Considering the advantages and limitations of traditional identification method

combined with the strategy of active detection

the principle of DC grid pilot protection based on active detection is proposed to improve the sensitivity and reliability of hybrid MMC DC grid protection

and to ensure the accurate identification of fault areas in DC grid. By using the DC fault ride-through control strategy of the hybrid sub-module MMC

the fault current at the converter station DC terminal is limited. Based on the high controllability of hybrid MMC

sinusoidal fault detection signals with the same frequency are injected into the line at each converter station. Based on model recognition

the capacitance model condition is satisfied by the detected signals at both ends during external faults whereas not satisfied during internal faults. The Spearman correlation coefficients is then introduced

and the correlation discriminant of capacitance model is constructed to realize fault area discrimination of DC grid. The simulation results show that the active detection protection scheme proposed in this paper can accurately identify the fault area of DC grid

and is not affected by fault impedance and has low sampling rate requirement.