Study Of Distribution Network Vulnerability Assessment Method Based On Distribution Information

Due to the frequent blackouts in recent years,the vulnerability of power network has attracted much more attention.At present,the research on vulnerability mainly focuses on transmission network,and the research on distribution network vulnerability is still in its infancy.The access of distributed generation(DG)increases the complexity of distribution network,and the vulnerability analysis and evaluation of distribution network has been paid attention to.At present,the commonly used complex network theory and risk theory can only unilaterally reflect the vulnerability of power grid from the aspects of structure or operation,which is not comprehensive enough.Based on complex network theory and risk theory,the vulnerability indexes of node and line are proposed,and the weights of each index are summated by analytic hierarchy process(AHP).The comprehensive vulnerability indexes of node and line are obtained and the weak links are identified.The main research contents are as follows:Firstly,a simplification principle is proposed for distribution network single-line graph,which simplifies the distribution network into a topological network composed of points and lines.The vulnerability of distribution network is defined to identify the weak nodes and lines in distribution network.Based on the introduction of vulnerability assessment methods currently used,it is decided to use complex network theory and risk theory to conduct distribution network vulnerability assessment from both structural and operational aspects.According to the definition of complex network theory and its characteristic parameters,the definitions of degree and degree distribution,betweeness,clustering coefficient and characteristic path length are extended to distribution network.Combining with the characteristics of radial network and open-loop operation of distribution network,the definition of improved node degree,improved node betweeness,improved line degree and improved line betweeness are proposed.The vulnerability assessment of nodes and lines is carried out separately,and the simulation analysis of IEEE 33 nodes distribution network is carried out.The results show that the proposed indicators are in line with the actual situation and can reflect the correct vulnerability law in structure.The definition of risk theory is introduced.According to the commonly used risk indicators,such as line overload risk indicator,transformer overload risk indicator,overvoltage risk indicator and low voltage risk indicator,combined with the operation characteristics and structural characteristics of distribution network,the node voltage overload indicator and line overload indicator are proposed.The vulnerability of nodes and lines is assessed in terms of operation.The actual 10 k V transmission line is simulated,and the simulation results can reflect the actual operation law.The maximum value is used to normalize each index,and the analytic hierarchy process is used to give weight to each index.The comprehensive vulnerability indexes of node and line are obtained,and the weak nodes and lines are found according to the calculation results of the comprehensive indexes.According to the thinking of the article,the specific process and steps of vulnerability assessment are introduced.In order to verify the correctness of the proposed evaluation system,the actual topological network is used for simulation analysis and calculation.Select half-load and full-load cases and take into account the impact of distributed power supply.The calculation results verify the practicability of the proposed vulnerability assessment system.It is proved that DG is helpful to alleviate vulnerability,and that the indicators mentioned in this paper can correctly reflect the vulnerability law.