PEMFC-Based Energy System For Underwater Gliders Propelled By Thermal Engine

Underwater gliders have a great potential in ocean observation in that low energyconsumption is required for a relatively long cruising range. Thermal gliders are atype of underwater gilders that are propelled by ocean thermal energy. They haveoutstanding advantages in cruising range and endurance and have become one of thetendencies in the technology of underwater glider. However, thermal gliders cannot berandomly used due to the low temperature gradient and the unstable heat source in theocean. In addition, the fluctuating power consumption caused by the intermittentshifting between diving and surfacing requires a high power output of the powersystem. In this dissertation, a PUTE (PEMFC-UC-Thermal Engine) energy system forthe thermal glider is presented to overcome the limit of ocean thermal energy supplybased on working characteristics of the proton exchange membrane fuel cell (PEMFC)and the energy storage capacity of the ultracapacitor (UC). The idea of heat andelectricity supply system is proposed and developed in detail. Theoretical analysis,systematic design, and physical experiments were performed on the PUTE energysystem. The main contributions of this dissertation are summarized as follows:The idea of PUTE heat and electricity supply system has been proposed based onthe heat and electricity requirement of the thermal glider. Electricity for measurementand control units are provided by the PEMFCs in the energy system, while the extra isstored in the UCs as the driven power for pulsing loads, such as solenoid valves andmotors. The reaction heat of the PEMFCs serves as the heat source of the thermalengine, making it possible for the thermal glider to be used in worldwide ocean and toextend the cruising range and endurance.The thermal energy requirement model and the electricity requirement modelhave been developed respectively according to the operational principle of the thermalengine and the operation mode of the onboard loads. A case study has been conductedon the thermal glider (THERMAL) developed by our laboratory. The total energyconsumption, as well as the heat and electrical power requirement curves have beenobtained for predetermined navigation parameters.Take THERMAL as an example, an evaluate method has been proposed forapplicability of the PEMFC-UC hybrid power scheme. The central idea of the method is to reach a match between heat and electricity demand. The heat-to-electricity ratiosneeded by the thermal glider under different navigation conditions have been obtainedin accordance with the operational parameters. Applicability of the PEMFC-UChybrid power system under various navigation conditions has also been obtainedaccording to the available heat-to-electricity ratio of the PEMFCs.The PUTE energy system has been designed for THERMAL according to theheat and electricity demand of the thermal glider. Thermodynamic model has beenestablished for the PUTE energy system. Thermodynamic analysis and optimizationfor the energy system have also been performed. The overall efficiency of PUTE isdescribed based on the thermodynamics analysis using mass balance and energybalance equations.A prototype of the PUTE energy systems has been developed. Experimentalstudies on the prototype show that the thermal engine can be reliably driven by thePEMFCs in the energy system and that the performance of the thermal engine can beeffectively improved. Experimental results also indicate that the UCs that act as theenergy storage unit in the energy system can provide the required power for pulsingloads. The proposed PUTE energy system is validated to meet the energy and powerdemands of the thermal glider.