DESIGN OF A HYBRID ELECTRIC UAV THROUGH MULTI-OBJECTIVE OPTIMISATION

Problem and purpose - In order to exploit the potentiality of hybridization and quantify the environmental advantages obtainable with today technologies while waiting for innovations in batteries and electric machines, it is necessary to develop advanced numerical tools that takes into account the size of the components, the energy management strategy, the flight trajectory, etc. This problem is addressed here through the application of multi-objective optimization methods to a parallel hybrid electric power system based on a Wankel engine. Methodology - The power request at propeller axis of each flight segment is used to calculate the overall fuel consumption of the mission (Mfuel) and the maximum payload weight (Wpay) through an average-point analysis. These outputs depend on the size of the components and on the energy strategy that is expressed by the power-split ratio of each mission phase between engine and motor. Originality – The novelty of the investigation is twofold: the application of hybridization to a Wankel engine for which a scaling method is proposed, and the inclusion of the energy management in the design of the power system. Main findings – Compared with a conventional power system based on a 56kW Wankel engine, a 3.24% saving of the fuel mass burned throughout the mission was found (allowing a -3.25% in total emissions of CO2 and a 2.34% reduction of the cost-per-mission). Limitations and recommendations - The method is based on simplified models, in particular for the electric machine and the propeller. Moreover, the scaling method uses a limited database of Wankel engines that, unlike piston engines, are a technology not yet fully consolidated.