A nonlinear observer for PEM fuel cell system

In this paper, a model-based robust observer is designed for the estimation of oxidizer mass flow rate of fuel cell system (FCS). The mass flow rates of reactant gases play a pivotal role in the reliable and efficient operation of FCS. Their precise and exact estimation is necessary and important for control and diagnostics of FCS. In the particular sense of inlet manifold of fuel cell system, appropriate air mass flow is very critical for proper maintenance of chemical reactions in the cathode and anode chambers. In the model, air mass flow rate is calculated by the product of proportionality parameter with pressure difference at up/down streams of air inlet manifold using linearized nozzle flow equation. The proportionality parameter is generally measured through extensive experimentations on the system by developing relationship between mass flow rate and pressure difference. The sliding mode techniques are employed for the design of observer to estimate the proportionality parameter. The estimates are quite similar to nominal values. The simulation results show robustness and fast convergence of observer estimates to nominal value of the parameter. The observer can replace the mass flow sensor which results in rid of expensive and hard instrumentation for measurement of mass flow rate.