IEEE Power Electronics Magazine - June 2014 - 17

can provide lower copper losses due to higher conductivity
of copper but, currently, the manufacturing cost for copper
Mode 2
Mode 3
Mode 4
die casting is higher than for aluminum die casting.
The SRM has no PMs or conductors on the rotor. It has a
simple and low-cost construction and is capable of operating in high temperatures and harsh operating conditions.
However, design steps must be taken to minimize torque
ripples, acoustic noise, and vibration. A well-designed SRM
can be built that combines the low-cost, robust, and rugged
fig 5 The displacement of a typical SRM with a frame in difstructure of the SRM with a proper electromagnetic, therferent vibrational modes of the stator.
mal, and structural design to achieve an optimized power
density as well. Low-cost and reliable SRM solutions will
In this case, they might match at lower speeds, resulting in
enable the automotive industry to manufacture more costexcessive vibration. This is undesirable for variable-speed
effective vehicles with electrified powertrains and, in turn,
operations, including traction applications. The best poslead to an increased market share for these vehicles. The
sible option is to design the motor such that the natural
mass commercialization of more effifrequency of the frame and the stator
cient vehicles will reduce the depenis higher than the maximum excitadency on fossil fuels, enabling a more
tion frequency. This task involves a
When the motor is
sustainable transportation system.
detailed analysis and an iterative prodesigned with a high
cess. Proper damping of the frame is
also important for reducing vibrations.
About the Authors
yield strength
Berker Bilgin (bilginb@mcmaster.
material, the rib
ca) is the senior principle research
Conclusions
engineer and program manager at the
Due to the low efficiency of ICE vehithickness can
Canada Excellence Research Chair in
cles and dependency on fossil fuels,
be small.
Hybrid Powertrain Program, McMasour conventional transportation syster University, Hamilton, Ontario, Cantem is not sustainable. Significant powada. He is a member of the organizing
ertrain improvements are needed, and
committee of the IEEE Transportation Electrification Conelectrification is a central focus of many new efficient powference and Expo.
ertrain designs. One or more electric motors are used in variAli Emadi (emadi@mcmaster.ca) is the Canada Excelous electrified powertrains. Considering the efficiency, perlence Research Chair in Hybrid Powertrain and director
formance, reliability, and cost requirements, electric traction
of the McMaster Institute for Automotive Research and
motors are desired to have high power density, deliver high
Technology at McMaster University in Hamilton, Ontario,
torque at low speeds, and operate in a wide speed range on
Canada. Before joining McMaster University, he was the
rough roads, under harsh temperature conditions, and over a
Harris Perlstein endowed chair professor of engineering
long lifetime. To achieve these targets, electric traction
and the director of the Electric Power and Power Electronmotors should be designed with a multidisciplinary
ics Center and Grainger Laboratories at the Illinois Institute
approach, where the electromagnetic, electromechanical,
of Technology in Chicago.
thermal, and structural aspects of the machine are analyzed
along with the effects of materials and manufacturing on the
motor characteristics.
References
[1] A. Emadi, "Transportation 2.0: Electrified-Enabling cleaner, greener,
IPMSMs, IMs, and SRMs are the most frequently conand more affordable domestic electricity to replace petroleum," IEEE Power
sidered electric machine types for traction applications.
Energy Mag., vol. 9, no. 4, pp. 18-29, July/Aug. 2011.
Each has its own advantages and challenges when con[2] A. Emadi, Handbook of Automotive Power Electronics and Motor
sidered for propulsion systems. The interior PM machine
Drives. New York: Marcel Dekker, May 2005.
type provides high efficiency and power density. However,
[3] U.S. Department of Energy. (2010, Dec. 7). Electrical and electronics
it has a high manufacturing cost mainly due to the high
technical teamroadmap. [Online]. Available: http://www.eere.energy.gov/
cost associated with the PMs. In addition, the PMs on the
[4] U.S. Department of Energy. (2010, Dec.). Multi-year program plan 2011rotor are sensitive to high temperatures. The ambient tem2015. [Online]. Available: http://www/eere/energy.gov/
perature under the hood of the car and the high tempera[5] U.S. Department of Energy. (2011, Dec.). Critical materials strategy.
ture rise due to the high power density during operation
[Online]. Available: http://www.energy.gov/
can be a significant limitation for the PM machines.
[6] G. C. Mechler, "Manufacturing and cost analysis for aluminum and copIMs do not have PMs on the rotor, but they have conducper die cast induction motors for GM's powertrain and R&D divisions," M.S.
tors. Therefore, IMs suffer from rotor copper losses. This
thesis, Dept. Materials Sci. Eng., Massachusetts Inst. Technol., Cambridge,
is the limiting factor for their use in traction applications,
MA, 2010.
especially for high-torque operation. Copper die-cast IMs
June 2014

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