Research On Fault Characteristics Analysis And Protection Strategy Of Microgrid

With the development of industrialization and the need of environmental protection,mankind's dependence on clean and renewable energy has gradually deepened.With its advantages of flexible power generation,friendly environment and high utilization of energy,microgrid has become a research hotspot in the world.However,the fault characteristics of the microgrid in the isolated island operation mode are very different from that of the grid operation.This makes the traditional relay protection technology protected by misoperation or rejection,and the traditional protection is difficult to meet the requirements of the reliable operation of the microgrid.Therefore,the protection strategy of microgrid needs to be studied in detail.The mathematical model and equivalent circuit of three kinds of photovoltaic cells,super capacitors and lead-acid batteries are studied and analyzed.On this basis,the simulation analysis of their working characteristics is carried out to verify the effectiveness of the simulation modeling.Furthermore,the control methods adopted for photovoltaic cells and hybrid energy storage devices composed of ultracapacitor and lead-acid batteries are described.In addition,the control strategy of the microgrid system is summarized and analyzed,which lays the foundation for the modeling and simulation analysis of the microgrid.The typical structural characteristics of the microgrid are analyzed and summarized,and the Matlab/Simulink simulation platform is used to model the microgrid.The fault output characteristics of the reverse variant distributed power supply under the control of PQ and V/f are analyzed and studied,and the fault characteristics of the microgrid in two operating modes of the grid and the isolated island.In order to identify the fault types in the operation of microgrid,this paper uses the method of combining phase mode transform and wavelet energy entropy to distinguish the type of fault.Considering that the fault current characteristic of the isolated island of the isolated island is not obvious,an improved differential protection scheme with the phase and amplitude of the fault current is proposed to protect the feeder line in real time.Theeffectiveness of the protection method is verified by the simulation and analysis of the two operating conditions of the grid and the island.As the protection strategy of microgrid should be the synthesis of various protection methods,the distributed power supply,the point of common coupling and the load in the microgrid are protected respectively,thus a complete protection scheme is formed.