Public Release: 

System To Improve Solar-Car Function May Work On Home Appliances

University of Illinois at Urbana-Champaign

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.

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