A single-ended protection scheme for multi-terminal HVDC grids based on Hilbert-Huang Transform

Protection is one of the major obstacles in realizing reliable and secure multi-terminal HVDC grids. This paper proposes a single-ended protection scheme that reliably detects internal faults in less than 1 ms and distinguishes them from external faults. The proposed algorithm employs the instantaneous features estimated by Hilbert-Huang Transform (HHT) to detect various fault events. First, Empirical Mode Decomposition (EMD) is applied to the local voltage measurements to extract the first intrinsic mode function (IMF), which contains the distinctive features of the fault-initiated traveling waves. Second, the instantaneous frequency and average instantaneous energy, estimated by HHT, are continuously tracked to rapidly detect the fault event. Various simulations applied to a four-terminal meshed HVDC grid are carried out on PSCAD/EMTDC to validate the effectiveness of the proposed algorithm under severe internal and external faults.