this invention relates to plug - in hybrid propulsion systems where the energy storage element of the hybrid drive train may be charged with externally supplied electricity as well as energy from the engine or regenerative braking . the invention is a plug - in hybrid system with a fast energy storage and delivery system . in a preferred embodiment the invention comprises a fuel powered engine , a battery , a fast energy storage system , power converters , controllers , drive motors , an electrical distribution system , and a drive train . additionally , the invention relates to plug - in hybrids that provide services to the electrical utility when the vehicle is connected to the utility grid .