Hybrid Energy Storage Systems: An Ultracapacitor-Battery Energy Storage System for Hybrid Electric Vehicles

The nickel metal hydride (NiMH) batteries used in most hybrid electric vehicles (HEVs) provide satisfactory performance but are quite expensive. In spite of their lower energy density, lead acid batteries are much more economical, but they are prone to sulfation in HEV applications. However, sulfation can be greatly reduced by a circuit that uses an ultracapacitor in conjunction with the battery. This research presents a new cost- effective method for using these two energy storage components together in order to extend the life of the battery. This system is presently quite expensive, but it will provide much cheaper energy storage if ultracapacitor prices can be reduced to the levels predicted by some manufacturers. This work studies two different methods for implementation on a hybrid electric vehicle and presents performance data for a variety of simulations.