Energy management strategy of hybrid PEMFC-PV-battery propulsion system for low altitude UAVs

As great potential to increase the endurance of low altitude electric unmanned aerial vehicles (UAVs), the hybrid power propulsion system with fuel cells, photovoltaic panels and batteries has been proposed. The energy management strategies special for this kind of UAVs are still not well developed. This paper presents a rule-based energy management strategy (EMS) to deal with the power flow among the three power sources for extending the endurance of low altitude UAVs. The EMS considers the characteristics and state of power sources simultaneously, including conversion efficiency, service life, state of charge, state of pressure, etc. The photovoltaic panels have the highest priority to supply energy. Li-Ion battery is mainly used for peak power demand and can be recharged by the photovoltaic panels. With limited storage of hydrogen, the PEMFC generally has the lowest output priority and mainly serves at night. The EMS process, independent of complex calculation, does not require high computational cost, thus it is easy to be embedded in the onboard controller. An 18kg UAV with classical flight profile is established to verify the proposed EMS. The results show that the EMS can select reasonable power sources in terms of different power demands. Finally, the relationship between the endurance and the key parameters including date and time of takeoff, conversion efficiency of photovoltaic panels, specific energy of the battery, and hydrogen storage mass ratio are discussed.