A Method for Determining Optimal Power Management Schedules for Hybrid Electric Airplanes

Hybrid-electric propulsion architectures have been proposed to meet aggressive future performance and environmental goals. However, hybrid-electric airplanes present a unique power management challenge since they have two energy sources that can compete to meet the thrust requirements. Electrical power provided by the installed battery packs and the gas engine, allow for a continuous range of power settings to produce the same required power within sizing limits. Choosing when to supplement the gas engine with electrical power will influence total fuel burn, even if the total amount of battery used remains the same. This paper reviews and compares various power management optimization methods in terms of theory, difficulty of implementation, and scope of results. The techniques considered are Optimal Control, Dynamic Programming, as well as three “rule-based” power schedules (constant power, power at climb, and power at cruise). Each optimization technique is applied to determine the optimal power management of a parallel hybrid-electric turbofan engine with the goal of reducing total mission fuel burn over the flight envelope. Various implementation techniques are investigated including off-line optimization using engine decks and surrogate models, and in-line approaches using a detailed gas turbine engine model running with an airplane model. Best fuel burn results are compared across all optimizer and implementation schemes. Finally, a consistent process algorithm, called the Systematic Hybrid Aircraft Power Schedule Optimizer (SHAPSO) is proposed, for choosing the best power scheduling method for hybrid-electric airplanes which was informed by the results of the comparison.