International Journal of Engineering & Technology, 7 (4.30) (2018) 317-321
International Journal of Engineering & Technology
Website: www.sciencepubco.com/index.php/IJET
Research paper
Design and Performances of Multi-Tooth Stator Permanent
Magnet Flux Switching Machine for Light Weight Applications
M. F. Omar1*, E. Sulaiman2*, L. I. Jusoh3, S. M. N. S. Othman4, S. A. L. S. Badrudden5
1,2,3,4,5 Research
Center For Applied Electromagnetics (EMCenter), Faculty of Electrical and Electronic Engineering,
Universiti Tun Hussein Onn Malaysia, 86400 Parit Raja, Johor, Malaysia.
*Corresponding authors E-mail: fairoz.omar@yahoo.com
Abstract
Permanent magnet flux switching machines (PMFSMs) in which their torque performance produced by interaction between armature
coils and permanent magnet (PM) have been widely designed for various applications. In this regard, single-phase 8Slots-12Poles
PMFSM with single tooth stator is considered the most suitable candidate for light weight applications because of their advantages of
lower copper loss, high efficiency and robust rotor. However, issues of low torque performance due to weak flux linkage, high of PM
volume, and high distortion in back-emf that need to be improved. In this paper, a new design of single-phase PMFSM using multi-tooth
stator is proposed. Both PMFSMs have been designed using JMAG Designer version 15 and analysed through 2D-FEA. Parameters of
stator outer radius, rotor outer radius, air gap, and stack length are set to 37.5mm, 22mm, 0.25mm, and 20.3mm, respectively. Based on
the 2D-FEA, PM flux linkage and torque performances of the PMFSM using multi-tooth are 5 times and 38% higher than PMFSM using
single-tooth. As a conclusion, single-phase 4Slot-12Poles PMFSM using multi-tooth stator considered as the best candidate for light
weight applications due to the less PM volume, and good performances of toque, power and based speed of 1.44Nm, 219W, 1,062rpm,
respectively.
Keywords: Flux Switching Machine; Light Weight Applications; Multi-Tooth Stator; Single-Phase; Permanent Magnet.
1. Introduction
Hybrid electric vehicles (HEV), using combination of an internal
combustion engine (ICE) and one or more electric traction motors,
are widely considered as the most promising green vehicles. As
viable candidates of electric machines for HEV drives, there are
several types of electric machines that synonym with HEV such as
DC machines, and permanent magnet synchronous machines
(PMSMs). DC machines should be widely accepted for electric
vehicles (EV) and HEV drives because they can use a battery as a
DC-supply as it is and have an advantage of simple control principle based on the orthogonal disposition of field and armature mmf.
However, the essential problem of DC drives, which is caused by
commutator and brush, makes them less reliable and unsuitable for
a maintenance-free drives [1]-[2].
On the other hand, PMSMs, in particular Interior Permanent Magnet Synchronous Motors (IPMSMs) have had no commutator and
brush and therefore, they have been most capable of competing
with other motors for the electric propulsion of HEVs. IPMSMs
have had many advantages in terms of lighter weight, smaller size,
high torque and power densities, high efficiency and high reliability. One of examples of successfully developed IPMSM has been
installed on LEXUS RX400h in 2005 [3]. This has been able to be
proved by the historical progress in the power density of main
traction motor installed on Toyota HEVs [4].
Besides, PMSMs and DC machines have also been used as a
prime mover for light weight applications that require low torque
and high speed performances such as electric bicycles [5]-[6]. The
use of electric bicycles has been increasing in recent years due to
their lower energy consumption and environmental friendly [7].
Other examples of electric motors used for electric bicycles are
Multi-Flux Permanent Magnet (MFPM), and Switch Reluctance
Motor (SRM) [8]-[9]. Nevertheless, problems such as low torque,
low power, constraint of rare earth permanent magnet, and high
noise have led many studies to find a new technology in improving the performance of electric motors.
Fig. 1: Working principle of PMFSM
Copyright © 2018 Authors. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original work is properly cited.
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International Journal of Engineering & Technology
Therefore, as one of the effective approaches to increase the motor
torque and power densities, permanent magnet flux switching
machines (PMFSMs) is introduced. The working principle of the
PMFSM is illustrated in Fig. 1. From the figure, the red arrows
indicate the flux line of PM. The rotor pole aligns with one of two
stator teeth over which a coil is wound. Then the permanent magnet (PM) flux linked in the coil stream from the stator and into the
rotor pole. When the rotor moves forward to align with another
stator tooth belonging to the same coil winding, the flux stream of
the rotor pole and into the stator tooth. Thus, as the rotor moves,
the flux linkage in the windings will change periodically [10]-[11].
In the previous design, a single-phase 8 Slots – 12 Poles (8S-12P)
has been designed based on conventional inner rotor PMFSM
using single tooth stator and salient rotor structure (PMFSM single-tooth) as shown in Fig. 2. Parameters of stator outer diameter,
rotor outer diameter, stack length, and air gap are set to 75 mm
and 22 mm, 20.3 mm and 0.25 mm, respectively. The 8S-12P
PMFSM consists 8 pieces of Neomax-35AH PM. These PM have
been placed between in each armature coil windings and the
weight of all PM is approximately 80g. In terms of performance, it
can be concluded that the single phase 8S-12P PMFSM has been
achieved the torque and power capabilities of 1.04 Nm and 674 W,
respectively [12]. However, the single-phase 8S-12P PMFSM
with single tooth stator structure can be improved due to low
torque performance, high PM usage, and high back-emf distortion.
In this research, a new single-phase PMFSM using multi-tooth
stator structure is proposed. The proposed motor consists of 4 slots
Armature coil
Table 1: Design restrictions, specifications and dimensions of the
proposed 4S-12P PMFSM using multi-tooth stator
Items
Dimensions
Number of phase
1
No. of slots
4
No. of poles
12
Stator inner radius (mm)
22.25
Stator outer radius (mm)
37.5
Rotor outer radius (mm)
22
Rotor inner radius (mm)
7.5
Rotor tooth width (mm)
4
Stator pole height (mm)
15.25
Air gap (mm)
0.25
Stack length (mm)
20.3
Shaft radius (mm)
2.5
Magnet material
Neomax-35AH
Magnet mass (g)
10.2
Speed (rpm)
500
Armature current density, J A (Arms/mm2)
10
Maximum current (A)
3.54
Number of turns armature coil
240
Permanent magnet
Rotor
Permanent
magnet
Stator
Armature coils
Fig. 3: Structure of the proposed PMFSM using multi-tooth
Stator
Rotor
Fig. 2: The conventional PMFSM design using single tooth rotor.
for copper windings, 4 multi-tooth stator, 12 rotor poles and, 4
pieces of PM. 2D finite element analysis (2D-FEA) through
JMAG Designer version 15 is used to analyse the flux linkage,
flux distribution, flux line, back-emf, torque capability, and
torque-power versus speed characteristics of the proposed motor.
2. Design Restrictions and Specifications of
The Proposed PMFSM
widths are is predictable to allow flux stream from stator to rotor
and vice versa smoothly with equal magnetic flux distribution.
Design methodology of the proposed PMFSM using multi-tooth
stator have three main sections in the implementation of this study:
Geometry editor, JMAG designer and 2D-FEA testing. The Geometric editor and JMAG designer sections are the process of designing each motor structure and the internal setup of the proposed
motors, respectively. Finally, the result performances of flux linkage, flux distribution, flux line, back-emf, various torque capability, and torque-power versus speed characteristics that have been
investigated are analysed are presented.
3. 2D-FEA Performances of PMFSM using
multi-tooth stator
3.1 Flux linkages
The machine configurations of single-phase 4S-12P PMFSM using multi-tooth stator (PMFSM multi-tooth) is demonstrated in
Fig. 3. From the figure, the armature coil windings are placed in
between of PM, and alternate configuration. Each stator tooth has
divided into 4 teeth. Table 1 shows the design specifications and
parameters for the proposed machines. The split ratio of rotor
outer diameter and stator outer diameter is set to 59% as standard
motor design requirement. While, parameters of stator inner radius,
air gap, stack length, and shaft radius are set to 22.25 mm, 0.25
mm, 20.3 mm, and 7.5 mm, respectively. Four pieces of PM with
weight of 10.2 g is 8 times lighter than conventional PMFSM with
single tooth stator. In short, equal stator back inner and stator pole
Fig. 4: Flux linkages of PMFSM using multi-tooth stator
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International Journal of Engineering & Technology
Fig. 4 shows flux linkages of the proposed PMFSM using multitooth stator. Flux profile has been plotted in two conditions, initially when PM only and secondly, when JA is set to a maximum
of 10 Arms/mm2 without PM. Clearly, JA flux linkage of 0.285 Wb
is approximately 3 times higher than PM flux linkage. This clarify
that the flux linkage generated from PM is moved around the stator and rotor before arriving at armature coil winding.
Besides, PM flux linkage lead 90° of JA flux linkage, ensure the
proposed motor is working based on standard operating principle
of single-phase motor. However, the flux linkage of JA only show
unbalance between positive and negative cycles due to the flux
leakage occurs between rotor and stator as illustrated in Fig. 5. Fig.
5(a) shows the rotor at a 90° electric cycle, and flux leakage that
has been occurred as marked in red cycle is due to the limited flux
path between the rotor and the stator. Compared to flux linkage
when rotor reach at 270° electric cycle as illustrated in Fig. 5(b),
the flux path is wider, and it has facilitated flux flows, hence reducing the probability of flux leakage. In addition, PM flux linkage of 0.086 Wb has produced from the PMFSM multi-tooth is 5
times higher than PMFSM single-tooth design as illustrated in Fig
6. This proves that the multi-tooth structure has facilitated flux
stream from stator to rotor and vice versa, thus strengthening the
flux linkage to form a complete cycle.
3.2 Flux Line
PM
Armature coil
Stator
Flux leakage
Rotor
PM
(a) Rotor at 90 degrees
Armature coil
PM
Fig. 7 shows the magnetic flux line generated by PM 90° and 180°
electric cycles. Fig. 7 (a) illustrates the flux line when the rotor at
90° electric cycle. Obviously, the flux has flowed between a set of
stator tooth and two rotor teeth, and flux attraction between rotor
and stator at this point is zero. While, the highest flux attraction
was recorded when the rotor at 180° electric cycles as demonstrated in Fig. 7 (b). From the figure, a complete cycle of flux has been
generated through 2 sets of stator teeth and 2 rotor teeth and produces a high flux attraction.
The flux line formed by maximum JA of 10 Arms/mm2 of the proposed PMFSM multi-tooth is illustrated in Fig. 8. Fig. 8 (a) shows
the flux line when the rotor at 90° electric cycle. From the diagram,
a complete cycle of flux has been linked between 2 sets of stator
teeth and 2 rotor teeth. Additionally, there is an auxiliary flux
cycle with shorter flux path in the center of the main flux cycle,
thus increasing the strength of flux linkage. Fig. 8(b) shows flux
line when rotor at 180° electric cycle. From the figure, the flux
linkage is zero because of flux does not legitimately flow from
stator to rotor and vice versa to form a complete cycle of flux. In
short, the flux line analyses have been proved the highest flux
linkages of PM and JA are achieved at 180° and 90°, respectively
as discussed in sub-topic 3.1.
S1
Stator
R
1
R1
S2
S1
No flux leakage
Rotor
R2
R
2
P
M
(a) 90 degrees
Fig. 7: Flux line of PM
(b) Rotor at 270 degrees
Fig. 5: Flux distributions of PMFSM multi-tooth
(b) 180 degrees
Main
cycle
flux
Auxiliary
cycle
flux
S1
R1
R1’
R2
’
R2
(a) 90 degrees
S2
(b) 180 degrees
Fig. 8: Flux line of armature current density, JA
Fig. 6: Comparison of PM Flux linkage between PMFSM multi-tooth
and PMFSM single-tooth.
3.4 Back-emf Profile
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International Journal of Engineering & Technology
Fig. 9 shows comparison of back-emf profile between the proposed PMFSM multi-tooth and PMFSM single-tooth. From the
figure, the highest back-emf of 57.8 V and 11.8 V have been recEmf [V]
70
Emf (H) Multi-tooth
Emf (H) Single-tooth
50
30
10
-10 0
30
60
90 120 150 180 210 240 270 300 330 360
-30
-50
-70
Electric cycle [°]
Fig. 9: Back-emf of PMFSM multi-tooth and PMFSM single-tooth.
Multi-tooth
THD [%]
Single-tooth
8
6.48
7
6
orded from PMFSM multi-tooth and PMFSM single-tooth, respectively. The back-emf of PMFSM single-tooth has been produced 5
times lower compared to the PMFSM multi-tooth due to the less
PM flux linkage. Though back-emf of PMFSM multi-tooth is
higher than PMFSM single-tooth, total harmonic distortion (THD)
of PMFSM multi-tooth has a much lower than PMFSM singletooth as shown in Fig. 10. Obviously, all THDs of PMFSM multitooth harmonic is below than 3%, only 7th harmonic indicates
THD exceeds of 2%, and other harmonics have been recorded
THD below 1.53%.
3.5 Torque at Various JA
Torque capabilities of PMFSM multi-tooth and PMFSM singletooth at various JA are plotted in Fig. 11. Obviously, the torque
increases parallelly with increase of JA. At maximum JA of 10
Arms/mm2, the PMFSM multi-tooth design has produced torque of
1.44 Nm, 38% higher than PMFSM single-tooth design. It has
proven that torque performance of PMFSM multi-tooth has been
improved and suitable for light weight applications such as electric bicycles. From this analysis, it can be summarized that the
higher flux linkage produced by multi-tooth stator structure has
increased the flux strength, hence producing high torque.
3.6 Torque-Power Versus Speed Characteristics
5
3.74
4
2.63
3
2
1.27
1.14
0.52
1
0
1
3
5
2.08
1.05
1.69
1.53
1.99
1.31 1.46
0.76 0.69 0.36
7
9
11
Harmonic order
13
15
17
Fig. 10: THD versus harmonic order
T [Nm]
Multi-tooth
Single-tooth
1.44
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1.24
1.04
0.98
0.73
0.68
0.49
0.36
0.26
0.12
0
2
4
6
8
10
JA [Arms/mm2]
Fig. 11: Torque at various armature current densities, JA of PMFSM
multi-tooth and PMFSM single-tooth.
Torque [Nm]
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
Torque
Power
Power [W]
240
1.44 Nm
210
219 W
217 W
180
150
120
160 W
90
0.35 Nm
0.26 Nm
60
30
0
1000 2000 3000 4000 5000 6000 7000 8000 900010000
Speed [rpm]
Fig. 12: Torque and power versus speed characteristics of PMFSM
multi-tooth.
The torque-power versus speed characteristics of the proposed
PMFSM multi-tooth is demonstrated in Fig. 12. The investigation
has been performed by diversifying JA from 0 to 10 Arms/mm2 and
varying armature current phase angle from 0° to 80°. Clearly, the
highest torque of 1.44 Nm is obtained under based speed and
power of 1,062 rpm and 160 W, respectively. While, the highest
power of 219 W is achieved at speed of 8,000 rpm, and the corresponding torque is 0.26 Nm. Moreover, at the medium speed conditions of 4,000 rpm to 7,000 rpm, the corresponding torque is
approximately 0.3 to 0.5 Nm, and the power capability is in the
range of 210 W to 218 W.
4. Conclusions
A new design of single-phase PMFSM using multi-tooth stator
structure has been presented. The procedure to design the proposed PMFSM multi-tooth has been clearly explained. The performance analyses of flux linkage, flux distribution, flux line,
back-emf, torque capability at various armature current density,
and torque-power versus speed characteristics have been investigated. Based on 2D-FEA, the proposed PMFSM multi-tooth has
high PM flux linkage due to great characteristics of flux line and
flux distribution.
The total weight for four pieces of PM is 10g, 8 times lighter than
PMFSM single-tooth. In addition, harmonic interference to backemf is also lower, in which all THDs are below 3%. As a conclusion, the proposed PMFSM using multi-tooth stator structure is
considered as the best candidate for light weight applications due
to the high initial performances of torque, power and based speed
of 1.44 Nm, 219 W and 1,062 rpm, respectively.
Acknowledgement
This work was funded by Ministry of Education Malaysia (MOE)
under FRGS Vot. 1651 grant thru Universiti Tun Hussein Onn
Ma-laysia (UTHM).
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