Innovative power system for autonomous underwater vehicle

The present paper proposes a study for the integration of a hybrid power system composed by rechargeable batteries and fuel cells with chemical gas storages for an Autonomous Underwater Vehicle (AUV) or Unmanned Undersea Vehicles (UUV). AUVs and UUVs are vehicles that are primarily used to accomplish oceanographic research data collection and auxiliary offshore tasks. At the present time they are usually powered by lithium-ion secondary batteries, which have insufficient specific energy. In order to enhance the usage of these vehicles and to exploit their capabilities an increased endurance is required. Fuel Cell Energy Power Systems (FCEPS) have been identified as an effective means to achieve this endurance[1]. From literature it could be found that the present technology to power AUV is based on rechargeable batteries implemented with some form of battery management system. In order to improve the autonomy of the vehicles different technologies should be used. The state of the art is represented by the HUGIN AUV[2]. This vehicle is powered by a Alkaline Aluminium/Hydrogen peroxide semi-fuel cell. This paper will present an alternative power generation system based on a Proton Exchange Membrane (PEM) fuel cell fed by pure hydrogen and oxygen produced by a replaceable chemical storage for AUV. A technical sizing of the system has been done, supported by an analysis of the performance of the considered technologies. Standard AUV-UUV works on daily operational profile and thus have about 24h of autonomy. FCEPS for UUV requires particular characteristics of the vehicle to be installed and exploited. Starting from a statistical assessment of the existing UUVs for military and civil application an analysis of the most suitable dimensions, form and weight of the vehicle has been done together with an assessment of the requirements for different operative conditions in order to identify the most profitable target parameters for a future market development of this technology. The analysis of the application of an innovative hydrogen storage technology based on aluminium-water reaction is introduced for the first time. The study consider the performances of the system developed by the Technion Institute of Haifa (Israel), and present an evaluation of the theoretical achievable performance of the storage system and it's exploitation for particular matching with the Fuel Cell System (FCS). An assessment of the performance of the FCEPS, that consider the combination of FCS and storage system, has been done through the procedure proposed by Davis and More[3] considering the best oxygen storage system and the best FCS. This procedure has been developed for the application of FCEPS on UUVs and gives the methodology to calculate key parameters that permit the comparison between different systems. Moreover this method has been also used by other researchers and today it's available a wide database of systems performances available.