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The mainly used local islanding detection methods may be classified as active and passive methods. Passive methods do not perturb the system but they have larger nondetection zones, whereas active methods have smaller nondetection zones but they perturb the system. In this paper, a new hybrid method is proposed to solve this problem. An over/undervoltage (passive method) has been used to initiate an undervoltage shift (active method), which changes the undervoltage shift of inverter, when the passive method cannot have a clear discrimination between islanding and other events in the system. Simulation results on MATLAB/SIMULINK show that over/undervoltage and undervoltage shifts of hybrid islanding detection method are very effective because they can determine anti-islanding condition very fast. ΔP/P > 38.41% could determine anti-islanding condition within 0.04 s; ΔP/P < −24.39% could determine anti-islanding condition within 0.04 s; −24.39% ≤ ΔP/P ≤ 38.41% could determine anti-islanding condition within 0.08 s. This method perturbed the system, only in the case of −24.39% ≤ ΔP/P ≤ 38.41% at which the control system of inverter injected a signal of undervoltage shift as necessary to check if the occurrence condition was an islanding condition or not.

Abstract-The objective of this paper is to investigate relationship between voltage and nondetection zone of OUV/OUF of local islanding detection techniques of distributed generation in electric power system network. This paper shows experimental results of inverter-based DG and synchronous-based DG with parallel RLC load that causes the most difficulty in detection. The experiments have shown that, case of inverter-based DG: variation of active power associated with variation of off-grid voltage at V PCC , case of synchronous-based DG: variation of off-grid voltage at V PCC was not associate with variation of active power but variation of off-grid voltage at V PCC associated with variation of reactive power. Nondetection zone of OUV of synchronous-based DG are very possibility that Q can more than -9.6 MVAR or Q can less than 3.6 MVAR which they can affect the V PCC to outside of normal voltage range when islanding condition is happen.

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