Evaluation of active hybrid fuel cell/battery power sources

Hybrid fuel cell/battery power sources have potentially widespread uses in applications wherein the power demand is impulsive rather than constant. Interposing a dc/dc converter between a fuel cell and a battery can create two configurations of actively controlled hybrid fuel cell/battery power sources. Those two configurations are compared using both theory and experiment with special attention to the peak power enhancement, and power losses in the converter. Both of the defined configurations were built, using a 35 W polymer electrolyte membrane (PEM) fuel cell, an 8-cell lithium-ion battery pack, and a high-efficiency power converter. Both two configurations yielded a peak power output of 135 W, about 4 times as high as the fuel cell alone could supply, with only a slight (13%) increase of weight. The converter losses were quantitatively analyzed. Which of the two configurations yields a smaller loss depends on the load power demand characteristics including peak power and load duty ratio. The study results provide guidance for the design of hybrid sources according to the particular load power requirements.