A new battery/ultra-capacitor hybrid energy storage system for electric, hybrid and plug-in hybrid electric vehicles

In this paper, a new battery/ultra-capacitor hybrid energy storage system (HESS) is proposed for electric drive vehicles including electric, hybrid electric, and plug-in hybrid electric vehicles. Compared to the conventional HESS design, which requires a larger DC/DC converter to interface between the ultra-capacitor and the battery/DC link, the new design uses a much smaller DC/DC converter to maintain the voltage of the ultra-capacitor at a value higher than the battery voltage. In addition, the battery directly provides power when the ultracapacitor voltage drops below the battery voltage. Therefore, a relatively constant load profile is created for the battery. In addition, the battery is not used to directly harvest energy from the regenerative braking; thus, the battery is isolated from random charges, which will increase the life of the battery. The proposed topology has the possibility of utilizing the system configuration for fast charging via the ultra-capacitor.