Modeling and Control of the Fuel Supply System in a Polymer Electrolyte Membrane Fuel Cell

Prolonging membrane longevity as well as improving fuel economy are essential steps toward utilization of fuel cells in industrial applications. Focusing on polymer electrolyte membrane (PEM) fuel cells, the present work elucidates a systematic approach to deal with cell durability issues, inflicted by membrane pinholes. This includes the model-based control of fuel overpressure, which is defined as the pressure difference between the anode and cathode compartments, at the inlet side of the fuel cell stack. Moreover, to enhance fuel savings, this work proposes a novel model-based technique for estimation of hydrogen concentration, which is used as the basis of fuel purging control. Employing a Ballard 3kW test station equipped with a 9-cell Mk1100 PEM fuel cell, the entire system is modeled using pneumatic variables. The developed model is experimentally validated. Depending on the underlying objective, a relevant system configuration for the PEM fuel cell anode is adopted. These include a flow-through anode, dead-ended anode, and anode with recirculation structures. A model predictive controller (MPC) is deployed to achieve the controller objectives, which include the improvement in control of the system transient response during the load change, reduction of hydrogen emission, and retaining the cell voltage level of a defective cell, by maintaining the fuel overpressure in the desired region. Furthermore, the controller performance is verified experimentally. Using the pressure drop across the fuel cell stack anode, the hydrogen concentration on the anode side is estimated in a hydrogen-nitrogen gas mixture. This pressure drop is correlated to the dynamic viscosity of a gas mixture. The estimation model which is verified experimentally for various scenarios provides a reliable and cost-effective method that can eliminate the use of the hydrogen sensor. This model is then utilized as the basis for controlling the fuel purging. Deploying an MPC based multivariable control strategy, both fuel overpressure and hydrogen concentration are controlled.