Research On Fault Location And Protection Scheme Of Multiterminal Hvdc Transmission Network

As a result of the development of renewable energy technology,different resources are continuously integrated into the power system.In order to solve the problem of power transmission,the existing end-to-end DC transmission system is also extended to the multiterminal HVDC system.Therefore,it is necessary to move the circuit breaker quickly and accurately to realize the excision and isolation of the fault area.The multiterminal DC network is composed of multiple converter stations and different network topology lines,which will play an important role in the development of the power grid in the future.Especially in recent years,the emergence and development of Hybrid DC circuit breaker has enhanced the stability of DC grid,and laid the foundation for the development of multi terminal HVDC transmission system.But when the multiterminal HVDC system fails,the region also increases.Therefore,a reliable,sensitive and selective protection algorithm is needed to identify the detection faults.And an accurate fault location scheme is also needed,which enables the circuit breaker to act quickly and accurately to achieve the isolation and isolation of the fault area.It ensures the stable operation of the DC transmission network.In this paper,the analysis of the end to end VSC-HVDC fault location scheme is based on the analysis of the three terminal star VSC-MTDC system.The main work is as follows:1)In this paper,a fault location scheme based on double end measurement combined with LMD and Teager energy operators is proposed.It uses the Morlet wavelet time frequency to analyze the boundary characteristics of the VSC-HVDC,and constructs the identification criterion of the fault region through the ratio of the energy of the PF component.Based on the difference between the high frequency current components in the fault line and the non fault line,the criterion of the pole selection is constructed.The fault location scheme based on the intelligent algorithm of single ended measurement takes full advantage of frequency,time and energy,and captures the feature input of fault by Hilbert Huang transform.The fault distance is obtained by using time delay,characteristic frequency,energy attenuation and high frequency energy as the input of support vector regression(SVR).The parameters of the model are optimized by cross validation,and the bat algorithm(BA)is compared with other optimization algorithms.The fault area is determined by the high frequency variance contribution rate(HVCR),and the model is built through the PSCAD platform.2)The VSC-MTDC protection scheme of infinite flow reactor constructed by transfer entropy is put forward,and the coupling model of bipolar DC transmission line without current limiting reactor is analyzed.The transmission entropy is used to identify the fault of the line and the fault selection is carried out by the zero mode current.In order to solve the problem of star topology fault line identification,the protection scheme proposed by the time domain signal index kurtosis factor is applied.3)The star type VSC-MTDC containing the current limiting reactor is considered,and the protection starting criterion is constructed by using the voltage transfer entropy of the bipole.By analyzing the difference of voltage transfer entropy between buses and lines under different fault locations,the action protection process of side circuit breaker and central bus side circuit breaker is put forward.The effectiveness and robustness of the protection scheme of transmission entropy construction is verified by building three terminal HVDC system using PSCAD platform.4)The fault time domain analysis is carried out for the single medium branch and the three stage multi terminal DC hybrid transmission line.In order to eliminate the influence of traveling wave speed variation on fault accuracy,a fault location scheme for hybrid transmission line of star type three terminal HVDC transmission system is constructed by combining traveling wave time domain localization with natural frequency.The scheme uses the variational mode decomposition(VMD)and the Teager energy operator to extract the arrival time and natural frequency of the wave head,and identify the fault regions under different topology using natural frequencies.The Schavemaker arc model is used to analyze the stability of the arc high resistance fault.