Framework of a Power Management System for a Hybrid Electric VTOL Aircraft using Optimal Control

Abstract

Electric-carbon fuel hybrid propulsion systems have increasingly come under investigation to utilize the advantages provided by electrical propulsion systems while maintaining the endurance and range of traditional carbon fuel systems. This paper presents the design of an energy management system for a hybrid-electric fixed-wing VTOL UAV to optimize performance during takeoff, which consists of a vertical climb followed by transition to horizontal flight. The fixed-wing VTOL UAV is equipped with a modular hybrid propulsion system (MHPS), a concept hybrid propulsion system where the electrical and carbon-fuel system components are interchangeable on a mission-to-mission basis, enabling aircraft performance flexibility. An optimal control approach is used to determine the flight path and power split between electric and carbon fuel to minimize the aircraft energy consumption during takeoff. The purpose of this work is to address the topic of optimal energy management applied to hybrid-electric aircraft, including its relevance to the conceptual design of novel aircraft propulsion systems, and to determine the advantages or disadvantages hybrid propulsion systems offer during demanding phases of flight. Optimization results show that the most time and energy efficient takeoff trajectories involve minimizing the vertical displacement/altitude gained during the transition from vertical to horizontal flight. The power management strategy during takeoff is largely dictated by propulsion component efficiencies.