Degradation-aware co-design and multi-level energy management of fuel cell–battery powertrains for hybrid-electric aircraft

Integrating proton exchange membrane fuel cell systems (PEMFCSs) with batteries can reduce aircraft emissions, but degradation must be addressed during design and operation. This study proposes a degradation-aware co-design framework determining the beginning-of-life PEMFCS rating to meet an end-of-life (EoL) power target, accounting for stack degradation, altitude-induced losses, and balance-of-plant (BoP) parasitic consumption. A multi-level control architecture is adopted, comprising a blended rule-based controller for mission power allocation and a low-level feedback controller linking BoL supervisory commands to stack operation. The latter adjusts the EoL stack operating point to compensate for voltage losses and reproduce the PEMFCS target power profile, while capturing increased BoP demand under higher-current and variable-altitude operation. For a 500 kW EoL target and 10% degradation, the rating is 626.89 kW, 14.6% above the healthy altitude-corrected design. Hydrogen consumption increases by 26.8% relative to healthy sea-level operation, while dynamic programming benchmarking supports the energy management strategy's effectiveness.