Unplanned islanding detection of renewable energy sources using sequence impedance with zero NDZ

Unintentional islanding, defined as the inadvertent separation of distributed generators from the main grid, is a significant issue for wind power and synchronous-based microgrid. Islanding events must be detected to ensure safety and protect utility workers and equipment. The improper detection islanding may lead to power quality degradation, grid protection interference, and out-of-phase reclosing. To overcome these issues, researchers developed the islanding detection technique. This paper proposes a method, for accurately discerning between instances of islanding and those that are not islanding-related events, that employs two new criteria: (1) superimposed positive sequence impedance (SPSI) and (2) superimposed negative sequence impedance (SNSI). The islanding detection indices (IDI₁ and IDI₂) are calculated using the SPSI and SNSI. If the values of IDI₁ and IDI₂ exceed a predefined threshold, islanding is detected. The performance of the proposed approach is tested using the MATLAB/Simulink platform. The simulation results show that the proposed technique detects islanding in 20 ms at nearly zero power mismatch and under balanced conditions. Therefore, it limits unwanted tripping caused by various types of non-islanding events. The proposed technique is compared with existing schemes to demonstrate its superiority.