Whether applied on land or sea, David Gao's research aims to launch new alternative, long-lived power sources.

Funded by the Office of Naval Research, Gao is pursuing fuel cell applications as distributed generation for all-electric ships. The research results can also be used in other naval war fighting platforms or in a new generation of fuel cell-powered electric vehicles.

"Traditionally, ships have a centralized power facility, and if that unit fails or is damaged in an attack, the ship's power system can be disabled," explains Gao, an assistant professor in the Electrical and Computer Engineering Department who has his base in our Center for Energy Systems Research. "We are working on distributed generation so that power can be generated from multiple sources, including fuel cells, microturbines and renewable energy, so the stability of the ship's power system can be improved."

Distributed generation would allow ships' commanders to keep critical loads functioning. For instance, during the attack of the U.S. Navy destroyer Cole on Oct. 12, 2000, in a Yemeni port, its power system was damaged and failed to power the water pumps. Distributed generation could help avoid such failure and loss of central command and radio communication.

Gao says electric ships also have improved war-fighting capability because they can be reconfigured after damage more easily than ships with large, centralized, diesel engine-driven propulsion systems.

So how can fuel cells help fill the power needs of a mammoth ship?
"A fuel cell alone can't fulfill the power requirement for a ship," says Gao. "To effectively use fuel cells, we have to develop controllers and interfaces that allow us to make the most of power electronics.

"Power electronics just means we seek to transform fuel cell output into the form of power we need," he continues. "The voltage characteristics of fuel cells are not very good. A fuel cell is DC at low voltage, so it needs to be converted into a more useful form."

The key is to use fuel cells within a hybrid system featuring other power storage devices and to be able to control them all accurately and efficiently.

That's where Gao's expertise as an electrical engineer comes in. Hybrid systems have super capacitors and batteries that can give the system a burst of energy. The challenges are how to connect the fuel cell, super capacitor and battery in the most efficient way and how to develop a controller strategy.

"There's a lot of juggling," says Gao. "We are in the final stage of developing a model of the system that includes a hybrid controller that will manage the power flow among different power sources under different load conditions.

"For instance, if you generate more power than is needed to efficiently run the fuel cell, the extra energy can be stored in the battery," he says. "If the load increases, the battery can be used to supply the increased load power. Our goal is to develop a controller that will find the optimal way to use electric power sources for an e-ship."

Gao received his bachelor's degree in aeronautical propulsion control engineering from Northwestern Polytechnic University in Xi'an China and his master's degree and doctorate in electrical and computer engineering, with a specialty in electric power engineering, from Georgia Tech. He worked as an assistant research professor at the University of South Carolina and Mississippi State University before joining our faculty this year.