Experimental evaluation of a soft-switching DC/DC converter for fuel cell vehicle applications

A soft-switched, isolated bi-directional DC/DC converter has been developed for fuel cell powered electric vehicles (FCPEV), in which the 12 V battery for the vehicle accessory loads is also used to start up the fuel cells and to store the energy captured during regenerative braking. The DC/DC converter interfaces the low voltage battery to the fuel cell powered higher voltage DC bus system (255 V similar to 425 V). Dual half-bridges interconnected through a transformer are employed to minimize the number of switching devices and their associated gate drive components. The transformer provides voltage level matching and galvanic isolation for safety requirements. Snubber capacitors and the transformer leakage inductance are utilized to achieve zero-voltage-switching (ZVS). Therefore, no extra resonant components are required for ZVS, further reducing component count. The inherent soft-switching capability and the low component count of the converter allows efficient power conversion and compact packaging. A prototype was built and successfully tested. This paper presents design considerations and testing data to evaluate the prototype's performance against the requirements for FCPEV applications.