Sixth Harmonic-based Distance Protection for VSC-DC Distribution Lines

Voltage source converter (VSC-based) DC distribution networks are vulnerable to DC-side faults and protection techniques are of great significance. However, it is challenging to find an efficient DC transient for reliable protection design. In this case, this paper proposed a sixth harmonic-based distance protection to guarantee the reliability of DC distribution networks. The overviews of the system topology and fault characteristics were introduced. We derived an equivalent circuit to analyze the sixth harmonic components during the "feeding phase". In order to remove the effects of multiple decaying components on the sixth harmonic-based protection, we proposed an improved discrete Fourier transform (IDFT). The simulation results verified the feasibility of the proposed protection. The protection operating time was about 10 ms and the errors of fault distance estimations were less than 1%. The proposed protection can meet the requirements of speed and selectivity without communications.