A hybrid micro grid islanding detection method

Islanding detection is a great challenge in connecting distributed generation (DG) in electrical power systems. Islanding detection methods are categorized into three groups, i.e., communication based methods, active, and passive methods. Communication based methods are established upon communication between utilities and DGs and have the inconvenience of being expensive and are limited in use. Active methods perturb the system with a disturbance and the system response to the disturbance is analyzed. Although, these methods have small Non Detection Zone, (NDZ) they degrade the power quality. Passive methods monitor one of the grid variables. Their implementation is easy but their NDZ is large. This paper proposes a hybrid islanding detection method which uses voltage unbalance (VU) and high-frequency (HF) impedance. The proposed method merges the advantages of both active and passive techniques. In addition, since the active method used in this paper does not change any of the system variables as a disturbance, it will not lead to any instability. To test the proposed method, UL1741 test system is simulated in PSCAD/EMTDC and the simulation results indicate that the proposed method can identify islanding in 32ms (2 cycles) and it does not mal-operate while other system events like faults and switchings.