Optimal design of series-hybrid electric system for unmanned convertiplane

A new method is proposed, for the optimal design of Series-Hybrid Electric System (S-HES) equipped on the unmanned convertiplane, to cope with the special power demand of this type of new aircraft. The method includes multiple physical and mathematical models to describe the characters of convertiplane's S-HES, such as the power requirement solving model in rotor, fixed-wing, and transition modes, the hybrid power solving model based on S-HES structures, and the battery mass sizing equation considering the power constraint, energy constraint, and battery charging. The mass sizing equations of other S-HES components are also established on large amounts of statistical data, and a fuel consumption analysis model considering the engine operating point variation is built based on the Willans line method. Based on the above physical and mathematical models, the hybrid control parameter optimization is carried out at each flight stage in the flight profile using the Cauchy mutation particle swarm optimization algorithm, and thus the top-level aircraft design demand can be translated into the optimal operating strategies, design power, and mass distribution scheme of S-HES. The proposed method was verified in urban freight and mountain freight application scenarios. The results reveal that the adjustment of the mission profile of the unmanned convertiplane and the performance requirement changes at each flight stage have an important impact on the final optimal S-HES design results, and the proposed method can well capture the impact and has good adaptability to various application scenarios of unmanned convertiplane.