Islanding Detection In Grid-Connected Inverter-Based Systems Using Synchro-Waveform Measurements

This paper presents a passive islanding detection method for grid-connected inverter-based system (IBS), leveraging synchro-waveform measurements. The proposed approach continuously monitors three-phase voltage and current signals at the point of common coupling (PCC) using a waveform measurement unit (WMU). A theoretical threshold is derived to represent the maximum permissible variation between consecutive samples of a sinusoidal waveform under normal grid-connected conditions. An islanding event is detected when the measured voltage variation exceeds this threshold. The method is validated through simulations of a photovoltaic (PV) plant connected to the IEEE 9-bus test system using the Hypersim real-time simulator. Results demonstrate reliable islanding detection in approximately 0.1 ms while remaining robust under large load variations and nonislanding disturbances. Unlike traditional RMS-based techniques, the proposed method exploits instantaneous waveform dynamics, enabling detection under challenging power balance conditions associated with the non-detection zone (NDZ). Since the technique does not rely on external perturbations or communication channels, it introduces no power quality degradation and is suitable for near real-time implementation in modern distributed inverterbased power systems.