Research On Fault Location Method Of Hybrid Three-terminal HVDC Transmission Line

Hybrid HVDC transmission system combines the advantages of conventional HVDC transmission and flexible HVDC transmission,so it has a good development prospect.However,due to the complex devices it contains and the environment it faces,the transmission line has problems such as difficulty in fault location.In order to reduce the losses and improve the work efficiency,fast and accurate fault location methods are very important.In this paper,by analyzing the working principle and control strategy of LCC converter and MMC converter,the model of hybrid three-terminal HVDC transmission system is completed in PSCAD/EMTDC.In order to solve the problem that it is difficult to accurately determine the traveling wave speed of traditional traveling wave location,fault location equations of hybrid three-terminal transmission lines that are not affected by the wave speed is proposed based on the model studied and traveling wave location principle.In order to solve the problem that traditional signal processing methods are difficult to accurately identify fault traveling waveheads,a fault location method based on CEEMD-HT and wavelet threshold denoising is proposed in this paper.Firstly,Karenbauer transform and wavelet threshold denoising are used to obtain the linear mode voltage of the fault signal after denoising.Then,CEEMD-HT transformation is performed on the denoising signal to obtain the time when the fault traveling wave arrives at each measuring end.Finally,the obtained time is substituted into the principle of fault location of hybrid three-terminal transmission line which is not affected by wave speed to complete the distance measurement.Simulation results show that the proposed method can accurately identify the wavehead,has high location accuracy,and the location accuracy is not affected by fault types,transition resistances and datas out of sync.In order to solve the problems of serious modal aliasing and end-point effect in traditional LMD identification,a fault location method based on improved LMD-HT is proposed in this paper.The CHI is used to replace the CSI of the original LMD to improve the overshoot and undershoot of the envelope,and the ISBM extension is used to replace the mirror extension of the original LMD to suppress the end effect of the LMD decomposition,thereby improving the wavehead calibration accuracy.Simulation results show that the proposed method can effectively improve the modal aliasing and endpoint effects of traditional LMD,and has high location accuracy,and the location accuracy is not affected by fault types,transition resistances and datas out-of-sync.Finally,the two location methods proposed in this paper are compared with the wavelet packet location,HHT location and two-terminal location with wave velocity,the simulation results show that the two locatted algorithms proposed in this paper have higher location accuracy and stronger noise robustness.