| The distributed generation(DG)and micro-grid with DGs,with the advantages of shorter period and less land demand for construction,have come to be the major form of renewable energy use.In recent years,researches on DGs organized in the form of micro grid has made great achievements.Under appropriate control strategy,the microgrid can be a controllable power supply or a controllable load,thus contributes to supporting the safe and reliable operation of the power system.The topology of distribution network will be changed from the original radiation network to the multisource grid,the help/draw effect and the reverse current caused by the micro-grids,and also the circuit transfer will result in unpredictable operation of the network protection.As a result,the traditional protection principle and of distribution network and the fixed value setting of protection will no longer be applicable.Though great efforts has been made,and a series of schemes are prompted,so far barely no one could meet the satisfactory.Therefore,it is necessary to carry out further research on the protection of micro-grid with DGs.In this paper,the fault characteristics of micro-grid with DGs under different control modes are studied and analyzed.Through research on the influence by the micro-grid with DGs on the distribution network protection,a new main&backup protection method based on regional protection information interacting and sharing is prompted.Further study on the coordination strategy between protection and automatic devices in active distribution network(AND)is done to realize the “Plug and play” requirement,which will bring positive significance to the large-scale application of micro-grids.This paper mainly discusses the following contents:(1)On the basis of simulation,the fault characteristics of DGs and micro-girds under different control modes(PQ control,U/f control and Droop control)are researched for different access points.Also this paper makes quantitative analysis of the impact micro-girds make on the protection scale,sensitivity and coordination with automatic devices.A relevant simulation is made to verify the compatibility of traditional protection to the multi-source intelligent distribution grid.(2)An improved adaptive protection scheme is prompted.This paper analyzes a current adaptive protection scheme based on calculation of equivalent impedance from the bus and protection info interacting,and further a distance adaptive protection scheme is raised,and a relevant verifying simulation is made through Matlab Simulink.(3)A new protection method based on regional protection information interacting and sharing is researched.Under the structure of Multi-agent system,this paper analyzes the control level division scheme,grouping scheme and protection operation logic of the ‘quasi differential protection’,which adapts to micro-grids under varies operation modes.The new protection method proves to be highly reliable,and could meet the “Plug and play” requirement.(4)A new protection system of AND based on hierarchical and distributed network structure is built up.And given the multi-source characteristic and active planning ability of AND,this paper also analyses of the corresponding requirement for fault detection,location,isolation and restoration.Finally the coordination strategy between protection and automatic devices is studied. |
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