Research On Topological Structure And Control Strategies Of PET Applied In AC/DC Hybrid Distribution Network

In rencent years,with the rapid development of the national economy and the ever-increasing standard of living of the people,energy shortages and worsening environmental conditions have become increasingly severe.The transformation of energy characterized by electricity and cleanliness has become a problem faced by all countries.The access of new energy and the diversified development of load types put forward higher requirements on the power grid structure.Therefore,the more flexible AC/DC hybrid power distribution network will become the development trend of the future distribution network.Under the new circumstance of power grid development,power transformers face enormous challenges in terms of reliability,economy and flexibility.With the development of power electronic converter technology and the improvement of device manufacturing process,a multi-port and multi-functional Power Electronic Transformer(PET)will play a crucial role in the future power grid.In this paper,PET used in AC/DC distribution network is taken as research object,a three-level PET topology is proposed and its working principle,control method and coordination control strategy of PET in AC/DC hybrid distribution network are analyzed.The specific research contents are as follows.(1)According to the demands of AC-DC distribution network,a three-level PET topology is proposed and its working principle is analyzed.The PET has many types of interfaces,which is suitable for the access of DC sources and DC loads.Besides,it has the capability of DC fault ride-through without the cooperation of circuit breaker when DC fault occurs.(2)Study on the method of grading and independent control of PET in the network.Based on the PET topology proposed in this paper,mathematical modeling and the control strategy design of input stage,isolation stage and output stage are carried out.Then,the rationality of control strategy is verified by simulation in PSCAD/EMTDC.(3)Research on the structure of AC/DC distribution grid and the voltage margin control strategy of PET.After comparing the structure and characteristics of the grid structure of the DC distribution network,the structure of AC/DC distribution network including PET is designed.On this basis,the operating mode and the margin control strategy of PET in the two-terminal AC/DC distribution network are studied.At last,the control effect is verified by simulation.In summary,the topological structure,working principle and control method of PET used in AC/DC distribution network are studied in this paper.The control effect is verified through simulation.The research above can lay a solid foundation for future engineering application.