Study on energy storage configurations and energy management strategy of an underwater hydrogen hybrid system

Enhancing the durability of unmanned underwater vehicles (UUVs) would facilitate maritime research, and hydrogen fuel cells are considered a feasible solution. In this paper, based on an underwater hydrogen hybrid system mainly driven by a hydrogen-air fuel cell stack and a battery, the energy management strategy and energy storage are investigated to enhance the endurance of UUV. The results exhibit that the proposed energy management strategy integrating equivalent hydrogen consumption minimization strategy with rule-based strategy (ECMS-RB strategy), effectively reduces fuel cell power fluctuations. It is noted that, this strategy increases the state of charge (SOC) of the battery by approximately 0.2 and prevents battery over-discharge, compared to the conventional state machine strategy under identical boundary conditions. Additionally, this paper compares the performance of energy storage systems and their coupling design with UUV. The results suggest that liquid hydrogen-liquid oxygen and metal hydride energy storage systems are preferable for UVVs to achieve neutral buoyancy. Under low-speed navigation conditions, increasing the UUV length from 1.5 m to 5.5 m enhances its endurance capability by a factor of 1.78, and raising the outer diameter from 0.1 m to 0.4 m increases the endurance capability by a factor of 5.44.