Proceedings of the 5th WSEAS Int. Conf. on Power Systems and Electromagnetic Compatibility, Corfu, Greece, August 23-25, 2005 (pp502-507)
Development of BLDC Motor using Metal Powdered Core for 42V Fan
Application of Hybrid Electric Vehicle
JIN HUR and HA-GYEONG SUNG
JUNG-PYO HONG
*Dept. of Electric Eng.
Intelligent Mechatronics Research Center,
Changwon National University
Korea Electronic Technology Institute (KETI))
641-773 Sarim-dong, Changwon,
203-103, 192 B/D Yakdae-dong, Wonmi-gu, Puchon,
KOREA
KOREA
http://www.keti.re.kr/premech
Abstract: - This paper aims to develop the 42V BLDC fan motor for hybrid electric vehicle using metal powdered
core. So, the influence on a motor design by metal powder is described and the powder is applied as a direct
replacement of lamination core. This point is focused upon a comparison of brushless dc motors, built with a
powdered stator and Si laminated stator, which also has been redesigned to take an advantage of the powdered core
for improving their performance on the same volume.
Key-Words: - 42V cooling fan motor, BLDC motor, Metal powdered core, Si laminated core, EMCN method
1 Introduction
The demands being placed on a car’s electrical
system today are unprecedented and so the 42V power
system will be applied to service the electrical needs of
future vehicle such as Luxury vehicle, HEV (Hybrid
Electric Vehicle) and FCEV (Fuel Cell Electrical
Vehicle) [1]. The load voltage for motors also is
recommended to be 42V because of several benefits
due to the higher voltage. The cooling fan motor is one
of main power consumed electric loads at the present
vehicle. So, the development of 42V fan motor is
needed. Generally, the 12V Brush type DC motor is
used for fan because of use of the existing
infrastructure. However, this need to be rated for
continuous operation at the highest current and the
motor lose 15 percent of their energy in the brushes
alone. So, brushless DC motor will be the choice for
most application such as fans and pumps because of its
efficiency at high voltage as well as it easy control and
high quality and reliability [2]. This paper presents the
development of BLDC motor using metal powdered
core for 42V cooling fan.
Metal powder materials as new magnetic materials
for improving the capability of magnetic circuit of
electric machine devices have been continually
developed and its applications have been expanded
according to the requirement of high performance.
That is, a magnetic material is used for all kinds of
motors converting an electromagnetic energy to a
mechanical energy and plays an important role in their
performance. So, much research is performed for
improving the performance. In such side, metal
powder materials allows improvements over the
lamination core with the respects of design freedom,
low manufacturing cost, simple manufacturing
processes, and low eddy current losses [3], [4],[5].
Since the particles of the powder are insulated by
the surface coating and adhesive used for composite
bonding, the eddy current loss is much lower than in
laminated steels, especially at higher frequencies, and
the hysteresis loss becomes the dominant component
of core loss. Motor designers can handle 3-D structure
for a more effective magnetic flux path contrary to
conventional laminated steel and expect the more
improved motor efficiency due to design trends of
smaller size, higher output in recent years [6].
In this paper, the design of BLDC motor for 42V
fan is performed first, and then the new structure of
BLDC motor with teeth overhang using the metal
powdered core, as shown in Fig. 1, are investigated to
improve the characteristics of the conventional
structure manufactured by Si laminated steel.
Fig. 1 SPM type BLDC Motor with Teeth overhang
Proceedings of the 5th WSEAS Int. Conf. on Power Systems and Electromagnetic Compatibility, Corfu, Greece, August 23-25, 2005 (pp502-507)
That is, the designed 42V conventional type BLDC
motor for cool fan has been redesigned and rebuilt
using the metal powdered core with the objective of
maximizing the performance. It must be noted that the
proposed structure using metal powder core has a
great advantage over conventional type for
maximization of the output.
2 Design of BLDC motor for 42V Fan
The fan with motor can be utilized for relatively long
operating hours in the vehicle. The BLDC motor is
especially advantages for fan application because of
their wide speed range, easy speed controllability,
high efficiency and long lifetime expectancy. The Fig.
2 shows the designed motor and their distribution of
magnetic flux density. The motor is inner-rotor type
BLDC motor with 8 poles and 12 teeth designed for
low torque ripple.
2.1 Design of Teeth overhang
In spite of many advantages of the metal powder
materials afore-mentioned, it has a disadvantage of
low permeability and high specific iron loss at low
frequencies. So, although it became very attractive for
use as magnetic core parts or for manufacturing the
stator cores of PM motor in general, it causes output
power density to be reduced [6]. In this paper, a stator
shape with teeth overhang of the BLDC motor is
designed and manufactured by the metal powder core
in the same volume as conventional type motor
laminated Si steel to maximize the effects of end
winding.
In order to analyze the effect of the teeth overhang
on the stator of BLDC motor, in this design, the
simplified magnetic equivalent circuit (MEC) model
considering the teeth overhang is developed as shown
in Fig. 3. As design variables, the overhang at the top
of stator core, Ra and Rb , is depicted.
This MEC model is applied to the initial design of
the overhang and investigation on the effect according
to the different overhang length. The advantage of this
kind of structure having teeth overhang is to be
generated the magnetic torque at the teeth overhang
region as well as at the conventional stator region,
which results in an increase of higher total torque.
However, due to their 3-D shape by the teeth overhang,
this type structure cannot be achieved by lamination of
steel sheet. This property makes the metal powder core
very attractive for producing a complex shaped stator
such as designed type. So, this structure makes up for
the weak point in the performance due to a low
permeability of metal powder.
The applied machine is a 150W BLDC motor, and
its stator has 12 slots and the rotor is built of 8 poles of
radial magnetic, Ferrite magnet. In order to compare
of the metal powder BLDC motor with lamination
core one, three BLDC motors manufactured by
conventional type Si core (Si model), conventional
type metal power core (MP model) and proposed
metal powder core with teeth overhang (OH model)
are applied to examine metal powder motor of the
same dimension as previously designed lamination
core one.
(a) Simplified MEC model for Overhang model
(b) MEC model of conventional stator yoke region
Fig.2 Distribution of magnetic flux density
(c) MEC model for Overhang model
Fig.3. MEC model
Proceedings of the 5th WSEAS Int. Conf. on Power Systems and Electromagnetic Compatibility, Corfu, Greece, August 23-25, 2005 (pp502-507)
N (i , j ,k )
(
)
The system matrix equation applied the magnetic flux
continuity condition can be obtained to all nodes as
following,
[P]n×n {U}n×1 = {F}n×1
(2)
where, n is total number of node, [P ]n× n is the
permeance coefficient matrix which is symmetric and
has a good sparsity and bandwidth, {U}n×1 is the matrix
of MSP and {F}n×1 is the forcing matrix.
The local values of flux density are calculated by
the solved MSP. Fig. 4 shows the mesh shape in x-y
plane of the designed motor. The comparison of 2D
FEA result and 3D EMCN results is shown in Fig. 5.
Fig. 6 shows also the torque characteristics according
to the rotation angle. As shown in Fig. 6, the proposed
type with a teeth overhang for using the flux leakage
of end winding have a superiority over the
conventional type in the torque point of view.
0.5
2D-FEM
3D-EMCN
0.4
Flux Density, B_y (T)
In order to accurately analyze the three models of
the BLDC with different stators, a calculation of the
magnetic field has to be performed for both models by
3-D equivalent magnetic circuit (3-D EMCN) method
[7], because 3-D analysis is required to evaluate and
design this type motor. 3-D EMCN method
supplements magnetic equivalent circuit by network
construction for getting the distribution of field
variable. In this method, the analysis model is divided
into hexahedral element and then equivalent magnetic
circuit network is constructed by connecting the node
of every elements center. The field variable of their
centroids, magnetic scalar potential (MSP), is decided
by the permeance involved with them. Thus, the
magnetic flux between two nodes (i, j, k) and (i, j-1, k)
are calculated such that
φ ( i , j ,k ) = 1
U (i , j ,k ) − U (i , j −1,k ) + F(i , j ,k )
(1)
R
0.3
0.2
0.1
0.0
-0.1
45
60
75
90
105
120
135
o
Mechincal angle ( )
Fig.5. MEC model
From these results, although the metal powder has
a disadvantage of low permeability, it can be
overcome the weakness by designing the 3D structure
using the advantage of metal powder. Also, it is noted
that the decision of overhang length is very important
and one can get a BLDC motor with the much
improved torque characteristics in the same volume.
The inductance of the proposed model (OH
model) compared conventional type (MP model)
using metal powder is described in Fig 7, which is
increased by overhang effect. From the analysis
results, more fluxes inclined into the stator, which is
due to increased linkage area as much as the area of the
teeth overhang and reduced leakages.
It means that the air gap flux becomes increased
and as the results of that the inductance is also
increased. The increased flux can be contributed
greatly to the torque characteristics of the motor.
6
Torque (kg.cm)
5
4
3
Si Model
OH Model
MP Model
2
1
60
70
80
90
100
110
120
Rotation Angle (degree)
Fig.4. MEC model
Fig. 6 Torque profile of different model according to
the rotation angle.
Proceedings of the 5th WSEAS Int. Conf. on Power Systems and Electromagnetic Compatibility, Corfu, Greece, August 23-25, 2005 (pp502-507)
5000
90
1000 Hz
80
4000
Core Loss ( W / kg )
Inductance [ mH ]
70
60
50
Developed type model
(Overhang:5.5[mm])
Conventional type model
40
30
20
3000
500 Hz
1000
10
0
700 Hz
2000
300 Hz
100 Hz
50 Hz
0
0
40
80
120
160
200
240
280
320
0.0
360
0.5
1.0
o
1.5
2.0
2.5
3.0
Peak Flux Density (T)
Electrical Angle [ ]
Fig.7 Inductance profile due to the electric angle.
Fig. 9 Core loss of metal powder
So, if the winding is redesigned to get the same
EMF, a design result of effective motor with higher
efficiency can be obtained by reducing the copper loss.
Therefore, in case of this kind of motor, if applying the
metal powder core can modify the stator, one can
dramatically increase the output characteristics in
view of toque, efficiency.
As shown in Fig. 8, the flux density at each element,
Be(t), is calculated and then analyzed by a Discrete
Fourier transform (DFT) as (3).
2.3 Analysis of Iron Loss
The flowchart for iron loss calculation is shown in Fig.
8 and the data for calculation of Iron loss, which is
interpolated using limited data, is also shown in Fig. 9.
Numerical Analysis
Spectrum
0.5
0.0
we = ∑ w(i × f )i
i =1
2
4
6
Harmonic order
8
10
30
Magnetic flux density vs.
Core loss
30
20
f = 400 (Hz)
10
f = 200 (Hz)
0
0.0
Calculation of Total Iron
loss in whole core
f = 100 (Hz)
0.5
B (T)
m
wtotal = ∑ we
e =1
1.0
∑ B p (n) e
(
j 2 πnk
N
)
(3)
n −0
Overhang (133.92AT)
Overhang (No load)
Non Overhang (133.92AT)
25
w (W/kg)
n
0
N −1
where k is the harmonic order, N is the number of the
discrete data, Bpk(k) is the peak value of the magnetic
flux density of the k-th harmonic, and Bp(n)is the
magnitude of the point n (n = 0, 1, 2, ‚‚‚, N-1).
It is used for summation of iron loss according to
harmonics of the magnetic flux density using a curve
of magnetic flux density vs. Iron loss. So, the total iron
loss in the whole core is calculated by summation of
iron loss at the each element. Fig. 10 shows the
analysis results for iron loss in both motor,
non-overhang (MP model) and overhang model (OH
model). At 3,000[rpm] the iron loss are respectively
7.0 [%] in non-overhang model and 8.8[%] in
overhang model.
Iron loss [W]
t
Summation of Iron loss
according to harmonics
of magnetic flux density
in each element
Be(t) : DFT Analysis
1.0
Be(t)
B pk ( k ) =
20
8.8[%] of
the rated power
15
7.9[%]
10
7.0[%]
5
0
0
1000
2000
3000
4000
5000
6000
Speed [rpm]
Fig. 8 Flowchart for iron loss calculation
Fig. 10 BLDC motor for characteristic comparison
Proceedings of the 5th WSEAS Int. Conf. on Power Systems and Electromagnetic Compatibility, Corfu, Greece, August 23-25, 2005 (pp502-507)
Because the main design objective of this paper
was the increase of torque per volume using the teeth
overhang, the different amount of iron loss can be
explained by the increased core due to the teeth
overhang. So, this result is totally acceptable for using
the overhang, because the improvement of motor
performance by using the overhang is predicted by
10% and over at the rated operation.
3 Experimentation Validations
A prototype of conventional type Si-laminated
Core, metal power core and proposed type metal
power core has been realized. Fig. 11 presents the
three-type stator of BLDC motor mad of Si-core and
metal powder; Si, MP and OH model respectively.
Fig. 11 Prototype of Stator of BLDC motor
(c) OH model
Fig. 12 EMF Comparison of three-type model at
1,000(rpm)
The experimental EMF waveforms of three-type
motors are shown in Fig. 12. The distinction for EMF
waveforms is very clear from the different of the
magnitude of the EMF. The use of overhang is
increasing the total flux and EMF by 10% when
compared to the non-overhang type, MP model.
Fig. 13 presents together the experimental results
for efficiency vs. the torque characteristics and Speed
vs. the torque characteristics respectively. This result
means that the use of the teeth overhang is very helpful
scheme for improving the motor performance.
Generally the copper losses take up much portion of
total loss at the rated operation and it means that the
reduction of copper loss has been obtained by the
overhang effect.
So, even though the core loss is little increased, the
efficiency vs. torque characteristics of the proposed
type is improved as shown in Fig. 13. Also, it is noted
that the optimal design for the teeth overhang is
necessary to maximize the effects of end winding in
the motor.
90
(a) Si Model
Efficiency [%]
80
70
Si Model
MP Model
OH Model
60
0
0
1
2
3
4
5
6
7
8
9
Torque [rpm]
(b) MP model
(a) Efficiency vs. the torque characteristics
10
Proceedings of the 5th WSEAS Int. Conf. on Power Systems and Electromagnetic Compatibility, Corfu, Greece, August 23-25, 2005 (pp502-507)
5000
Speed (rpm)
4000
3000
2000
Si Model
MP Model
OH Model
1000
0
0
2
4
6
8
10
Torque (kg-cm)
(b) Speed vs. the torque characteristics
90
Efficiency [%]
80
70
Si Model
MP Model
OH Model
60
0
0
1
2
3
4
5
6
7
8
9
10
Torque [rpm]
(c) Output Power and Input power
Fig. 13 Experimental results
4 Conclusion
In order to sucessfully apply the metal powder
materials on BLDC motors, three different type BLDC
motors, conventional type Si core (Si model),
conventional type metal power core (MP model) and
proposed metal powder core with teeth overhang (OH
model), with the same dimensions are investigated.
From experimental results, the torque performance
of the lamination core motor is little higher than the
metal powder material motor on the whole. However,
the performance of the new structure of stator teeth
made of metal power core having a teeth overhang can
be much the same as the Si lamination core. So, it is
highly expected that this kind of model with teeth
overhang can be applied for mass production of
various application required high power density.
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