Sandia frequency shift parameter selection for multi-inverter systems to eliminate non-detection zone

Among frequency drift islanding detection methods, Sandia frequency shift (SFS) is considered as one of the most effective methods in detecting islanding conditions for grid connected photovoltaic (PV) inverters. The performance of the SFS method during an islanding condition and its non-detection zone (NDZ) depends to a great extent on its parameters. Furthermore, the capability of the SFS method to detect an islanding condition deteriorates with multiple PV inverters. A mathematical formula is derived to aid protection engineers in determining the optimal setting of the SFS islanding detection parameters with multiple inverter-based distributed generation (DG), such as PV systems, to eliminate the NDZ. The derived formula is applied to multiple DG systems equipped with the over frequency/under frequency protection, active frequency drift and SFS islanding detection methods and is verified through NDZ analysis and simulation results on PSCAD/EMTDC. The derived formula provides an effective guideline for designing frequency drift methods in multi-inverter-based DG systems.