Analysis of ΔP-ΔQ area of uncontrolled islanding in low voltage grids with PV generators

The large penetration of Distributed Energy Resources (DERs), especially PhotoVoltaic (PV), in Low Voltage (LV) distribution grids has raised the concern of unintentional islanding operations. The probability of unintentional islanding is increased due to the newly introduced standards with extended frequency and voltage thresholds and additional grid support functions, such as active and reactive power regulation using P/f and Q/V droop characteristics, which can make ineffective the anti-islanding provisions each PV is equipped with. Moreover, islanding operation due to faulty events at the Medium Voltage (MV) distribution level may be dangerous in presence of automatic reclosing procedure leading to out of phase reconnections. In this paper, an analysis of this phenomena is provided using a simplified characterization of the generators and the loads. Simulation results based on Matlab and DIgSILENT tools on a simplified LV distribution network are reported together with preliminary experimental results on a lab-scale prototype.