ABSTRACT
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Hybridization of a vehicle propulsion system can improve performance and ef”ciency by splitting the power required to propel a vehicle between multiple energy sources. The essential improvement of a hybrid electric vehicle (HEV) is the more ef”cient use and design of the primary energy source (e.g., internal combustion engine, fuel cell) than can be obtained in a conventional vehicle. In conventional vehicles, the internal combustion engine (ICE) acts as the only source of power. This single source design is less ef”- cient since the ICE must operate at low power or idle speeds where it consumes more fuel or consumes fuel without providing power for propulsion. As a result, only 10 to 15% of the energy contained in gasoline is used to propel the vehicle [1]. In a hybrid propulsion system, the power demand of the primary energy source can be decoupled from the instantaneous road load requirements through the use of a secondary energy source(s) (batteries, electrochemical capacitors, ˜ywheels, etc.) resulting in improved ef”ciency.
