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NREL's diverse team of engineers and scientists focuses on many aspects of advanced transportation systems, including vehicle components, systems development and optimization, and vehicle simulation, as discussed here.
Hybrid electric and fuel cell vehicles are electrically driven, albeit with dramatically different ways of producing the electricity. In both cases these advanced vehicles require high-power electric battery packs for optimal performance. That's why NREL devotes much attention to Energy Storage.
Thermal management is central to the science of energy storage, and has long been a mainstay of NREL research, as it affects life-cycle cost, performance, power, and charge acceptance. The operating temperature of high-power battery packs must be regulated because temperature variations between modules can greatly reduce performance. NREL's energy storage team also focuses on enhancing the performance and extending the life of ultracapacitors, which store electricity by physically separating positive and negative charges—unlike batteries that do so chemically. Ultracapacitors are efficient at capturing electricity from regenerative braking, and can quickly deliver power for acceleration. They are important and promising for HEV and FCV designs.
Heavy-duty vehicles are considered prime targets for the fuel economy improvements achievable through advanced vehicles, especially because their fuel consumption rates are much higher than those of passenger cars. NREL's Heavy Hybrid Propulsion Systems Project develops HEV technology for that specialized market. In partnership with industry, NREL is developing advanced heavy hybrid components and systems projected to increase the fuel efficiency of Class 3-8 heavy trucks by as much as 100%, while meeting the U.S. Environmental Protection Agency's 2007-2010 emission standards.
A key to making HEVs and FCVs practical is the development of low-cost, high-power integrated Power Electronics devices. NREL, DOE, industry, and other national laboratories are working on advancing power electronic components, such as the motor controller, DC to DC converters, and inverters that condition the electrical signal between the power generation unit (a fuel cell or battery) and the electric motor.
Ancillary loads such as air conditioning cause all vehicles to experience reduced fuel economy and increased emissions. Hybrids are particularly susceptible because their combustion engines are relatively small. That's why NREL engineers devote much attention to Ancillary Load Reduction. They evaluate the impacts of advanced window glazings; cooling heat-pipe systems; parked car ventilation; heated, cooled, and ventilated seats; and direct energy recovery and adsorption cooling systems. A life-size thermal manikin uses advanced climate control concepts to evaluate passenger comfort and reduce auxiliary loads.
Vehicles Systems Analysis is another NREL project with powerful implications for the development of advanced vehicle technology. Engineers use computer simulation to increase the life of components, improve vehicle performance, optimize vehicle system designs, and reduce development times. For example, the vehicle systems analysis team and industry partners developed ADVISOR (the Advanced Vehicle Simulator) in 1994. ADVISOR can be used to simulate and analyze conventional, advanced, light, and heavy vehicles, including hybrids and FCVs. It tests the effects of changes in vehicle components (such as motors, batteries, catalytic converters, climate control systems, and alternative fuels) and other modifications that might affect fuel economy, performance, and emissions.
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