Design and testing of DC/DC converters for miniature fuel cell power systems

Fuel cells have great promise for use as lightweight, portable power systems. Currently, miniature power systems rely on batteries which rely on periodic grid connections (powered by fossil fuels) for recharging. There is a need for portable power that is not charged by fossil fuels. For fuel cells to become a viable portable option there needs to be an increase in specific energy density, which can be done through design of cell and/or reduction in the mass of the subsystem components. We focus on a combination that leverages a DC/DC converter to decrease the mass of the fuel cell. This thesis presents on an electrical configuration that combines an existing miniature proton exchange membrane (PEM) fuel cell with a direct current to direct current (DC/DC) converter in order to create a portable power system fueled by hydrogen and air. Three DC/DC converters (LTC3539, LV Boost, and Pololu) were chosen which whose specifications the closest to meeting the design criteria. The LTC3539 required fabrication of external components which was achieved using a printed circuit board (PCB), however when an input voltage was applied, the LTC3539 did not operate as desired and was not subject to further testing. An experimental procedure was developed to test the DC/DC converters as stand-alone systems and connected to a one cell fuel cell stack. The input and output response for both static and dynamic conditions were evaluated for the stand-alone system. The input and output response for static conditions was evaluated for the DC/DC converter and fuel cell system. The LV Boost and Pololu converters were evaluated as stand-alone systems. These two converters were more easily packaged but did not have currents close to the range of interest. Both converters regulate voltage well in normal region; each converter has a different region of normal operation which is the region where output voltage is no longer a function of input voltage. The region of normal operation for the LV Boost is input voltages of 0.9 V or greater for all resistances. The electrical efficiency of the LV Boost is least dependent on load resistance for resistance greater than 75Ω. The region of normal operation for the Pololu ranges from input voltages of 1.2 V or greater for resistances of 50 Ω or greater. The Pololu converter is most efficient for load resistances around 100 Ω. Future experiments should be conducted for both converters with a two cell fuel cell stack. Additional future work would include successful fabrication and testing of the LTC3539