Frequency fuzzy anti-islanding for grid-connected and islanding operation in distributed generation systems

This study proposes an islanding detection method for distributed generation systems, namely frequency fuzzy positive feedback (FFPF).The goal is to reduce the injection of disturbances, from the anti-islanding methods, during the grid-connected operation, as well as standardise the PF gain, with no adjustments needed according to the type of loads. This method is designed from fuzzy inference rules and two inputs are also considered in the design procedure. Since the classical active methods do not identify whether the frequency variation arises from the islanding condition or from a power quality issue in the grid, the fuzzy PF enables the proposed method to differentiate the islanding condition from other grid events. In contrast to classical methods that have a fixed PF gain, a dynamic fuzzy gain that adapts to any type of load is obtained by means of the fuzzy inference rules. The classical active technique is compared with the proposed approach in terms of detection time and injected disturbances during the grid-connected operation. The simulation and experimental results are presented to demonstrate the effectiveness of the proposed approach.