A battery with ultra capacitor hybrid energy storage system in electric vehicles

For electric drive vehicles including electric vehicles, hybrid electric vehicles and plug-in hybrid electric vehicles a new battery/ultra-capacitor hybrid energy storage system (HESS) is proposed. The conventional HESS design uses a larger DC/DC converter to interface between the ultra capacitor and the battery/DC link to satisfy the real time peak power demands. The proposed design uses a much smaller DC/DC converter which works as a controlled energy pump to maintain the voltage of the ultra-capacitor at a higher value than the battery voltage for city driving conditions. The battery provides power directly only when the ultra-capacitor voltage drops below the battery voltage. Therefore, a relatively constant load profile is created for the battery. Energy from the regenerative braking is not used directly, thus the battery is isolated from frequent charges which increases the life of the battery.