Stack Level Modeling and Validation of Low Temperature Fuel Cells andSystems for Active Water Management.

Fuel Cell;Modeling;Dynamics;Humidification;Membrane;Control;Civil and Environmental Engineering;Engineering;Environmental Engineering

McKay, Denise A.Lastoskie, Christian M. ;

University of Michigan

关键词: Fuel Cell;    Modeling;    Dynamics;    Humidification;    Membrane;    Control;    Civil and Environmental Engineering;    Engineering;    Environmental Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/58400/dmckay_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Fuel cells are gaining increased attention as viable energy generators for a range of applications. To optimize performance, these systems require active coordination leveraging an understanding of the system dynamics. This thesis describes a reproducible process for modeling, calibrating, and experimentally validating system dynamics for control applications, applied to two membrane-based systems, namely a proton exchange membrane fuel cell (PEMFC) stack and a gas humidification system.A two-phase dynamic model that predicts the experimentally observed temporal behavior of a PEMFC stack and a methodology to experimentally identify tunable physical parameters, namely the membrane water vapor diffusion coefficient and the thickness of the liquid water film restricting the fuel cell active area, is presented. The temporal calculation of the species concentrations throughthe gas diffusion layers, the water vapor transport through the membrane, and the degree of water flooding in the gas channels, enables a prediction of temporal voltage degradation. The calibrated model is validated under anode flooding conditions for a 24 cell, 300 cm2 stack with a supply of pressure-regulated hydrogen.To regulate the humidity of the supplied reactants to actively manage water within the PEMFC, a membrane based gas humidification system is designed and constructed. This apparatus utilizes a gas bypass and a series ofeaters to regulate gas temperature while maintaining the desired relative humidity of the gas supplied to the PEMFC. To design and calibrate the heater controllers, as well as the fraction of air diverted through the bypass, a low order, control-oriented model based on first principles is developed. As with the fuel cell model, the humidification system model is parameterized and validated using experimental data under a wide range of operating conditions. A relative humidity estimator is employed, for the air-vapor mixture leaving the humidifier system (supplied to the PEMFC), to eliminate the need for a bulky and expensive humidity sensor. With this validated model of the humidification system thermal dynamics, on/off and variable heat controllers are designed and tested for accurate and fast humidity control despite changes in the PEMFC air mass flow rate due to load disturbances.