Microgrid Adaptive Protection: Decentralised Hybrid Schemes for Islanding Detection

Passive schemes for islanding detection and adaptive protection offer potential benefits due to their simplicity and cost-effectiveness. However, these schemes have limitations in accuracy. Moreover, most were developed and tested in a grid dominated by inverter interfaced-renewable (IBRs), without adequately considering the substantial presence of emerging technologies like grid-forming (GFM) type of distributed generations (DGs). This paper comprehensively evaluates the performance of passive islanding detection schemes in a future grid with GFM DGs, using three indices, namely, rate of change of frequency (RoCoF), rate of change of voltage (RoCoV), and rate of change of phase angle (RoCoPA). The analysis highlights the performance limitations of individual passive schemes. To address these limitations, two hybrid schemes are proposed: one that uses a traditional approach for combining the three passive methods with AND-logic and another that computes a new composite index derived from the three indices. While both schemes are found to be effective, the composite index-based hybrid scheme demonstrates superior performance and a smaller non-detection zone (NDZ). Extensive testing is conducted in DIgSILENT PowerFactory software for various practical scenarios to assess the performance of the individual and proposed hybrid islanding detection schemes, confirming the superior performance of the later.