ABSTRACT
Hybrid electric vehicles (HEVs), as the name stands for, have two kinds of power sources. An electric power source is added to the conventional internal combustion engine (ICE), which helps to improve the fuel economy through load sharing and regenerative braking. The ICEs have relatively inferior performances in urban driving where there are many stop-go situations. If the vehicle is propelled by a motor in a low-speed region, the overall fuel economy will be improved significantly. The efficiency of an engine is based on the fuel flow rate per useful power output, and brake specific fuel consumption (BSFC) is a measure of fuel efficiency. The engine is controlled to operate along the optimal operation line (OOL) by controlling the generator speed and motor torque. The battery is the most typical energy storage system for EVs, and should be evaluated according to energy density, power density, life time, safety, and cost.
