Grid-interfaced fuel cell energy system based on a boost-inverter with a bi-directional back-up battery storage

When low-voltage unregulated fuel cell (FC) output is conditioned to generate AC power, two stages are required: a boost stage and an inversion one. In this paper, the boost-inverter topology that achieves both boosting and inversion functions in a single-stage is used to develop a grid-tied 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 instantaneous load changes. The output voltage of the boost-inverter is voltage-mode controlled and the DC-DC bi-directional converter is current-mode controlled. The load low-frequency current ripple is supplied by the battery which minimizes the effects of such ripple being drawn directly from the FC itself. Analysis, simulation and experimental results are presented to confirm the operational performance of the proposed system.