A combined ultracapacitor-lead acid battery storage system for mild hybrid electric vehicles

Improvements in ultracapacitor technology indicate that the automotive industry should re-examine the energy storage system for hybrid electric vehicles (HEVs). With the combination of an ultracapacitor and a lead acid battery, a system can be implemented in which the lead acid battery can be maintained at 100% state of charge, lengthening the lifetime of the battery. Although performance of the current technology, nickel metal hydride, seems satisfactory, this technology is still very expensive. The ultracapacitor-lead acid battery system described here will provide a cheaper solution if ultracapacitor prices continue to drop as predicted by manufacturers.