Implementation of Islanding Detection Using Phase-Locked Loops in Three-Phase Electrical Grid-Interface Power Convertors

Abstract

In order to encounter the necessities for gridinterconnection, it is essential that the control of DistributedPower Generation systems (DPGSs) should be improved.Therefore, grid synchronization algorithms play a vital rolefor Distributed Power Generation Systems (DPGSs).Phase locked loop and synchronization techniques are one of the most important issues for operating grid-interfaced converters inpractical applications, which involve Distributed Power Generation Systems, Flexible AC Transmission Systems (FACTS), and High Voltage DirectCurrent (HVDC) Transmission, and so on.This paper proposes a systematic PLL modeling anddesign approach to evaluate different frequency-based islandingdetection methods. Two different types of PLL-based islandingdetection solution are discussed, accounting for a majority ofthe existing methods. The first method is to modify the PLL toconstantly move the stable equilibrium point. The second methodis to modify the PLL small-signal characteristics to achieve amonotonic instability behavior under the islanded conditions.The design procedures of these methods are presented using theproposed PLL modeling approach.