Analysis of a new type islanding detection method for micro-grid based on the calculation of variance

UL1741 rules that to realize the islanding detection, the inverter must stop running within 2s after the main grid failure occurs. However, with the increasing of the capacity of distributed generation system, in order to guarantee the stability and reliability of power supply simultaneously, IEEE Std.1547 proposed the concept that DG runs off-grid after islanding occurs. The concepts of the traditional islanding protection were attacked, the original islanding detection methods are no longer suitable for the flexible micro power grid operation system. This paper presents a new active islanding detection method which could suitable for micro-grid operation and control. The method, which under the premise of without destroying islanding operation conditions, fine-tunes the PWM modulation wave, real-time acquisition the voltage of point of common coupling, using the mathematical statistics method to extract the quadratic differential of the output voltage, according to the changes of the mathematical characteristic value in the grid connected mode and the islanding mode to judge if there was islanding occurred, and the theory basis of quantitative analysis of the disturbance quantity selection. Simulation and experiment results verify the correctness and feasibility of the proposed method.