IEEE Electrification Magazine - June 2014 - 59

advancement of IPM machines, the interest in the use of
SRMs for EV applications declined. However, with the cost of
rare-earth magnets soaring, there is again a strong interest
in advancing the SRM technology for EV applications. The
magnetic and electric independence of the machine phases
and the absence of PMs provide fault tolerance and also
improve reliability. The mechanical integrity of the rotor
permits high-speed and high-power-density operation. The
switched-reluctance starter/generator system is considered
a prime candidate technology that meets the requirements
and constraints of the embedded generation in aircraft
applications. The salient features of this system include
fault tolerance, suitability to operate at high speeds and in
harsh environments, and relatively high power density.

energy Storage
Energy storage is a very important component for the
advancement of electric and hybrid vehicles. Several companies and research organizations have done extensive
research and development to advance the technology to
improve the specific energy and power of the batteries.
The main considerations in the selection of EV/HEV batteries are: power density, energy density, weight, volume,
cycle life, temperature range, and environmental conditions. Lithium-based technologies and lithium-ion batteries are leading the way to meet the requirements of EVs/
HEVs. The most prevalent chemistry is the carbon/graphite anode and lithium metal oxide cathode, with the metal
being either cobalt, manganese, nickel, or a mixture of
these, with lithium salt dissolved in an organic solvent.
Another prevalent chemistry is a lithium titanate anode
with a lithium manganese cathode. Lithium-ion batteries
have the potential to deliver about 400-450 Wh of electricity per kilogram. These batteries can output high energy
and power per unit of battery mass, allowing them to be
lighter and smaller than other rechargeable batteries. The
integrated thermal, electrical, and mechanical pack design
has significantly increased the pack metrics of specific
power and specific energy in combination with electrode
and material advancement. Other advantages of lithiumion batteries compared to lead acid and nickel metal
hydride batteries include high energy efficiency, no memory effects, and a relatively long cycle life. Lithium-ion is
obviously a better and more efficient way to power modern hybrids and EVs, but is more expensive.
In MEAs, the batteries are required to provide the transient power needed for the electric loads, capture the
regenerative energy, provide emergency power, and provide the additional power (as needed) to balance the rectified dc power from the engine-driven ac generator. The
battery will also assist in providing the power for starting
the engine. The advances in lithium-ion and lithium-air
battery technologies for EVs/HEVs could be simply adapted for MEA systems, and, thus, would help reduce the total
weight of the overall system for a given power and energy
requirement. Lithium-air batteries could significantly

increase the range of EVs because of their high energy
density, which could be of the order of five to ten times
the energy of lithium-ion batteries of the same weight and
twice the energy for the same volume. They have the
potential of achieving energy density in the range of 2,000-
3,500 Wh/kg. No other known battery has as high of an
energy density as lithium-air batteries. These batteries
have an anode made of lithium and an air cathode made
of a porous material that draws in oxygen from the surrounding air. Several companies and organizations are
developing lithium-air batteries.

Summary/Conclusions
More Electric is a technology driver for power generation,
energy storage, conversion systems, and other technologies
in transportation systems. There will be an exponential
growth in electrical power demands in transportation systems. The basic technologies of electric machines, power
electronics, energy storage, and modeling and simulation
are equally applicable for electric/hybrid vehicles and MEA
systems. Developing each of these technologies from the
ground up by both the automotive and aerospace industries is quite expensive and time consuming. In addition to
power conversion and storage technologies, the automotive
companies have invested a lot of capital, time, and effort to
solve many of the problems related to power distribution,
protection, safety aspects, and standards related to highvoltage dc inside an automobile.
Significant work has also been done in the area of fuel
cells, passive components, and EMI technologies. The fuel
cells being developed for automotive propulsion could be
used as APUs for powering a dedicated load, such as the
galley or wing de-icing load, in MEAs. Because of the similar
voltage and power ranges in EVs/HEVs and MEAs, the electrical systems for aircraft could be developed using similar
technologies with modifications to meet the MEA requirements, particularly related to high-altitude conditions, wide
temperature variations, and safety. The common goal for
both EV/HEV and MEA systems is to have high-reliability
and high-performance electrical power components and
systems that would improve performance, reduce fuel
usage, and reduce emissions. The More Electric architecture
is expected to play a significant role in the future of the
overall airplane system design, operation, and performance.

For Further Reading
K. Rajashekara, "Power electronics for the future of automotive industry," in Proc. PCIM Europe , Nuremberg,
Germany, May 14-16, 2002.
C. R. Avery, S. G. Burrow, and P. H. Mellor, "Electrical
generation and distribution for the more electric aircraft," in Proc. 42nd Int. Universities Power Engineering
Conf. (UPEC 2007), Sept., pp. 1007-1012.
J. S. Cloyd, "A status of the United States Air Force's More
Electric Aircraft Initiative," in Proc. 32nd Intersociety Energy
Conversion Engineering Conf. (IECEC-97), pp. 681-686.

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