1. College of Electrical Engineering Yanshan University Qinhuangdao 066004 China; 2. Jiangsu Vocational College of Information Technology Wuxi 214153 China
Abstract：Islanding detection is an essential function of grid-connected inverters. Its basic requirement is to detect islanding state without non-detection zone (NDZ) within the specified time and minimize the impacts on power quality. With its unique advantages in rapid detection, high efficiency and no NDZ, the negative-sequence current perturbation method is widely used. However, because of the fluctuations arising from unbalance factor of grid voltage, the negative-sequence current perturbation method with positive feedback of unbalance factor will affect the symmetry of grid current. Thus, this paper proposes a novel islanding detection with nonlinear positive feedback, which injects less negative-sequence perturbation current. The feedback function is greater than the positive feedback threshold and is less than the restrictive value under the maximum unbalance factor of grid voltage. The proposed method can not only detect islanding successfully, but also quantitatively restrain the unbalance factor of grid current. Theoretical analysis, simulation and experimental results verify the correctness and feasibility of the method.
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2016, Vol. 31 
