therefore,
the ampere turns and the motor volume increase to achieve the same torque as PMSMs.
Moreover, SRMs decrease the motor efficiency since the iron loss increases in the high-speed
drive. To overcome these disadvantages, SRMs using low-iron-loss steel, 0.1 mm thick
high-silicon steel, and amorphous steel sheets was proposed to achieve high efficiency in
the high-speed region [8,9].
Induction motors (IMs) have also been considered for application as traction mo-
tors [
10
]. IMs have several merits such as low manufacturing costs and the high mechanical
strength of their rotors, since there are no permanent magnets in their rotors. Moreover,
high efficiency can be expected by using more flexible and better flux weakening control
compared with PMSMs, since the field flux of the rotor can be changed with the stator
current [
11
]. However, the efficiency under high load conditions is much lower due to the
generation of joule loss in the rotor. Therefore, an IM with a copper rotor cage has been
studied with the aim of decreasing the joule loss in the rotor [12].
As mentioned above, PMSMs, SRMs, and IMs have advantages and disadvantages,
and their performances as motors for automobiles have been compared [
13
,
14
]. However,
most of the previous studies have evaluated the performance at the operating speed of
a typical automobile motor in less than 15,000 min
1
. It is predicted that the maximum
speed of automobile motors will increase in the future due to reductions in size and weight,
and it is necessary to evaluate the characteristics of each motor in the higher speed range
from both electrical and mechanical points of view. In this research, motors that achieve
output powers of 85 kW and maximum speeds of 52,000 min
1
are proposed as EV traction
motors, and the study reveals which motor type is most suitable for the realization of the
output power and the maximum speed in terms of mechanical and electrical characteristics.
The PMSM, SRM, and IM are designed to achieve the performances required for use in a
high-speed drive. The performances of these designed motors are evaluated using FEA,
and the advantages and disadvantages of their use in a high-speed drive are clarified.
2. Target Performances and Design Flow
The specifications for EV traction motors are shown in Table 1, and the required
speed–torque characteristics are shown in Figure 1. As shown in Table 1and Figure 1, the
output power is 85 kW, the maximum torque is 70 Nm, the base speed is 11,500 min
1
, and
maximum speed is 52,000 min
1
. The maximum phase current, maximum DC voltage, and
the current density are constant at 356 Arms, 365 V, and less than 15 A/mm
2
, respectively.
The stack length is a constant 100 mm, and the motor diameter can be changed by the
design to be less than 200 mm. As shown in the specification, the maximum speed of
52,000 min
1
is very high compared with a general EV traction motor. It is possible to
greatly downsize a motor’s volume using high-speed rotation while obtaining high output
power. To achieve these specifications and the smallest motor volume, the PMSM, SRM,
and IM are designed, and the performances such as maximum torque, maximum output
power, loss, and efficiency are evaluated at each rotation speed.
World Electr. Veh. J. 2022,13, 57 3 of 17
Table 1. Target performances.
Output power [kW] 85
Maximum torque [N m] 70
Voltage source [V] 365
Maximum current [Arms] 356
Current density [A/mm2]15
Maximum diameter [mm] 200
Stack length of core [mm] 100
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 3 of 16
Output power [kW] 85
Maximum torque [N m] 70
Voltage source [V] 365
Maximum current [Arms] 356
Current density [A/mm2] 15
Maximum diameter [mm] 200
Stack length of core [mm] 100
Figure 1. Target speed–torque characteristic.
Figure 2 shows the design flow. As shown in Figure 2, the design flow is separated into three
parts, including the design of mechanical strength, the design of electric characteristics, and
evaluation of motor performance. In the design of mechanical strength, the diameter and the shape
of rotor to achieve enough mechanical strength with the maximum speed of 52,000 min1, which is
determined using centrifugal force analysis. In the design of the electric characteristics, the number
of turns, the shape of the stator, and the pole number are determined to obtain the maximum torque
of 70 Nm and to retain the induced voltage as less than the DC voltage. In this study, PMSM and
IM are assumed to be driven sinusoidally by the vector control with a sensor in all speed region,
while SRM is assumed to be driven by hysteresis control at the low-speed region and voltage single
pulse control at high-speed region. Actually, the driving by the sinusoidal wave in the high-speed
region requires the high switching frequency in the inverter. However, the purpose of this paper is
to evaluate the motor characteristics under ideal conditions, and the effects of drive conditions of
the inverter are not considered.
Figure 2. Design flow.
3. Design of PMSM
In this section, the specifications of the designed PMSM and the design process used
to realize the required performances are described. Figure 3 shows the dimension of the
designed PMSM, and Table 2 shows the specifications. As shown in Figure 3 and Table 2,
the SPMSM is selected in this design. In general, the IPMSM has been widely used as
traction motors since high output torque and a wide speed range can be obtained by
utilizing not only the magnet torque but also the reluctance torque. On the other hand, the
SPMSM is more appropriate in terms of the mechanical strength compared with the
70Nm
Torque
Speed
11,500rpm 52,000rpm
19.3Nm
85kW
(1)Maximum
torque
42,000rpm
15.6Nm
(2)Maximum
speed
Design fo r
mechanical strength
Design fo r
electric characteristics
Diameter and shape of rotor
Number o f turn
Diameter of stator
Current density
Evaluation of
motor performances
Speed-torque characteristic
Loss and efficiency
Constant
design parameters
Combinat ion of pole and slot
Stack length:100mm
Air gap:0.5mm
Winding type
Figure 1. Target speed–torque characteristic.
Figure 2shows the design flow. As shown in Figure 2, the design flow is separated into
three parts, including the design of mechanical strength, the design of electric characteristics,
and evaluation of motor performance. In the design of mechanical strength, the diameter
and the shape of rotor to achieve enough mechanical strength with the maximum speed of
52,000 min
1
, which is determined using centrifugal force analysis. In the design of the
electric characteristics, the number of turns, the shape of the stator, and the pole number are
determined to obtain the maximum torque of 70 Nm and to retain the induced voltage as
less than the DC voltage. In this study, PMSM and IM are assumed to be driven sinusoidally
by the vector control with a sensor in all speed region, while SRM is assumed to be driven
by hysteresis control at the low-speed region and voltage single pulse control at high-speed
region. Actually, the driving by the sinusoidal wave in the high-speed region requires the
high switching frequency in the inverter. However, the purpose of this paper is to evaluate
the motor characteristics under ideal conditions, and the effects of drive conditions of the
inverter are not considered.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 3 of 16
Output power [kW] 85
Maximum torque [N m] 70
Voltage source [V] 365
Maximum current [Arms] 356
Current density [A/mm2] 15
Maximum diameter [mm] 200
Stack length of core [mm] 100
Figure 1. Target speed–torque characteristic.
Figure 2 shows the design flow. As shown in Figure 2, the design flow is separated into three
parts, including the design of mechanical strength, the design of electric characteristics, and
evaluation of motor performance. In the design of mechanical strength, the diameter and the shape
of rotor to achieve enough mechanical strength with the maximum speed of 52,000 min1, which is
determined using centrifugal force analysis. In the design of the electric characteristics, the number
of turns, the shape of the stator, and the pole number are determined to obtain the maximum torque
of 70 Nm and to retain the induced voltage as less than the DC voltage. In this study, PMSM and
IM are assumed to be driven sinusoidally by the vector control with a sensor in all speed region,
while SRM is assumed to be driven by hysteresis control at the low-speed region and voltage single
pulse control at high-speed region. Actually, the driving by the sinusoidal wave in the high-speed
region requires the high switching frequency in the inverter. However, the purpose of this paper is
to evaluate the motor characteristics under ideal conditions, and the effects of drive conditions of
the inverter are not considered.
Figure 2. Design flow.
3. Design of PMSM
In this section, the specifications of the designed PMSM and the design process used
to realize the required performances are described. Figure 3 shows the dimension of the
designed PMSM, and Table 2 shows the specifications. As shown in Figure 3 and Table 2,
the SPMSM is selected in this design. In general, the IPMSM has been widely used as
traction motors since high output torque and a wide speed range can be obtained by
utilizing not only the magnet torque but also the reluctance torque. On the other hand, the
SPMSM is more appropriate in terms of the mechanical strength compared with the
70Nm
Torque
Speed
11,500rpm 52,000rpm
19.3Nm
85kW
(1)Maximum
torque
42,000rpm
15.6Nm
(2)Maximum
speed
Design fo r
mechanical strength
Design fo r
electric characteristics
Diameter and shape of rotor
Number o f turn
Diameter of stator
Current density
Evaluation of
motor performances
Speed-torque characteristic
Loss and efficiency
Constant
design parameters
Combinat ion of pole and slot
Stack length:100mm
Air gap:0.5mm
Winding type
Figure 2. Design flow.
3. Design of PMSM
In this section, the specifications of the designed PMSM and the design process used
to realize the required performances are described. Figure 3shows the dimension of the
designed PMSM, and Table 2shows the specifications. As shown in Figure 3and Table 2,
the SPMSM is selected in this design. In general, the IPMSM has been widely used as
traction motors since high output torque and a wide speed range can be obtained by
World Electr. Veh. J. 2022,13, 57 4 of 17
utilizing not only the magnet torque but also the reluctance torque. On the other hand,
the SPMSM is more appropriate in terms of the mechanical strength compared with the
IPMSM since the rotor shape of the SPMSM can reduce the Mises stress generated in the
rotor more effectively than that of the IPMSM. The combination of the pole and slot is 4/6,
and the diameter of the stator and the stack length are 174 mm and 100 mm. In addition, the
permanent magnet is axially segmented by 16 layers to decrease the eddy current loss, and
the permanent rotor magnet is assumed to be reinforced with a 0.2 mm retaining sleeve that
is made of carbon-fiber-reinforced plastic (C-FRP), which has a high electrical resistivity of
1.5
×
10
5
m. The PMSM is assumed to be driven by a sinusoidal wave. The detailed
design process is stated as follow.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 4 of 16
IPMSM since the rotor shape of the SPMSM can reduce the Mises stress generated in the
rotor more effectively than that of the IPMSM. The combination of the pole and slot is 4/6,
and the diameter of the stator and the stack length are 174 mm and 100 mm. In addition,
the permanent magnet is axially segmented by 16 layers to decrease the eddy current loss,
and the permanent rotor magnet is assumed to be reinforced with a 0.2 mm retaining
sleeve that is made of carbon-fiber-reinforced plastic (C-FRP), which has a high electrical
resistivity of 1.5 × 10
5
Ωm. The PMSM is assumed to be driven by a sinusoidal wave. The
detailed design process is stated as follow.
Table 2. Specifications of PMSM.
Number of poles 4
Stator slots 6
Number of turns [turn/slot] 7
Resistance of winding [Ω] 0.0018
Winding type Concentrated
Air gap [mm] 0.5
Magnet thickness [mm] 5
Current density[A/mm
2
] 10
Material of magnetic steel sheet 35H230
Material of permanent magnet NEOMAX-42
Number of magnet segmentations 16
Figure 3. Dimensions of designed PMSM.
3.1. Mechanical Design of PMSM
The Mises stress generated in the rotor at the maximum speed of 52,000 min
1
is
evaluated using FEA. JMAG-designer is used as the simulation tool. Figure 4 shows the
comparison of Mises stress in the IPMSM and SPMSM. The two types of magnet
arrangements (Model A and Model B) in the IPMSM and SPMSM, which are designed
with constant rotor diameters of 70 mm, are considered. Surface permanent magnet type
and interior permanent magnet type are abbreviated as SPM type and IPM type,
respectively. For the magnet and core, sintered magnet (NEOMAX-42) and magnetic steel
sheet (35H230) materials are used. Then, the Young’s modulus and Poisson ratio of the
magnetic steel sheet are 210,000 MPa and 0.3, respectively. Those of the magnet are 120,000
MPa and 0.3, respectively. As shown in Figure 4, in Model A and Model B of the IPM type,
the high Mises stress is concentrated at the edge of flux barrier. On the other hand, the
Mises stress of the SPM type is concentrated at the surface permanent magnet on the rotor,
and it is much lower than that of the IPM type. Although these models of IPM types are
not optimized to reduce the Mises stress, it is obvious that SPM types are more suitable
for decreasing Mises stress compared with IPM types. Figure 5a shows Mises stress
distribution for the rotor diameter in the SPM type. As shown in Figure 5a, the Mises stress
can be reduced by decreasing the rotor diameter. Figure 5b shows the maximum Mises
Figure 3. Dimensions of designed PMSM.
Table 2. Specifications of PMSM.
Number of poles 4
Stator slots 6
Number of turns [turn/slot] 7
Resistance of winding [] 0.0018
Winding type Concentrated
Air gap [mm] 0.5
Magnet thickness [mm] 5
Current density [A/mm2]10
Material of magnetic steel sheet 35H230
Material of permanent magnet NEOMAX-42
Number of magnet segmentations 16
3.1. Mechanical Design of PMSM
The Mises stress generated in the rotor at the maximum speed of 52,000 min
1
is
evaluated using FEA. JMAG-designer is used as the simulation tool. Figure 4shows
the comparison of Mises stress in the IPMSM and SPMSM. The two types of magnet
arrangements (Model A and Model B) in the IPMSM and SPMSM, which are designed with
constant rotor diameters of 70 mm, are considered. Surface permanent magnet type and
interior permanent magnet type are abbreviated as SPM type and IPM type, respectively.
For the magnet and core, sintered magnet (NEOMAX-42) and magnetic steel sheet (35H230)
materials are used. Then, the Young’s modulus and Poisson ratio of the magnetic steel
sheet are 210,000 MPa and 0.3, respectively. Those of the magnet are 120,000 MPa and 0.3,
respectively. As shown in Figure 4, in Model A and Model B of the IPM type, the high Mises
stress is concentrated at the edge of flux barrier. On the other hand, the Mises stress of the
SPM type is concentrated at the surface permanent magnet on the rotor, and it is much
lower than that of the IPM type. Although these models of IPM types are not optimized
to reduce the Mises stress, it is obvious that SPM types are more suitable for decreasing
Mises stress compared with IPM types. Figure 5a shows Mises stress distribution for the
rotor diameter in the SPM type. As shown in Figure 5a, the Mises stress can be reduced
by decreasing the rotor diameter. Figure 5b shows the maximum Mises stress for the rotor
World Electr. Veh. J. 2022,13, 57 5 of 17
diameter. As shown in Figure 5b, considering the limit of the yield stress of 300 MPa, the
rotor diameter is determined to be less than 70 mm. Moreover, the rotor magnet can be
reinforced with a retaining sleeve made of carbon-fiber-reinforced plastic (C-FRP).
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 5 of 16
stress for the rotor diameter. As shown in Figure 5b, considering the limit of the yield
stress of 300 MPa, the rotor diameter is determined to be less than 70 mm. Moreover, the
rotor magnet can be reinforced with a retaining sleeve made of carbon-fiber-reinforced
plastic (C-FRP).
(a)
IPM type_ModelA
(b)
IPM type_ModelB
(c)
SPM type
Figure 4. Mises stress in the rotor for IPM type (Model A and Model B) and SPM type.
(a)
Mises stress distribution for rotor diameter
(b)
Maximum Mises stress for rotor diameter
Figure 5. Mises stress of SPMSM at 52,000 min
-1
.
3.2. Electrical Design of PMSM
In the electrical design, the number of turns is determined to achieve the maximum
torque of 70 Nm and to maintain the induced voltage at less than half of the DC voltage
in each rotation speed. The torque equation is expressed as follows:
dq
Tpi
ψ
=
(1)
where T, p, ψ
d
, and i
q
are output torque, the number of pole pairs, magnet flux linkage,
and the q-axis current, respectively. Additionally, the magnet flux linkage is expressed as
follows:
dd
N
ψφ
=
(2)
where N is number of turns, and
d
φ
is magnet flux linkage in one turn/slot. From
Equations (1) and (2), the relationship between the output torque and the number of turns
is shown in Figure 6. Then, there are four pole pairs, and the phase current is constant at
356 Arms. As shown in Figure 6, the maximum torque of 70 Nm is obtained in more than
six turns/slot.
In addition, the phase voltage has to be limited to less than half of the DC voltage.
The condition of phase voltage is expressed as follows:
22
2
32
dc
dq
V
vv+<
(3)
0
100
200
300
400
500
600
700
60 70 80 90 100
Mises stress [MPa]
Rotor di ameter [mm]
Yield stres s :300Mpa
Figure 4. Mises stress in the rotor for IPM type (Model A and Model B) and SPM type.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 5 of 16
stress for the rotor diameter. As shown in Figure 5b, considering the limit of the yield
stress of 300 MPa, the rotor diameter is determined to be less than 70 mm. Moreover, the
rotor magnet can be reinforced with a retaining sleeve made of carbon-fiber-reinforced
plastic (C-FRP).
(a)
IPM type_ModelA
(b)
IPM type_ModelB
(c)
SPM type
Figure 4. Mises stress in the rotor for IPM type (Model A and Model B) and SPM type.
(a)
Mises stress distribution for rotor diameter
(b)
Maximum Mises stress for rotor diameter
Figure 5. Mises stress of SPMSM at 52,000 min
-1
.
3.2. Electrical Design of PMSM
In the electrical design, the number of turns is determined to achieve the maximum
torque of 70 Nm and to maintain the induced voltage at less than half of the DC voltage
in each rotation speed. The torque equation is expressed as follows:
dq
Tpi
ψ
=
(1)
where T, p, ψ
d
, and i
q
are output torque, the number of pole pairs, magnet flux linkage,
and the q-axis current, respectively. Additionally, the magnet flux linkage is expressed as
follows:
dd
N
ψφ
=
(2)
where N is number of turns, and
d
φ
is magnet flux linkage in one turn/slot. From
Equations (1) and (2), the relationship between the output torque and the number of turns
is shown in Figure 6. Then, there are four pole pairs, and the phase current is constant at
356 Arms. As shown in Figure 6, the maximum torque of 70 Nm is obtained in more than
six turns/slot.
In addition, the phase voltage has to be limited to less than half of the DC voltage.
The condition of phase voltage is expressed as follows:
22
2
32
dc
dq
V
vv+<
(3)
0
100
200
300
400
500
600
700
60 70 80 90 100
Mises stress [MPa]
Rotor di ameter [mm]
Yield stres s :300Mpa
Figure 5. Mises stress of SPMSM at 52,000 min-1.
3.2. Electrical Design of PMSM
In the electrical design, the number of turns is determined to achieve the maximum
torque of 70 Nm and to maintain the induced voltage at less than half of the DC voltage in
each rotation speed. The torque equation is expressed as follows:
T=pψdiq(1)
where T,p,
ψd
, and i
q
are output torque, the number of pole pairs, magnet flux linkage,
and the q-axis current, respectively. Additionally, the magnet flux linkage is expressed
as follows:
ψd=Nφd(2)
where Nis number of turns, and
φd
is magnet flux linkage in one turn/slot. From
Equations (1) and (2), the relationship between the output torque and the number of
turns is shown in Figure 6. Then, there are four pole pairs, and the phase current is
constant at 356 Arms. As shown in Figure 6, the maximum torque of 70 Nm is obtained
in more than six turns/slot.
World Electr. Veh. J. 2022,13, 57 6 of 17
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 6 of 16
where vd, vq, and Vdc are the d-axis voltage, q-axis voltage, and DC voltage source,
respectively. Then, the inductance condition to achieve the base speed and the output
power is given by:
2
2
3
8
dc
d
b
b
q
V
Li
ω



(4)
where ωb and Lb are the base angular velocity and inductance (there is a relationship Lb =
Ld = Lq due to SPMSM). In Equation (4), the maximum torque per ampere control is
assumed under base speed; therefore, the d-axis current is 0 A. Moreover, the inductance
condition to achieve the maximum speed and the output power is given by:
22
2()( )
32
dc
mbq bdd
V
Li Li
ωψ
+− + <
(5)
Using Equation (5), the inductance condition is derived as follows:
240
2
b
bb ac
La
−± −
=<
, 12b
LLL<<.
(6)
Then, parameters a, b, c are as follows:
2
2
2
2
3
8
m
dd
dc
d
m
aI
bi
V
c
ψ
ψω
=
=−

=−


(7)
where ωm, Im, and id are the maximum angular velocity, the current vector amplitude, and
the d-axis current, respectively. The functions of a, b, and c can be calculated using the
parameters of a phase current of 356 Arms and a d-axis current at a beta angle of 78
degrees. From Equations (4) and (6), the inductance range of Lb to achieve the condition
of phase voltage at the base speed and maximum speed is shown in Figure 7. As shown
in Figure 7, the number of turns, seven turns/slot, which satisfied Equations (4) and (6), is
selected. A stator diameter that retained the slot area is used, which achieves less than 15
A/mm2 of the current density.
Figure 6. Relationship between output torque and number of turns.
0
10
20
30
40
50
60
70
80
90
100
110
3456789
Tor qu e [ N m]
Number o f turns [turn/ slot]
70Nm is achieved
in more than 6turn/slot.
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
3456789
Inductance [mH]
Number of turns [turn/slot]
Lb L1 L2
LbL1L2
Figure 6. Relationship between output torque and number of turns.
In addition, the phase voltage has to be limited to less than half of the DC voltage. The
condition of phase voltage is expressed as follows:
r2
3qvd2+vq2<Vdc
2(3)
where vd,vq,and Vdc are the d-axis voltage, q-axis voltage, and DC voltage source, respec-
tively. Then, the inductance condition to achieve the base speed and the output power is
given by:
Lbr3
8Vdc
ωb2ψd2
iq(4)
where
ωb
and L
b
are the base angular velocity and inductance (there is a relationship
L
b
=L
d
=L
q
due to SPMSM). In Equation (4), the maximum torque per ampere control is
assumed under base speed; therefore, the d-axis current is 0 A. Moreover, the inductance
condition to achieve the maximum speed and the output power is given by:
ωmr2
3q(Lbiq)2+ (Lbid+ψd)2<Vdc
2(5)
Using Equation (5), the inductance condition is derived as follows:
Lb=b±b24ac
2a<0, L1<Lb<L2. (6)
Then, parameters a,b,care as follows:
a=Im2
b=2ψdid
c=ψd23
8Vdc
ωm2(7)
where
ωm
,I
m
, and i
d
are the maximum angular velocity, the current vector amplitude, and
the d-axis current, respectively. The functions of a,b, and ccan be calculated using the
parameters of a phase current of 356 Arms and a d-axis current at a beta angle of 78 degrees.
From Equations (4) and (6), the inductance range of L
b
to achieve the condition of phase
voltage at the base speed and maximum speed is shown in Figure 7. As shown in Figure 7,
the number of turns, seven turns/slot, which satisfied Equations (4) and (6), is selected. A
stator diameter that retained the slot area is used, which achieves less than 15 A/mm
2
of
the current density.
World Electr. Veh. J. 2022,13, 57 7 of 17
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 6 of 16
where vd, vq, and Vdc are the d-axis voltage, q-axis voltage, and DC voltage source,
respectively. Then, the inductance condition to achieve the base speed and the output
power is given by:
2
2
3
8
dc
d
b
b
q
V
Li
ψ
ω



(4)
where ωb and Lb are the base angular velocity and inductance (there is a relationship Lb =
Ld = Lq due to SPMSM). In Equation (4), the maximum torque per ampere control is
assumed under base speed; therefore, the d-axis current is 0 A. Moreover, the inductance
condition to achieve the maximum speed and the output power is given by:
22
2()( )
32
dc
mbq bdd
V
Li Li
ωψ
+− + <
(5)
Using Equation (5), the inductance condition is derived as follows:
240
2
b
bb ac
La
−± −
=<
, 12b
LLL<<.
(6)
Then, parameters a, b, c are as follows:
2
2
2
2
3
8
m
dd
dc
d
m
aI
bi
V
c
ψ
ψω
=
=−

=−


(7)
where ωm, Im, and id are the maximum angular velocity, the current vector amplitude, and
the d-axis current, respectively. The functions of a, b, and c can be calculated using the
parameters of a phase current of 356 Arms and a d-axis current at a beta angle of 78
degrees. From Equations (4) and (6), the inductance range of Lb to achieve the condition
of phase voltage at the base speed and maximum speed is shown in Figure 7. As shown
in Figure 7, the number of turns, seven turns/slot, which satisfied Equations (4) and (6), is
selected. A stator diameter that retained the slot area is used, which achieves less than 15
A/mm2 of the current density.
Figure 6. Relationship between output torque and number of turns.
0
10
20
30
40
50
60
70
80
90
100
110
3456789
Tor qu e [ N m]
Number o f turns [turn/ slot]
70Nm is achieved
in more than 6turn/slot.
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
3456789
Inductance [mH]
Number of turns [turn/slot]
Lb L1 L2
LbL1L2
Figure 7.
Inductance condition which achieves the demand torque at base speed 11,500 min
1
and
maximum speed 52,000 min1.
3.3. Torque and Phase Voltage at Required Speed of PMSM
The performances of PMSM are evaluated using FEA. Figures 8and 9show the
torque waveforms and phase voltage waveform at the operation speed of 11,500 min
1
and 52,000 min
1
, respectively. As shown in Figure 8a, the designed PMSM can achieve
the maximum torque of 70 Nm at 11,500 min
1
. As shown in Figure 9b, the phase voltage
is also suppressed to less than half of the DC voltage of 365 V at 52,000 min
1
, and the
output power of 85 kW is obtained. However, a lot of the d-axis current is energized by the
flux weakening control in 52,000 min
1
to cancel out the magnet flux and to sustain the
induced voltage.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 7 of 16
Figure 7. Inductance condition which achieves the demand torque at base speed 11,500 min-1 and
maximum speed 52,000 min-1.
3.3. Torque and Phase Voltage at Required Speed of PMSM
The performances of PMSM are evaluated using FEA. Figures 8 and 9 show the
torque waveforms and phase voltage waveform at the operation speed of 11,500 min1 and
52,000 min1, respectively. As shown in Figure 8a, the designed PMSM can achieve the
maximum torque of 70 Nm at 11,500 min1. As shown in Figure 9b, the phase voltage is
also suppressed to less than half of the DC voltage of 365 V at 52,000 min1, and the output
power of 85 kW is obtained. However, a lot of the d-axis current is energized by the flux
weakening control in 52,000 min1 to cancel out the magnet flux and to sustain the induced
voltage.
(a) Torque waveform (b) Voltage waveform
Figure 8. Torque waveform and phase voltage waveform in rotation speed of 11,500 min1, input
current of 356 Arms, and beta angle of 0 degrees.
(a) Torque waveform (b) Voltage waveform
Figure 9. Torque waveform and phase voltage waveform in rotation speed of 52,000 min1, input
current of 356 Arms, and beta angle of 78 degrees.
4. Design of SRM
In this section, the specifications of the designed SRM and the design process used to
obtain the required performances are described. Figure 10 shows the dimensions of the
designed SRM, and Table 3 shows the specifications of the SRM. As shown in Figure 10
and Table 3, the 8 poles and 12 slots are selected, and the motor diameter and stack length
are 200 mm and 100 mm, respectively. The detailed design process is stated as follow.
Table 3. Specifications of SRM.
Number of poles 8
Stator slots 12
Number of turns [turn/slot] 5
Resistance of winding [Ω] 0.003
Winding type Concentrated
Air gap [mm] 0.5
Magnet thickness [mm] 5
Current density[A/mm2] 12.7
0
10
20
30
40
50
60
70
80
90
0 60 120 180 240 300 360
Tor que [N m]
Electric angle [deg]
Average:70.0Nm
-200
-150
-100
-50
0
50
100
150
200
0 60 120 180 240 300 360
Voltage [V]
Electric angle [deg]
0
10
20
30
40
50
60
70
80
90
0 60 120 180 240 300 360
Tor que [ N m ]
Electric angle [deg]
Average:16.1Nm
-200
-150
-100
-50
0
50
100
150
200
0 60 120 180 240 300 360
Voltage [V]
Electric angle [deg]
Figure 8.
Torque waveform and phase voltage waveform in rotation speed of 11,500 min
1
, input
current of 356 Arms, and beta angle of 0 degrees.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 7 of 16
Figure 7. Inductance condition which achieves the demand torque at base speed 11,500 min-1 and
maximum speed 52,000 min-1.
3.3. Torque and Phase Voltage at Required Speed of PMSM
The performances of PMSM are evaluated using FEA. Figures 8 and 9 show the
torque waveforms and phase voltage waveform at the operation speed of 11,500 min1 and
52,000 min1, respectively. As shown in Figure 8a, the designed PMSM can achieve the
maximum torque of 70 Nm at 11,500 min1. As shown in Figure 9b, the phase voltage is
also suppressed to less than half of the DC voltage of 365 V at 52,000 min1, and the output
power of 85 kW is obtained. However, a lot of the d-axis current is energized by the flux
weakening control in 52,000 min1 to cancel out the magnet flux and to sustain the induced
voltage.
(a) Torque waveform (b) Voltage waveform
Figure 8. Torque waveform and phase voltage waveform in rotation speed of 11,500 min1, input
current of 356 Arms, and beta angle of 0 degrees.
(a) Torque waveform (b) Voltage waveform
Figure 9. Torque waveform and phase voltage waveform in rotation speed of 52,000 min1, input
current of 356 Arms, and beta angle of 78 degrees.
4. Design of SRM
In this section, the specifications of the designed SRM and the design process used to
obtain the required performances are described. Figure 10 shows the dimensions of the
designed SRM, and Table 3 shows the specifications of the SRM. As shown in Figure 10
and Table 3, the 8 poles and 12 slots are selected, and the motor diameter and stack length
are 200 mm and 100 mm, respectively. The detailed design process is stated as follow.
Table 3. Specifications of SRM.
Number of poles 8
Stator slots 12
Number of turns [turn/slot] 5
Resistance of winding [Ω] 0.003
Winding type Concentrated
Air gap [mm] 0.5
Magnet thickness [mm] 5
Current density[A/mm2] 12.7
0
10
20
30
40
50
60
70
80
90
0 60 120 180 240 300 360
Tor que [N m]
Electric angle [deg]
Average:70.0Nm
-200
-150
-100
-50
0
50
100
150
200
0 60 120 180 240 300 360
Voltage [V]
Electric angle [deg]
0
10
20
30
40
50
60
70
80
90
0 60 120 180 240 300 360
Tor que [ N m ]
Electric angle [deg]
Average:16.1Nm
-200
-150
-100
-50
0
50
100
150
200
0 60 120 180 240 300 360
Voltage [V]
Electric angle [deg]
Figure 9.
Torque waveform and phase voltage waveform in rotation speed of 52,000 min
1
, input
current of 356 Arms, and beta angle of 78 degrees.
4. Design of SRM
In this section, the specifications of the designed SRM and the design process used to
obtain the required performances are described. Figure 10 shows the dimensions of the
designed SRM, and Table 3shows the specifications of the SRM. As shown in Figure 10
and Table 3, the 8 poles and 12 slots are selected, and the motor diameter and stack length
are 200 mm and 100 mm, respectively. The detailed design process is stated as follow.
World Electr. Veh. J. 2022,13, 57 8 of 17
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 8 of 16
Material of magnetic steel sheet 35H230
Figure 10. Dimension of designed SRM.
4.1. Mechanical Design of SRM
Figure 11 shows the Mises stress distribution for the rotor diameter at the maximum
speed of 52,000 min
1
. As shown in Figure 11a, high Mises stress is generated around the
shaft and the edge of the teeth. As shown in Figure 11b, considering the limit of the Mises
stress is under 300 MPa, the rotor diameter has to decrease to less than 114 mm.
Figure 11. Mises stress of SRM in the rotor at 52,000 min
1
.
4.2. Electrical Design of SRM.
In the electrical design, the number of turns is determined to achieve the maximum
torque of 70 Nm. The torque of the SRM is generally expressed as follows:
2
2
PL
Ti
θ
=
(8)
where P, /L
θ
∂∂
, and i are number of poles in the rotor, the self-inductance variation,
and phase current, respectively. In the SRM, the torque is proportional to the variation of
self-inductance and the square of phase current. Equation (8) is rewritten as follows:
Figure 10. Dimension of designed SRM.
Table 3. Specifications of SRM.
Number of poles 8
Stator slots 12
Number of turns [turn/slot] 5
Resistance of winding [] 0.003
Winding type Concentrated
Air gap [mm] 0.5
Magnet thickness [mm] 5
Current density [A/mm2]12.7
Material of magnetic steel sheet 35H230
4.1. Mechanical Design of SRM
Figure 11 shows the Mises stress distribution for the rotor diameter at the maximum
speed of 52,000 min
1
. As shown in Figure 11a, high Mises stress is generated around the
shaft and the edge of the teeth. As shown in Figure 11b, considering the limit of the Mises
stress is under 300 MPa, the rotor diameter has to decrease to less than 114 mm.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 8 of 16
Material of magnetic steel sheet 35H230
Figure 10. Dimension of designed SRM.
4.1. Mechanical Design of SRM
Figure 11 shows the Mises stress distribution for the rotor diameter at the maximum
speed of 52,000 min
1
. As shown in Figure 11a, high Mises stress is generated around the
shaft and the edge of the teeth. As shown in Figure 11b, considering the limit of the Mises
stress is under 300 MPa, the rotor diameter has to decrease to less than 114 mm.
Figure 11. Mises stress of SRM in the rotor at 52,000 min
1
.
4.2. Electrical Design of SRM.
In the electrical design, the number of turns is determined to achieve the maximum
torque of 70 Nm. The torque of the SRM is generally expressed as follows:
2
2
PL
Ti
θ
=
(8)
where P, /L
θ
∂∂
, and i are number of poles in the rotor, the self-inductance variation,
and phase current, respectively. In the SRM, the torque is proportional to the variation of
self-inductance and the square of phase current. Equation (8) is rewritten as follows:
Figure 11. Mises stress of SRM in the rotor at 52,000 min1.
World Electr. Veh. J. 2022,13, 57 9 of 17
4.2. Electrical Design of SRM
In the electrical design, the number of turns is determined to achieve the maximum
torque of 70 Nm. The torque of the SRM is generally expressed as follows:
T=P
2
L
∂θ i2(8)
where P,
L/∂θ
, and iare number of poles in the rotor, the self-inductance variation, and
phase current, respectively. In the SRM, the torque is proportional to the variation of
self-inductance and the square of phase current. Equation (8) is rewritten as follows:
T=P
2
l
∂θ (Ni)2(9)
where
l/∂θ
is the inductance variation in one turn/slot. As shown in Equation (9), the
output torque is proportional to the inductance variation in one turn/slot and the square of
the number of turns and the current. The inductance variation depends on the salient pole
ratio of the rotor. As shown in Equation (9), the number of turns is adjusted to obtain the
maximum torque of 70 Nm under the maximum current of 356 Arms. In general, SRMs
are driven by a unipolar excitation current. Therefore, the number of turns is considered
in the application of the ideal square waveform. Figure 12 shows the current waveform
and torque waveform in five turns/slot. As shown in Figure 12a, the ideal phase current
is 356 Arms, and the excitation is continued from the turn-on angle of 0 degrees to the
turn-off angle of 90 degrees in one electrical period of 180 degrees. As shown in Figure 12b,
it is confirmed that the output torque of 70 Nm can be obtained in five turns/slot. A stator
diameter that retained the slot area is used, and a winding diameter under the coil factor of
0.6 is used, which achieves less than 15 A/mm2of the current density.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 9 of 16
2
()
2
Pl
TNi
θ
=
(9)
where /l
θ
∂∂
is the inductance variation in one turn/slot. As shown in Equation (9), the
output torque is proportional to the inductance variation in one turn/slot and the square
of the number of turns and the current. The inductance variation depends on the salient
pole ratio of the rotor. As shown in Equation (9), the number of turns is adjusted to obtain
the maximum torque of 70 Nm under the maximum current of 356 Arms. In general, SRMs
are driven by a unipolar excitation current. Therefore, the number of turns is considered
in the application of the ideal square waveform. Figure 12 shows the current waveform
and torque waveform in five turns/slot. As shown in Figure 12a, the ideal phase current
is 356 Arms, and the excitation is continued from the turn-on angle of 0 degrees to the
turn-off angle of 90 degrees in one electrical period of 180 degrees. As shown in Figure
12b, it is confirmed that the output torque of 70 Nm can be obtained in five turns/slot. A
stator diameter that retained the slot area is used, and a winding diameter under the coil
factor of 0.6 is used, which achieves less than 15 A/mm2 of the current density.
(a) Ideal phase current and inductance (1AT). (b) Torque waveform.
Figure 12. Torque waveform for applying ideal phase current.
4.3. Torque and Phase Voltage at Required Speed of SRM
Using the drive method in the SRM, the current excitation started around the position
where the inductance variation is positive by using the hysteresis control or the voltage
single-pulse drive. Then, it has to be eliminated before the inductance variation becomes
negative to avoid the generation of negative torque. From this drive method, the output
current is changed by some parameters such as the DC voltage, inductance distribution,
the turn-on angle, and the turn-off angle. In the performance evaluation, the turn-on angle
and turn-off angle are determined under a constant input voltage of 365 Vdc to achieve the
required torque for each operation speed.
Figure 13 shows the current waveform, voltage waveform, and torque waveform at
11,500 min1. As shown in Figure 13, the hysteresis current control is used in 11,500 min1,
and the output torque is about 70 Nm, while the phase current is 345 Arms. Figure 14
shows their waveforms at 52,000 min1. As shown in Figure 14, the voltage single pulse
control is used in 52,000 min1. In the high-speed region, the current can be raised, and the
torque can be obtained by setting the turn-on angle to an early timing as rotation speed
increases. The turn-off angle is also set to a timing earlier than the aligned position of rotor
and stator to avoid negative torque.
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0
100
200
300
400
500
600
0 20 40 60 80 100 120 140 160 180
Inductance [mH]
U phase current[A]
Electrical angle [deg]
U phase current
Inductance(1AT)
0
10
20
30
40
50
60
70
80
90
0 20 40 60 80 100 120 140 160 180
Tor que [ Nm]
Electrical angle [deg]
Average:70.0Nm
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250 300
Torque [Nm]
Electrical angle[deg]
-800
-600
-400
-200
0
200
400
600
800
-800
-600
-400
-200
0
200
400
600
800
-50 0 50 100 150 200 250 300
U-phase Voltage [V]
U-phase current [A]
Electrical angle [deg]
U-phase current
U-phase voltage
Average:68Nm
Effective curent:345Arms
Figure 12. Torque waveform for applying ideal phase current.
4.3. Torque and Phase Voltage at Required Speed of SRM
Using the drive method in the SRM, the current excitation started around the position
where the inductance variation is positive by using the hysteresis control or the voltage
single-pulse drive. Then, it has to be eliminated before the inductance variation becomes
negative to avoid the generation of negative torque. From this drive method, the output
current is changed by some parameters such as the DC voltage, inductance distribution,
the turn-on angle, and the turn-off angle. In the performance evaluation, the turn-on angle
and turn-off angle are determined under a constant input voltage of 365 V
dc
to achieve the
required torque for each operation speed.
Figure 13 shows the current waveform, voltage waveform, and torque waveform at
11,500 min
1
. As shown in Figure 13, the hysteresis current control is used in 11,500 min
1
,
and the output torque is about 70 Nm, while the phase current is 345 Arms. Figure 14
shows their waveforms at 52,000 min
1
. As shown in Figure 14, the voltage single pulse
control is used in 52,000 min
1
. In the high-speed region, the current can be raised, and the
torque can be obtained by setting the turn-on angle to an early timing as rotation speed
World Electr. Veh. J. 2022,13, 57 10 of 17
increases. The turn-off angle is also set to a timing earlier than the aligned position of rotor
and stator to avoid negative torque.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 9 of 16
2
()
2
Pl
TNi
θ
=
(9)
where /l
θ
∂∂
is the inductance variation in one turn/slot. As shown in Equation (9), the
output torque is proportional to the inductance variation in one turn/slot and the square
of the number of turns and the current. The inductance variation depends on the salient
pole ratio of the rotor. As shown in Equation (9), the number of turns is adjusted to obtain
the maximum torque of 70 Nm under the maximum current of 356 Arms. In general, SRMs
are driven by a unipolar excitation current. Therefore, the number of turns is considered
in the application of the ideal square waveform. Figure 12 shows the current waveform
and torque waveform in five turns/slot. As shown in Figure 12a, the ideal phase current
is 356 Arms, and the excitation is continued from the turn-on angle of 0 degrees to the
turn-off angle of 90 degrees in one electrical period of 180 degrees. As shown in Figure
12b, it is confirmed that the output torque of 70 Nm can be obtained in five turns/slot. A
stator diameter that retained the slot area is used, and a winding diameter under the coil
factor of 0.6 is used, which achieves less than 15 A/mm2 of the current density.
(a) Ideal phase current and inductance (1AT). (b) Torque waveform.
Figure 12. Torque waveform for applying ideal phase current.
4.3. Torque and Phase Voltage at Required Speed of SRM
Using the drive method in the SRM, the current excitation started around the position
where the inductance variation is positive by using the hysteresis control or the voltage
single-pulse drive. Then, it has to be eliminated before the inductance variation becomes
negative to avoid the generation of negative torque. From this drive method, the output
current is changed by some parameters such as the DC voltage, inductance distribution,
the turn-on angle, and the turn-off angle. In the performance evaluation, the turn-on angle
and turn-off angle are determined under a constant input voltage of 365 Vdc to achieve the
required torque for each operation speed.
Figure 13 shows the current waveform, voltage waveform, and torque waveform at
11,500 min1. As shown in Figure 13, the hysteresis current control is used in 11,500 min1,
and the output torque is about 70 Nm, while the phase current is 345 Arms. Figure 14
shows their waveforms at 52,000 min1. As shown in Figure 14, the voltage single pulse
control is used in 52,000 min1. In the high-speed region, the current can be raised, and the
torque can be obtained by setting the turn-on angle to an early timing as rotation speed
increases. The turn-off angle is also set to a timing earlier than the aligned position of rotor
and stator to avoid negative torque.
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0
100
200
300
400
500
600
0 20 40 60 80 100 120 140 160 180
Inductance [mH]
U phase current [A]
Electrical angle [deg]
U phase current
Inductance(1AT)
0
10
20
30
40
50
60
70
80
90
0 20 40 60 80 100 120 140 160 180
Tor qu e [ Nm]
Electrical angle [deg]
Average:70.0Nm
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250 300
Torque [Nm]
Electrical angle[deg]
-800
-600
-400
-200
0
200
400
600
800
-800
-600
-400
-200
0
200
400
600
800
-50 0 50 100 150 200 250 300
U-phase Voltage [V]
U-phase current [A]
Electrical angle [deg]
U-phase current
U-phase voltage
Average:68Nm
Effective curent:345Arms
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 10 of 16
(a) Phase current and voltage waveforms. (b) Torque waveform.
Figure 13. Rotation speed of 11,500 min
-1
, turn-on angle of 5 degrees, and turn-off angle of 85
degrees.
(a) Phase current and voltage waveforms. (b) Torque waveform.
Figure 14. Rotation speed of 52,000 min
-1
, turn-on angle of 40 degrees, and turn-off angle of 51
degrees.
5. Design of IM
In this section, the specifications of the designed IM and the design process used to
realize the required performances are described. Figure 15 shows the dimension of the
designed IM, and Table 4 shows the specifications of the IM. As shown in Figure 15 and
Table 4, 4 poles and 24 slots are used, and distributed winding is applied. The number of
bars are 36, and the bars are made of aluminum. The motor diameter and stack length are
160 mm and 100 mm, respectively. The detailed design process is stated as follows.
Table 4. Specifications of IM.
Number of poles 4
Stator slots 24
Number of bars 36
Number of turns [turn/slot] 4
Resistance of winding [Ω] 0.003
Winding type Distributed
Air gap [mm] 0.5
Current density[A/mm
2
] 11
Material of magnetic steel sheet 35H230
Material of bar Aluminum
Figure 15. Dimension of designed IM.
5.1. Mechanical Design of IM
Figure 16 shows the Mises stress distribution for the rotor diameter at the maximum
speed of 52,000 min
1
. As shown in Figure 16, high mises stress is generated around the
-800
-600
-400
-200
0
200
400
600
800
-800
-600
-400
-200
0
200
400
600
800
-50 0 50 100 150 200 250 300
U-phase Voltage [V]
U-phase current [A]
Electrical angle [deg]
U-phase current
U-phase voltage 0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250 300
Tor que [ Nm]
Electrical angle[deg]
Average:14.0Nm
Effective current:149Arms
Figure 13.
Rotation speed of 11,500 min
1
, turn-on angle of
5 degrees, and turn-off angle of 85 degrees.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 10 of 16
(a) Phase current and voltage waveforms. (b) Torque waveform.
Figure 13. Rotation speed of 11,500 min
-1
, turn-on angle of 5 degrees, and turn-off angle of 85
degrees.
(a) Phase current and voltage waveforms. (b) Torque waveform.
Figure 14. Rotation speed of 52,000 min
-1
, turn-on angle of 40 degrees, and turn-off angle of 51
degrees.
5. Design of IM
In this section, the specifications of the designed IM and the design process used to
realize the required performances are described. Figure 15 shows the dimension of the
designed IM, and Table 4 shows the specifications of the IM. As shown in Figure 15 and
Table 4, 4 poles and 24 slots are used, and distributed winding is applied. The number of
bars are 36, and the bars are made of aluminum. The motor diameter and stack length are
160 mm and 100 mm, respectively. The detailed design process is stated as follows.
Table 4. Specifications of IM.
Number of poles 4
Stator slots 24
Number of bars 36
Number of turns [turn/slot] 4
Resistance of winding [Ω] 0.003
Winding type Distributed
Air gap [mm] 0.5
Current density[A/mm
2
] 11
Material of magnetic steel sheet 35H230
Material of bar Aluminum
Figure 15. Dimension of designed IM.
5.1. Mechanical Design of IM
Figure 16 shows the Mises stress distribution for the rotor diameter at the maximum
speed of 52,000 min
1
. As shown in Figure 16, high mises stress is generated around the
-800
-600
-400
-200
0
200
400
600
800
-800
-600
-400
-200
0
200
400
600
800
-50 0 50 100 150 200 250 300
U-phase Voltage [V]
U-phase current [A]
Electrical angle [deg]
U-phase current
U-phase voltage 0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250 300
Tor que [ Nm]
Electrical angle[deg]
Average:14.0Nm
Effective current:149Arms
Figure 14.
Rotation speed of 52,000 min
1
, turn-on angle of
40 degrees, and turn-off angle of
51 degrees.
5. Design of IM
In this section, the specifications of the designed IM and the design process used to
realize the required performances are described. Figure 15 shows the dimension of the
designed IM, and Table 4shows the specifications of the IM. As shown in Figure 15 and
Table 4, 4 poles and 24 slots are used, and distributed winding is applied. The number of
bars are 36, and the bars are made of aluminum. The motor diameter and stack length are
160 mm and 100 mm, respectively. The detailed design process is stated as follows.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 10 of 16
(a) Phase current and voltage waveforms. (b) Torque waveform.
Figure 13. Rotation speed of 11,500 min
-1
, turn-on angle of 5 degrees, and turn-off angle of 85
degrees.
(a) Phase current and voltage waveforms. (b) Torque waveform.
Figure 14. Rotation speed of 52,000 min
-1
, turn-on angle of 40 degrees, and turn-off angle of 51
degrees.
5. Design of IM
In this section, the specifications of the designed IM and the design process used to
realize the required performances are described. Figure 15 shows the dimension of the
designed IM, and Table 4 shows the specifications of the IM. As shown in Figure 15 and
Table 4, 4 poles and 24 slots are used, and distributed winding is applied. The number of
bars are 36, and the bars are made of aluminum. The motor diameter and stack length are
160 mm and 100 mm, respectively. The detailed design process is stated as follows.
Table 4. Specifications of IM.
Number of poles 4
Stator slots 24
Number of bars 36
Number of turns [turn/slot] 4
Resistance of winding [Ω] 0.003
Winding type Distributed
Air gap [mm] 0.5
Current density[A/mm
2
] 11
Material of magnetic steel sheet 35H230
Material of bar Aluminum
Figure 15. Dimension of designed IM.
5.1. Mechanical Design of IM
Figure 16 shows the Mises stress distribution for the rotor diameter at the maximum
speed of 52,000 min
1
. As shown in Figure 16, high mises stress is generated around the
-800
-600
-400
-200
0
200
400
600
800
-800
-600
-400
-200
0
200
400
600
800
-50 0 50 100 150 200 250 300
U-phase Voltage [V]
U-phase current [A]
Electrical angle [deg]
U-phase current
U-phase voltage 0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250 300
Tor qu e [ Nm]
Electrical angle[deg]
Average:14.0Nm
Effective current:149Arms
Figure 15. Dimension of designed IM.
World Electr. Veh. J. 2022,13, 57 11 of 17
Table 4. Specifications of IM.
Number of poles 4
Stator slots 24
Number of bars 36
Number of turns [turn/slot] 4
Resistance of winding [] 0.003
Winding type Distributed
Air gap [mm] 0.5
Current density [A/mm2]11
Material of magnetic steel sheet 35H230
Material of bar Aluminum
5.1. Mechanical Design of IM
Figure 16 shows the Mises stress distribution for the rotor diameter at the maximum
speed of 52,000 min
1
. As shown in Figure 16, high mises stress is generated around the
shaft. Considering the limit of Mises stress is under 300 MPa, the rotor diameter has to
decrease to less than 80 mm. Therefore, the rotor diameter is set to 80 mm.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 11 of 16
shaft. Considering the limit of Mises stress is under 300 MPa, the rotor diameter has to
decrease to less than 80 mm. Therefore, the rotor diameter is set to 80 mm.
(a) Mises stress distribution for the rotor diameter.
(b) Maximum Mises stress for the rotor diameter.
Figure 16. Mises stress of IM in the rotor at 52,000 min
1
.
5.2. Electrical Design of IM
In the electrical design, the number of turns is determined using FEA to achieve the
required maximum torque of 70 Nm. Figure 17 shows the frequency–torque
characteristics for the number of turns. The electrical frequency is changed under the
locked rotor condition. As shown in Figure 17, the number of turns changed from one
turn/slot to four turns/slot, and the required maximum torque of 70 Nm is obtained using
four turns/slot. Then, machine parameters such as the secondary resistance, the primary
leakage inductance, the secondary leakage inductance, and the mutual inductance are
obtained by carrying out the locked test and the no-load test using FEA. The machine
parameters are shown in Table 5.
Table 5. Machine parameters of IM.
Secondary resistance [Ω] 0.071
Primary leak inductance [μH] 26.2
Secondary leak inductance [μH] 26.2
Mutual inductance [μH] 278
Figure 17. Torque characteristics for number of turns of designed IM.
5.3. Torque and Phase Voltage at Required Speed of IM
The performances of the IM are evaluated using FEA. Figures 18 and 19 show the
torque waveforms and phase voltage waveform at the operation speed of 11,500 min
1
and
52,000 min
1
, respectively. As shown in Figure 18, the designed IM can achieve the
0
50
100
150
200
250
300
350
400
60 70 80 90 100
Mises stress [MPa]
Rotor diameter [mm]
0
10
20
30
40
50
60
70
80
90
100
10 20 30 40 50 60 70 80 90 100
Torque[Nm]
Electrical frequency[Hz]
1turn 2turn 3turn 4turn
Figure 16. Mises stress of IM in the rotor at 52,000 min1.
5.2. Electrical Design of IM
In the electrical design, the number of turns is determined using FEA to achieve the
required maximum torque of 70 Nm. Figure 17 shows the frequency–torque characteristics
for the number of turns. The electrical frequency is changed under the locked rotor
condition. As shown in Figure 17, the number of turns changed from one turn/slot to four
turns/slot, and the required maximum torque of 70 Nm is obtained using four turns/slot.
Then, machine parameters such as the secondary resistance, the primary leakage inductance,
the secondary leakage inductance, and the mutual inductance are obtained by carrying
out the locked test and the no-load test using FEA. The machine parameters are shown
in Table 5.
World Electr. Veh. J. 2022,13, 57 12 of 17
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 11 of 16
shaft. Considering the limit of Mises stress is under 300 MPa, the rotor diameter has to
decrease to less than 80 mm. Therefore, the rotor diameter is set to 80 mm.
(a) Mises stress distribution for the rotor diameter.
(b) Maximum Mises stress for the rotor diameter.
Figure 16. Mises stress of IM in the rotor at 52,000 min
1
.
5.2. Electrical Design of IM
In the electrical design, the number of turns is determined using FEA to achieve the
required maximum torque of 70 Nm. Figure 17 shows the frequency–torque
characteristics for the number of turns. The electrical frequency is changed under the
locked rotor condition. As shown in Figure 17, the number of turns changed from one
turn/slot to four turns/slot, and the required maximum torque of 70 Nm is obtained using
four turns/slot. Then, machine parameters such as the secondary resistance, the primary
leakage inductance, the secondary leakage inductance, and the mutual inductance are
obtained by carrying out the locked test and the no-load test using FEA. The machine
parameters are shown in Table 5.
Table 5. Machine parameters of IM.
Secondary resistance [Ω] 0.071
Primary leak inductance [μH] 26.2
Secondary leak inductance [μH] 26.2
Mutual inductance [μH] 278
Figure 17. Torque characteristics for number of turns of designed IM.
5.3. Torque and Phase Voltage at Required Speed of IM
The performances of the IM are evaluated using FEA. Figures 18 and 19 show the
torque waveforms and phase voltage waveform at the operation speed of 11,500 min
1
and
52,000 min
1
, respectively. As shown in Figure 18, the designed IM can achieve the
0
50
100
150
200
250
300
350
400
60 70 80 90 100
Mises st ress [MPa]
Rotor diameter [mm]
0
10
20
30
40
50
60
70
80
90
100
10 20 30 40 50 60 70 80 90 100
Torque[Nm]
Electrical frequency[Hz]
1turn 2turn 3turn 4turn
Figure 17. Torque characteristics for number of turns of designed IM.
Table 5. Machine parameters of IM.
Secondary resistance [] 0.071
Primary leak inductance [µH] 26.2
Secondary leak inductance [µH] 26.2
Mutual inductance [µH] 278
5.3. Torque and Phase Voltage at Required Speed of IM
The performances of the IM are evaluated using FEA. Figures 18 and 19 show the
torque waveforms and phase voltage waveform at the operation speed of 11,500 min
1
and 52,000 min
1
, respectively. As shown in Figure 18, the designed IM can achieve the
maximum torque of 70 Nm under conditions with a phase current of 356 Arms and slip of
0.16. However, as shown in Figure 17, the output torque is 8.1 Nm, the required torque of
15.6 Nm and 85 kW cannot be obtained at 52,000 min
1
. The phase voltage is more than
200 V, and the voltage source required is 420 Vdc.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 12 of 16
maximum torque of 70 Nm under conditions with a phase current of 356 Arms and slip
of 0.16. However, as shown in Figure 17, the output torque is 8.1 Nm, the required torque
of 15.6 Nm and 85 kW cannot be obtained at 52,000 min1. The phase voltage is more than
200 V, and the voltage source required is 420 Vdc.
(a) Torque waveforms. (b) Voltage waveform.
Figure 18. Rotation speed of 11,500 min1, input current of 356 Arms, and slip of 0.16.
(a) Torque waveforms. (b) Voltage waveform.
Figure 19. Rotation speed of 52,000 min1, input current of 159 Arms, and slip of 0.096.
6. Performance Comparison of Designed Motors
In this section, the motor performances of the motor volume, the mechanical strength,
the output power, the loss, and efficiency of the designed PMSM, SRM, and IM are
compared, and the results clarify which motor is most suitable for use as a high-speed
traction motor.
6.1. Motor Volume
Table 6 shows the comparison of motor volume. As shown in Table 6, the comparison
is based on the SRM volume of 1.0 p.u. The PMSM and IM are smaller than the SRM in
terms of volume. The rotor diameter is determined depending on the limitation of
mechanical strength at the maximum speed, and the stator diameter is determined by the
slot area which can achieve the condition of the current density and ensure the number of
turn and the current to obtain the maximum torque. The PMSM has the smallest motor
volume, since the slot area can be easily secured by the combination of poles/slots and
concentrated winding and the required torque can easily be obtained using the magnet
torque.
Table 6. Comparison of motor volume.
PMSM SRM IM
Size [mm] φ174 × L100 φ200 × L100 φ180 × L100
Rotor outer diameter [mm] 70 114 80
Motor volume [p.u.] 0.76 1.0 0.81
Current density [A/mm2] 10 12.7 11
0
10
20
30
40
50
60
70
80
90
0 60 120 180 240 300 360
Torque[Nm]
Electric angle[deg]
Average: 72.5Nm
-300
-200
-100
0
100
200
300
0 60 120 180 240 300 360
Voltage[V]
Electric angle[deg]
0
10
20
30
40
50
60
70
80
90
0 60 120 180 240 300 360
Torque[Nm]
Electric angle[deg]
Average: 8.1Nm
-300
-200
-100
0
100
200
300
0 60 120 180 240 300 360
Voltage[V]
Electric angle[deg]
Figure 18. Rotation speed of 11,500 min1, input current of 356 Arms, and slip of 0.16.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 12 of 16
maximum torque of 70 Nm under conditions with a phase current of 356 Arms and slip
of 0.16. However, as shown in Figure 17, the output torque is 8.1 Nm, the required torque
of 15.6 Nm and 85 kW cannot be obtained at 52,000 min1. The phase voltage is more than
200 V, and the voltage source required is 420 Vdc.
(a) Torque waveforms. (b) Voltage waveform.
Figure 18. Rotation speed of 11,500 min1, input current of 356 Arms, and slip of 0.16.
(a) Torque waveforms. (b) Voltage waveform.
Figure 19. Rotation speed of 52,000 min1, input current of 159 Arms, and slip of 0.096.
6. Performance Comparison of Designed Motors
In this section, the motor performances of the motor volume, the mechanical strength,
the output power, the loss, and efficiency of the designed PMSM, SRM, and IM are
compared, and the results clarify which motor is most suitable for use as a high-speed
traction motor.
6.1. Motor Volume
Table 6 shows the comparison of motor volume. As shown in Table 6, the comparison
is based on the SRM volume of 1.0 p.u. The PMSM and IM are smaller than the SRM in
terms of volume. The rotor diameter is determined depending on the limitation of
mechanical strength at the maximum speed, and the stator diameter is determined by the
slot area which can achieve the condition of the current density and ensure the number of
turn and the current to obtain the maximum torque. The PMSM has the smallest motor
volume, since the slot area can be easily secured by the combination of poles/slots and
concentrated winding and the required torque can easily be obtained using the magnet
torque.
Table 6. Comparison of motor volume.
PMSM SRM IM
Size [mm] φ174 × L100 φ200 × L100 φ180 × L100
Rotor outer diameter [mm] 70 114 80
Motor volume [p.u.] 0.76 1.0 0.81
Current density [A/mm2] 10 12.7 11
0
10
20
30
40
50
60
70
80
90
0 60 120 180 240 300 360
Torque[Nm]
Electric angle[deg]
Average: 72.5Nm
-300
-200
-100
0
100
200
300
0 60 120 180 240 300 360
Voltage[V]
Electric angle[deg]
0
10
20
30
40
50
60
70
80
90
0 60 120 180 240 300 360
Torque[Nm]
Electric angle[deg]
Average: 8.1Nm
-300
-200
-100
0
100
200
300
0 60 120 180 240 300 360
Voltage[V]
Electric angle[deg]
Figure 19. Rotation speed of 52,000 min1, input current of 159 Arms, and slip of 0.096.
6. Performance Comparison of Designed Motors
In this section, the motor performances of the motor volume, the mechanical strength,
the output power, the loss, and efficiency of the designed PMSM, SRM, and IM are com-
pared, and the results clarify which motor is most suitable for use as a high-speed trac-
tion motor.
World Electr. Veh. J. 2022,13, 57 13 of 17
6.1. Motor Volume
Table 6shows the comparison of motor volume. As shown in Table 6, the comparison is
based on the SRM volume of 1.0 p.u. The PMSM and IM are smaller than the SRM in terms
of volume. The rotor diameter is determined depending on the limitation of mechanical
strength at the maximum speed, and the stator diameter is determined by the slot area
which can achieve the condition of the current density and ensure the number of turn and
the current to obtain the maximum torque. The PMSM has the smallest motor volume,
since the slot area can be easily secured by the combination of poles/slots and concentrated
winding and the required torque can easily be obtained using the magnet torque.
Table 6. Comparison of motor volume.
PMSM SRM IM
Size [mm] ϕ174 ×L100 ϕ200 ×L100 ϕ180 ×L100
Rotor outer diameter [mm] 70 114 80
Motor volume [p.u.] 0.76 1.0 0.81
Current density [A/mm2]10 12.7 11
6.2. Mechanical Strength
Figure 20 shows the comparison of maximum Mises stress for the rotor diameter.
As shown in Figure 20, the rotor diameters of PMSM, SRM, and IM that achieve yield
stress less than 300 MPa are 70 mm, 114 mm, and 80 mm, respectively. The Mises stress in
the SRM is maintained at a low value for increasing of the rotor diameter since the rotor
structure consists of a magnetic steel sheet alone. That is, it is confirmed that the SRM has
the highest mechanical strength.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 13 of 16
6.2. Mechanical Strength
Figure 20 shows the comparison of maximum Mises stress for the rotor diameter. As
shown in Figure 20, the rotor diameters of PMSM, SRM, and IM that achieve yield stress
less than 300 MPa are 70 mm, 114 mm, and 80 mm, respectively. The Mises stress in the
SRM is maintained at a low value for increasing of the rotor diameter since the rotor
structure consists of a magnetic steel sheet alone. That is, it is confirmed that the SRM has
the highest mechanical strength.
Figure 20. Comparison of Mises stress at the maximum speed of 52,000 min-1.
6.3. Output Characteristics
Figure 21 shows the output power characteristics. As shown in Figure 21, the PMSM
realizes the maximum torque of 70 Nm and the output power of 85 kW at 11,500 min1
and 52,000 min1, although the magnet flux has to be strongly weakened by flux
weakening control to suppress the induced voltage at the maximum rotational speed of
52,000 min1. In the SRM, the output torque is 67.8 Nm at 11,500 min1, and it is 14.2 Nm
at 52,000 min1. Although the output power is slightly lower than the required torque for
the output power of 85 kW, the required torque can be obtained by optimizing the turn-
on angle and turn-off angle. In the IM, the output torque is 71 Nm at 11,500 min1, and it
achieves the required maximum torque. However, the output torque at 52,000 min1 is
much lower than the required torque for the output power of 85 kW, since the voltage is
limited by increasing the rotor flux due to the second current.
Figure 21. Output power characteristics.
6.4. Loss and Efficiency
The loss and efficiency at the base speed of 11,500 min1 and the maximum speed of
52,000 min1 are evaluated. Figure 22 shows losses of joules in the rotor and stator and
core loss. As shown in Figure 22, the joule loss and the core loss in the PMSM are low,
since the input current and the number of turns are small under the small-sized motor
volume, owing to utilization of the permanent magnet. On the other hand, the joule loss
in the stator of the PMSM is higher than that of the SRM at 52,000 min1, since a lot of d-
axis current is needed by the flux weakening control. The SRM also achieves low levels of
joule loss in the stator, since the input current and number of turns are almost same for
the PMSM instead of the rotor diameter increasing. On the other hand, the core loss
increases compared with the PMSM. The IM generates high levels of joule loss, since the
joule loss in the rotor accounts for a large percentage (the stator joule loss and the rotor
0
100
200
300
400
500
50 70 90 110 130
Mises stress [MPa]
Rotor diameter [mm]
PMSM
SRM
IM
Yield stress
:300Mpa
0
10
20
30
40
50
60
70
80
0 10000 20000 30000 40000 50000
Torque [N m]
Speed [rpm]
85kW
PMSM
SRM
IM
Figure 20. Comparison of Mises stress at the maximum speed of 52,000 min1.
6.3. Output Characteristics
Figure 21 shows the output power characteristics. As shown in Figure 21, the PMSM
realizes the maximum torque of 70 Nm and the output power of 85 kW at 11,500 min
1
and
52,000 min
1
, although the magnet flux has to be strongly weakened by flux weakening
control to suppress the induced voltage at the maximum rotational speed of 52,000 min
1
.
In the SRM, the output torque is 67.8 Nm at 11,500 min
1
, and it is 14.2 Nm at 52,000 min
1
.
Although the output power is slightly lower than the required torque for the output power
of 85 kW, the required torque can be obtained by optimizing the turn-on angle and turn-off
angle. In the IM, the output torque is 71 Nm at 11,500 min
1
, and it achieves the required
maximum torque. However, the output torque at 52,000 min
1
is much lower than the
required torque for the output power of 85 kW, since the voltage is limited by increasing
the rotor flux due to the second current.
World Electr. Veh. J. 2022,13, 57 14 of 17
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 13 of 16
6.2. Mechanical Strength
Figure 20 shows the comparison of maximum Mises stress for the rotor diameter. As
shown in Figure 20, the rotor diameters of PMSM, SRM, and IM that achieve yield stress
less than 300 MPa are 70 mm, 114 mm, and 80 mm, respectively. The Mises stress in the
SRM is maintained at a low value for increasing of the rotor diameter since the rotor
structure consists of a magnetic steel sheet alone. That is, it is confirmed that the SRM has
the highest mechanical strength.
Figure 20. Comparison of Mises stress at the maximum speed of 52,000 min-1.
6.3. Output Characteristics
Figure 21 shows the output power characteristics. As shown in Figure 21, the PMSM
realizes the maximum torque of 70 Nm and the output power of 85 kW at 11,500 min1
and 52,000 min1, although the magnet flux has to be strongly weakened by flux
weakening control to suppress the induced voltage at the maximum rotational speed of
52,000 min1. In the SRM, the output torque is 67.8 Nm at 11,500 min1, and it is 14.2 Nm
at 52,000 min1. Although the output power is slightly lower than the required torque for
the output power of 85 kW, the required torque can be obtained by optimizing the turn-
on angle and turn-off angle. In the IM, the output torque is 71 Nm at 11,500 min1, and it
achieves the required maximum torque. However, the output torque at 52,000 min1 is
much lower than the required torque for the output power of 85 kW, since the voltage is
limited by increasing the rotor flux due to the second current.
Figure 21. Output power characteristics.
6.4. Loss and Efficiency
The loss and efficiency at the base speed of 11,500 min1 and the maximum speed of
52,000 min1 are evaluated. Figure 22 shows losses of joules in the rotor and stator and
core loss. As shown in Figure 22, the joule loss and the core loss in the PMSM are low,
since the input current and the number of turns are small under the small-sized motor
volume, owing to utilization of the permanent magnet. On the other hand, the joule loss
in the stator of the PMSM is higher than that of the SRM at 52,000 min1, since a lot of d-
axis current is needed by the flux weakening control. The SRM also achieves low levels of
joule loss in the stator, since the input current and number of turns are almost same for
the PMSM instead of the rotor diameter increasing. On the other hand, the core loss
increases compared with the PMSM. The IM generates high levels of joule loss, since the
joule loss in the rotor accounts for a large percentage (the stator joule loss and the rotor
0
100
200
300
400
500
50 70 90 110 130
Mises stress [MPa]
Rotor diameter [mm]
PMSM
SRM
IM
Yield stress
:300Mpa
0
10
20
30
40
50
60
70
80
0 10000 20000 30000 40000 50000
Torque [N m]
Speed [rpm]
85kW
PMSM
SRM
IM
Figure 21. Output power characteristics.
6.4. Loss and Efficiency
The loss and efficiency at the base speed of 11,500 min
1
and the maximum speed of
52,000 min
1
are evaluated. Figure 22 shows losses of joules in the rotor and stator and
core loss. As shown in Figure 22, the joule loss and the core loss in the PMSM are low,
since the input current and the number of turns are small under the small-sized motor
volume, owing to utilization of the permanent magnet. On the other hand, the joule loss
in the stator of the PMSM is higher than that of the SRM at 52,000 min
1
, since a lot of
d-axis current is needed by the flux weakening control. The SRM also achieves low levels
of joule loss in the stator, since the input current and number of turns are almost same
for the PMSM instead of the rotor diameter increasing. On the other hand, the core loss
increases compared with the PMSM. The IM generates high levels of joule loss, since the
joule loss in the rotor accounts for a large percentage (the stator joule loss and the rotor
joule loss are 1.1 kW and 23 kW at 11,500 min
1
, respectively, and the stator joule loss and
the rotor joule loss are 0.23 kW and 7.8 kW at 52,000 min
1
, respectively). The core loss of
the IM is also higher than that of the PMSM.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 14 of 16
joule loss are 1.1 kW and 23 kW at 11,500 min1, respectively, and the stator joule loss and
the rotor joule loss are 0.23 kW and 7.8 kW at 52,000 min1, respectively). The core loss of
the IM is also higher than that of the PMSM.
(a) Joule loss in rotor and stator. (b) Core loss.
Figure 22. Comparison of joule loss and core loss.
Figure 23 shows the eddy current loss of the magnet and retaining sleeve for the
PMSM. As shown in Figure 23a, it can be seen that the increase in eddy current loss of the
magnet in the high-speed rotation is serious in the PMSM. The number of magnet layers
needed to be increased to reduce the eddy current loss. In the design, the magnet eddy
current loss is suppressed by dividing the magnet into 16 layers. However, a further
reduction in eddy current loss is required to avoid thermal demagnetization in the
magnet. As shown in Figure 23b, the eddy current loss also increased in the retaining
sleeve of the magnet in high-speed rotation. Therefore, it is necessary to use a material
with high electrical resistance and thinness for the retaining sleeve. In the design, eddy
current loss is suppressed by using the C-FRP as the reinforcement material, which has a
high electrical resistivity of 1.5 × 105 Ω m. Actually, the number of layers and the material
of retaining sleeve should be determined in consideration of the trade-off with
manufacturing cost.
Figure 24 shows the windage loss. The windage loss is calculated by the following
equation [15]:
43
adh
WKCR L
πρω
= (10)
where Wa, K, Cd, ρ, R, and L are the windage loss, salient-pole correction factor, skin
friction coefficient, air density, radius of high-speed rotor, and motor stack length,
respectively. In the SRM, the windage loss increases considerably at 52,000 min1 due to
the salient-pole structure of the rotor. The windage loss can be reduced by using the
shroud or cylindrical rotor structure [16]. Figure 25 shows the comparison of the
efficiency. As shown in Figure 25, the PMSM can achieve the highest efficiency of 97% at
11,500 min1 and 86% at 52,000 min1. The SRM achieves the efficiency of 95% at 11,500
min1 and 81% at 52,000 min1. The efficiencies of the IM are 77.8% at 11,500 min1 and
80.3% at 52,000 min1.
(a) Eddy current loss of magnet. (b) Eddy current loss of retaining sleeve.
Figure 23. Eddy current loss of PMSM.
0.52
1.3
3.1
5.1
0.72
2.8
0
2
4
6
8
11500 52000
Core loss [kW]
Speed [min
-1
]
PMSM
SRM
IM
0.68 0.68
1.1 0.2
24.1
8.0
0
5
10
15
20
25
30
11500 52000
Joule loss [kW]
Speed [min
-1
]
PMSM
SRM
IM
11,500 52,000 11,500 52,000
0
0.2
0.4
0.6
0.8
Eddy current loss
of retaining sleeve [kW]
11500 52000
Speed [min
-1
]
0
10
20
30
40
481216
Number of magnet laimination
12000 /min
52000 /min
11500 min
-1
52000 min
-1
Eddy current loss
of magnet [kW]
11,500 52,000
Figure 22. Comparison of joule loss and core loss.
Figure 23 shows the eddy current loss of the magnet and retaining sleeve for the
PMSM. As shown in Figure 23a, it can be seen that the increase in eddy current loss of
the magnet in the high-speed rotation is serious in the PMSM. The number of magnet
layers needed to be increased to reduce the eddy current loss. In the design, the magnet
eddy current loss is suppressed by dividing the magnet into 16 layers. However, a further
reduction in eddy current loss is required to avoid thermal demagnetization in the magnet.
As shown in Figure 23b, the eddy current loss also increased in the retaining sleeve of
the magnet in high-speed rotation. Therefore, it is necessary to use a material with high
electrical resistance and thinness for the retaining sleeve. In the design, eddy current loss is
suppressed by using the C-FRP as the reinforcement material, which has a high electrical
resistivity of 1.5
×
10
5
m. Actually, the number of layers and the material of retaining
sleeve should be determined in consideration of the trade-off with manufacturing cost.
World Electr. Veh. J. 2022,13, 57 15 of 17
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 14 of 16
joule loss are 1.1 kW and 23 kW at 11,500 min1, respectively, and the stator joule loss and
the rotor joule loss are 0.23 kW and 7.8 kW at 52,000 min1, respectively). The core loss of
the IM is also higher than that of the PMSM.
(a) Joule loss in rotor and stator. (b) Core loss.
Figure 22. Comparison of joule loss and core loss.
Figure 23 shows the eddy current loss of the magnet and retaining sleeve for the
PMSM. As shown in Figure 23a, it can be seen that the increase in eddy current loss of the
magnet in the high-speed rotation is serious in the PMSM. The number of magnet layers
needed to be increased to reduce the eddy current loss. In the design, the magnet eddy
current loss is suppressed by dividing the magnet into 16 layers. However, a further
reduction in eddy current loss is required to avoid thermal demagnetization in the
magnet. As shown in Figure 23b, the eddy current loss also increased in the retaining
sleeve of the magnet in high-speed rotation. Therefore, it is necessary to use a material
with high electrical resistance and thinness for the retaining sleeve. In the design, eddy
current loss is suppressed by using the C-FRP as the reinforcement material, which has a
high electrical resistivity of 1.5 × 105 Ω m. Actually, the number of layers and the material
of retaining sleeve should be determined in consideration of the trade-off with
manufacturing cost.
Figure 24 shows the windage loss. The windage loss is calculated by the following
equation [15]:
43
adh
WKCR L
πρω
= (10)
where Wa, K, Cd, ρ, R, and L are the windage loss, salient-pole correction factor, skin
friction coefficient, air density, radius of high-speed rotor, and motor stack length,
respectively. In the SRM, the windage loss increases considerably at 52,000 min1 due to
the salient-pole structure of the rotor. The windage loss can be reduced by using the
shroud or cylindrical rotor structure [16]. Figure 25 shows the comparison of the
efficiency. As shown in Figure 25, the PMSM can achieve the highest efficiency of 97% at
11,500 min1 and 86% at 52,000 min1. The SRM achieves the efficiency of 95% at 11,500
min1 and 81% at 52,000 min1. The efficiencies of the IM are 77.8% at 11,500 min1 and
80.3% at 52,000 min1.
(a) Eddy current loss of magnet. (b) Eddy current loss of retaining sleeve.
Figure 23. Eddy current loss of PMSM.
0.52
1.3
3.1
5.1
0.72
2.8
0
2
4
6
8
11500 52000
Core loss [kW]
Speed [min
-1
]
PMSM
SRM
IM
0.68 0.68
1.1 0.2
24.1
8.0
0
5
10
15
20
25
30
11500 52000
Joule loss [kW]
Speed [min
-1
]
PMSM
SRM
IM
11,500 52,000 11,500 52,000
0
0.2
0.4
0.6
0.8
Eddy current loss
of retaining sleeve [kW]
11500 52000
Speed [min
-1
]
0
10
20
30
40
481216
Number of magnet laimination
12000 /min
52000 /min
11500 min
-1
52000 min
-1
Eddy current loss
of magnet [kW]
11,500 52,000
Figure 23. Eddy current loss of PMSM.
Figure 24 shows the windage loss. The windage loss is calculated by the following
equation [15]:
Wa=KπCdρR4ωh3L(10)
where W
a
,K,C
d
,
ρ
,R, and Lare the windage loss, salient-pole correction factor, skin friction
coefficient, air density, radius of high-speed rotor, and motor stack length, respectively.
In the SRM, the windage loss increases considerably at 52,000 min
1
due to the salient-
pole structure of the rotor. The windage loss can be reduced by using the shroud or
cylindrical rotor structure [
16
]. Figure 25 shows the comparison of the efficiency. As
shown in Figure 25, the PMSM can achieve the highest efficiency of 97% at 11,500 min
1
and 86% at 52,000 min
1
. The SRM achieves the efficiency of 95% at 11,500 min
1
and
81% at 52,000 min
1
. The efficiencies of the IM are 77.8% at 11,500 min
1
and 80.3% at
52,000 min1.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 15 of 16
Figure 24. Windage loss.
Figure 25. Motor efficiency.
7. Conclusions
In this paper, the type of motor suitable for use as a high-speed motor in EV traction
applications was clarified in terms of the motor volume, mechanical strength, output
power, loss, and efficiency. The PMSM, SRM, and IM were designed with the aim of
achieving an output power of 85 kW, a maximum torque of 70 Nm, and a maximum speed
of 52,000 min1, and the performances were evaluated using FEA. Table 7 shows the
comparison of these motor performances. As shown in Table 7, the PMSM was
advantageous in terms of the downsizing of the motor volume and motor efficiency.
However, it is necessary to reduce the eddy current loss of the magnet at 52,000 min1 by
increasing the number of magnet layers and reducing the harmonic flux by applying
distributed winding. They have to be designed considering the trade-off between
increased cost and larger motor size. On the other hand, the SRM was advantageous in
terms of the high mechanical strength of the rotor, and it is suitable for high-speed
rotation. The motor volume of the SRM was larger than that of the PMSM. Although the
efficiency of the SRM was lower than that of the PMSM at the high load condition of 11,500
min1, the efficiency at 52,000 min1 can be improved by decreasing windage loss using the
shroud or cylindrical rotor structure. In this study, the efficiency of the IM at 11,500 min1
was considerably lower due to the joule loss in the rotor. On the other hand, the IM had
the advantage of no magnet eddy current loss, and lower iron loss and wind loss than the
SRM, so it has potential as a high-speed traction motor if the joule loss can be reduced.
Table 7. Motor performances of high-speed drive.
Motor size Mises Stress at Maximum Speed Motor Efficiency
PMSM Φ174 mm × L100 mm 287MPa
(Rotor diameter: 70mm)
11
,
500 min1: 97%
52,000 min1: 86%
SRM Φ200 mm × L100 mm 291MPa
(Rotor diameter: 114mm)
11,500 min1: 95%
52,000 min1: 81%
IM Φ180 mm × L100 mm 258MPa
(Rotor diameter: 80mm)
11
,
500 min1: 78%
52,000 min1: 79%
0
2
4
6
8
10
12
14
11500 52000
Windage loss [kW]
Speed [min
-1
]
SPMSM
SRM
IM
11,500 52,000
97
86
95
81
78 79
0
20
40
60
80
100
11500 52000
Efficiency [%]
Speed [min
-1
]
PMSM
SRM
IM
11,500 52,000
Figure 24. Windage loss.
World Electr. Veh. J. 2022, 13, x FOR PEER REVIEW 15 of 16
Figure 24. Windage loss.
Figure 25. Motor efficiency.
7. Conclusions
In this paper, the type of motor suitable for use as a high-speed motor in EV traction
applications was clarified in terms of the motor volume, mechanical strength, output
power, loss, and efficiency. The PMSM, SRM, and IM were designed with the aim of
achieving an output power of 85 kW, a maximum torque of 70 Nm, and a maximum speed
of 52,000 min1, and the performances were evaluated using FEA. Table 7 shows the
comparison of these motor performances. As shown in Table 7, the PMSM was
advantageous in terms of the downsizing of the motor volume and motor efficiency.
However, it is necessary to reduce the eddy current loss of the magnet at 52,000 min1 by
increasing the number of magnet layers and reducing the harmonic flux by applying
distributed winding. They have to be designed considering the trade-off between
increased cost and larger motor size. On the other hand, the SRM was advantageous in
terms of the high mechanical strength of the rotor, and it is suitable for high-speed
rotation. The motor volume of the SRM was larger than that of the PMSM. Although the
efficiency of the SRM was lower than that of the PMSM at the high load condition of 11,500
min1, the efficiency at 52,000 min1 can be improved by decreasing windage loss using the
shroud or cylindrical rotor structure. In this study, the efficiency of the IM at 11,500 min1
was considerably lower due to the joule loss in the rotor. On the other hand, the IM had
the advantage of no magnet eddy current loss, and lower iron loss and wind loss than the
SRM, so it has potential as a high-speed traction motor if the joule loss can be reduced.
Table 7. Motor performances of high-speed drive.
Motor size Mises Stress at Maximum Speed Motor Efficiency
PMSM Φ174 mm × L100 mm 287MPa
(Rotor diameter: 70mm)
11
,
500 min1: 97%
52,000 min1: 86%
SRM Φ200 mm × L100 mm 291MPa
(Rotor diameter: 114mm)
11,500 min1: 95%
52,000 min1: 81%
IM Φ180 mm × L100 mm 258MPa
(Rotor diameter: 80mm)
11
,
500 min1: 78%
52,000 min1: 79%
0
2
4
6
8
10
12
14
11500 52000
Windage loss [kW]
Speed [min
-1
]
SPMSM
SRM
IM
11,500 52,000
97
86
95
81
78 79
0
20
40
60
80
100
11500 52000
Efficiency [%]
Speed [min
-1
]
PMSM
SRM
IM
11,500 52,000
Figure 25. Motor efficiency.
7. Conclusions
In this paper, the type of motor suitable for use as a high-speed motor in EV trac-
tion applications was clarified in terms of the motor volume, mechanical strength, output
power, loss, and efficiency. The PMSM, SRM, and IM were designed with the aim of
achieving an output power of 85 kW, a maximum torque of 70 Nm, and a maximum speed
of 52,000 min
1
, and the performances were evaluated using FEA. Table 7shows the com-
parison of these motor performances. As shown in Table 7, the PMSM was advantageous in
terms of the downsizing of the motor volume and motor efficiency. However, it is necessary
to reduce the eddy current loss of the magnet at 52,000 min
1
by increasing the number
World Electr. Veh. J. 2022,13, 57 16 of 17
of magnet layers and reducing the harmonic flux by applying distributed winding. They
have to be designed considering the trade-off between increased cost and larger motor size.
On the other hand, the SRM was advantageous in terms of the high mechanical strength
of the rotor, and it is suitable for high-speed rotation. The motor volume of the SRM was
larger than that of the PMSM. Although the efficiency of the SRM was lower than that of
the PMSM at the high load condition of 11,500 min
1
, the efficiency at 52,000 min
1
can be
improved by decreasing windage loss using the shroud or cylindrical rotor structure. In
this study, the efficiency of the IM at 11,500 min
1
was considerably lower due to the joule
loss in the rotor. On the other hand, the IM had the advantage of no magnet eddy current
loss, and lower iron loss and wind loss than the SRM, so it has potential as a high-speed
traction motor if the joule loss can be reduced.
Table 7. Motor performances of high-speed drive.
Motor Size Mises Stress at Maximum Speed Motor Efficiency
PMSM Φ
174 mm
×
L100 mm
287 MPa
(Rotor diameter: 70mm)
11,500 min1: 97%
52,000 min1: 86%
SRM Φ
200 mm
×
L100 mm
291 MPa
(Rotor diameter: 114mm)
11,500 min1: 95%
52,000 min1: 81%
IM Φ
180 mm
×
L100 mm
258 MPa
(Rotor diameter: 80mm)
11,500 min1: 78%
52,000 min1: 79%
Author Contributions:
Conceptualization, K.A. (Kan Akatsu); Investigation, K.A. (Kohei Aiso);
Writing—original draft, K.A. (Kohei Aiso). All authors have read and agreed to the published version
of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
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