The Application of Fuel Cell and Battery Technologies in Unmanned Aerial Vehicles (UAVs): A Dynamic Study

Pourrahmani, Hossein

The harmful influences of the fossil fuels on the environments have convinced the authorities to set official targets to 100% phase out the sales or registrations of new internal combustion engines (ICEs). As alternatives, batteries and fuel cells are suggested to provide the required power for different applications such as cars, buses, trucks, etc. Although there have been many investigations on the possibility of using integrated fuel cell and battery system as the prime mover for different types of vehicles, limited number of investigations have been developed in the airplane sector.

At the current stage, the current suggested integrated system of battery and fuel cell is not able to provide the required power for huge passenger planes, but they can generate the needed electricity to run small size planes (around 100kW to 300 kW), hence the objective of the current study is related to the domain of Unmanned Aerial Vehicles (UAVs). UAVs are designed to fulfill long and high-altitude flight missions. The flight duration and flight altitude have been proved to be improved using the proton exchange membrane fuel cells (PEMFCs) as the prime-mover of the UAVs. However, the low acceleration of the PEMFCs has triggered the idea of combining PEMFCs and Lithium-Ion (Li-ion) battery. Thus, the integrated system can improve the low range of batteries by maintaining high acceleration and fast re-fueling time.

Among different types of fuel cells, PEMFCs are established to be the best option for mobility applications, and the well-known Nickel Manganese Cobalt (NMC), and Lithium Titanite Oxide (LTO) Li-Ion batteries are considered as the most efficient types. Among the existing Li-Ion batteries in the market, LTO enjoys from the highest performance, lifespan, and safety by higher costs, whereas NMC provides acceptable performance with low costs and high specific energy. In comparison to the batteries, proton exchange membrane fuel cells (PEMFCs) have faster refueling time and higher ranges, hence the integration of batteries and fuel cells can provide the needs of UAVs.

The utilization of PEMFC in an UAV results in the size and weight reduction of the system in addition to improving the flight endurance. Batteries can also ameliorate the acceleration and thrust of the system. So far, it is believed that fuel cells can be suitable for cruise flight while batteries are more appropriate for other flight modes. This study analyzes the possibility of integrating the PEMFC technology to the batteries as an alternative for fossil fuel-based combustion engines for the small sized UAV application. The proposed hybrid system, which is shown in Fig. 1., is designed to provide around 950W power for a UAV with a weight of 14 kg. PEMFC will be used as the selected type of fuel cell while NMC is the considered type of Li-Ion battery. The goal of this study is the characterize the dynamic performance of the current integrated system in an optimized condition. The integrated model of the fuel cell and battery is developed in the MATLAB/Simulink software to be controlled by an energy management system, which provides power to a DC variable power load, representing the different loads of an UAV flight. The load is mainly supplied by the fuel cell, while the battery intervenes in the following cases:

As a support when the load is too high for the fuel cell,
As a support when the fuel cell takes too long to respond to a load variation,
As an additional load when the state of the charge of the battery is low (meaning that the fuel cell recharges the battery).