Energy-optimal off-design power management for hybrid-electric aircraft

Among the advantages associated with the adoption of hybrid-electric power-trains in aviation is the greater flexibility that this type of propulsion system offers. This results in the ability to fly an assigned mission profile making suitable use of both the electric and fuel-burning power components, based on a power management strategy targeting diverse alternative specific needs, like for instance reduced energy consumption or lower noise emission. However, the greater flexibility of a hybrid-electric power-train comes together with an increased complexity in its design and operation. Integrated design procedures for hybrid-electric aircraft have been the target of previous works, whereas the present paper focuses on the quantification of the off-design characteristics of an already defined hybrid-electric design. To this aim, the power management strategy is considered as configurable. The problem of how to balance electric and mechanical power, accounting for the limited energy availability on board while coping with generic mission requirements, is investigated. In order to smartly obtain the desired strategy, the paper introduces an optimal approach, capable of reducing energy expenditure by properly setting the throttle of the fuel-burning and electric components, in coordination with the amount of battery recharging power. The method is explained with a rigorous mathematical approach, and thoroughly tested on a realistic test-bed.