CHAMPAIGN, Ill. -- A power-tracking circuit, developed for use in a
solar-powered race car, may improve the efficiency of large home appliances.
Designed by a University of Illinois professor and his students, the power
tracker maximizes the efficiency of electrical power-conversion processes.
"One of the most important components in a solar-powered car is the
one that gathers energy from the solar cells and provides it for the electrical
needs of the car," said Philip Krein, professor of electrical and computer
engineering at the U. of I. "We designed a circuit that automatically
adjusts itself so that it is always getting the maximum possible energy
out of the solar cells, and at the same time converts that energy into the
right form for the car's batteries."
Conventional power-conversion and tracking systems work by actively imposing
a change on the system, Krein said. "A computer continuously compares
various operating points and selects the one that yields maximum power.
But, because you have to repeatedly take the system away from the best point
to make sure you are at the best point, that means you are not always getting
the highest output."
While this procedure works well for satellites in space -- where there is
not a lot of variability in the amount of sunlight striking the solar cells
-- the method is too slow and inefficient for dynamic applications such
as solar-powered race cars.
"The car's environment is constantly changing," Krein said. "The
car may pass under trees or over bridges. On hills and curves, the angle
at which sunlight strikes the car changes. And the sun may be partially
obscured by clouds. We wanted to get the greatest possible energy out of
the cells, even under all these varying and unpredictable conditions."
The solution Krein and his student racers came up with is not only simple,
inexpensive and lightweight, it also is fast, reliable and efficient. "Instead
of hunting around trying to find the best point, we examine what's occurring
during the conversion process and adjust that for maximum power," Krein
said. "Our power tracker takes advantage of its own internal information
to drive the operation to its best point, automatically, all the time."
The circuit that monitors the current and voltage fluctuations occurring
within the power-conversion process and then adjusts for maximum output
can be used in many other applications, Krein said. "For example, the
power tracker could be used to maximize the efficiency of electric motors
in large industrial operations as well as in household appliances such as
refrigerators and air conditioners."
The power tracker was developed for use in a U. of I. student-built, solar-powered
car that ran in the 1995 Sunrayce -- a biennial competition sponsored by
the U. S. Department of Energy and the General Motors Corp. An improved
version of the power tracker will be used in the Photon Torpedo, the university's
solar-powered car being built for the 1997 Sunrayce. The researchers have
applied for a patent for the power tracker.