Research On Fault Location Method Of AC/DC Distribution Network

With the continuous development of power electronics technology,DC distribution lines are connected to distributed power sources and provide higher efficiency than AC distribution lines when supplying power to DC loads.Therefore,attention has been paid to the technology and application of DC distribution networks.Future distribution networks It will become a hybrid distribution network for AC and DC distribution lines.The breakdown of AC-DC hybrid distribution lines,reliable and accurate fault location plays an important role in repairing line faults in time and ensuring the stable operation of the distribution system.The fault point of the AC-DC hybrid distribution network may be located in the AC distribution line,converter station or DC distribution line.The paper mainly studies the method of locating the line and bus faults.Aiming at the typical AC/DC hybrid power distribution system,the fault characteristics of AC/DC hybrid power distribution line were analyzed,and the fault location method of AC line hybrid power distribution network AC line was summarized.Aiming at the DC line of AC/DC hybrid distribution network,a traveling wave method for multi-terminal DC distribution line was constructed based on traveling wave method.The main work and conclusions of this paper are as follows:(1)The research background and significance of fault location in AC-DC hybrid distribution network are introduced,and the fault location methods of existing AC distribution lines and DC distribution lines are summarized and analyzed.The existing researches on fault segmentation and location of AC distribution lines are quite sufficient.However,there are relatively few researches on fault location methods for DC distribution lines and further research is needed.(2)On the basis of summarizing the topological structure and connection mode of typical AC/DC distribution networks,the fault characteristics of AC and DC lines in AC/DC distribution networks and the impact on the other side of distribution network are analyzed.For the AC line fault,the current differential protection method and the small current line selection and positioning method based on the transient signal principle can handle the fault location of the AC line in the AC/DC hybrid power grid.For fault location of DC lines,it is necessary to study the use of ranging methods based on the principle of traveling waves.(3)The principle of single-end and double-end traveling wave ranging in DC distribution lines is studied.The initial traveling wave propagation process of the fault andthe initial traveling wave modulus and its time-frequency characteristics of the DC line fault are analyzed.Aiming at the multi-terminal DC line of AC/DC hybrid distribution network,the use of traveling wave information based on multi-terminal faults was studied and an extended dual-end traveling wave method was proposed.(4)For the multi-terminal DC system of AC-DC hybrid power distribution network,a traveling wave fault location algorithm for multi-terminal DC distribution lines is constructed.The algorithm is based on the initial traveling wave speed and arrival time of the fault,and depicts the topology of the distribution system according to the adjacency matrix of the power network.According to the proposed fault line and ranging rules,the possible fault points are obtained,and the initial fault line is processed through data verification.The problem of multiple propagation paths of waves,obtaining accurate fault location results.(5)A multi-terminal DC system based on two-level VSC was built by simulation software PSCAD.The bus fault scenes of DC line and DC converter station were simulated.The traveling wave fault location algorithm for multi-terminal DC distribution lines was tested.Simulation results Verify the effectiveness of the algorithm.The research and application of fault location method for AC-DC hybrid distribution network can speed up the fault processing and improve the reliability of AC-DC hybrid distribution network.