Control of the transient behaviour of polymer electrolyte membrane fuel cell systems

The transient behaviour of a polymer electrolyte membrane fuel cell (PEMFC) system following abrupt changes in the stack current is analysed using a non-linear dynamic, control-oriented computer model. Such changes in the stack current are associated with the abrupt changes in power demanded by a Vehicle powered by the fuel cell system. The PEMFC system analysed consists of air and fuel supply subsystems, a perfect air/fuel humidifier, and a fuel cell stack, and is assumed to operate under a constant fuel cell temperature. The model is next used to develop a feedback control scheme to regulate the transient behaviour of the PEMFC system with respect to maintaining the necessary level of the oxygen partial pressure in the cathode following abrupt changes in the stack current demanded by the user. Maintaining the level of oxygen in the cathode is critical to prevent short circuit and membrane damage. The results obtained indicate that the oxygen level in the cathode can be successfully maintained using a feedback control of the air-compressor-motor voltage. However, the net power provided by the fuel cell system is compromised during the transients following abrupt changes in the stack current, suggesting a need for power management via a secondary power source, such as an electric battery.