Control of methanol fuelled HTPEM fuel cell system

Studenteropgave: Kandidatspeciale og HD afgangsprojekt

• Simon Lennart Sahlin
• Jesper Kjær Sørensen
2. semester, Elektromekanisk Systemdesign, Kandidat (Kandidatuddannelse)
This project investigates the efficiency of a methanol fuelled high temperature PEM fuel cell system. The system is created to run in two operation modes; startup mode and running mode. The purpose of the project is also to investigate a general control approach for the system, using a feedforward approach. The system contains an evaporator unit, a reformer and burner unit and a fuel cell stack. The system is modeled with the start up and a running stage. The start up stage uses pure methanol for the burner and convection is used for heating up the respective components of the system. The nonlinear model simulates the start up and the running stage. In the running stage the reformer unit is heated by burning the excess hydrogen from the fuel cell stack exhaust gas. The system reformer unit uses the endothermic steam reforming process and is heated directly by the burner. To obtain a constant stoichiometry for the hydrogen, in the exhaust gas, an estimator is presented. The estimator shows good theoretical results but has not been tested on a physical system. The feedforward approach is used in the system to feed the reactions happening in both the reformer and fuel cell stack. The electric efficiency for the system is calculated to approximately 18 % based on the higher heating value of methanol. The nonlinear model is converted to a linear model and is used for testing a PI-controller. The investigation of a fuel estimator, based on the current density, has been presented. To obtain a good set of controller parameters, a mathematical parameter search routine is presented in MatLab. Experimental work is presented to obtain knowledge about the hydrogen stoichiometry. The experiments are performed by simulating the fuel cell exhaust using a mass flow controller. The hydrogen needed, for keeping a constant reformer temperature, is found by varying the flow of hydrogen in the burner. The hydrogen stoichiometry is varied ,in the nonlinear model, until the model has the same amount of excess hydrogen as shown in the experiments.
Sprog Engelsk 2009 198 Aalborg Universitet
Emneord brændselscelle, Regulering
ID: 17642689