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To date hybrid-electric vehicles (HEV) make use of high-power density ac propulsion systems to provide comparable performance with vehicles using internal combustion engine (ICE) technology. Electric motor, inverter, and associated control technology has made substantial progress during the past decade and it is not the limiting factor to either vehicle performance or the large-scale production of hybrid vehicles. The search for a compact, lightweight, and efficient energy storage system that is both affordable and has acceptable life cycle remains the major roadblock to large-scale production of HEVs. This paper deals with an original HEV propulsion system that includes fuel cell generator and an energy storage system combining ultracapacitor tank and battery. The three on-board power sources supply the vehicle traction drive through a multi-input dc-to-dc power converter which provides the desired management of the power flows.

Two testing campaigns were performed in Turin by CRF (the Fiat Research Center), and in Rome by ENEA (the Italian National Agency for New Technologies, Energy and the Environment) and the University "ROMA TRE". The work demonstrates the feature of a FC emulator to characterize fuel-cell-propelled drivetrains without employing an expensive PEM fuel cell and it points out how the vehicle fuel consumption, on a specific mission, depends on two fundamental parameters, the accordance of the FC nominal power with the requested power of the mission and the battery State-of-Charge. In the ENEA Research Center "Casaccia", near Rome, the behaviors of PEM Fuel Cells of different sizes (7, 15, 22 kW) were simulated by replacing them with a controlled AC/DC converter, this fuel cell emulator powering a full-scale hybrid drive train.