Improved Controller Performance of Selected Hybrid SOFC-GT Plant Signals Based on Practical Control Schemes

This paper compares and demonstrates the efficacy of implementing two practical single input single output multiloop control schemes on the dynamic performance of selected signals of a solid oxide fuel cell gas turbine (SOFC-GT) hybrid simulation facility. The hybrid plant located at the U.S. Department of Energy National Energy Technology Laboratory in Morgantown, WV is capable of simulating the interaction between a 350 kW solid oxide fuel cell and a 120 kW gas turbine using a hardware in the loop configuration. Previous studies have shown that the thermal management of coal based SOFC-GT hybrid systems is accomplished by the careful control of the cathode air stream within the fuel cell (FC). Decoupled centralized and dynamic decentralized control schemes are tested for one critical airflow bypass loop to regulate cathode FC airflow and modulation of turbine electric load to maintain synchronous turbine speed during system transients. Improvements to the studied multivariate architectures include: feed-forward control for disturbance rejection, antiwindup compensation for actuator saturation, gain scheduling for adaptive operation, bumpless transfer for manual to auto switching, and adequate filter design for the inclusion of derivative action. Controller gain tuning is accomplished by Skogestad’s internal model control tuning rules derived from empirical first order plus delay time transfer function models of the hybrid facility. Avoidance of strong input-output coupling interactions is achieved via relative gain array, Niederlinski index, and decomposed relative interaction analysis, following recent methodologies in proportional integral derivative control theory for multivariable processes.