Temperature dynamics and control of fuel cell systems

In this thesis, a time-varying proportional-integral (PI) controller is designed for controlling the temperature of a water-cooled 5 kW hydrogen fuel cell stack. This controller is designed using a mathematical model for the stack temperature which is derived using basic chemical engineering material and energy balances. The controller affects the stack temperature by changing the flow rate of cooling water that passes across the stack. The model is then analyzed using a number of power demand profiles to determine the effectiveness of the controller. One of the most common forms of hydrogen production is reforming of hydrocarbons, so aspects of the reformer dynamics for steam reformation of ethanol are analyzed to determine how they might affect the controller for stack temperature. The results show that a time-varying PI controller is adequate for maintaining the stack temperature within 5 K of the target point.