Hybrid Fuel Cell/Battery Power System for a Lower Limb Assistive Exoskeleton: A First‐Order Sizing Assessment

ABSTRACT

This study evaluates the feasibility of a hybrid hydrogen fuel cell–battery power supply for lower limb assistive exoskeletons. The objective is to determine whether this architecture can provide a realistic alternative to conventional lithium‐ion batteries in terms of autonomy, mass, and responsiveness to dynamic loads. Starting from a gait‐cycle power profile, the electrical demand of a six‐joint exoskeleton is estimated for a reference scenario of 10 000 assisted steps per day, corresponding to approximately 170 Wh. A battery‐only configuration and a hybrid fuel cell–battery system are then sized and compared at first‐order system‐level. The results indicate that, under the current technological assumptions, the hybrid configuration is heavier than the battery‐only solution while providing a lower driving range, demonstrating that it offers no practical advantage. A sensitivity analysis identifies gravimetric hydrogen storage capacity as the dominant parameter affecting system performance, whereas improvements in fuel cell stack specific power have a more limited effect. Increasing the storage capacity of the selected metal‐hydride system from 1.5 to 3 wt% would substantially reduce total mass and increase specific energy, making hybrid architectures more competitive for wearable robotics.