A three-level hybrid islanding detection method for inverter-based DGs by using ROCOV, ROCOF, and voltage phase angle

This paper proposes a three-stage hybrid islanding detection method tailored for inverter-based distributed generation systems. In the first stage, the system passively monitors voltage deviations that may signal a power imbalance. If the rate of change of voltage (ROCOV) exceeds a predefined threshold, the second stage introduces a controlled disturbance into the inverter’s control loop, specifically phase-locked loop, within a targeted observation window. The third stage evaluates the rate of change of frequency (ROCOF) to determine whether the event indicates true islanding, a transient condition, or the need of an additional disturbance injection. The effectiveness of the controlled disturbances is rigorously assessed for reliable islanding detection. By limiting disturbance injections to brief periods following identified voltage or frequency anomalies, the proposed method minimizes adverse effects while progressively distinguishing between islanding and non-islanding events. Extensive validation under a broad spectrum of conditions, aligned with UL 1741 and related standards, demonstrates the method’s reliability, selectivity, and non-intrusive performance in various distributed generation scenarios.