Energy-Optimal Guidance of Hybrid Ultra-Long Endurance UAV

Abstract The paper addresses the problem of calculating energy optimal trajectory for a novel class of hybrid UAV equipped with hydrogen fuel cell and solar photovoltaic energy production technologies. The objective of the design is to minimize the energy used for propulsion by optimally utilizing the finite energy stored in the onboard hydrogen fuel cell and routing the aircraft through the time-varying energy fields of solar irradiance and wind. The optimal guidance task is formulated as a two-point boundary value problem with an objective of finding the minimum energy route and the associated controls. The task is solved by applying Pontryagin minimum principle to the resulting 2D kinematics of a UAV along with its aerodynamics, energy management, and propulsion models. The paper derives the necessary conditions and synthesizes the optimal control laws of the bank angle and the airspeed which depend on the time and position derivatives of the wind, and the total angle of incidence toward the sun. The developed method is used to solve a task of path planning of a long endurance flight of a hybrid UAV over multiple 1000 nmi.