Modeling hybrid energy systems for use in AUVs

Specifying an energy source for an AUV is usually a compromise between performance and cost. For most vehicles and most missions, high specific energy primary lithium batteries are not a practical option due to cost. One solution that shows promise and affordable cost is to use a hybrid approach that combines low cost secondary batteries with a fuel cell or combustion energy source. Exploring the design space for these more complex energy systems requires suitable tools for modelling and assessment. One such tool is VirtualTest Bed. To build confidence in the tool, itssimulations have been assessed against experimentaldata for 18650 lithium ion cells and a Ballard fuel cell,with encouraging results. Subsequently, a conceptual design for a lithium ion battery and fuel cell hybrid energy source was modelled and the performance of two variants assessed for two different 7-day mission scenarios. In both cases, the hybrid system exhibited a specific energy comparable to primary lithium manganese dioxide batteries, with full account taken for the mass overhead of realistic reactant storage for the fuel cell.