A Single-Stage Fuel Cell Energy System Based on a Buck--Boost Inverter with a Backup Energy Storage Unit

An energy system powered by a low-voltage fuel cell (FC) is conditioned to generate higher--voltage regulated ac voltage. The power conditioning system typically requires two power stages: a boost stage and an inversion stage. In this paper, the buck--boost inverter topology that achieves both boosting and inversion functions in a single stage is used as a building block to develop a single-phase FC-based energy system that offers high conversion efficiency, low-cost and compactness. The proposed system incorporates a backup energy storage unit to support the slow dynamics of the FC. The single-phase buck--boost inverter is voltage-mode controlled and the backup unit is current-mode controlled. The low-frequency current ripple is supplied by the backup unit that minimizes the detrimental effects of such ripple being drawn directly from the FC itself. Experimental results from a 1-kW prototype operating at 20 kHz are presented to validate the analysis and performance of the proposed system.