Instability criterion to eliminate the Non-Detection Zone of the Sandia Frequency Shift method

Sandia frequency shift (SFS) islanding detection method is considered amongst the most efficient islanding detection methods that possesses small non-detection zone (NDZ) for inverter based distributed generation (DG). The NDZ of the SFS depends to a great extent on its design parameters. In this paper, the SFS parameters are determined through an instability criterion to guarantee negligible NDZ for the different loading conditions. The optimal SFS setting is calculated by setting the phase angle - frequency curve slope of the inverter to be greater than the slope of all expected island loads. A non-linear optimization program is formulated on GAMS to calculate the SFS parameters. The analytical results are verified through digital simulation on PSCAD/EMTDC.