Design methodology of a combined battery-ultracapacitor energy storage unit for vehicle power management

Hybrid and electric vehicles (HEV, EV) require some form of energy storage in order to achieve load leveling or efficiently manage power flows, mainly when accelerating or decelerating. Traditionally, batteries have been used but recently ultracapacitors have become potential candidates for energy storage in HEV/EV applications. To this end, this paper first presents a methodology for determining whether an energy storage unit (ESU) should consist of only batteries, only ultracapacitors or a combination of both. An example illustrates the feasibility of the proposed ideas. Finally, the paper concludes with a cost analysis of the different ESU alternatives.