Analysis of load-induced unintentional islanding in Low Voltage grids with PV generators

The interest of unintentional islanding operation has recently grown in Low Voltage (LV) distribution grids because of the large penetration of Distributed Energy Resources (DERs), especially the ones based on the PhotoVoltaic (PV) energy source. The probability of unintentional islanding is increased also due to the newly introduced standards with extended frequency and voltage limits before the PV protection trips and due to the large number of PV generators, which can make ineffective the anti-islanding provisions each PV is equipped with. Moreover, interconnection standards of DERs require some additional grid support functions, such as active and reactive power regulation using P/f and Q/V droop characteristics, which can further increase the probability of unintentional islanding. In this paper, an analysis of this phenomena is provided using a simplified static and dynamic 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.