Flexible direct current line direction pilot protection method independent of line parameters and boundary elements

The invention discloses a flexible direct current line direction pilot protection method independent of line parameters and boundary elements, and the method comprises the steps: obtaining the voltage and current of a positive electrode and a negative electrode of a direct current line in a selected time window, and calculating the corresponding line mode voltage and line mode current; extracting high-frequency and low-frequency components of the line mode voltage and the line mode current through wavelet transform, and respectively calculating high-frequency measurement impedance and low-frequency measurement impedance according to the high-frequency and low-frequency components; calculating a high-frequency and low-frequency measurement impedance amplitude ratio, and judging a fault direction according to the high-frequency and low-frequency measurement impedance amplitude ratio; and finally, reliably identifying internal and external faults. Compared with the prior art, the method does not need to depend o