Inter-city urban air mobility charging system design and operation: bi-level energy optimization framework with consumer demand flexibility

Low-altitude urban air mobility (UAM) provides emerging mobility solutions for consumer travel in smart cities. This paper addresses a new challenge of inter-city UAM with longer distances and higher energy requirements, posing critical challenges for energy-efficient and consumer-oriented smart city charging system. In inter-city UAM scenarios, charging system design and operation are characterized by high charging demand, strong spatiotemporal interactions, and strict service time constraints. To address these challenges, this paper proposes a bi-level energy optimization framework for UAM smart city charging system, explicitly accounting for coordinated charging strategies, photovoltaic (PV) generation uncertainty, and consumer-side demand flexibility. The upper-level design capacity planning minimizes annualized investment and operational cost via optimal sizing of PV generation, hydrogen fuel cell (FC), and energy storage system (ESS), and is solved using a modified Animated Oat Optimization Algorithm (MAOO) with chaotic initialization and t-distribution-based local search to address non-convexity and computational complexity. The lower-level co-optimizes energy dispatch and charging schedules by exploiting charging window flexibility and consumer-side demand flexibility, and is formulated as a mixed-integer linear programming (MILP) problem. The coordinated solution algorithm enables iterative solutions of optimal capacity planning and energy dispatch. Simulation results demonstrate that the proposed UAM energy system charging strategy reduces peak charging demand by 40% compared to uncoordinated charging method, lowers total system cost by 16%, and significantly reduces distributed resource capacity. The proposed load shifting mechanism further enables grid supply reduction under emergency conditions by adjusting UAM travel schedules with delay compensation. These results highlight the importance of renewable energy integration and consumer demand flexibility in enabling cost-effective and consumer-centric UAM charging system in smart cities.