A single-stage fuel cell energy system based on a buck-boost inverter with a back-up unit

When low-voltage unregulated fuel cell (FC) output is conditioned to generate AC power, two stages are usually required: a boost stage and an inversion one. 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 which offers high conversion efficiency, low-cost and compactness. The proposed system incorporates additional battery-based energy storage and a DC-DC bi-directional converter to support the slow dynamics of the FC. The single-phase buck-boost inverter is voltage-mode controlled and the DC-DC bi-directional converter is current-mode controlled. The low-frequency current ripple is supplied by the battery which minimizes the effects of such ripple being drawn directly from the FC itself. Experimental results from a 1kW prototype are presented to validate the performance of the proposed system.