Dynamics of a Microgrid Supplied by Solid Oxide Fuel Cells,” iREP Symposium

Abstract — The paper presents a model for a solid oxide fuel cell (SOFC) stack operating at relatively low pressures. The model in-corporates the electrochemical reaction dynamics and the major voltage losses in SOFCs, but is not concerned with the thermal dynamics. A DC-DC boost converter interfaces the SOFC stack to a DC bus, where an ultra-capacitor provides energy storage. The paper presents a control system for the converter which regulates the DC-bus voltage along with the fuel cell current. A control strategy is proposed for the inverter that interfaces the SOFC plant to the AC grid. The controller regulates the grid-side voltage and the active power delivered to the grid, and takes into account the phase-locked loop (PLL) dynamics. The results of an example in which two SOFC plants provide power to a microgrid are presented. The simulation includes disconnection from the main grid, autonomous operation, and re-synchronization with the main grid