School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, China

For the problems of high resistance tolerance, noise interference, and operation refusal on remote high-resistance internal fault of the existing flexible DC line protection, this paper proposes a single-end protection scheme for the flexible DC transmission line based on the similarity of energy spectrum matrix of traveling waves. By analyzing the boundary effect of current limiting inductors in the flexible DC power grid, the difference of voltage traveling waves of internal and external faults in time and frequency domains is obtained. The S-transform is used to construct the energy spectrum matrix to increase the difference of energy spectrum distribution between internal and external faults. The principal components analysis is used to reduce the dimension and the storage space of sample data. By using the normalized cross-correlation coefficient, the similarity between the fault energy spectrum matrix and the fault sample matrix is calculated, and the single-end flexible DC protection criterion is constructed to distinguish the internal and external faults. Considering the factor that overhead lines are vulnerable to lightning, the lightning interference identification criterion is constructed. Simulation results show that the proposed algorithm is not affected by the fault location, the high resistance and the noise interference.