Current research into fuel cell technology is primarily focused on understanding the basic science and engineering of critical components of the fuel cell. Since fuel cell components are highly interactive and integrated by design, how these components are controlled during fuel cell operation is also of critical importance. This paper addresses control of a fuel cell system by first detailing the development of an integrated fuel cell system model consisting of fuel reformer and fuel cell stack subsystems. The subsystems are coupled by virtue of the fuel reformer producing the hydrogen required by the fuel cell stack, with the amount of hydrogen required varying with electric load demands on the fuel cell system. Constraints are also important to consider, as material properties and degradation issues limit the maximum practical subsystem temperatures and reaction kinetics limit the minimum subsystem temperature. The presence of constraints in a coupled multivariable system lead to the natural development of a model predictive control strategy. The development of a multiple model predictive control strategy is detailed, with a multiple model approach chosen to take advantage of the dynamic performance differences of the fuel reformer under varying load conditions. The strategy uses the fuel cell stack as a supervisory controller, feeding hydrogen flowrate setpoints to the fuel reformer. The fuel reformer then uses the steam to carbon ratio and natural gas flowrate to the fuel reformer to control the exiting hydrogen flowrate and fuel reformer temperature. Results are presented demonstrating how changes in electric load demand, and subsequent hydrogen demand on the fuel cell stack, impact the performance and control of the fuel reformer. Also investigated is the effect of fuel cell stack degradation on the fuel reformer, with the results illustrating how degradation in one subsystem impacts the performance and control of other fuel cell subsystems.

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