When you drive
the next-generation car, advanced electronics will be in charge of the
vehicle's energy use. Some people are already driving hybrid vehicles
designed in Japan, such as the Toyota Prius and Honda Insight. But the
next-generation car likely to come out of Detroit by 2004 will get 80
miles per gallon, while maintaining the size, comfort, and performance
of today's family sedan. Because less fuel is burned per mile and the
energy is used more efficiently, this car will also emit less carbon
dioxide and other pollutants. Power electronics, which controls the
flow of electrical energy, will be the key to making the car high in
efficiency and low in emissions, meeting the goals of the U.S. Partnership
for a New Generation of Vehicles (PNGV).
Each car company
has its own unique approach to vehicle design and power control. Generally,
the American hybrid car will have a smaller gasoline or diesel engine,
sized to meet the average power requirement rather than the peak power
required in normal driving. Electric motors powered by batteries will
provide extra power to the wheels when needed to accelerate the car
or help it climb a hill.
When you step
on the brakes, the kinetic energy of the car won't be completely dissipated
as heat. Instead, in what is called regenerative braking, the electric
motor will act as a generator, capturing energy from the wheels and
charging the batteries.
How and when fuel
and electricity are used in hybrid cars will be dictated by a computer
aided by power electronics. An inverter will convert direct current
(dc) from the car's batteries to alternating current (ac) to drive the
electric motor that provides power to the wheels. The inverter also
converts ac to dc when it takes power from the generator to recharge
the batteries.
Don Adams, leader
of the Power Electronics and Electric Machinery Research Group in ORNL's
Engineering Technology Division (ETD), is spearheading an effort to
reduce the sizes, weights, and costs and to increase the efficiencies
and useful life of automotive electric motors and inverters. Using Department
of Energy funding, he and his colleagues are collaborating with researchers
in the U.S. automobile industry to reach these technical targets.
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Hui
Li checks a converter being developed at NTRC for a hybrid electric
vehicle project. (Photo by Curtis Boles and enhanced by LeJean
Hardin.)
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"We are trying
to reduce the electric motor to about one-third the volume and one-half
the weight of today's motors," says Adams. "So we have developed a series
of highly efficient electric motors. Another goal is to develop the
right materials and manufacturing techniques to reduce the cost of inverters
from $200/kilowatt to $7/kilowatt. The industry knows how to achieve
cost, size, or performance goals, but not all three simultaneously."
The ETD group
has already developed an evolving series of "soft-switching inverters"
that are more efficient, more compact, and more reliable than conventional
inverters. Leon Tolbert, a member of the ETD group and a University
of Tennessee professor, says, "To meet PNGV goals, we are trying to
reduce the size and cost of the new inverter module by developing circuits
that are more efficient so that the heat sink can be made smaller. Our
inverter is a strong candidate for electric cars and buses, partly because
its lighter weight will increase vehicle energy efficiency."
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One
of Chattanooga's electric buses has an ORNL-developed soft-switching
inverter (shown here) that makes the vehicle lighter and more
energy efficient. This inverter also eliminates the problems of
voltage spikes, waste heat, and electro-magnetic interference
that can disrupt operations of other electronic devices.
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"Far more electrical
power will be required in new vehicles than in today's automobiles,"
Adams says. "We must make sure that there is enough electricity to operate
the wheels, air conditioning, power steering, lights, and information
systems, such as the auto PC and displays of navigational information.
We must ensure that these systems work well together. We're doing all
this work hand-in-hand with the auto companies and their suppliers.
Furthermore, we help DOE decide the appropriate direction of the research
and assess the progress toward the goals."
At the National Transportation
Research Center, researchers are charging ahead with power electronics
projects that may help make future cars cleaner, more efficient, and
affordable. In the not-too-distant future, that fossil-fuel-driven engine
will be replaced by a fuel cell. When that happens, the role of power
electronics and electric motors will become even more prominent.
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Related Web
sites
ORNL's
Power Electronics and Electric Machinery Research Group
ORNL's
Engineering Technology Division (ETD)
Partnership
for a New Generation of Vehicles
