Stability Impacts of Sandia Frequency Shift Anti-Islanding on a Grid-Connected Inverter

The Sandia Frequency Shift (SFS) method of anti-islanding protection is considered to be the most effective scheme built into grid-connected inverters. What makes it so effective is the positive feedback loop that it creates when the inverter’s connection to the bulk power system is lost. However, this same positive feedback can have negative impacts on the stability of the inverter even when it is connected to the bulk power system. We were able to show that SFS can impact the small signal stability of a grid-connected inverter by impacting the system’s eigenvalues and can reduce the inverter’s power transfer stability limit. The extent of these impacts depends on the SFS formulation used and whether the inverter is connected to a "weak grid". This impact may be even greater in an intentionally islanded microgrid.