New energy-storage unit for heavy-duty vehicles encompassing cold-weather starting

A standard light ignition (SLI) battery, the vehicle energy storage element, must deliver maximum energy and maximum power. These design requirements are self-excluding; consequently, compromises must be made in the battery design. Increasing energy demands of the vehicle electric accessories are moving this technology towards its limits. New SLI battery designs are not providing the required energy density and cold cranking capabilities (i.e., maximum power) at temperatures as cold as -40 /spl deg/F. This paper explores a solution that uses an ultracapacitor pack in parallel with the starter motor and a unidirectional dc-dc converter allows optimal charging of the pack. The service battery could contribute a portion of the starter motor power using the converter. Lastly, load levelling of the vehicle electric accessories, and hence improved voltage regulation, can be provided to the vehicle power system at a cost by adding to the converter the bi-directional power flow feature.