Current technologies and challenges of applying fuel cell hybrid propulsion systems in unmanned aerial vehicles

Recent developments in fuel cell (FC) technologies show great potential to increase flight duration of unmanned aerial vehicles (UAVs) with satisfactory fuel economy. The three most common FCs used to power UAVs are: 1) polymer electrolyte membrane FC, 2) direct methanol FC, and 3) solid oxide FC. Because of the power performance limitation of pure FC propulsion systems, hybrid propulsion systems that integrate FCs with other power sources such as batteries, supercapacitors, solar cells, and conventional internal combustion engines are recommended for UAVs. This paper reviews the current developments in FC hybrid propulsion systems applied to UAVs. The topics covered include the operating principles and characteristics of three typical FCs, issues faced by FC-powered UAVs, specific roles of other electric power sources, pure electric hybrid constructions of FC hybrid propulsion systems, hybrid engine-electric FC hybrid propulsion systems, potential impacts of various flight factors, energy management strategies of FC hybrid propulsion systems, and similarities/differences of FC hybrid propulsion systems in other vehicle applications. Finally, future trends and challenges of FC hybrid propulsion systems are discussed, which could be valuable for the development of next-generation UAVs.