Impact of Supercapacitors on a Fuel-Cell-Based Triple Hybrid for Small Unmanned Aircraft

Abstract

Hybrid fuel-cell-based propulsion systems have the potential to transform the use of small electric powered unmanned aircraft. Offering the possibility of greatly increased flight endurance and range over existing battery systems, hybrid systems also overcome some of the limitations inherent with fuel cell only systems such as low specific power and comparatively slow dynamic response. However, although there have been many fuel-cell/battery hybrid systems developed for unmanned aerial vehicle (UAV) propulsion, alternative power storage devices such as supercapacitors have not been adequately explored. Supercapacitors are fast acting with a high specific power and cycle lifetime, making them ideal candidates for use in a fuel cell hybrid system. This research develops and evaluates the use of hybrid fuel cell propulsion systems incorporating supercapacitors in the overall hybrid architecture. First, the performance of supercapacitors is evaluated and compared with the performance of fuel cells and batteries to enable an assessment of the strengths and weaknesses of the different energy sources. Next, the integration of supercapacitors with fuel cells is performed in a robust and efficient manner that ensures the hybrid system architecture maximises the benefits inherent in each of the power sources. A comparison is made between fuel-cell/battery, fuel-cell/supercapacitor, and fuel-cell/battery/supercapacitor hybrids for a UAV propulsion application through hardware-in-the-loop simulation. Finally, flight testing of a fuel-cell-based triple hybrid in a small UAV is performed to validate the operation and performance of the power system.