Hybrid fuel-cell auxiliary system for an aquaculture vessel

Abstract

Emission reduction in shipping and marine operations is important for the future of this planet and its oceans. This thesis looks into the operation of a hybrid fuel-cell power production system on an aquaculture vessel. The hybrid fuel-cell system uses a proton exchange membrane fuel-cell (PEMFC) for main power production and lithium-ion battery for energy storage, and will produce electrical energy for the vessel auxiliary systems. Fuel-cell and battery must cooperate to deliver the desired power levels, and an energy management system (EMS) is needed to set the operation point for both-fuel-cell and battery. The EMS will have a great effect in influencing the fuel economy, dynamic performance and service life for both fuel-cell and battery.

A simple model of a PEMFC and a lithium-ion battery is developed using \textit{Matlab} and \textit{Simulink}. The PEMFC operates on 65 degrees Celsius and pure hydrogen and air is pressurised to 3 bar, before fuelling the PEMFC. The fuel-cell compressor loads are estimated and added to the total loads. A simple lifetime prediction is also added for the battery. The models developed are simplified and only visualises how the power dynamics for a hybrid system would act during the given operation.

Two different energy management systems, a PI-controlled and a state-based EMS was developed and tested for the hybrid system. The PI-controlled EMS was set to control the battery state of charge (SOC) to a reference value of 70$\%$. The PI-controller sets the fuel-cell power output, while the battery takes care of the remaining/excess power. The state-based EMS is rule based, and consists of 11 states for optimal operation of both fuel-cell and battery. Battery SOC and load condition are used to decide at what state to operate the battery and fuel-cell.

Sizing of the fuel cell and battery was done during simulations. The resulting fuel-cell has a nominal power of 240 kW, while the battery has a maximum capacity of 238.97 kWh. Simulations was done for both EMS on the hybrid system and the results are presented in the report. Both EMS worked as intended, operating the fuel-cell at steady power levels, while the battery took care of the remaining/excess power. While the PI-controlled EMS gave a smoother operation of the fuel-cell, the state-based EMS gave better results regarding fuel consumption and battery cycling.