Mission-adaptive energy management for hybrid-electric distributed propulsion aircraft with in-flight recharging and asymmetric regeneration

This paper presents a mission-adaptive energy management framework for a series hybrid-electric distributed propulsion (DEP) system inspired by the NASA X-57 Maxwell aircraft. The framework combines nonlinear simulation models with mission-aware control to address energy efficiency, safety, and environmental performance across all flight phases. A derivative-based adaptive time-stepping scheme is embedded within the DEP simulation loop, enabling dynamic modulation of time-step resolution in response to evolving system dynamics and transient phase effects. By contracting time steps during high-rate events such as takeoff and climb and expanding them during steady cruise, the approach improves numerical stability and computational efficiency. Energy recovery and storage management are advanced through phase-specific strategies. During cruise, the framework proactively exploits turbine-generator headroom to inject surplus power whenever excess capacity exists, enforcing a predefined power margin and driving net charging until the state of charge (SOC) reaches 95%. Conversely, the system employs asymmetric regenerative braking by selectively reversing the cruise-tip motors, supporting sustained SOC preservation during these low-demand mission segments during descent and landing. For efficient power trade-offs, a multi-objective model predictive controller (MPC) dynamically allocates battery and turbine power across all flight phases, jointly optimizing performance, thermal constraints, and fuel consumption. Simulation results for a representative 0.38-h mission reveal detailed energy flows, phase-wise power allocation, battery thermal behavior, range, mission-average energy intensity, and emissions. With only 25 kg of fuel, the hybrid configuration achieves 6.5 times higher endurance (3.5 hr) and 6.4 times higher range (990 km) compared to pure-electric baselines. SAF variants deliver 97% of Jet-A performance while cutting CO₂ emissions by 70%, demonstrating near-carbon-neutral long-range capability with minimal performance penalty. The high-fidelity, open-architecture simulation platform bridges detailed aero-propulsive modeling with mission-level energy management and regenerative capability, facilitating rapid exploration of hybrid-electric DEP configurations, control strategies, and environmental trade-offs.