Research On Fault Location Of HVDC Hybrid Transmission Lines Based On VMD And TEO

HVDC based on voltage source converter(VSC-HVDC)has unique technical advantages.It supplies power to remote areas,increases capacity of urban distribution network,and improves power quality of distribution network.The technology can transmit a large amount of wind power from the sea to the distant land simultaneously.The use of submarine cables at sea and the use of overhead lines on the ground,the system of this hybrid line has a high probability of line failure due to long-distance transmission and the difficulty of patrolling lines.It is of great research value to achieve timely and accurate fault location.This paper first introduces the development of VSC-HVDC technology,and then summarizes the current research status of fault location at home and abroad.In view of the development of global positioning system,modern data acquisition technology and the advantages of the double-ended method of traveling wave fault location,the double-ended traveling wave method is adopted.The working principle and control strategy of the VSC-HVDC system are introduced in detail.The principles of variational mode decomposition(VMD)and Teager energy operator(TEO)are described in detail.Owing to the advantage of the TEO method to analyze the single component of AM-FM signals,this paper considers using VMD to convert the multiple components of AM-FM fault signal into a single-component signal,then it is analyzed to accurately identify the arrival time of the wave head by TEO,finally the position of the fault point is calculated according to the formula of the double-ended traveling wave method.In PSCAD / EMTDC,the model of VSC-HVDC system with hybrid line is built.Firstly,the fault type and fault distance are set,then the fault signal is extracted for phase-mode transformation to eliminate the electromagnetic coupling between the two poles to obtain the aerial-mode and the earth-mode component.The characteristics of the earth-mode component are used to judge the fault type on the DC side,and the aerial-mode component is used for fault location by using the double-ended traveling wave method of WT,HHT,EEMD and VMD-TEO,respectively,and the error analysis is performed.The above experimental results show that the WT method has difficulty in selecting the wavelet basis function and the decomposition scale,and the accuracy of fault location is affected.The EMD in HHT has serious modal aliasing phenomenon and fault location cannot be performed.The modal aliasing is suppressed by EEMD to a certain extent but it cannot be completely eliminated.The false components are still present in each modal component,and the accuracy of fault location is also affected.The accuracy of VMD-TEO is compared with the other three.The method is better,and the result is less affected by transition resistance,fault type and noise.