Design of a Variable Geometry Turbine control strategy for Solid Oxide Fuel Cell and Gas Turbine hybrid systems

Solid Oxide Fuel Cell (SOFC) and Gas Turbine (GT) hybrid systems have been widely studied in recent years as a promising alternative power sources for various applications. The fundamental concept of this system is combining a GT with the SOFC system to recuperate the energy left in the SOFC exhaust, thereby improving the overall system efficiency. However, because of the coupling dynamics between SOFC and GT, the system is susceptible to shutdown in the case of an abrupt load change. This work investigates the use of the Variable Geometry Turbine (VGT) to address this shutdown problem and improve the transient system performance. A model of a 60-kW class SOFC/GT hybrid system is developed for the study. Based on the insights learned from the open-loop analysis, a feedback design is proposed for VGT control, analysis of transient dynamics for the closed-loop is performed, and simulation results demonstrating the performance are presented.