Adaptive Cutoff Frequency EMS Tuning Methodology Applied on a Long Range UAV Powered by a Hybrid Fuel-Cell System

Multi-source hybrid power systems combining fuel cells (FC), lithium-ion batteries, and supercapacitors (SC) are increasingly considered as viable alternatives to fossil-fuel propulsion for long-endurance unmanned aerial vehicles (UAVs), due to their improved energy efficiency, extended mission duration, and reduced environmental impact. For these systems, the energy management stratregy (EMS) must alocate the power demand in a way to maximize the life-time. This paper compares two strategies using a rule-based approach within the frequency domain. The first strategy is based on a fixed cut-off frequency to distribute load current across multiple sources. In contrast, the second strategy dynamically adapts the switching frequency according to the state of charge of the SC. A complete model of the hybrid energy system is developed, and a systematic tuning procedure for both control strategies is presented. Performance comparison on different flight cycles shows a significant reduction in FC current variations with the adaptive frequency strategy, thus limiting ageing. The results show that this approach requires low computing power, does not require additional equipment, but improves performance for all flight cycles.