Efficient Maximum Power Point Tracking and Battery Charging for an Underwater Thermoelectric Generator

A thermoelectric power generation system was developed to extend the mission time of an unmanned underwater vehicle. Thermoelectrics are used to convert available heat into electricity, which is then used to charge a lithium-ion (LiIon) battery. The proof-of-concept system uses free convection over a heat sink to reject heat to the surrounding water. The battery charging circuit developed includes an integrated maximum power point tracker (MPPT) and protection against battery overheating. The MPPT/charging circuit uses a ZETA converter topology. The tested efficiency of the converter is 47%, which is poor, but the overall heat conversion efficiency of the system is 3.5%, which compares favorably to other thermoelectric power generation systems. The proposed system used a novel electrical and mechanical approach to investigate the application of thermoelectric systems in an unusual, underwater environment. Improvements to the electrical design are suggested. The maximum power point tracking circuit developed may be applicable to a wide range of small-scale generators if the efficiency can be improved.