Research On Reliability Evaluation Method Of Multi-terminal Flexible Power Distribution System

With the development of power electronic equipment technology,more and more power electronic equipment begin to access the distribution network.The distributed power supply and energy storage devices are constantly connected to the grid,and the supporting role for the distribution network is becoming more and more prominent.The composition of urban electricity load is more and more diverse.As a result,the composition of distribution networks has become increasingly complex.Compared with traditional AC power distribution system,flexible power distribution system has attracted the attention of many scholars due to its advantages of convenient access to distributed power supply and energy storage devices and high power quality.It can be predicted that in the field of power supply and distribution,the flexible distribution system will gradually replace the traditional AC distribution system and form a new form of AC-DC hybrid distribution system.To this end,the paper proposed the research object for flexible connectivity distribution network of guizhou university city demonstrative project of key technology and equipment research multiterminal of flexible ac/dc interconnected power distribution system,on the basis of the project in multiterminal flexible distribution system reliability assessment method of research.Specific research contents are as follows:Firstly,the research on the reliability of AC distribution network and DC distribution network by domestic and foreign scholars is introduced,and the existing reliability evaluation methods: simulation method and analytical method are expounded.Then three typical topology structures of flexible distribution network are compared and analyzed to show the superiority of multi-terminal flexible distribution system.The key technology and equipment research demonstration project of urban flexible interconnection distribution network in Guizhou University is emphatically introduced.Secondly,based on the existing theory of reliability evaluation,the method of component reliability modeling is introduced.The fault tree method and reliability block diagram method are selected to model the reliability of MMC and DAB of flexible power electronic equipment in multi-terminal flexible distribution system.The redundant configuration of the hybrid MMC and DAB and the influence of the DC side fault blocking capability on the reliability of the hybrid MMC are emphatically expounded.Then the reliability modeling of distributed power supply,energy storage device,AC/DC converter and DC/DC converter in the system is carried out.It provides data basis for reliability evaluation of multi-terminal flexible distribution system.Thirdly,based on the analysis of the advantages and disadvantages of the traditional analytical method and the simulation method,combined with the practical engineering application based on the AC-DC hybrid multi-terminal flexible distribution system.It is concluded that there are some defects in using the analytical method or simulation method to evaluate the reliability of the system.Therefore,a hybrid reliability evaluation method of AC side-simulation method and DC side-analysis method is proposed for multi-terminal flexible AC-DC interconnected distribution system.The advantages of this method are confirmed by qualitative comparison.Finally,the reliability of the multi-terminal flexible distribution system is evaluated based on the topological structure of the AC-DC interconnection distribution system of the key technologies and equipment research demonstration project of Guizhou University's urban flexible interconnection distribution network.The results show that reasonable redundancy configuration can improve the reliability of MMC and DAB.After the introduction of DC distribution system into traditional AC distribution network,the overall reliability of the system has been improved.The access of distributed power supply and energy storage device can improve the reliability of the system.The connection of flexible power electronic equipment to the multi-terminal flexible distribution system also improves the reliability of the system.The change of system operating mode has different influence on the load point and the reliability of the system.