A novel anti-islanding protection method based on the combination of a Q-f droop and RPV

All distributed generating units need to be equipped with an anti-islanding (AI) protection scheme in order to avoid unintentional islanding. Unfortunately most AI methods fail to detect islanding when the islanded load matches with the production in the island. Another concerning issue is that certain active AI protection schemes may cause power quality problems. This paper proposes an AI protection method which is based on the combination of a specially designed reactive power versus frequency (Q-f) droop, and a constantly injected reactive power variation (RPV) pulse. The method is designed so that the injection of reactive power is of minor scale during normal operating conditions. Yet, the method shows high performance during islanding. Simulations were performed with the help of PSCAD/EMTDC in order to analyze the performance of the method. The results indicate that the method is able to detect islanding within 2 seconds even in a perfectly balanced island.