Dynamic Behavior and Control of a Tubular Solid-Oxide Fuel Cell System

A dynamic compartmental model based on first principles is developed for a tubular solid oxide fuel cell system. The model accounts for diffusion processes, inherent impedance, transport (heat and mass transfer) processes, electrochemical processes, anode and cathode activation polarizations, and internal reforming/shifting reactions, among others. Dynamic outlet voltage, current and fuel-cell-tube temperature responses of the cell to step changes in external load resistance and conditions of feed streams are presented. Simulation results show that the fuel cell is a multi-time-scale system; some of the cell output responses exhibit consecutive apparent dominant time constants ranging from about 0.2 ms to about 40 s. They also reveal that the temperature and pressure of the inlet air stream and the temperature of the inlet fuel stream strongly affect the dynamics of the fuel cell system. A simple control system is then implemented to control the fuel cell outlet voltage and cell-tube temperature. The results show that the control system can successfully reject unmeasured step changes (disturbances) in the load resistance, the velocity of the inlet air stream, and the pressure, temperature and velocity of the inlet fuel stream.