The 14th IFToMM World Congress, Taipei, Taiwan, October 25-30, 2015
DOI Number: 10.6567/IFToMM.14TH.WC.PS20.013
Thermal Analysis of the AFPM Motor with Air and Water Cooling Simulations
P. C. Chen1
Industrial Technology Research Institute
Chutung, Hsinchu, Taiwan
itriA00256@itri.org.tw
Abstract: In the paper, the thermal analysis of the axial-flux
brushless DC motor with air and water cooling simulations is
performed to obtain the temperature distribution of the stator,
rotor, and housing during operation. The simulation results are to
serve as a reference for heat dissipation design of the electric
motor. In order to accurately calculate the thermal loss of the
AFPM motors, the finite element method is adopted here.
Electromagnetic-thermal and fluid-thermal coupling analysis is
performed using the ANSYS software. The copper loss and core
loss were obtained from the simulation results of the AFPM
motor by inputting the three phase current in the electromagnetic
simulation. Then the surface convection coefficient were
obtained from simulation results of the fluid field, and the copper
and core losses were simultaneously inputted into the steady state
thermal module for calculation. The temperature (less than 72C)
of the stator in the electric motor with fins comparing with that in
the electric motor without fins is greatly lowered. From the
simulation results, the air and water coolings keep the motor
temperature rise within the required value.
Keywords: Heat dissipation, Electric motor, Axial flux,
Thermofluid Field
1. Introduction
An axial flux permanent magnet (AFPM) motors with
pancake shape have been widely used in recent years due
to their high torque density, modular and compact
construction, high efficiency, reliability and easy
integration with other mechanical components. The
products with the special need for the axial compactness
and high efficiency motors include cleaning robots,
electric fans, electric vehicles, electric bicycles and so on.
Besides, the advent of modern high energy permanent
magnet (PM) materials, such as NdFeB, has resulted in the
rapid development of these types of machines. The high
temperature rise of the AFPM motor may cause the
magnetic degradation and further lead to the failure of the
electric motor. Hence, the heat dissipation is extremely
important for solving the problem. Here the air and water
cooling are used to keep the temperature rise within the
required value.
Thermal analysis of the electric motor has attracted
Scientists’attention in recent years. Vilar [1] proposed a
lumped parameter thermal network model for the
stationary single sided axial-flux permanent magnet motor
in 2005. Huang [2] presented the thermal analysis of a
high-speed motor with soft magnetic composite (SMC) in
2009. Mezani [3] presented a model for coupling
electromagnetic and thermal phenomena in an induction
motor. Gilson [4] set up a design strategy which is capable
of optimizing both the electromagnetic as well as the
thermal design of permanent magnet synchronous
machines (PMSM) for aerospace actuation system in 2010.
Staton [5] dealt with the formulations used to predict
Y. J. Cheng2
Industrial Technology Research Institute
Chutung, Hsinchu, Taiwan
eric_cheng@itri.org.tw
convection cooling and flow in electric machines. For
motor temperature rise prediction, Yabiku [6] outlined a set
of useful calculations and design guidelines. Popescu [7]
built a thermal model for a duplex three-phase induction
machine for fault-tolerant applications in 2013. Kefalas [8]
conducted a thermal investigation of a surface-mounted
permanent-magnet synchronous motor designed for
high-temperature aerospace actuation applications. In
computational dynamics, Wang [9] developed a
thermofluid model combining a lumped parameter heat
transfer model and an air-flow model of a typical
axial-field
permanent-magnet
(AFPM)
machine.
Jungreuthmayer [10] presented a comprehensive
computational fluid dynamics (CFD) model of a radial flux
permanent magnet synchronous machine with interior
magnets. Boglietti [11] proposed an extended survey on
the evolution and the modern approaches in the thermal
analysis of electrical machines in 2009. In addition, the
water cooling of the AFPM machine has been studied in
[12-14].
The proposed AFPM motor is shown in Fig. 1 and its
schematic model with 30 stators and 60 coils is shown in
Fig. 2. In order to enhance the torque of the AFPM motor,
the stators are designed in the form of C shape and have
transverse flux shown in Fig. 3. The topology of the
C-shape stator and the rotor form two airgaps.
Fig. 1. The photo of the proposed AFPM motor
Fig. 2. The schematic model of the AFPM motor
Air gap 1
Stator
Coil 1
Rotor
Air gap 2 Stator
Coil 2
Fig. 3. The transverse flux stator of the AFPM motor with
double air gaps
Table 1. Basic parameters of the AFPM motor with double
air gaps
28.7
Outer diameter of rotor D (mm)
160
Aspect ratio L/D
0.18
Rated voltage (V)
110
Rated speed (rpm)
450
Rated output power (W)
400
1.75
1.50
B (tesla)
Effect axial length L (mm)
Fig. 5. The 3D model of the AFPM motor for
electromagnetic simulation
1.00
0.50
Rotor core material
NdFe35
Pole, Phase, Slot
40, 3, 30
0.00
0.00E+000
1.25E+004
2.50E+004
H (A_per_meter)
3.75E+004
Fig. 6. The B-H curve of the soft magnetic composite
material
2. The Simulation structure of thermal analysis
The simulation structure of the thermal analysis is
explained in this part. All the computation is completed in
the ANSYS Workbench as shown in Fig. 4. The software
ANSYS Maxwell is used to perform the 3D
electromagnetic simulation. Besides, the software modules
ANSYS Fluent and ANSYS Steady-State Thermal are used
in the coupling calculation of fluid and thermal field.
ANSYS Workbench
Maxwell 3D
Fluent
Steady-State Thermal
Fig. 7. The driving circuit of the AFPM motor
Fig. 4. The simulation structure of the AFPM motor
A. The electromagnetic simulation of the AFPM motor
The 3D model of the AFPM motor for
electromagnetic simulation is shown in Fig. 5. To
reduce the calculation time, the one tenth of the 3D full
model of the AFPM motor is used through the
advantage of symmetry. The B-H curve of the soft
magnetic composite material is shown in Fig. 6. In
addition, Fig. 7 indicates the driving circuit of the
AFPM motor and the torque of the proposed electric
motor is shown in Fig. 8. The copper and core losses
of the AFPM motor are shown in Fig. 9 and Fig. 10.,
respectively.
Fig. 8. The torque of the AFPM motor
Fig. 9. The copper loss of the AFPM motor
Fig. 11. The simulation model of the AFPM motor with
the two-hole shroud
Fig. 10. The core loss of the AFPM motor
B. The air cooling simulation of the brushless DC motor
The simulation model of the AFPM motor with the
two-hole shroud including the stators, coils, rotors, the
housing, fins, and the shroud is shown in Fig. 11 and the
air is ventilated by the fan at the outlet on the right side.
The air cooling of the BLDC motor at various velocities
from 0.1 m/s to 5 m/s is investigated. One of the
simulation results is shown here. The inlet pressure is 1
atm and the outlet velocity is 5 m/s. The computational
mesh for the air cooling simulation is shown in Fig. 12.
The convection coefficients on the surface of the fin are
computed and later will be applied to obtain the
temperature distribution of the housing of the electric
motor. Vilar [1] and Gilson [4] use 21.5 C and 24 C as
the initial temperature respectively for the numerical
simulation and the default value in ANSYS is 22 C.
Hence, the initial temperature 22 C is adopted in this
paper. Fig. 14 indicates the flow velocity distribution of
the AFPM motor with the two-hole shroud and Fig. 15
shows the temperature distribution of the housing.
Additionally, the temperature distribution of the stators
and coils of the AFPM motor with the two-hole shroud
is shown in Fig. 16. In the simulation result of air
cooling, the highest temperature of the stator in the
electric motor without fins is generally greater than
100C.
Fig. 12. The mesh of the models for air cooling
Fig. 13. The mesh of the BLDC motor for the thermal
analysis
Fig. 14. The flow velocity distribution of the AFPM motor
with the two-hole shroud
Fig. 18. The 3D mesh of the water cooling channel of the
AFPM motor
Fig. 15. The temperature distribution of the housing of the
AFPM motor with the two-hole shroud
Fig. 19. The velocity vectors of the flow in the water cooling
channel of the AFPM motor
Fig. 16. The temperature distribution of the stators and coils
of the AFPM motor with the two-hole shroud
C. The water cooling simulation of the AFPM motor
First the 3D model of the AFPM motor for water
cooling simulation is shown in Fig. 17. The inlet and
the outlet are on the same side as shown in Fig. 18.
The water cooling of the BLDC motor at various
velocities is investigated. One of the simulation
results of the water cooling is shown in Fig 19.
3. Conclusions
After performing the above air cooling simulation of the
proposed AFPM motor with two-hole shroud, it indicates
that the temperature near the outlet is higher than that near
the inlet during the heat dissipation of the electric motor. In
the simulation result of air cooling, it can be seen that the
temperature (less than 72C) of the stator in the electric
motor with fins comparing with that in the electric motor
without fins is greatly lowered. Additionally, it also shows
that the higher outlet velocity results in the lower
temperature rise of the AFPM motor. As for the water
cooling, the form of water cooling channel can provide an
even temperature of the AFPM motor. From the simulation
results, it demonstrates that the air and water coolings keep
the motor temperature rise within the required value.
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Fig. 17. The 3D model of the AFPM motor for the water
cooling simulation
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