Bi-directional power architectures for electric vehicles

Although electric vehicles (EVs) and plug in hybrid electric vehicles (PHEVs) yield significant gains in driving efficiency and CO₂ reduction, the value of these systems are diminished by the cost of the battery subsystem. To offset the cost of electric vehicles, this paper presents two bi-directional charging architectures that use the batteries from electric vehicles for grid ancillary and facility level services. Grid-scale frequency regulation with Vehicle to Grid (V2G) technology and facility peak demand reduction with Vehicle to Base technology (V2B) for military bases, commonly known as Vehicle to Building for commercial applications, are shown as promising potential avenues to make the economics of electric vehicles viable. To effectively analyze the benefit of either technology, the cost of battery cycle life lost and bi-directional inverter purchase are quantified as the main costs of the services. The revenues or savings from using the battery in either scenario are calculated using real utility usage data and rates for three utilities and typical military installations. The optimum V2B vehicle fleet sizes for cars and trucks are derived from these models. V2B operations are sized to offset the transient peak demands in facility electrical loads, while V2G operations make use of contracted frequency regulation with the local grid. The results show that both V2B and V2G can offset a large part of the cost premium of electric vehicles. These services, combined with the enhanced driving efficiency of electricity over liquid fuel, make the life cycle cost of the electric vehicles attractive compared to conventional ones. V2B and V2G can be implemented separately or in combination to greatly improve the economics of electric vehicles in the near future. The magnitude of benefits of either make electric vehicles more attractive to early buyers, and present an opportunity to push the technology into production quantities sufficient to drive the price- of electric vehicles down to a level that is economically feasible for the general population.