Preliminary design of power control strategies for the hybrid-electric propulsion system of a lightweight fixed-wing UAV

This paper deals with the design of power control strategies for the hybrid electric propulsion system of lightweight fixed-wing UAVs for long-endurance surveillance missions. Using as reference application a UAV with conventional thermal propulsion, the basic objective of the work is to substantiate the feasibility of its hybrid conversion, up to overcome the limitation of climb performances due to the engine overheating as well as to enhance the propulsion efficiency. Thanks to a control electronic box dedicated to the power management, the UAV electric generator is temporarily switched into motor operation, reducing the thermal engine power request, and thus avoiding its overheating. The paper demonstrates that a management of propulsion system commands (engine throttle and motor current) based on dynamic ideal-decoupling techniques is effective to track a target performance signal (as a relevant case, the engine efficiency has been selected in the work), while limiting the transient deviations of propeller speed, i.e. the UAV thrust.