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Fuel Cells are electrochemical devices that convert the chemical energy of a gaseous fuel directly into electricity. They are widely regarded as a potential future stationary and mobile power source. The response of a fuel cell system depends on the air and hydrogen feed, flow and pressure regulation, and heat and water management. In this paper, we develop a dynamic model suitable for the control study of fuel cell systems. The transient phenomena captured in the model include the flow and inertia dynamics of the compressor, the manifold filling dynamics (both anode and cathode), reactant partial pressures, and membrane humidity. It is important to note, however, that the fuel cell stack temperature is treated as a parameter rather than a state variable of this model because of its long time constant. Limitations and several possible applications of this model are presented.

A nonlinear fuel cell system dynamic model that is suitable for control study is presented. The transient phenomena captured in the model include the flow characteristics and inertia dynamics of the compressor, the manifold filling dynamics, and consequently, the reactant partial pressures. Characterization of the Fuel Cell polarization curves based on time varying current, partial oxygen and hydrogen pressures, temperature, membrane hydration allows analysis and simulation of the transient fuel cell power generation. An observer based feedback and feedforward controller that manages the tradeoff between reduction of parasitic losses and fast fuel cell net power response during rapid current (load) demands is designed.

Fuel cell stack systems are under intensive development by several manufacturers since they complement heat engines and reduce the ubiquitous dependence on fossil fuels and thus have significant environmental and national security implications. To compete with ICE engines, however, fuel cell system must operate and function at least as well as conventional engines. Transient behavior is on of the key requirements for the success of fuel cell vehicles. The fuel cell system power response depends on the air and hydrogen feed, flow and pressure regulation, and heat and water management. During transient, the fuel cell stack control system is required to maintain optimal temperature, membrane hydration, and partial pressure of the reactants across the membrane in order to avoid degradation of the stack voltage, and thus, efficiency reduction. In this paper, we developed a fuel cell system dynamic model suitable for control study. The transient phenomena captured in the model include the flow characteristics and inertia dynamics of the compressor, the manifold filling dynamics (both anode and cathode), and consequently, the time-evolving reactant partial pressures, and membrane humidity. The effects of varying oxygen concentration and membrane humidity on the fuel cell voltage were included. Simulation results are presented to demonstrate the model capability.

Model-based control strategies are utilized to analyse and optimize the transient behaviour of a polymer electrolyte membrane (PEM) fuel cell system consisting of air and fuel supply subsystems, a perfect air/fuel humidifier and a fuel cell stack at constant fuel cell temperature. The model is used to analyse the control of the fuel cell system with respect to maintaining a necessary level of oxygen partial pressure in the cathode during abrupt changes in the current demanded by the user. Maintaining the oxygen partial pressure in the cathode is necessary to prevent short circuit and membrane damage. The results obtained indicate that the oxygen level in the cathode can be successfully maintained through feedforward 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 the use of a secondary power source such as a battery.