Modeling and Design of Islanding Detection Using Phase-Locked Loops in Three-Phase Grid-Interface Power Converters

摘要

Islanding detection is critical to safety and powerrnquality as well as the control mode of grid-interface powerrnconverters. This paper addresses the islanding-detection methodsrnon the basis of the grid synchronization instability mechanism.rnAlthough many modified phase-locked loop (PLL) methods havernbeen proposed to achieve islanding detection, the PLL modelingrnand design are not clear in the existing literature andrna cut-and-trail process is usually required during the designrnphase. This paper proposes a systematic PLL modeling andrndesign approach to evaluate different frequency-based islandingdetectionrnmethods. Two different types of PLL-based islandingdetectionrnsolution are discussed, accounting for a majority ofrnthe existing methods. The first method is to modify the PLL tornconstantly move the stable equilibrium point. The second methodrnis to modify the PLL small-signal characteristics to achieve arnmonotonic instability behavior under the islanded conditions.rnThe design procedures of these methods are presented using thernproposed PLL modeling approach. The impact of the modifiedrnPLLs to the converter’s operation is also analyzed.