This study is based on a complete hybrid system emulator test rig developed at the University of Genoa (Savona laboratory) by the Thermochemical Power Group (TPG). The plant is mainly composed of a 100 kW recuperated micro gas turbine coupled with both anodic and cathodic vessels for high temperature fuel cell emulation. The test rig was recently equipped with a real-time model for emulating components not physically present in the laboratory (SOFC block, reformer, anodic circuit, off-gas burner, cathodic blower). This model is used to fully evaluate thermodynamic and electrochemical performance related to solid oxide fuel cell systems. Using a UDP based connection with the test rig control and acquisition software, it generates a real-time hardware-in-the-loop (HIL) facility for hybrid system emulation. Temperature, pressure and air mass flow rate at the recuperator outlet (downstream of the compressor) and rotational speed of the machine are inputs from the plant to the model. The turbine outlet temperature (TOT) calculated by the model is fed into the machine control system and the turbine electric load is moved to match the model TOT values.
In this study various tests were carried out to characterize the interaction between the experimental plant and the real-time model; double step and double ramp tests of current and fuel provided the dynamic response of the system.
The control system proved to be fast, compared to the slow thermal response of the SOFC stack, and also reliable. The hybrid systems operated at 90% of nominal power with electrical efficiency of about 56% based on natural gas LHV.