A Novel Active Anti-Islanding Protection Scheme for Grid-Interactive Roof-Top Solar PV Systems

The rising popularity of renewable resources has resulted in increased penetration levels of Distributed Generation (DG) into the utility grid. Unintentional islanding is one of the most important safety concerns associated with grid connected roof-top solar Photovoltaic (PV) systems. The occurrence of islanding can be fatal to utility workers who may not realize that the local area is still powered and encounter severe electric shock. For this reason, DG must be equipped to detect islanding and isolate itself from the grid immediately,

which is commonly referred to as anti-islanding. In conventional systems, there exists a scenario in which exact balance of PV generation and load would result in failure of passive anti-islanding schemes. This problem if rectified by changing the limits of Overvoltage/Undervoltage (OV/UV) and verfrequency/Underfrequency (OF/UF) relay, would result in nuisance tripping which causes further malfunction of the protection system. This thesis work proposes a novel active anti-islanding scheme for inverter fed roof-top solar PV generation connected to Low Tension (LT) distribution grid with unbalanced

non-linear loads. The method is based on creating a perturbation in the system using positive feedback and d-q implementation algorithm. The conventional passive schemes fail to detect islanding during power balancing conditions, but the novel active anti-islanding controller ensures that the voltage (or frequency) at the point of common coupling (PCC) is automatically driven beyond the threshold preset values. This proposed scheme has been tested in the presence of non-linear loads and development has found faster

islanding detection compared to the existing methods. Further, the islanding conditions are simulated and accurately verified on real time.