A hybrid electric-drive system will soon undergo testing that, if successful, could achieve significant fuel savings for the surface fleet. A Navy contract teams General Atomics and DRS Technologies to build the drive.
Glen Sturtevant, director of science and technology for the Program Executive Office/Ships and the Naval Sea Systems Command's Surface Warfare Directorate, explained that while the Navy pushes toward a long-term goal of completely integrated electric drive for new ships, the hybrid system represents a power-saving solution for the in-service Fleet.
The Navy awarded General Atomics a contract last July for the proof-of-concept effort to build and test the system and finalized the design by the year's end. The system will consist of a permanent magnet motor built by DRS, integrated with a motor drive, power converter, and system electronics provided by General Atomics.
The team will deliver the drive system to the Naval Surface Warfare Center Carderock Division's Philadelphia land-based site for testing in 2011. It will later undergo at-sea testing on board the Arleigh Burke-class Aegis destroyer Truxtun (DDG-103) in 2012.
Sturtevant noted, "the Navy is going to electric drive. But for the ships already built, the hybrid electrical-mechanical system is a modification that will allow ships to shut down one of the main engines for low speeds and save a lot of gas."
The LM2500 gas turbine engine
in service on board cruisers, destroyers, and other ships with two engines per shaft, or generally four per ship is designed for peak efficiency at top speeds. Because ships often cruise at lower speeds, it's possible to use a highly efficient electric motor to run the shaft at low speed and shut down one gas turbine to save fuel. The system could be installed on in-service ships without extensive modifications.The arrangement already has been demonstrated at sea in a new ship. The Makin Island (LHD-8), the last of the Wasp class of big-deck amphibs, is fitted with similar technology, referred to as an auxiliary propulsion system (APS).
PEO Ships Rear Admiral William E. Landay III noted last fall that the ship saved an estimated $2 million in fuel costs by using the APS on a transit from Pascagoula, Mississippi, around South America to San Diego in July, in advance of her October commissioning.
In the Navy electric-drive vision, the hybrid system points the way toward full electric drive based on an integrated power system (IPS), which uses an electric motor powered by a generator. The IPS uses the same engines (gas turbines or diesels) both for propulsion and ship services, including sensors and weapons, using a zonal power distribution system. The IPS also will eliminate the gearbox and the requirement for the power architecture to be linked directly to the shafts.
The Office of Naval Research's Sea Warfare and Weapons Department is leading a number of electric-drive initiatives in support of the Navy's next-generation integrated power system vision. These efforts, officials say, will offer capabilities beyond those of the LHD-8 and DDG-1000. The department's Ship Systems and Engineering Research Division is developing advanced switches and power controllers that will allow bi-directional distribution of power, permitting storage of excess power for later use rather than dissipating it.
These advanced devices also aim at development of an energy storage module for the hybrid-drive program for the DDG-51s and potentially other surface ships. ONR has sponsored development of a high-temperature superconducting motor, a potential alternative to the permanent magnet motor, and collaborated with the Defense Advanced Research Projects Agency to build a prototype of a solid-state transformer. Both have been delivered to the Philadelphia test site.
The department also manages an Electric Ship Research and Development Consortium of seven universities, based at Florida State University, with support from the NSWC Carderock's Philadelphia lab. The consortium is developing modeling and simulation software that creates physics-based models of a shipboard electrical distribution system and other IPS components.
An important ONR initiative is development of a medium-voltage DC distribution system, which would eliminate the need for circuit breakers and transformers. The conceptual DC system also could be tested in the modeling environment.