IEEE Electrification Magazine - March 2017 - 18
associated with a table of this type because each of the
machine types can be designed in a nearly endless
number of ways that may sacrifice one or more of the
listed features to strengthen the machine's perfor-
mance in another feature category. However, this table
is intended to focus on each of the machines types as a
class to highlight those features where the underlying
physics gives the machine type in question a relative
strength or weakness compared to the competing trac-
tion machine types.
Inspection of the table entries indicates that none of
the machines rises above all of the others as a clearly
superior choice in all of the traction machine feature cat-
egories. Each machine type exhibits noteworthy strengths
in two or more categories and comparative weaknesses in
at least one of the other feature categories. The reason
sintered neo IPM machines play such a major role in pro-
duction passenger EV powertrains is that the specific fea-
ture areas where they demonstrate their comparative
strengths align closely with the most important pow-
ertrain requirements in many EV applications.
In contrast, the lack of success that SR machines have
achieved to date in production passenger EVs despite the
comparative strengths that they display in several feature
categories is that the one machine feature where they
exhibit comparative weakness-acoustic noise and
torque ripple-is a very important requirement for the
majority of the passenger EV applications. In those elec-
trified vehicle applications, such as off-road construction
and mining vehicles, where acoustic noise is not very
important, the SR machine has achieved wide accep-
tance, as discussed previously.
Before closing, it should be noted that space limitations
in this article prevented discussion of other interesting
machine types that are also being considered in both aca-
demia and industry as candidates for eliminating the use
of sintered neo magnets in HEVs and BEVs. These include
the classic wound-field synchronous machine that has
already been manufactured in limited numbers by Conti-
nental for production EVs introduced by Renault (Fluence
and Kangoo) in 2012. Alternatively, variable-flux PM
machines that use either Alnico or samarium-cobalt mag-
nets with reduced magnetic coercivities compared to neo
magnets are also being seriously investigated because of
their ability to actively adjust the magnetization level in
the magnets during operation. Both of these alternative
machines share in common the objective of minimizing
the traction motor's total energy usage over typical EV
drive cycles by optimizing the rotor field flux amplitude
for every machine torque/speed operating point.
The search for better traction machines for future EVs
is certain to continue during the coming years as EVs
evolve and machine performance characteristics im-
prove as well, based on the availability of new materials
that are likely to open the door to innovative machine
topologies. As a result, the competition between the
18
I E E E E l e c t r i f i c ati o n M agaz ine / march 2017
machine types compared in this article and new entries
that have not yet appeared is certain to continue for the
foreseeable future. There is good reason to believe that
the sintered neo IPM machines that have been so suc-
cessful during the past 15 years will face strong competi-
tion to maintain their dominant position in production
passenger vehicles during the next 15 years. Competition
is a powerful motivator, so stay tuned for the next
chapter in this unfolding story!
For Further reading
J. S. Hsu, C. W. Ayers, and C. L. Coomer, "Report on Toyota/
Prius motor design and manufacturing assessment," Oak
Ridge Nat. Lab., Oak Ridge, TN, ORNL/TM-2004/137, July 2004.
T. Burress, C. L. Coomer, S. L. Campbell, A. A. Wereszczak, J. P.
Cunningham, L. D. Marlino, L. E. Seiber, and H. T. Lin, "Evaluation
of the 2008 Lexus LS 600H hybrid synergy drive system," Oak
Ridge Nat. Lab., Oak Ridge, TN, ORNL/TM-2008/185, Jan. 2009.
I. Boldea, L. N. Tutelea, L. Parsa, and D. Dorrell, "Automotive
electric propulsion systems with reduced or no permanent
magnets: An overview," IEEE Trans. Ind. Electron., vol. 61, no. 10,
pp. 5696-5711, Oct. 2014.
B. Sarlioglu, C. T. Morris, D. Han, and S. Li, "Driving toward
accessibility: A review of technological improvements for
electric machines, power electronics, and batteries for elec-
tric and hybrid vehicles," IEEE Ind. Appl. Mag., vol. 23, no. 1, pp.
14-25, Jan.-Feb. 2017.
Z. Q. Zhu and C. C. Chan, "Electrical machine topologies
and technologies for electric, hybrid, and fuel cell vehicles," in
Proc. 2008 IEEE Vehicle Power and Propulsion Conf., Harbin, China,
2008, pp. 1-6.
S. Jurkovic, K. Rahman, B. Bae, N. Patel, and P. Savagian,
"Next generation Chevy Volt electric machines: Design, opti-
mization and control for performance and rare-earth mitiga-
tion," in Proc. 2015 IEEE Energy Conversion Congr. Exposition
(ECCE), Montréal, Québec, 2015, pp. 5219-5226.
G. Pellegrino, T. M. Jahns, N. Bianchi, W. Soong, and F. Cuperti-
no, The Rediscovery of Synchronous Reluctance and Ferrite Permanent
Magnet Motors: Tutorial Course Notes (SpringerBriefs in Electrical
and Computer Engineering). New York: Springer -Verlag, 2016.
C. Oprea, A. Dziechciarz, and C. Martis, "Comparative
analysis of different synchronous reluctance motor topolo-
gies," in Proc. 2015 IEEE 15th Int. Conf. Environment and Electrical
Engineering (EEEIC), Rome, Italy, 2015, pp. 1904-1909.
S. Jurkovic, K. M. Rahman, J. C. Morgante, and P. J. Savagian,
"Induction machine design and analysis for General Motors
e-assist electrification technology," IEEE Trans. Ind. Appl., vol.
51, no. 1, pp. 631-639, Jan.-Feb. 2015.
A. Chiba and K. Kiyota, "Review of research and develop-
ment of switched reluctance motor for hybrid electrical vehi-
cle," in Proc. 2015 IEEE Workshop on Electrical Machines Design,
Control, and Diagnosis (WEMDCD), Turin, Italy, 2015, pp. 127-131.
T. Raminosoa, A. El-Refaie, D. Pan, K.-K. Huh, J. Alexander,
K. Grace, S. Grubic, S. Galioto, P. Reddy, and X. Shen, "Reduced
rare-earth flux-switching machines for traction applica-
tions," IEEE Trans. Ind. Appl., vol. 51, no. 4, pp. 2959-2971, July-
Aug. 2015.
Biography
Thomas Jahns ( jahns@engr.wisc.edu) is with the Wiscon-
sin Electric Machines and Power Electronics Consortium,
University of Wisconsin-Madison.
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