-
COMPEL: The International Journal for Computation and
Mathematics in Electrical and Electronic EngineeringEmerald
Article: Design issues of an IPM motor for EPSC.F. Wang, J.X. Shen,
P.C.K. Luk, W.Z. Fei, M.J. Jin
Article information:To cite this document: C.F. Wang, J.X. Shen,
P.C.K. Luk, W.Z. Fei, M.J. Jin, (2012),"Design issues of an IPM
motor for EPS", COMPEL: The International Journal for Computation
and Mathematics in Electrical and Electronic Engineering, Vol. 31
Iss: 1 pp. 71 - 87
Permanent link to this document:
http://dx.doi.org/10.1108/03321641211184832
Downloaded on: 12-12-2012
References: This document contains references to 19 other
documents
To copy this document: [email protected]
This document has been downloaded 127 times since 2012. *
Access to this document was granted through an Emerald
subscription provided by VIT UNIVERSITY
For Authors: If you would like to write for this, or any other
Emerald publication, then please use our Emerald for Authors
service. Information about how to choose which publication to write
for and submission guidelines are available for all. Please visit
www.emeraldinsight.com/authors for more information.
About Emerald www.emeraldinsight.comWith over forty years'
experience, Emerald Group Publishing is a leading independent
publisher of global research with impact in business, society,
public policy and education. In total, Emerald publishes over 275
journals and more than 130 book series, as well as an extensive
range of online products and services. Emerald is both COUNTER 3
and TRANSFER compliant. The organization is a partner of the
Committee on Publication Ethics (COPE) and also works with Portico
and the LOCKSS initiative for digital archive preservation.
*Related content and download information correct at time of
download.
-
Design issues of an IPMmotor for EPS
C.F. WangCollege of Electrical Engineering, Zhejiang University,
Hangzhou, China and
Department of Engineering Systems and Management,Cranfield
University, Shrivenham, UK
J.X. ShenCollege of Electrical Engineering, Zhejiang University,
Hangzhou, China
P.C.K. Luk and W.Z. FeiDepartment of Engineering Systems and
Management, Cranfield University,
Shrivenham, UK, and
M.J. JinCollege of Electrical Engineering, Zhejiang University,
Hangzhou, China
Abstract
Purpose The purpose of this paper is to present the design
procedure of an interior permanentmagnet (IPM) motor used in
electric power steering (EPS), and some critical issues which have
considerableimpacts on the machines performance are fully discussed
before detailed sizing optimization.
Design/methodology/approach The design specifications are
derived according to applicationoverall requirements. Critical
issues which have considerable impacts on the machines
performance,such as operation mode, rotor structure and slot/pole
combination, are analyzed based on literaturereview. The proposed
machine is optimized, and the losses and efficiency are computed,
using 2-Dfinite element analysis (FEA).
Findings Before detailed sizing optimization, machine type
selection is fully discussed. Aspectssuch as brushless ac (BLAC)
operation mode, IPM rotor structure and combination of
12-slot/10-poleare quite suitable for EPS application.
Consequently, a 12-slot/10-pole sinusoidally excited IPMmachine
with concentrated windings is selected, since it is convenient to
obtain sinusoidal backelectromotive force (back-EMF), minimum
cogging torque and torque ripple, short end windings andhigh
efficiency, as well as simple rotor assembly. The estimated
excellent performance confirms thatthe proposed machine can be an
attractive solution for EPS.
Research limitations/implications The excitation current is
ideal sinusoidal, while some harmoniccomponents are neglected.
Besides, in future, the experimental test should be carried out for
validation.
Originality/value A reasonable design procedure, where the motor
type selection should be firstaddressed before detailed sizing
design, is carried out. A 12-slot/10-pole sinusoidally excited
IPMmachine with concentrated windings is provided as a quite
competitive candidate for EPS application.
Keywords Electric power steering, Interior permanent magnet,
Motor design, Finite element analysis,Road vehicles
Paper type Research paper
The current issue and full text archive of this journal is
available at
www.emeraldinsight.com/0332-1649.htm
The first author gratefully acknowledges the internship
supported by the Department ofEngineering Systems and Management,
Cranfield University, UK, to which this work relates. Allauthors
would like to thank Nanyuan Electric Machinery Co., China for
manufacture of theprototype machine, and MagneForce Software
Systems Inc., USA for offering evaluation licenseof MagneForce
V4.0.
IPM motorfor EPS
71
COMPEL: The International Journalfor Computation and Mathematics
inElectrical and Electronic Engineering
Vol. 31 No. 1, 2012pp. 71-87
q Emerald Group Publishing Limited0332-1649
DOI 10.1108/03321641211184832
-
1. IntroductionGlobal warming is becoming a very important
world-wide issue. It was even one of thethree main topics in the
recent 2009 G8 Summit. Carbon dioxide (CO2) emission is themain
contributor of green house gas which leads to global warming.
Transportationaccounts for more than 20 percent of man-made CO2. It
is therefore highly desirable toreduce green house gas emission by
improving vehicles fuel efficiency. On the otherhand, the number of
electric machines installed in modern vehicles has been
increasingat a rapid pace. The more luxury the vehicle, the more
electric machines will beequipped. Well optimised electric machines
with high efficiency will therefore play apivotal role in improving
the vehicles overall efficiency, and thus in reducing the
CO2emission to mitigate global warming.
An apparent trend that electric power steering (EPS) is becoming
an alternative tothe hydraulic power steering (HPS) can be seen in
recent developments in automotiveindustry. In the HPS system, a
pump driven by the engine is constantly running tokeep the
hydraulic pressure, no matter assistance is required or not. While
in the EPSsystem, the electric motor is driven only when the
steering wheel is turned. EPS thusoffers much better fuel economy,
which can account for 3 percent improvements in fuelefficiency
(Yoneda et al., 2006).
Electric machines, the key actuators in the EPS system, are
crucial in influencingthe vehicles steering performance. A brushed
DC motor was equipped in the worldsfirst EPS system in 1993 by
Honda, on Acura NSX (Oprea and Martis, 2008). Presenceof brushes
limits its performance especially at higher speeds, and the sparks
may causesafety and electromagnetic interference problem. A much
more competitive solutionbased on permanent magnet (PM) brushless
machines has drawn considerableinterests from both industrial and
academic research communities. The hightorque/volume ratio, high
dynamics, high speed due to field-weakening capability,elimination
of brushes, simple machine structure and high efficiency are some
of theadvantages of PM machines. For the disadvantages, the magnets
will subject to therisk of irreversible demagnetization in
overloading or high temperature conditions.Various PM machine
topologies have been developed for EPS applications. Researchhave
been focusing on some particular aspects, such as cogging torque
reduction andtorque ripple minimization (Jahns and Soong, 1996;
Bianchi and Bolognani, 2002; Islamet al., 2003, 2004; Ombach et
al., 2006), saturation effect (Seong et al., 2009; Stumbergeret
al., 2003; Chedot and Friedrich, 2004), losses (Yamazaki and
Ishigami, 2010;Zivotic-Kukolji et al., 2006), and fault tolerance
(Oprea and Martis, 2008; Bianchi et al.,2006; Aroquiadassou et al.,
2005). Whereas most studies principally focus on theelectromagnetic
design level on the size and shape of the magnets of the machine,
itappears that few studies emphasize on machine topology selection
level prior todetailed machine electromagnetic design. For a
complete EPS system designprocedure, it is strongly felt that
essential issues for machine characteristics, includingmachine
topology, operation mode, and slot/pole combination, should be
first decided.
This paper concerns the design of a PM machine for EPS
applications. Therequirements of the EPS application are introduced
and the specifications of thedesired machine are then derived.
Before detailed design, some critical issues whichessentially
affect the final performance, viz., operation mode of either
brushlessalternating current (BLAC) or brushless direct current
(BLDC), rotor structure of eithersurface-mounted permanent magnet
(SPM) or interior permanent magnet (IPM), as
COMPEL31,1
72
-
well as slot/pole combination, are analyzed in details.
Subsequently, a 12-slot/10-polesinusoidally excited IPM machine
with concentrated windings is optimally designedand verified with
finite element analysis (FEA). A prototype has been built
forvalidation.
2. Application requirements and design specificationsA.
Application overall requirementsEPS is an important subsystem on
vehicles, which works extremely frequently duringdriving. In such a
safety critical application, high reliability must be fully
consideredduring the whole design process. Besides, in terms of
limited available space and thedemanded working environments, the
desired electric machine is to have followingfeatures: compact
size, low weight, low cost, variable speed over wide
torque-speedareas, low acoustic and electromagnetic noise, high
efficiency, as well as smooth torqueoutput for the precision
steering and driving comfort.
B. Design specificationsFor small and middle sized vehicles, the
electric machine is mounted on the pinionsteering gear or on the
steering column. Assistant torque is applied to the steeringcolumn
via a worm-gear. Therefore, the electric machine can run at
relatively higherspeed. About 6-8 kN column force is required in
this EPS system, which corresponds to7 Nm torque demand for
electric machine (Ombach and Junak, 2007, 2008). Thespecifications
for the desired electric machine under study, which is to be used
in acolumn-type EPS, are summarized in Table I. The required
torque-speed curve isshown in Figure 1.
DC-bus voltage 42 VStall torque 7 NmBase speed 600 rpmMaximum
speed 2,000 rpmTorque ripple ,3%
Table I.Specifications of desiredelectric machine for EPS
application
Figure 1.Torque-speed curve of
desired electric machinefor EPS application
01
2
34
567
8
0 500 1,000 1,500 2,000 2,500speed (rpm)
torq
ue (N
m)IPM motor
for EPS
73
-
3. Discussion on critical design issuesGreat attention should be
paid to certain critical issues which primarily impact themachines
output characteristics. These critical issues mainly include
operation mode,rotor structure and slot/pole combination.
A. Operation modePM brushless machines could be driven in both
BLDC and BLAC modes. Thedefinitions of BLDC and BLAC mode are
related to the waveforms of the backelectromotive force (back-EMF)
and the driving current (Zhu, 2009), viz.:
. BLDC. Trapezoidal back-EMF with rectangular current.
. BLAC. Sinusoidal back-EMF with sinusoidal current.
The typical torque-speed performances (Shi et al., 2006) of
brushless motor driven withBLDC and BLAC modes are shown in Figure
2.
For EPS applications, the electric machine usually runs at low
or medium speeds.Then the BLAC mode is preferred as it can achieve
a higher torque output at lowerspeed. Additionally, the BLAC mode
usually results in much lower torque ripple thanthe BLDC mode
(Islam et al., 2004), which is highly desirable in EPS
applications.Hence, the BLAC mode should be employed, whilst the
sinusoidal back-EMF has to beguaranteed.
B. Rotor structurePM machines provide many possibilities to
place magnets on rotors, which can bebroadly divided into the SPM
or IPM categories according to the fixtures of the PMonto the rotor
core. The main SPM types are shown in Figure 3(a) and (b); whereas
themain IPM types are shown in Figure 3(c) and (d).
Based on dq-coordinates, the electromagnetic torque can be
calculated as:
Te 32plm iq Ld 2 Lqid iq 1
where p is the number of pole pairs, lm is the PM-excited flux
linkage, id, iq, Ld and Lqare d, q-axes currents and inductances,
respectively.
Figure 2.Typical torque-speedcurves with differentoperation
modes
speed
torq
ue/c
urre
nt
BLDC-120
BLDC-180
BLAC
COMPEL31,1
74
-
For SPMs of type shown in Figure 3(a), where Ld Lq, the last
item in equation (1) iszero. On the contrary, Ld , Lq for SPMs of
type shown in Figure 3(b) and also for theIPMs. Thus, an extra
torque boost can be obtained by applying appropriate id and
iq,which is so-called reluctance torque (Otaduy and McKeever,
2006).
Though SPMs can offer slightly better dynamics due to smaller
inductances as aresult of low (air-like) permanence of the magnets,
IPMs can easily achieve the idealsinusoidal back-EMF which is
tremendously required in BLAC mode. Furthermore,IPMs own many other
advantages over SPMs, as will be discussed in the next section.
C. Slot/pole combinationThe concentrated windings allow many
combinations of slots and poles to PMmachines. Different slot/pole
combinations have extensive influence on machinecharacteristics,
such as back-EMF, cogging torque, losses and efficiency (Yoneda et
al.,2006; Zhu, 2009).
Common slot/pole number combinations for three-phase,
non-overlapping windingelectric machines are:
Ns
Np k 3
2
; k 1; 2; 3. . . 2
where Ns and Np are numbers of slots and poles, respectively.
These machines, 3s/2p,6s/4p, 9s/6p and 12s/9p, inevitably suffer
low usage of windings with a winding factorof 0.866.
In order to maximize the winding flux-linkage and power density,
coil-pitch shouldbe equal to pole-pitch, which means slot number is
equal to pole number. Thesecombinations present maximum
flux-linkage and power density, but also largecogging torque, and
are therefore only suitable for single phase motors. Thus,
therealistic combination of slots and poles should aim at
coil-pitch < pole-pitch ratherthan coil-pitch pole-pitch.
Therefore, Ns and Np differing by equations (1) and (2)are the two
closest cases:
. Case 1: Ns and Np differed by 1, viz.:
Ns 2 Np 1 3
Electric machines with these slot/pole combinations such as
3s/2p, 3s/4p, 9s/8p, 9s/10p,show a number of merits, including high
flux linkage per coil, high torque density andnegligible cogging
torque. However, there will be a potential weakness in terms of
Figure 3.Different PM rotor
structures(a) (b) (c) (d)
Notes: (a) and (b): SPM; (c) and (d): IPM
IPM motorfor EPS
75
-
unbalanced magnetic force, which results in vibration and
acoustic noise, as well asdecreased lifecycle.
. Case 2: Ns and Np differed by 2, viz.:
Ns 2 Np 2 4
Machines with these slot/pole combinations, for instance, 6s/4p,
6s/8p, 12s/10p,12s/14p, indicate similarly remarkable attributes,
such as high torque density andsmall cogging torque. Moreover,
there is no risk of unbalanced magnetic force.
The analysis shows that case 2 to be the better option, and the
12s/10p combinationhas therefore been chosen for this application.
The potential merits are confirmed bythe comparison of back-EMF
waveforms with different slot/pole combinations, asshown in Figure
4. It is clearly shown that the 12s/10p offers more
sinusoidalback-EMF than others.
4. Proposed machineThe foregoing discussion has led to an
initial model selection of a 12s/10p IPMmachine, which is to be
driven in BLAC mode. The design of the PMs shape and othermachine
parameters can now be effectively completed. The key parameters are
listedin Table II, including the winding configuration and rotor
shape modification.The proposed machine optimized by FEA is shown
in Figure 5.
A. Winding configurationNon-overlapping concentrated windings
are adopted, which exhibit outstandingfeatures of high winding
factor (0.933) and short end winding. Only phase A is shownin
Figure 6.
B. Rotor shape modificationAs mentioned previously, sinusoidal
back-EMF is required for the BLAC drivingmode, while the essential
condition is to attain the sinusoidal air gap flux
densitydistribution. A practical technique of rotor shape
modification is employed. One ofIPMs important advantages over SPM
can be clearly shown in Figure 7, where it canbe seen that it is
much simpler to precisely manufacture the rotor laminations
outer
Figure 4.Back-EMF waveformswith different
slot/polecombinations
8
6
4
2
0
2
4
6
8
0 60 120 180 240 300 360Angular position (elec deg)
Phas
e ba
ck-E
MF
(V)
10s/10p
15s/10p
12s/10p
12s/14p
COMPEL31,1
76
-
Symbol Machine parameter Value Unit
Ns Number of slots 12Np Number of poles 10m Number of phases
3Ncoil Number of turns per coil 30
PM material NdFeB35Magnetization orientation ParallelStator and
rotor lamination material 35W470
Kp Slot fill factor 54%Rso Stator outer radius 75.0 mmRsi Stator
inner radius 41.0 mmRo Rotor outer radius 40.0 mmg Air gap 0.5-0.95
mmwpm PM width 10.0 mmtpm PM thickness 2.0 mmwst Stator tooth width
5.0 mmla Active axial length 70 mmJpeak Rated peak current density
1.7e7 A/m
2
Udc DC-link voltage 42 VPem Rated power output 435 WIpeak Rated
peak phase current 14 ARph Phase resistance (1008C) 0.27 V
Table II.Machine parameters
Figure 5.Cross section of the
proposed machine
IPM motorfor EPS
77
-
shape in IPMs, than the magnets outer shape in SPMs. This also
leads to some otherdesirable characteristics:
. IPMs use simple rectangular-shape magnets with parallel
magnetization reducing magnet price and manufacturing cost.
. The magnets are mechanically protected suitable for high speed
operationwithout protective rings or retaining sleeves on the
rotor.
. Presence of flux bridge makes the magnets better protected
againstdemagnetization offering high overloading capability.
Besides, it is noteworthy that cogging torque minimization comes
along with the gainof sinusoidal air gap flux density
distribution.
Figure 6.Winding configuration ofthe proposed machine
22
23A2
A3
A4
A3+
A4+
Phase AA2+
A1+
A1
24
1
2
310
11
12
13
14
15
Figure 7.Rotor outer shapemodifications forsinusoidal air gap
fluxdensity
(a) (b)Notes: (a) IPM; (b) SPM
COMPEL31,1
78
-
5. Performance evaluationA commercial FE software MagneForce is
used to evaluate the machine performanceby two-dimensional (2D)
FEA.
A. Air gap flux densityAs analyzed before, a non-uniform air gap
is introduced to obtain sinusoidal fluxdensity distribution, hence
sinusoidal back-EMF and negligible cogging torque. Theair gap flux
density distributions at conditions of no load and full load are
shown inFigure 8. And the corresponding harmonic components are
shown in Figure 9. Sincethe third harmonic will be eradicated
across the line windings, the effective higherharmonic contents are
seen relatively small compared with the fundamental, and agood
sinusoidal back-EMF is expected.
B. Back-EMFThe three phase back-EMF at the rated speed of 600
rpm is shown in Figure 10, whichare visually seen very symmetrical.
Fourier analysis is then undertaken to evaluate theharmonic content
of the spectrum. The total harmonic distortion is found to be
0.67percent, which means that the back-EMF is essentially
sinusoidal.
Figure 8.Air gap flux density
distribution1.5
1.0
0.5
0.0
0.5
1.0
1.5
2.0
Br (
T)
no load full load
720 480 240 0 240 480 720Angular position (elec deg)
Figure 9.Harmonic components of
air gap flux density0.0
0.2
0.4
0.6
0.8
1.0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Harmonic order
Br a
mpl
itude
(T)
no load full load
IPM motorfor EPS
79
-
C. InductanceTaking the saturation effects into account, the
load will affect the permeance, whichwill result in inductance
variation. Based on FEA, Ld and Lq are calculated withdifferent
load conditions, i.e. variation of phase current with different
amplitudes andadvanced commutation angles. The results are shown in
Figures 11 and 12,respectively. The ratio Lq/Ld represents for the
saliency level of a PM machine, which isdetermined by the physical
structure and load condition, and is related to thereluctance
torque. Figure 13 shows the variation of Lq/Ld.
During operations at higher load, Lq varies in the range of
almost 40 percent, whileLd varies in the range of 5 percent only.
This can be explained by the cross-couplingeffects between d- and
q- axes, as a result of high magnetic saturation. It is
generallyknown that operations with high magnetic saturation are
inherent design features forelectric machines with high power
density (Ombach and Junak, 2008).
Figure 11.Ld as a function of phasecurrent and
advancedcommutation angle
15 13 11 9 7 5 3 1 015
3565
3.00
3.20
3.40
3.60
3.80
4.00
Ld (m
H)
gamma
(deg)
Iphase (A)
Figure 10.Back-EMF waveforms ofthe proposed motor atspeed of 600
rpm
18.0
12.0
6.0
0.0
6.0
12.0
18.0
24.0
0 120 240 360 480 600 720Angular position (elec deg)
Bac
k-EM
F (V
)
phase-A phase-B phase-CCOMPEL31,1
80
-
D. TorqueThe electromagnetic torque is calculated according to
equation (1) under different loadconditions, as shown in Figure 14.
The maximum torque occurs when the advancedcommutation angle is
about 258. And the separated reluctance torque component is
alsocomputed according to equation (5) by utilizing the FEA data
obtained in calculating theelectromagnetic torque, in order to save
simulation time, as shown in Figure 15:
Tr 32pLd 2 Lqid iq 5
Torque ripple should be completely minimized to ensure accurate
steering andcomfortable driving experience. In general, torque
ripple consists of two components, viz.,
Figure 12.Lq as a function of phase
current and advancedcommutation angle
15 13 11 9 7 5 3 10
1535
653.003.403.804.204.605.005.405.80
Lq (m
H)
Iphase (A) gamma
(deg)
Figure 13.Lq/Ld as a function of
phase current andadvanced commutation
angle
15 13 11 9 7 5 3 10
15
35
651.00
1.10
1.20
1.30
1.40
1.50
Lq/L
d
Iphase (A) gam
ma(de
g)
IPM motorfor EPS
81
-
the load dependent component and the load independent component.
The former can beextensively ameliorated by employing BLAC mode,
and the latter is essentially thecogging torque of the machine,
which has already been reduced by means of a sinusoidalair gap flux
density distribution, as shown in Figure 16. Figure 17 shows the
output torquewaveform at full load condition, where the smoothness
of the torque is evident. From thezoomed-in view of the torque
ripple in Figure 18, it is further confirmed that the peak topeak
torque ripple is 0.17 Nm, or 2.2 percent of the average output
torque, which wellexceeds the requirement of less than 3
percent.
Figure 14.Electromagnetic torque asa function of phase
currentand advancedcommutation angle
0123456789
0 10 20 30 40 50 60 70 80 90gamma (deg)
Torq
ue (N
m)
Iphase from 1 A to 15 A
Figure 15.Reluctance torque as afunction of phase currentand
advancedcommutation angle
0
0.3
0.6
0.9
1.2
1.5
1.8
0 10 20 30 40 50 60 70 80 90gamma (deg)
Rel
ucta
nce
torq
ue (N
m)
Iphase from 1 A to 15 A
Figure 16.Cogging torque waveform
6
4
2
0
2
4
6
0 6 12 18 24 30 36Angular position (mech deg)
Cogg
ing
torq
ue (m
Nm)
COMPEL31,1
82
-
E. Losses and efficiencyFor EPS applications, the machine runs
at low and moderate speed, whereelectromagnetic losses dominate the
total losses. Thus, only the electromagneticlosses are evaluated
here. Electromagnetic losses mainly include copper losses in
thestator windings PCu, iron losses in the stator and rotor
laminations PFe and eddy currentlosses in the magnets PPM. The
power flow can be expressed by:
Pin PCu PFe PPM Pout 6Apparently, copper losses are the main
part considering that the iron losses and eddycurrent losses are
often small or negligible at low speed. Based on these assumptions,
theefficiency map of the proposed motor as a function of phase
current and advancedcommutation angle is computed and is shown in
Figure 19.
F. Frame and prototypeConsiderable efforts have also been spent
on the final mechanical design of themachine, which is shown in
Figure 20. A prototype, shown in Figure 21, has been builtfor
validation, which will be the subject of future work.
6. ConclusionsA full design procedure of a brushless PM motor
drive system used for EPS applicationsis proposed. The requirements
of the EPS application are first introduced and the
Figure 17.Output torque waveform
0123456789
0 120 240 360 480 600 720Angular position (elec deg)
Torq
ue (N
m)
Figure 18.Zoomed-in view of torque
ripple7.50
7.60
7.70
7.80
7.90
8.00
0 120 240 360 480 600 720Angular position (elec deg)
Torq
ue (N
m)
Peak to peak value is 0.17 Nm
IPM motorfor EPS
83
-
specifications of the desired machine are then deduced. For
correct selection of the rightmachine topology before detailed
electromagnetic machine design, critical issuesincluding operation
mode, rotor structure and slot/pole combination are first
analyzed.Consequently, the IPM rotor type, BLAC operation mode and
12s/10p combination havebeen selected for further design. The final
design is fully optimized by FEA.Subsequently, the characteristics
of the proposed machine such as air gap flux density,back-EMF,
inductance, output torque, cogging torque, torque ripple, losses
andefficiency, are evaluated. The comprehensive 2D FEA results
verify that the design fullymeets the requirements of the steering
system. Finally, the mechanical design is shownand a prototype
motor has been built for verification in future work.
Figure 19.Efficiency map as afunction of phase currentand
advancedcommutation angle
Figure 20.Frame of the proposedmotor
COMPEL31,1
84
-
References
Aroquiadassou, G., Henao, H., Lanfranchi, V., Betin, F.,
Nahidmobarakeh, B., Capolino, G.,Biedinger, M. and Friedrich, G.
(2005), Design comparison of two rotating electricalmachines for 42
V electric power steering, 2005 IEEE International Conference on
ElectricMachines and Drives, pp. 431-6.
Bianchi, N. and Bolognani, S. (2002), Design techniques for
reducing the cogging torque insurface-mounted PM motors, IEEE
Trans. on Industry Applications, Vol. 38 No. 5,pp. 1259-65.
Bianchi, N., Pre, M.D. and Bolognani, S. (2006), Design of a
fault-tolerant IPM motor for electricpower steering, IEEE Trans. on
Vehicular Technology, Vol. 55 No. 4, pp. 1102-11.
Chedot, L. and Friedrich, G. (2004), A cross saturation model
for interior permanent magnetsynchronous machine. Application to a
starter-generator, IEEE Ind. App. Society Annu.Meeting, Seattle,
pp. 64-70.
Islam, M.S., Mir, S. and Sebastian, T. (2003), Issues in
reducing the cogging torque ofmass-produced permanent magnet
brushless dc motor, Proc. 38th IEEE Ind. App. Annu.Meeting, Salt
Lake City, UT, USA, pp. 393-400.
Islam, M.S., Mir, S., Sebastian, T. and Underwood, S. (2004),
Design considerations ofsinusoidally excited permanent magnet
machines for low torque ripple applications, Ind.App. Conf., 2004.
39th IAS Annu. Meeting, Vol. 3, pp. 1723-30.
Figure 21.Prototype of theproposed motor
IPM motorfor EPS
85
-
Jahns, T.M. and Soong, W.L. (1996), Pulsating torque
minimization techniques for permanentmagnet AC motor drives a
review, IEEETrans. on Ind. Electronics, Vol. 43 No. 2, pp.
321-30.
Ombach, G. and Junak, J. (2007), Two rotors designs comparison
of permanent magnetbrushless synchronous motor for an electric
power steering application, EuropeanConference on Power Electronics
and Applications, pp. 1-9.
Ombach, G. and Junak, J. (2008), Comparison of double-layer
interior permanent magnetsynchronous motor design with two
different pole numbers, 18th InternationalConference on Electrical
Machines (ICEM 2008), pp. 1-6.
Ombach, G., Junak, J. and Ackva, A. (2006), Vibrations
optimization of brushless power steeringmotor with taking into
account magnetostriction effects, paper presented at
17thInternational Conference on Electrical Machines, Chania,
Greece.
Oprea, C. and Martis, C. (2008), Fault tolerant permanent magnet
synchronous machine forelectric power steering systems,
International Symposium on Power Electronics, ElectricalDrives,
Automation and Motion (SPEEDAM 2008), pp. 256-61.
Otaduy, P.J. and McKeever, J.W. (2006), Modeling
Reluctance-Assisted PM Motors, Oak RidgeNational Laboratory, Oak
Ridge, TN.
Seong, T.L., Burress, T.A. and Tolbert, L.M. (2009),
Power-factor and torque calculation withconsideration of cross
saturation of the interior permanent magnet synchronous motorwith
brushless field excitation, IEEE International Electric Machines
and DrivesConference (IEMDC09), pp. 317-22.
Shi, Y., Zhu, Z.Q. and Howe, D. (2006), Torque-speed
characteristics of interior-magnet machinesin brushless AC and DC
modes, with particular reference to their
flux-weakeningperformance, CES/IEEE 5th International Power
Electronics and Motion ControlConference (IPEMC 2006), Vol. 3, pp.
1-5.
Stumberger, B., Stumberger, G., Dolinar, D., Hamler, A. and
Trlep, M. (2003), Evaluation ofsaturation and cross-magnetization
effects in interior permanent-magnet synchronousmotor, IEEE Trans.
on Ind. App., Vol. 39 No. 5, pp. 1264-71.
Yamazaki, K. and Ishigami, H. (2010), Rotor shape optimization
of interior permanent magnetmotors to reduce harmonic iron losses,
IEEETrans. on Ind.Electronics, Vol. 57 No. 1, pp. 61-9.
Yoneda, M., Shoji, M., Kim, Y. and Dohmeki, H. (2006), Novel
selection of the slot/pole ratio ofthe PMSM for auxiliary
automobile, 41st IAS Annu. Meeting Ind. App. Conf. 2006,Conference
Record, Vol. 1, pp. 8-12.
Zhu, Z.Q. (2009), Fractional slot PM brushless machines and
drives for electric and hybridpropulsion systems, plenary speech
the International Conference and Exhibition onEcological Vehicles
and Renewable Energies (EVER09), Monaco.
Zivotic-Kukolji, V., Soong, W.L. and Ertugrul, N. (2006), Iron
loss reduction in an interior PMautomotive alternator, IEEE Trans.
Ind. App., Vol. 42 No. 6, pp. 1478-86.
About the authors
C.F. Wang is a PhD student at Zhejiang University, China. He
received the BEngdegree from Zhejiang University in 2007, and took
an internship at CranfieldUniversity, UK, in 2009.
COMPEL31,1
86
-
J.X. Shen is a Professor at Zhejiang University, China. He
received the BEng andMEng degrees from Xian Jiaotong University,
China, in 1991 and 1994,respectively, and a PhD degree from
Zhejiang University in 1997. He was withNanyang Technological
University, Singapore (1997-1999), University ofSheffield, UK
(1999-2002), and IMRA Europe SAS, UK (2002-2004). His mainresearch
interests include design and applications of
permanent-magnetmachines and drives. J.X. Shen is the corresponding
author and can becontacted at: [email protected]
P.C.K. Luk is a Senior Lecturer and the Head of Power and Drive
Systems Groupat Cranfield University, UK. He received his high
diploma with merit fromPolytechnic University (PolyU), HK, in 1983,
MPhil from Sheffield University,UK, in 1989, and PhD from Glamorgan
University, UK, in 1992. He was with GEC(HK), PolyU, and
Universities of Glamorgan, Robert Gordon and Hertfordshire,UK. His
current main research interests are in electrical drives for
electric vehiclesand renewable energy applications.
W.Z. Fei is working towards a PhD degree at Cranfield
University, UK, andmeanwhile doing joint projects under an MOU
between Zhejiang University,China and Cranfield University. He
received the BEng and MEng degrees fromZhejiang University, in 2004
and 2006, respectively.
M.J. Jin received the B.S. degree and PhD degree from Zhejiang
University,Hangzhou, China, in 2001 and 2006, respectively. Since
2006, he has been with thedepartment of Electrical Engineering,
Zhejiang University, where he currently isa lecturer. His research
interests are electrical machine design and drives. Dr Jinis a
member of IEEE Industry Applications.
IPM motorfor EPS
87
To purchase reprints of this article please e-mail:
[email protected] visit our web site for further
details: www.emeraldinsight.com/reprints