An Anti-Islanding Protection Method Based on Reactive Power Injection and ROCOF

All distributed-generation units need to be equipped with an anti-islanding protection (AIP) scheme in order to avoid unintentional islanding. Unfortunately, most AIP methods fail to detect islanding if the demand in the islanded circuit matches the production in the island. Another concern is that many active AIP schemes cause power-quality problems. This paper proposes an AIP method which is based on the combination of a reactive power versus frequency droop and rate of change of frequency (ROCOF). The method is designed so that the injection of reactive power is of minor scale during normal operating conditions. Yet, the method can rapidly detect islanding which is verified by PSCAD/EMTDC simulations.