| VSC-HVDC is the high voltage direct current transmission system, which is based on turn-off thyristor IGBT and PWM technology. In the new energy grid, power islands, urban power grid and other fields, it has broad application prospects. HVDC lines generally longer, prone to failure. In order to ensure reliability of supply HVDC and fault diagnosis of HVDC transmission line. Research on fault classification and fault location based on the current transient amount was done.In this thesis, the basic structure of VSC-HVDC system were analyzed, and a simulation model of VSC-HVDC system was build using PSCAD simulation software. In VSC-HVDC transmission line, research on fault location was done based on DC side fault feature. A method of extracting traveling wave natural frequency by Hilbert-Huang transform was proposed. In bipolar short circuit fault, phase-mode transformation was applied to bipolar current transform. Extracting the dominant natural frequency and the secondary natural frequency from result of spectral analysis for line mode component. The relationship of the natural frequency and fault location was used to complete fault location. The difference between the dominant natural frequencies at two ends of a transmission line was used as primary criterion. The secondary natural frequency was utilized as secondary criterion to achieve fault protection of bipolar short circuit fault. The study on fault location of VSC-HVDC was done. From the energy point of view, current rms values was considered troubleshooting feature amount. With technical fault dictionary, neural network theory was used to design troubleshooter to achieve fault diagnosis of VSC-HVDC system.The simulation results in PSCAD/EMTDC and MATLAB analysis validate the feasibility of the proposed method that was used to achieve protection of bipolar circuit short and fault location. The simulation results also verify the reliability of the different fault diagnosis. The research is significant for the safe operation of VSC-HVDC system. |
