Dynamic characteristics of an automotive fuel cell system for transitory load changes

A dynamic model of Polymer Electrolyte Membrane Fuel Cell (PEMFC) system is developed to investigate the behavior and transient response of a fuel cell system for automotive applications. Fuel cell dynamics are subjected to reactant flows, heat management and water transportation inside the fuel cell. Therefore, a control-oriented model has been devised in Aspen Plus Dynamics, which accommodates electrochemical, thermal, feed flow and water crossover models in addition to two-phase calculations at fuel cell electrodes. The model parameters have been adjusted specifically for a 21.2 kW Ballard stack. Controls for temperatures, pressures, reactant stoichiometry and flows are implemented to simulate the system behavior for different loads and operating conditions. Simulation results for transitory load variations are discussed. Cell voltage and system efficiency are influenced by current density and operating temperature as well. Together, air blower and radiator consume 10% of the stack power at steady-state; nevertheless their power consumption could reach 15% during load surges. Furthermore, water crossover in the fuel cell has shown a significant impact on anode inlet flows, humidity and recirculation pump during these load changes. Also, the amount of water saturation at cathode is found to be abruptly fluctuating and its removal from cathode is dependent on operating temperature and reactant stoichiometry.