Research On Detection Method Of Micro Grid Isolated Island

Distributed power bring many merits, but at the same time its access to distribution network causes a series of problems. In order to solve these problems, scholars had put forward the concept of micro-grid. The development of micro-grid is restricted by some technologies, and one of the important technologies is fault detection and protection.On the basis of understanding and learning of the existing island detection technology, this thesis describes the detection principle of all kinds of detection methods and analyzes their advantages and disadvantages. A specific analysis is made for the distributed power supply which is composed of power electronic devices. The topology structure design of grid connected inverter, the analysis of the grid connected control strategy and the design of the grid connected filter are completed. And the grid connected model is completed in Simulink.With the new energy simulation laboratory micro-grid system as the experimental platform, the TCP0150 current differential probe and DPO505 mixed signal oscilloscope are used for the detection of waveform. The effectiveness of detection method are compared between single source and two sources; between the different load characteristics and between different line power. There are three conclusions: first, multiple micro sources detection will produce dilution effect; second, different load characteristics cause different effectiveness of detection; the third, the contact line power of 0 will lead to failure of detection.Finally, the corresponding solutions are proposed for the problems found in the experiments. This thesis will take Sandia frequency offset method as an example, the generation mechanism of dilution effect was analyzed in detail, and the compensation module was designed to weaken the dilution effect by changing the parameters. The effectiveness of the method is verified by the simulation in Simulink. The changes of the load characteristics affect the detection performance, proposed by the combination of the island detection method to avoid the impact of load characteristics on the detection performance. Taking the combination of phase mutation detection method and Sandia frequency offset method as an example, the simulation analysis in Simulink is carried out to verify that the isolated island can be effectively detected in the case of either pure resistive load or load quality factor of 2.5. According to the principle of islanding detection, when the power of distributed generation is matched with the required power of the load, it will result in the failure of the detection method. So there is a certain power of the contact line is a necessary condition for effective detection methods. The concept of island division is proposed for the problem of power shortage in the contact line. By active smooth switching or cut off load to avoid failure detection.