Research On Fault Identification Method Of MMC-HVDC Transmission Line

Modular multi-level converter(MMC),as a new multi-level converter topology with many advantages,has gained a high degree of attention in the field of high-voltage direct current transmission,and has gradually developed into a representative of flexible DC transmission.Sexual technology.The modular multi-level converter flexible direct current transmission(MMC-HVDC)system has good development prospects and technical advantages.At present,the research on MMC-HVDC mainly focuses on the control strategy,and the simulation analysis of MMC-HVDC protection and faults.The aspect has yet to be improved.In this paper,bipolar MMC-HVDC system simulation model based on electromagnetic transient simulation software PSCAD/EMTDC grounded by grounded electrode leads,the grounding pole lead grounded bipolar MMC-HVDC system simulation model is analyzed.The topology structure of MMC and the basic operation principle of the submodule are analyzed.The existing MMC-HVDC line fault protection principle Based on the research,the modulation and protection strategies of MMC-HVDC are analyzed,and the operation of the MMC-HVDC system is analyzed.At the same time,the division of the fault range in the MMC-HVDC system is also discussed.The research done is of great significance to the research of MMC-HVDC system operation mode and line fault identification.In terms of fault characteristics of MMC-HVDC system,combined with simulation analysis system AC side,converter and DC line fault characteristics and system response characteristics;and simple analysis and comparison of voltage and current sudden change direction of different fault types.Combined with wavelet theory and trapezoidal numerical integration theory,an internal and external fault identification method based on MMC-HVDC voltage and current sudden change direction is proposed,and the influence of line fault distance and transition resistance on fault transients is fully considered.The paper also analyzes the sensitivity of HHT transform different layer curves of the voltage abrupt change at the measuring point of MMC-HVDC direct current transmission line under fault conditions,and extracts the information entropy feature from the curve with the highest sensitivity.Based on this,HHT improvement is proposed.The energy entropy MMC-HVDC line fault identification method can improve the identification of AC and DC side faults by improving the energy entropy difference of the HHT of the fault signal,and can pass the voltage abrupt change of the fault pole and the sound pole in the occurrence of the unipolar ground fault.The ratio of HHT energy entropy selects the fault pole,and the simulation verifies that the method is effective and effective in identifying the fault.