Experimental and theoretical evidence for control requirements in solid oxide fuel cell gas turbine hybrid systems

Hybrid fuel cell gas turbine sensitivity to ambient perturbations is analyzed using experimental and dynamic simulation results. Experimental data gathered from the world's first pressurized hybrid SOFC–GT system tested at the University of California, Irvine, capture performance variations due to diurnal temperature oscillations. A dynamic modeling methodology demonstrates accuracy, robustness, and clearly identifies critical system sensitivities that require additional control systems development. Simulation results compare favorably with dynamic experimental responses. Predictions of component temperatures, pressures, voltage and system power exhibited 5 °C, 2 kPa, 2 mV, and 0.5% error respectively. Moderate ambient temperature fluctuations, 15 °C, caused variations in stack temperature of 30 °C, and system power of 5 kW. Small to moderate changes in fuel composition produced 30 °C shifts in stack temperature and 25% changes in system power. Simple control loops manipulating fuel cell air flow through SOFC bypass and inlet temperature through recuperator bypass are shown to effectively mitigate internal temperature transients at the expense of reduced system output. The observed temperature fluctuations resulting from typical environmental perturbations are of concern for performance loss and diminished longevity. Experiments and dynamic simulation results indicate the importance of integrated control systems development for hybrid fuel cell gas turbine systems.

► A dynamic physical model was developed for a 220 kW hybrid SOFC/GT system.
► Measured responses to ambient temperature perturbation were well simulated by the model.
► Reasons for amplified thermal responses to diurnal temperature changes are discussed.
► Control strategies were developed and tested to show good mitigation of temperature excursions.
► Control strategies were also developed and tested to address potential variations in fuel composition.