Grid-Forming Control for Solid Oxide Fuel Cells in an Islanded Microgrid Using Maximum Power Point Estimation Method
Chao Shen, Wei Gu, Xia Shen
Abstract
Solid oxide fuel cells (SOFCs) are promising distributed generation technologies for their controllability and efficiency. Traditional SOFCs are controlled as a current source to deliver predefined power to the grid. Since a microgrid can operate in both grid-connected mode and islanded mode, grid-forming control ability is required for SOFCs to achieve voltage/ frequency regulation. However, when subjected to load transients, nonlinear output characteristics of SOFCs would probably lead to the collapse of dc-link voltage and unintentional disconnection of SOFCs. To deal with this issue, grid-forming control for SOFCs is presented considering nonlinear characteristics between output current and voltage. The maximum power point (MPP) of SOFCs is tracked using proposed incremental impedance (INI) method and dc-link voltage difference is delivered to adjust output frequency of ac side. In this condition, stable operation and load sharing can be achieved simultaneously during load transients. Simulation results based on PSCAD/EMTDC are provided to validate the effectiveness of proposed grid-forming control.