Traveling Wave Bus Protection for MMC Based Multi-terminal DC Distribution Network

For Flexible Medium-voltage DC distribution network, this paper proposes a traveling wave bus protection and a fault pole selection method. The method is to extract the polarity relationship of current traveling waves in each branch of the bus by wavelet transform, it distinguishes the internal and external faults and chooses the fault pole by comparing the polarity of positive and negative poles' modulus maxima. Entensive simulations are based on three-terminal DC distribution network model established in PSCAD/EMTDC. The simulation results show that the proposed method not only can identify internal and external faults of DC bus reliably and rapidly, but is also effective in detecting fault poles.