Reduced-order dynamic model of carbonate fuel cell system for distributed generation control

Internally reformed carbonate fuel cell-based power plants have the capability of rapid load cycling provided that operational constraints are met during load perturbations. These constraints include acceptable deviations in stack temperature and stack pressure, both of which exhibit slow dynamics due to a large stack thermal time constant. Fuel cell stack dynamics exhibit multi-time scale behavior, however, when considering fast electrochemical reactions that occur. Therefore, in grid transient studies involving fuel cells, the slower dynamics can be neglected. This results in a simpler, reduced-order dynamic model. In this paper we present a complete model for direct reforming carbonate fuel cell stack and then simplify the equation set under the condition of constant temperature. A comparison is made between the full order model and reduced-order model by examining gas composition and system DC voltage under a severe transient.