International Review of Electrical Engineering (I.R.E.E.), Vol. 6, N. 2
March-April 2011
Axial-Flux Permanent-Magnet Brushless DC Traction Motor
for Direct Drive of Electric Vehicle
N. A. Rahim, W. P. Hew, A. Mahmoudi
Abstract – This paper presents the design of an inside-out axial-flux permanent-magnet
brushless dc motor for direct traction drive in an electric vehicle. The prototype motor is a
double-sided axial-flux permanent-magnet motor with non-slotted stator. The preliminary design
had 16 rotor poles, for high torque density and stable rotation at low speed. The design was
simulated via Finite Element Method Magnetics (FEMM) Software, for obtainment of design
parameters. The motor was fabricated and tested in an in-wheel test-bed. There exist close
agreements between the simulated and experimental results. Copyright © 2011 Praise Worthy
Prize S.r.l. - All rights reserved.
Keywords: Axial-Flux Permanent-Magnet Motor, Electric Vehicle, Finite Element Analysis
Ki
Bg
fe
fm
A
Nomenclature
Frm
fro
fst
fl
fr
M
g
Cd
S
v
v0
min
r
Pmin
m
a
Paccel
Pout
m
e(t)
i(t)
T
Kp
fe(t)
fi(t)
Epk
Ipk
Irms
P
Kw
Nph
Vehicle driving resistance
Rolling-resistance force
Climbing-resistance force
Aerodynamic-resistance force
Rolling-resistance coefficient
Vehicle mass [kg]
Gravity acceleration [m/s2]
Vehicle movement angle
Air density
Air-resistance coefficient
Frontal projected area
Vehicle speed
Headwind speed
Minimum required torque [N m]
Position vector
Minimum required power [W]
Rotor angular speed [rad/s]
Vehicle acceleration [m/s2]
Power required to accelerate [W]
Rated power
Motor efficiency
Number of phases
Phase-air-gap EMF [V]
Phase current [A]
Period of one EMF cycle [s]
Electrical power waveform factor
Normalized EMF waveforms
Normalized current waveforms
Peak value of phase-air-gap EMF
Phase current peak value
Phase current rms value [V]
Number of motor pole pairs
Winding distribution factor
Number of winding turns per phase
Do
Di
K
Ke
m1
Ar
As
KL
Dtot
Ltot
den
Wcu
Dave
Kcu
Js
Lss
Le
Ls
Lcs
p
Bcs
Lr
Lcr
Lpm
Bcr
Bu
g
µr
Br
Manuscript received and revised March 2011, accepted April 2011
Current waveform factor
Air-gap flux density [Wb/m2]
Electrical frequency [Hz]
Mechanical frequency [Hz]
Electrical loading total [A]
Diameter ratio
Machine stator outer diameter [m]
Machine stator inner diameter [m]
Electrical loading ratio
EMF factor
Number of phases of each stator
Rotor electrical loading [A]
Stator electrical loading [A]
Aspect ratio coefficient
Machine outer diameter total [m]
Machine axial length total [m]
Torque density [N m/cm3]
End-winding protrusion from iron stack [m]
Machine stator average diameter [m]
Copper fill factor
Current density [A/m2]
Stator slot depth [m]
Effective axial length of motor [m]
Stator axial length [m]
Stator-core axial length [m]
Average air-gap flux density to its peak value
ratio
Stator-core flux density [T]
Rotor axial length [m]
Rotor-core axial length [m]
Permanent-magnet length [m]
Rotor-disc flux density [T]
Flux density on permanent-magnet surface [T]
Air-gap length [m]
Recoil relative permeability of magnet
Permanent-magnet residual-flux density [T]
Copyright © 2011 Praise Worthy Prize S.r.l. - All rights reserved
760
N. A. Rahim, W. P. Hew, A. Mahmoudi
Kd
Kc
Kf
Bgpk
Pe
Pm
II.
Leakage-flux factor
Carter factor
Peak value corrected factor of air-gap flux
density
Peak value of air-gap flux density [Wb/m2]
Electrical power [W]
Mechanical power [W]
I.
Design Procedure
II.1.
Vehicle Dynamics
A simple vehicle dynamics model to evaluate vehicle
performance is presented. A simplified vehicle driving
resistance or road load (Frm) consists of rolling resistance
force (fro), climbing resistance force (fst), and
aerodynamic drag force (fl):
Introduction
Frm
Protection of natural environments sparked interest in
electric vehicle (EV), which is non-polluting. EV was
first introduced in 1870; it had light electric motor and
very heavy storage batteries. Battery, electric motor,
motor drive circuit, and transmission gears make up EV
power system.
Range of EV driving speeds was limited. Researchers
and designers keep attempting more-efficient and morereliable EV power systems. Improvements to each
subsystem have increased overall efficiency and driving
range [1]-[6].
Attempts at finding the most suitable EV motor are
keen pursuits of researchers and engineers throughout
the world. Permanent-magnet motors already developed
for electric vehicles fulfill requirements for, e.g., high
power-density, high efficiency, high starting torque, and
high cruising speed. Low cost, high speed, low torqueripple, high reliability, established manufacturing
technology that includes converter, and absence of
position sensors make induction motor the preferred
drive system [7]. Compactness, low weight, and high
efficiency of permanent-magnet brushless DC motors are
suitable options for EV propulsion [8]-[11]. Motors
designed for EV drive can be classified as direct drive
[12] or indirect drive [13]. Direct-drive motor is wheelmounted. Mechanical deferential and transmission gears,
including the associated energy losses, are thus
eliminated.
Not only is efficiency improved, but vehicle weight is
reduced. Slotless AFPM motors have over conventional
radial-flux motors advantages such as high torque-toweight ratio, high efficiency, adjustable air gap, balanced
motor-stator attractive forces, and better heat-removal
[14]-[17].
This paper presents the design of and experimental
work on slotless AFPM motor for EV. The motor is
designed for placement inside the wheel of a motorcycle.
Its specifications are according to typical vehicle
dynamics.
Sizing equations of TORUS AFPM machines are
derived via generalized sizing equation, to calculate
motor’s power-production potential. The sizing equation
is used for optimum machine design. Finite-element
analysis is then performed in field analysis of the
proposed motor topology.
Finally, a prototype motor is fabricated, and
experiments performed, for information on possible
current driving patterns.
f ro
f st
fl
(1)
Rolling resistance (fro) is caused by on-road tire
deformation:
f ro f r M g
(2)
where fr, M, and g are rolling resistance coefficient,
vehicle mass, and gravity acceleration, respectively.
Climbing resistance (fst with positive operational sign)
and downward force (fst with negative operational sign)
are given by:
f st
M g Sin
(3)
where,
is angle of vehicle movement relative to
horizon. Aerodynamic drag force (fl) is air viscous
resistance on vehicle:
1
2
fl
Cd S v v0
2
(4)
where, is air density, Cd is air-resistance coefficient, S
is frontal projected area, v is vehicle speed, and v0 is
headwind speed. Acting as propulsion, driving force is
applied to wheels to overcome driving resistance.
Driving force lower than driving resistance does not
make vehicle roll. In angular movement, minimum
required torque for vehicle propulsion is:
r Frm
min
(5)
where, r is position vector. Minimum power required is
thus:
Pmin
(6)
min
where, m is rotor angular speed. Acceleration is
important to vehicle movement; energy losses caused by
it (a) must factor in calculations. Power required to
accelerate EV is thus:
Paccel
M va
(7)
Power at wheels is:
Pout
Copyright © 2011 Praise Worthy Prize S.r.l. - All rights reserved
Paccel
Pmin
(8)
International Review of Electrical Engineering, Vol. 6, N. 2
761
N. A. Rahim, W. P. Hew, A. Mahmoudi
e(t) is phase air-gap EMF, i(t) is phase current, is
machine efficiency, m is number of machine phases, and
T period of one EMF cycle. Epk and Ipk are peaks of
phase air-gap EMF and of current, respectively. Kp is
electrical power waveform factor, defined as:
Kp
Fig. 1. Proposed Driving Cycles for Electric-Vehicle Design
e t i t dt
mK p E pk I pk
1
T
T
0
fe t
fi t dt (10)
I pk
1
1
T
T
0
(11)
2
i t
I pk
dt
K e N ph Bg
f
1
p
2
Do2
(12)
Ke is EMF factor incorporating winding distribution
factor (Kw) and per-unit portion of air-gap area-total
spanned by machine’s salient poles (if any); Nph is
number of turns per phase; Bg is flux density in air gap; f
is converter frequency; P is machine pole pairs; is
AFPM diameter ratio Di /Do; Do is diameter of machine
outer surface; Di is diameter of machine inner surface.
Equation (9)’s peak phase current is:
Sizing Equation
I pk
A Ki
1
Do
2 2m1 N ph
(13)
where, m1 is number of phases of each stator, and A is
electrical loading. Other authors have provided a
general-purpose sizing equation for AFPM machines; it
takes the following form:
Pout
Main dimensions of each electrical machine are
determined
via
electrical-machine-output
power
equation. Assuming negligible leakage inductance and
resistance, rated power is expressed as [18]:
0
dt
I rms
E pk
TABLE II
DESIGN RESTRICTIONS AND REQUIREMENTS
Dimensional Constraints
Stator Outer Diameter
460 mm
Total Axial-Length
80 mm
Air-Gap
1 mm
Limits on Power Systems
Permanent Remanence
1.3 T
Rated Line-to-Line Voltage (rms)
70V
Input Phase Current (rms)
30A
Requirements
Maximum Torque
36.5 N.m
Output Power
1.8 kw
Motor Efficiency
>90%
Pout
E pk I pk
where, Irms is phase-current rms value. Table III lists
typical waveforms and their corresponding powerwaveform factor (Kp) and current-waveform factor (Ki)
[14]. Peak value of phase-air-gap EMF for equation (8)’s
AFPM motor is:
An optimum design would be maximized torque
density while desired efficiency is maintained within
design restrictions and requirements (see Table II).
T
e t i t
Ki
TABLE I
PARAMETERS USED IN THIS STUDY
Vehicle Specification
Weight of Vehicle
80 kg
Weight of Passengers
70 kg
Wheel Radius (Rd)
0.30 m
Tire Set
3 units
Drive System
Front drive
Frontal Area (S)
0.4 m2
Air Resistance Coefficient (Cd)
0.35
Tire Resistance Coefficient (fr )
2.5×10-3
Air Density ( )
1.22 kg/m3
Maximum Speed (vmax)
60 km/h
m
T
T
0
where fe(t)=e(t)/Epk and fi(t)=i(t)/Ipk are expressions for
normalized EMF and current waveforms. For effect of
current waveform, current waveform factor (Ki) is
defined and presented:
To design EV motor propulsion, vehicle dynamics
should first be determined. Fig. 1 is EV cruising
scenario, which includes an EV’s typical-trip elements
such as increasing speed, constant speed, and braking
action. Power needed by the vehicle is calculated from
the proposed driving cycle in Fig. 1, together with
Equations (1) to (8). Table I lists the parameters used in
the study.
II.2.
1
T
1 m
K e Ki K p K L Bg A
1 K m1 2
f
1
P
2
1
2
Do2
(14)
Le
m1 is number of phases of each stator; Le is effective
axial length of the motor; K is electrical loading ratio on
rotor and stator; KL is aspect ratio coefficient pertinent to
a specific machine structure, with considerations for
effects of losses, temperature rise, and the design’s
(9)
Copyright © 2011 Praise Worthy Prize S.r.l. - All rights reserved
International Review of Electrical Engineering, Vol. 6, N. 2
762
N. A. Rahim, W. P. Hew, A. Mahmoudi
efficiency requirements. Also, machine torque density
for volume total is defined as:
Pout
den
m
4
Le
Ls
3
Pout
m
f
K e K p Ki ABg
1
2 m1
p
2
Lcs
Model
Do
TABLE III
TYPICAL PROTOTYPE WAVEFORMS
e(t)
i(t)
(17)
Ki
2
0.5Cos
Sinusoidal
2
0.5
Rectangular
1
1
Trapezoidal
1.134
0.777
Triangular
3
Wcu
Di2
2
p Do
1
Lcr
(21)
(22)
L pm
r Bg
Br
Kf
Kd
Kc g
(24)
Bg
where µr is magnet’s recoil relative permeability, Br is
permanent-magnet material residual-flux density, Kd is
leakage flux factor, Kc is Carter factor, Kf =Bgpk/Bg is
peak value corrected factor of air-gap flux density in
radial direction of AFPM motor. These factors can be
obtained from FEM analysis [19].
In AFPM motors, air-gap flux density and diameter
ratio are the two important design parameters having
significant effect on motor characteristics. To optimize
motor performance, diameter ratio and air-gap flux
density must be chosen carefully. The optimum design
should maximize power density while maintaining
desired efficiency within design restrictions (Table II). In
design studies, diameter ratio and air-gap flux density are
design parameters. Fig. 2 shows power density variation
as a function of air-gap flux density, and diameter ratio
of the AFPM motor.
0.333
2 ADave
K cu J s
(20)
4 pBcs
Lcr
where, Wcu is protrusion of end winding from iron stack,
in radial direction. For back-to-back wrapped winding,
protrusions exist towards machine axis as well as
towards the outsides, and can be calculated as:
Di
2 Lss
where Bcr is flux density in rotor disc core, and Bu is
attainable flux density on permanent-magnet surface.
Permanent-magnet length Lpm can be calculated as:
Kp
Sinusoidal
Lcs
Lpm is permanent-magnet length; axial length of rotor
core Lcr is:
Bu Do 1
Lcr
(23)
8 pBcr
2
2Wcu
Bg
Lr
Machine outer diameter total Dtot for the TORUS
motor is given by:
Dtot
(19)
where Bcs is flux density in stator core, and p is ratio of
average air-gap flux density to peak air-gap flux density.
Axial length of rotor Lr becomes:
(16)
1
2g
Axial length of stator core Lcs can be written as:
m is rotor angular speed, Dtot and Ltot respectively are
machine outer diameter total and machine length total
including stack outer diameter and end-winding
protrusion from radial and axial iron stacks.
The generalized sizing equation approach can easily
be applied to double-sided axial-flux permanent-magnet
TORUS type motor. The outer surface diameter (Do) can
be written as:
Do
2 Lr
Lr is axial length of rotor, and g is air-gap length.
Axial length of stator Ls can be written as:
(15)
2
Dtot
Ltot
Ls
III. Simulation and
Finite Element Analysis
(18)
The design was simulated via Finite Element Method
Magnetics (FEMM) Software. The simulation model
reached the output (2.7 kW) targeted for the electric
motorcycle.
where, Dave is average diameter of the machine, Js is
current density, and Kcu is copper fill factor. Note that for
slotted machines, depth of stator slot is Lss=Wcu. Axial
length Le of machine is given by:
Copyright © 2011 Praise Worthy Prize S.r.l. - All rights reserved
International Review of Electrical Engineering, Vol. 6, N. 2
763
N. A. Rahim, W. P. Hew, A. Mahmoudi
of magnet inner to outer diameter (Dave=(Di+Do)/2).
Corresponding materials and circuit currents were
assigned to each block of the model; see Fig. 3(a). The
motor’s 2-D model is symmetric, so 16 magnetic poles
were sliced to reduce simulation/calculation time, and the
FEMM model became six magnetic pole pieces. Results
from the model were calculated via LUA programming
language, to obtain values for the entire motor. For
simulation, input parameters needing consideration were
permanent-magnet thickness, air-gap width, and
magnetic properties of all active materials.
Fig. 3(b) shows the magnetic flux density generated
by the permanent magnets.
Fig. 2. Torque density vs. air-gap flux density and diameter ratio
The FEMM 4.0 software allows calculating in 2-D
space, so the actual motor had to be modified to the flat
model, in which all curvatures were developed relative to
average diameter placed middle of stator core or average
(a) AFPM motor model in 2D with Fine Meshing
(b) Magnetic-flux density FEMM simulation
Figs. 3. AFPM motor simulation using FEMM
The relatively symmetrical distribution of the
magnetic-flux density relative to radial symmetrical axis
of the magnets indicates current’s negligible influence on
resultant magnetic field. Maximum flux density is higher
in the stator core than in the rotor because the stator core
is laminated steel that saturates at much higher values.
Table IV shows the parameters and the optimized
TORUS motor dimensions calculated via sizing
equations.
TABLE IV
MOTOR DIMENSIONS
Rotor Inner Diameter
130 mm
Rotor Outer Diameter
230 mm
Number of Windings
48
Number of Turns
12
Magnetic Pole
16
Magnet Thickness
Magnet Arc
Magnet Material
Back-Iron Thickness
Rated Voltage Line-to-Line
(rms)
Rated Phase Current (rms)
Output Power
FEA was for overview of saturation levels in various
parts of the machine, for comparison of flux densities
obtained from FEM with sizing analysis.
Table V tabulates results for the comparison, which
was done at no load and for various parts of the machine.
The no-load flux density plots show consistency with
sizing analysis, maximum flux density of rotor and of
stator almost equal. Maximum and average air-gap flux
densities from FEM and from sizing analysis agree, too.
Fig. 4 compares calculated back-EMF against
electrical angle of the designed motor, from FEA and
from the no-load experiment at 700 rpm. The
experiment’s peak back-EMF was 90.4V, slightly less
than the 95V computed value, agreeing closely with the
computed waveform.
Fig. 5 compares experiment torque against electrical
angle variation, and predicted torque from FEA; both
closely agree. At 30A rated current and 700rpm rated
speed, the motor produces 37.4Nm maximum torque
while the simulation showed 36.78Nm.
7 mm
18o
Nd-Fe-B, N35
12 mm
TABLE V
FLUX DENSITY COMPARISON OF THE DESIGNED MOTOR
Rotor
Air-gap
stator
Bcr
Bmax
Bave
Bcs
FEM
1.2
0.81
0.52
1.15
Sizing Eq.
1.1
0.8
0.5
1.1
64V
30A
1.8 kW
Copyright © 2011 Praise Worthy Prize S.r.l. - All rights reserved
International Review of Electrical Engineering, Vol. 6, N. 2
764
N. A. Rahim, W. P. Hew, A. Mahmoudi
Fig. 4. Back-EMF at 700 rpm
Fig. 6. Surface-mounted permanent-magnet arrangement
on rotor back-iron
Fig. 5. Mechanical torque at 30A
The results show the motor’s ability to fulfill the
electric motorcycle’s power requirement.
IV.
Fabrication and Experiment Works
Fig. 7. Toroidal windings for a slot-less stator
The motor costs relatively low to manufacture, as
there are no stator teeth. The stator lamination silicon
steels are rolled; no need to wire-cut or laser-cut.
Components such as rotor plate and shaft are also
designed simply and also cost relatively low to
manufacture. Absence of teeth makes windings difficult
to assemble. The motor uses encapsulated thermal
conductor epoxy; good for releasing heat, but stands up
to only 80°C before its rigidity decreases.
The shaft was embedded with stator components; see
Fig 8. It kept the stator from returning to a direction
opposite to rotor (wheel), so the shaft had to be strong
enough for the stator to hold up to the motor’s torque.
IV.1. Manufacturing
Design challenge in manufacturing the AFPM motor
is maintaining air gap between stator and rotor. Magnetic
interaction between rotor magnet and stator back-iron is
quite large (752 N simulated value for this motor). The
air-gap needs to be the smallest possible; in the design,
1mm. Fig. 6 shows the active parts assembled and the
rotor’s fabricated surface-mounted permanent-magnet
mount.
Windings were professionally hand-made; see Fig. 7.
They were placed on flat-stator-core surface. To prevent
the windings from missing its position and from
vibration during motor operation, a type of epoxy resin
was applied, giving the windings characteristics such as
stiffness in working temperature, original dimensions,
and good thermal conductivity for heat-release.
Fig. 8. Shaft with hole-through for phase-winding terminal outlet
IV.2. Driving System
To rotate the motor, the stator windings should be
energized in sequence. Knowledge of the rotor’s
positioning is important, to understand which winding is
energized following the energizing sequence. Rotor
Copyright © 2011 Praise Worthy Prize S.r.l. - All rights reserved
International Review of Electrical Engineering, Vol. 6, N. 2
765
N. A. Rahim, W. P. Hew, A. Mahmoudi
position was sensed by Hall Effect sensors embedded in
stator. Whenever rotor magnetic poles passed near the
Hall sensors, they gave high or low signals, indicating
which pole (the N or the S) is passing. A combination of
three of the Hall sensor signals enables determination of
the exact sequence of commutation. Fig. 9 exemplifies
Hall sensor signals related to back-EMF and phase
current. Fig. 10 shows the Hall sensor’s position on a
three-phase coreless stator.
(a) Switching diagram
Fig. 9. Single Hall-sensor position signal (green)
on three-phase back-EMF
windings
Hall
sensors
(b) Current-Flow to the Motor Winding at One Commutation-Step
Figs. 11. Switching sequence
stator
back iron
Fig. 10. Hall-Sensor Position on Stator
Fig. 11(a) shows the switching sequence to be
followed relative to signals of the Hall sensors. Fig.
11(b) shows current to the motor winding at one
commutation step. Each commutation sequence of a
three-phase motor has one winding energized to positive
power (current enters the winding), another to negative
(current exits it), and another is not energized.
Figs. 12 show the commutator circuit and the six-gate
drive. One Hall sensor changes state for every 60
electrical degrees of rotation. One electrical cycle (360
electrical degrees) takes six steps to complete. Every 60
electrical
degrees,
phase-current
switching
is
synchronously updated. One electrical cycle, however,
may not correspond to one rotor revolution (mechanical).
(a) Commutator circuit
(b) Six gate-drive
Figs. 12. Commutator circuit and six gate-drives
Copyright © 2011 Praise Worthy Prize S.r.l. - All rights reserved
International Review of Electrical Engineering, Vol. 6, N. 2
766
N. A. Rahim, W. P. Hew, A. Mahmoudi
Completion of a mechanical rotation is determined by
rotor-pole pairs, via number of electrical cycles to be
repeated.
One rotor-pole pair completes one electrical cycle:
fm
fe
2P
(25)
fe and fm are electrical and mechanical frequency
respectively.
V.
Experiment Results
Fig. 13 shows the experiment test-bench set-up in
University of Malaya’s Department of Electrical
Engineering, for performance test of the in-wheel motor.
A National Instrument Data Acquisition System with
LabVIEW™ interface was used to obtain test data and
plot performance curves. Motor torque and back-EMF
were the main performance parameters obtained. During
cruising-speed test, secondary measurements such as
temperature rise in the motor’s critical parts were also
recorded.
Figs. 14 and 15 show graphs of back-EMF and torque.
Back-EMF maximum output was 180V peak-to-peak,
and torque output at rated current (30A) was about 37.4
N.m. Back EMF was acquired by mechanically turning
the wheel at a particular speed, and then measuring
terminal voltage.
Motor speed was captured on a tachometer, which
obtained the speed from the Hall-sensor pulse train.
Under such conditions, the machine then acted as
generator. At no-load condition, terminal voltage of the
machine equaled generated back-EMF. Motor torque was
measured on a load-cell force sensor, which was
mounted on a free-rolling shaft. Constant, controlled
current was injected into the motor from an inverter. The
wheel was loaded with roller brake. Torque could be
increased to maximum value quickly, and to twice the
rated value.
Input power (Pi) is the electric energy that runs the
motor. Mechanical power delivered by the motor (Pm) is
torque and speed, and overall motor efficiency is the
ratio of input power to mechanical power:
Pi
3V ph I ph
Pm
m
Pm
Pi
Fig. 13. Motor experiment test-bench set-up with NI® data logger
Fig. 14. Comparison of Back-EMF results obtained from experiment
and from FEM simulation
Fig. 15. Comparison of torque results obtained from experiment and
from FEM simulation
(26)
(27)
(28)
Fig. 16 is a plot of measurement results, showing
input power, mechanical output power, and overall
efficiency. Results indicate the machine’s efficiency is
more than 90%.
Fig. 16. The motor’s performance-test results
Copyright © 2011 Praise Worthy Prize S.r.l. - All rights reserved
International Review of Electrical Engineering, Vol. 6, N. 2
767
N. A. Rahim, W. P. Hew, A. Mahmoudi
VI.
Conclusion
[12] F. Caricchi, F. Crescimbini, F. Mezzetti, E. Santini, Multistage
Axial-Flux PM Machine for Wheel Direct Drive,
IEEE
Transactions on Industry Applications, Vol. 32 n. 4, July-August
1996, pp. 882-888.
[13] C. C. Chan, K. T. Chau, J. Z. Jiang, W. Xia, M. Zhu, R. Zhang,
Novel Permanent Magnet Motor Drives for Electric Vehicles.
IEEE Transactions on Industrial Electronics, Vol. 43 n.2, April
1996, pp. 331-339.
[14] A. Mahmoudi, N. A. Rahim, W. P. Hew, Analytical Method for
Determining Axial-Flux Permanent-Magnet Machine Sensitivity
to Design Variables, International Review of Electrical
Engineering (IREE), vol. 5, no. 5, September-October 2010, pp.
2039-2048.
[15] S. Asghar Gholamian, M. Ardebili. K. Abbaszadeh, Selecting and
Construction of High Power Density Double-Sided Axial Flux
Slotted Permanent Magnet Motors for Electric Vehicles,
International Review of Electrical Engineering (IREE), vol. 4. n.
3, June 2009, pp. 477-484.
[16] D. C. Hanselman, Brushless Permanent Magnet Motor Design
(McGraw-Hill New York, 1994).
[17] K. Sitapati and R. Krishnan, Performance Comparison of Radial
and Axial Field Permanent Magnet Brushless Machines, IEEE
Transactions on Industry Applications, vol.37, n. 5, SeptemberOctober 2001, pp. 1219-1226.
[18] S. Huang, J. Luo, F. Leonardi and T. A. Lipo, A Comparison of
Power Density for Axial Flux Machines Based on the General
Purpose Sizing Equation, IEEE Transaction on Energy
Conversion, Vol.14 n.2, June 1999, pp. 185-192.
[19] J. F. Gieras, R. J. Wang, M. J. Kamper, Axial Flux Permanent
Magnet Brushless Machines (Kluwer Academic Publisher, 2008).
The design, simulation, and testing of an AFPM wheel
motor have been presented. Its high torque-density was
the parameter of concern. The aim was for maximumtorque-density double-sided AFPM motor. Flux-densities
of various parts of the motor were compared via sizing
analysis, FEM, and experiment, each at no-load, all
agreed in their results.
Results of experiment and simulation show the
motor’s actual back-EMF value during testing to be 90.4
Vmax at 700rpm. The test result was 4.8% less than that of
the simulated result (95 Vmax). The difference could be
due to the winding arrangement, which was slightly
different during fabrication. Torque produced during
experiment was 37.4Nm, with 30A input current,
whereas torque produced in simulation was about
36.78Nm for the same condition. The motor’s design
achieved the required motor specification. Its efficiency
was 90%, and its design suits EV application.
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Authors’ information
Corresponding Author:
Tel: +60136778050
Fax: 03-7967 5317
E-mail: amaminmahmoudi@gmail.com
Nasrudin Abd. Rahim was born in Johor,
Malaysia, in 1960. He received his B.Sc. (Hons.)
degree in 1985, and his M.Sc. degree in 1988,
both from the University of Strathclyde,
Glasgow, UK. His Ph.D. degree was awarded in
1995 by Heriot-Watt University, Edinburgh,
U.K.
He is a Professor at the Department of Electrical
Engineering, University of Malaya, Malaysia, Director of the
University of Malaya Power Electronics, Drives, Automation and
Control (UMPEDAC) Research Centre, and Chairman of University of
Malaya Advanced Engineering & Technology Research Cluster.
Dr. Rahim is a Fellow of the Institution of Engineering and
Technology, UK, and a Chartered Engineer. He had been Chairman of
IEEE’s Power Engineering Society/Electric Machinery Committee
Motor Subcommittee Working Group 8 (WG-8) covering reluctance
motors. His research interests include power electronics, real-time
control systems, electrical drives, and renewable energy (solar and
wind).
Hew Wooi Ping was born in Kuala Lumpur,
Malaysia, in 1957. He obtained his Bachelor of
Engineering (Electrical) degree in 1981, and his
Master of Electrical Engineering degree from
University of Technology, Malaysia. His Ph.D.
degree was awarded in 2000 by University of
Malaya, Kuala Lumpur, Malaysia.
He is an Associate Professor at the Department
of Electrical Engineering, University of Malaya.
Dr. Hew is a Member of IET and a Chartered Engineer. His research
interests include electrical drives, electrical machine design, application
of fuzzy logic/neural network to electrical-machine-related applications,
and renewable energy (solar and wind).
Copyright © 2011 Praise Worthy Prize S.r.l. - All rights reserved
International Review of Electrical Engineering, Vol. 6, N. 2
768
N. A. Rahim, W. P. Hew, A. Mahmoudi
Amin Mahmoudi was born in Bandar Abbas,
Iran, in 1983. He received the B.S. degree in
electrical engineering from Shiraz University,
Shiraz, Iran in 2005 and the M.S. degree in
electrical power engineering was awarded from
Amirkabir University of Technology, Tehran,
Iran, in 2008.
He is currently a lecture at the Department of
Engineering, HELP College of Arts and Technology, Kuala Lumpur,
Malaysia. Mr. Mahmoudi is working toward the PhD degree in the
Department of Electrical Engineering at University of Malaya, Kuala
Lumpur, Malaysia. His research interests are numerical methods in
electrical engineering, modeling and design of electrical machinery.
Copyright © 2011 Praise Worthy Prize S.r.l. - All rights reserved
International Review of Electrical Engineering, Vol. 6, N. 2
769