Full-bridge dc-dc converter with planar transformer and center-tap rectifier for fuel cell powered uninterruptible power supply

This paper shows the design of a galvanically isolated phase-shifted dc-dc converter. The converter, rated at a power of 1kW and an input current of 50 A, is designed to connect a fuel cell to a 48V dc bus of a UPS system. Special attention is given to the design of the planar transformer, which consists of several stacked PCBs. The copper losses, including skin and proximity effects, as well as the core losses are analyzed for the design process of the transformer. A construction method to reach high interleaving of the primary and secondary windings is developed and efficiency measurements of the system are performed and analyzed. A snubber circuit is used to limit the overvoltage on the rectifier. The effects of the snubber circuit on the current waveforms and the switching behavior of the input H bridge are analyzed. Furthermore, a control strategy is shown that reduces the effect of a fluctuating dc-bus voltage on the transfered power.