A Soft-Switched DC/DC Converter for Fuel Cell Vehicle Applications *

Fuel cell-powered electric vehicles (FCPEV) require an energy storage device to start up the fuel cells and to store the energy captured during regenerative braking. Low-voltage (12 V) batteries are preferred as the storage device to maintain compatibility with the majority of today's automobile loads. A dc/dc converter is therefore needed to interface the low-voltage batteries with the fuel cell-powered higher-voltage dc bus system (255 V ∼ 425 V), transferring energy in either direction as required. This paper presents a soft-switched, isolated bi-directional dc/dc converter developed at Oak Ridge National Laboratory for FCPEV applications. The converter employs dual half-bridges interconnected with an isolation transformer to minimize the number of switching devices and their associated gate drive requirements. Snubber capacitors including the parasitic capacitance of the switching devices 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 high power density, efficient power conversion, and compact packaging. A prototype rated at 1.6 kW was built and successfully tested. Experimental results confirmed soft-switching operation and an average model based analysis.