Investigation of two anti-islanding methods in the multi-inverter case

As photovoltaic systems proliferate on grids, larger numbers of inverters will be interconnected with each other through their host utility. This becomes especially true if string inverters (SIs) or AC module ldquomicroinvertersrdquo are used. It will thus become increasingly important to ensure that the islanding detection methods used are effective in this so-called ldquomulti-inverter caserdquo. In this paper, two methods, one that uses classical controls concepts to obtain positive feedback (the dasiaclassical linear instability methodpsila, or CLIM), and a more recent method called the Sandia frequency shift (SFS) that applies positive feedback directly to the inverterpsilas output frequency, are investigated in multi-inverter use via MATLAB/Simulink simulation. The results indicate that the effectiveness of these two anti-islanding methods can depend on the number of inverters on the system, depending on the system configuration.