Study On The Islanding Detection In Micro-grid System

Along with the social demand for electricity power, human being subject to the constraints of traditional energy and natural environmental, New sources of energy can make up traditional energy sources, it will be the main human resource for future energy, get attention and rapid development of countries in the world, is an important development direction of power. Micro-grid power generation system can solve the contradiction between environment and resources, reduce costs, enhance the stability of large power systems, and Micro-grid is flexible installation, which can reduce the loss.Micro-grid power systems and large grid produce electricity together, resulting in a tremendous challenge the large power grids with the power generation, how to ensure that a complex power system generate power is reliable and safe is the key issue, which is considerd by micro-grid , the detection of islanding detection and related content are important aspects. Nowadays, many kinds of island effect detection methods at home and abroad, according to the test location, there are remote detection of large network and the local detection of micro-grid system. since the former is too costly and technology is very difficult, and thus rarely used, generally use the latter. Local detection have passive and active detection of the detection method, passive detection has largely non-detection zone, but active detection ,whose testing speed is very fast, has an impact on power quality.This paper puts forward the active variable-intrusive detection, through PLL tracks power grid voltage and frequency and so on, the Micro-grid can be safe to produce electricity with large grid synchronization operation, by judgment on local load type, and then take the initiative interfere with the common point, In the case of large grid power cut, it makes the common point of voltage or frequency without the allowed values, to determine the occurrence of islanding effects. In this paper, through the study of simulation of MATLAB, the results shows that variable interference method can detect the occurrence of islanding quickly and reliably, can meet the requirements of power quality, it has no limit to the type of Micro-grid and is a simple method.The 5KW PV micro-grid is operated test in the laboratory, which is designed with variable interference type islanding effect of detection method inverter equipment, micro-grid can produce power with large grid and separately, can promptly judge the case of the power grid, if the power grid cannot be normal operation, micro-grid can separate with large power grid in time, the shortcoming is that the harmonic content is a little higher. Its power quality is slightly lower than the requirement of grid, the reason is not installed the isolated transformer.