In this paper, an adaptive islanding detection method is presented. The technique is applied in inverter based distributed generation(DG) and relies on the change of active power reference (Pref) of DG in inverter control interface. Pref has a fixed value in normal condition(Pref0) and is determined as a piecewise linear function of voltage when voltage changes. The slope of Pref depends on the load active power(Pl) and is determined for each amount of load active power. In this algorithm, Pref is designed to decrease the voltage of the point of common coupling(PCC) and hence to decrease that of the DG active power generation(PDG) in islanding condition. Therefore, the method can be used for the case that the DG operates at its maximum power. The method does not have any harmful effects on the distribution system and is relatively fast. In the proposed method, the PCC voltage in islanding condition is always settled in a point that its voltage is less than the lower bound of under voltage relay(UVR) setting. The proposed method is evaluated on a grid connected DG system with local load using PSCAD/EMTDC software. Simulation results show that the method operates correctly in the islanding and non-islanding conditions.

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