Cold-air Bypass Characterization for Fuel Cell Thermal Management in Fuel Cell Turbine Hybrids

International audienceThe effect of cathode airflow variation on the dynamics of a fuel cell gas turbine hybrid system was evaluated using a cyber-physical emulator. The coupling between cathode airflow and other parameters, such as turbine speed or pressure, was analyzed comparing the results at fixed and variable speed. In particular, attention was focused on the fuel cell temperatures, since cathode airflow is generally employed for thermal management of the stack. A significant difference was observed in the two cases in terms of turbine inlet, exhaust gas, cathode inlet, and average cell temperatures. When the turbine speed was held constant, a change in cathode airflow resulted in a strong variation in cathode inlet temperature, while average cell temperature was not significantly affected. The opposite behavior was observed at variable speed. The system dynamics were analyzed in details in order to explain this difference. Open loop response was analyzed in this work for its essential role in control systems development. But, the significant difference shown in this work proved that some trends are not adequately captured with a standard system identification procedure, because of the high coupling between turbine speed and cathode airflow. Cold air valve bypass position also showed a strong impact on surge margin in both cases