On dynamic operation modes of fuel cell: A comparison between the single-loop and multi-loop controls

Solid Oxide Fuel Cell (SOFC) is a promising alternative in power generation due to its reliable, efficient, and pollution free characteristics. However, the existing operation modes proposed for the SOFC dynamic control remain inconsistent and even conflicting. To this end, this paper compares the existing control schemes, detailing the merits and deficiencies, respectively. The dynamic model of a tubular SOFC is developed by formulating the disturbance input as load resistance instead of the load current, because the load current is coupled with the voltage during the transient. Different operation modes, i.e., constant fuel flow, constant fuel utilization, and constant voltage operation, are respectively investigated under load fluctuation. Simulation results show that constant fuel flow is advantageous in terms of simplicity; constant fuel utilization is superior in terms of efficiency; constant voltage operation will ease the necessity of using a converter. Finally, based on the nonlinearity, pairing, and coupling analyses, a multivariable operation strategy is explored to maintain fuel utilization and terminal voltage, simultaneously. The results show that this proposed operation strategy is able to achieve the merits of both the constant fuel utilization and constant voltage operation.