An islanding detection method based on measuring impedance at the point of common coupling

This paper develops an approach to islanding detection based on computing the frequency dependent impedance at the point of common coupling (PCC) that exploits the existing harmonics injected by the electric power system (EPS) and the harmonics injected by the distributed generator (DG). To this aim, a frequency dependent model is developed to characterize the change in the circuit interconnection topology, among the DG, the EPS, and the local load when the islanding occurs. The change in the topology of the system when the island occurs will result in a change in the impedance at the PCC. This approach may be used as a basis for selecting features from the impedance that distinguishes islanding from normal operation. The islanding condition can be detected when certain changes are detected in the measured impedance at different existing harmonics. A passive approach will be proposed based on monitoring how the impedance changes at the different harmonics. The approach uses the variation of the frequency dependent feature to characterize a non-detection zone (NDZ). Although the method is categorized as a passive islanding detection technique, it also can be applied as an active scheme where certain harmonics will be intentionally injected at the PCC rather than being inherent.