Research On Traveling Wave Fault Location In Multi-terminal Meshec Flexible HVDC Transmission System

With the development of renewable energy and electronic techniques,the VSC-based multi-terminal DC power networks,which cause less energy loss and easier network connection,have become more and more important in the research of smart grid.The complicated connections of multi-terminal DC networks produce some technical problems such as location of the DC faults.However,the research on the fault location with the terminal information of DC networks was rarely reported.This paper aims to solve some critical issues of fault location in multi-terminal DC networks such as the simplification of DC network topology,the characterization of transient signals,and so on.Based on the analysis of DC network topology,DC faults and characteristics of transient fault signals,traveling wave fault location will be proposed.Finally,a fault location system of multi-terminal DC networks will be setup.Such system can help improving the techniques of protection,fault isolation and system recovery of multi-terminal DC networks.Therefore,based on the actual topology,this paper studies the fault location algorithm for the multi-terminal meshed flexible DC transmission system.Firstly,the propagation of traveling wave in a HVDC transmission system is studied,including the attenuation and distortion of the traveling wave when it propagates on the line,the change of the wavefront when the traveling wave passes the inductance or the bypass capacitor,and the Traveling wave generation mechanism when the fault occurs.At the same time,it discusses whether the existing method of traveling wave locating used in AC system is suitable for DC system.Secondly,the Fourier transform is used to analyze the form of the time-domain traveling wave in the frequency domain.The ratio of the current traveling wave and the voltage traveling wave in the frequency domain at the same point on the fault line is a periodic function.The fault traveling wave satisfies the relationship that the fault distance is inversely proportional to the frequency in the condition that the traveling wave velocity is constant in the frequency domain.Draw the image of the periodic function through MATLAB and find the period to determine the distance between the point of failure and the point of measurement.Then,the paper analyzes the line topology of multi-terminal meshing HVDC transmission system,and discusses the location blind area in detail.Aiming at the particularity of fault localization of multi-terminal DC mesh networks,this paper proposes a new method for traveling wave fault location based on the actual topology.This method only needs the moment when the traveling wavefront arrives at the traveling wave recorder at each converter station,You can find the actual fault line.In order to solve the problem of blind area,the wavelet transform modulus maximum of the fault traveling wave is substituted for the first occurring wavelet transform modulus maxima.Based on the PSCAD simulation and subsequent data processing of MATLAB,we can find that it can locate the fault line and fault point accurately,and can correctly judge whether the fault occurs in the blind zone and the specific location in the blind zone.Finally,based on the above algorithm,a fault location software is designed based on the MATLAB GUI platform.The software,from waveform recognition,phase-mode transformation,wavelet transform,modulus maxima extraction,to identify the faulty line and the location of the fault point,are completed automatically.Just import the original data,you can get the final fault location results.The design and application of this software also create better conditions for the promotion and application of the proposed method.