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A single energy storage element (ESE) has been used in fuel cell (FC) vehicles to improve the FC dynamic response and to recover the braking energy. An energy storage system (ESS) consisting of hybrid ESEs extends the capabilities of single ESE and is, therefore, capable of achieving an optimized performance with improved life cycles for ESS. In this paper, an FC vehicle power train configuration is presented, where a three-port isolated triple-half-bridge dc/dc converter is applied to interface a power dense ultracapacitor (UC) and an energy dense battery unit (BU). A design routine is provided to size the BU and UC to achieve the lightest mass at a 95 % efficiency. Furthermore, a control strategy is developed to achieve the maximum fuel economy of the FC. The state of charge of the BU and UC is also controlled in a dynamic environment and maintained after the driving cycle. Two different approaches of the proposed control strategy have been implemented. The system loss of each method has been compared. The simulation and experimental results based on simplified urban driving cycles are presented to validate the proposed maximum fuel economy design.
Date of Publication: May-june 2010