A Pilot VSC-HVDC Line Protection Principle Based on Similarity of Time-Frequency Matrix of Initial Current Traveling Wave

In order to satisfy the ultra-fast, high reliability and high sensitivity requirements of the voltage source converter based high voltage DC (VSC-HVDC) systems, a pilot protection principle based on similarity of time-frequency matrix of initial current traveling wave (ICTW) is proposed in this paper. First of all, the fault characteristics of the double-ended ICTWs in the VSC-HVDC grids are studied. It is concluded that within a specific time window, the frequency-domain similarity of the double-ended ICTWs under internal faults is much higher than external faults. On this basis, S transform is utilized to analyze the time-frequency characteristics of the double-ended ICTWs, and the time-frequency matrices are obtained. Then singular value decomposition (SVD) is performed on the matrices. Afterwards the similarity calculation formula of the double-ended ICTWs is constructed based on the feature matrices, and the DC line fault can be discriminated accurately by utilizing the value of similarity. Finally, numerous test studies performed in PSCAD/EMTDC validate the superiority of the proposed protection principle.