The Research On Islanding Detection For Grid-connected Distributed Generation

In recent years, with the continuous decrease of fossil energy and the increasingly severe environment pollution, more and more distributed generation technology which based on renewable energy has been developed and applied rapidly. However, there are a number of hidden perils while the distributed generation system runs under the state of grid-connected. The phenomenon of islanding is one of the basic problems, the islanding phenomenon is that when the main gridsuddenly breakdown due to electrical failure, equipment maintenance, or other factors, each inverter remains supply power to the local load without making corresponding adiustment. While the islanding appearance, it will increase the difficulty of maintenance and threaten the safety of power maintainer, Therefore, it has great practical significance to research islanding detection methods.Firstly, this paper describes the background significance and research status of the islanding detection for the distributed generation, and then the main research contents are outlined. Secondly, the basic problems of the islanding detection are sorted out, analyzing the relation between the capacity match and the variation of voltage or frequency of PCC. Thirdly, the commonly used detection methods has been analyzed, and divides these methods into remote methods and local methods, local methods including passive methods and active methods, the advantages, disadvantages and the improved schemes of several detection methods are evaluated comprehensively. Finally, aiming at the shortcoming that the traditional AFD scheme has a great influence on the quality of the power, the improved frequency disturbance detection is designed, and a distributed generation grid-connected system is modeled using MATLAB/Simulink. Analyzing the mechanism of dilution phenomenon for SFS method, SMS method and improved AFD method under multi-inverter parallel operation condition, verifying the conclusions using simulation.Through the analysis of the mechanism of islanding, an islanding detection based on phase jump and improved frequency perturbation combination is designed. The theoretical analysis and simulation results show that the detection time and THD are less than AFD scheme. Through the analysis of the mechanism of dilution phenomenon, the theoretical analysis and Simulation results show that the SFS method may have dilution phenomenon and result in aborted detection under multi-inverter parallel operation condition, while the SMS method is almost unaffected by the dilution phenomenon, and the AFD method have no dilution phenomenon.