This paper reports the results of an experimental investigation of two-by-two scenario of a multi-input multi-output (MIMO) control strategy for a direct-fired fuel cell turbine hybrid power system using the Hyper facility at the National Energy Technology Laboratory. Real-time control architecture was used to control the interaction between a virtual fuel cell model and a gas turbine recuperated cycle. Specifically, the gas turbine electric load was used to control the turbine speed, and the cold air and/or hot air bypass valves were used to control the airflow to the cathode of a fuel cell. The transient variation of the waste heat during fuel cell operation provided the primary challenge in terms of control or disturbance rejection for a gas turbine in the hybrid configuration. It was found that the strong coupling in the system due to actuator operability creates critical issues in terms of control. During fuel valve perturbation, the system performed well in terms of the deviation of the turbine speed and the cathode airflow from the nominal operating points. However, a critical oscillation on the turbine shaft during transient operations explicitly illustrated critical instabilities in the system and demonstrated the need for development of a more robust design for MIMO controllers for application in advanced power systems.
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