A comparison of power systems for autonomous underwater vehicles
Date
1992
Authors
Schubak, Gary E. (Gary Edward)
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Abstract
Autonomous underwater vehicles (AUV's) can provide operational advantages in comparison to other subsea work systems. One of the principal barriers to the market development of A UV 's has been the limited submerged endurance capability of lead-acid batteries. Recently, advanced battery systems, closed-cycle dynamic converters and Hr02 fuel cells have become available for subsea applications. These power systems can provide greater submerged endurance than can lead-acid batteries and consequently improve market opportunities for AUV's.
This thesis presents a techno-economic comparison of power systems for AUV applications. The power system technologies included within this study are the lead-acid battery, sodium-sulfur battery, solid polymer fuel cell and closed cycle diesel engine. A generic A UV is considered, which is common to all power systems and consistent throughout the analysis. The AUV application is described in terms of a parametric mission and life cycle. Power systems are evaluated by two criteria: 1) maximum submerged endurance and 2) life cycle cost. This thesis seeks categories of AUV applications for which each power system is preferred in terms of techno-economic performance.
The results show that the SPFC can provide measures of submerged endurance greater than all other power systems examined. This result is particularly strong for missions characterized by: 1) great depth, for which the high specific energy of liquid hydrogen storage is advantageous, and 2) high degree of part load operation, for which the SPFC benefits by its high part load efficiency. Consequently, despite its high present cost, the SPFC system has a market niche for long duration AUV missions, for which no other power system is technically feasible.
This thesis considers cost project ions for the power system technologies, allowing each to benefit from the economies of scale. The results show that each power system exhibits a characteristic domain of preference in terms of prescribed techno-economic criteria. The lead-acid battery is preferred in terms of life cycle cost for those AUV applications for which it is technically feasible. Nevertheless, it is restricted to extremely short mission durations by its inherent low energy density. The sodium-sulfur battery can provide roughly 2.5 times the submerged endurance capability of the lead-acid battery, and is preferred for short mission durations coupled with high peak power requirements. Beyond the performance envelope of advanced battery systems, and within its own domain of mission feasibility, the closed cycle diesel engine is typically preferred in terms of life cycle cost . Nevertheless, the ability of the solid polymer fuel cell to compete with the diesel engine in terms of cost in this domain increases with increasing mission duration and mission frequency. For high values of both, the solid polymer fuel cell can exhibit lower life cycle cost than the closed cycle diesel engine.
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UN SDG 12: Responsible Consumption and Production