Line fault location for multi-terminal MMC-HVDC system based on SWT and SVD

This study presents a travelling wave (TW)-based method for locating DC line faults in a modular multilevel converter (MMC)-based high-voltage direct current (HVDC) system by using local information. Pole voltage signals are adopted and denoised via stationary wavelet transform (SWT) with improved threshold functions. Hankel matrix-based singular value decomposition (SVD) is utilised to detect TW arrivals. The arrival times of incidental and reflected wave heads are observed in SVD result. The reflected wave heads from the fault point and the opposite end can be discriminated by comparing surge polarities in SVD result. The proposed method relies on the TW principle but is independent of TW propagation velocity. The feasibility of the proposed algorithm is evaluated considering potential factors, such as fault resistance, close-in fault, remote fault, sampling rate and noise. The superiority of this method is validated by comparing it with other signal-processing techniques and TW-based fault location principles. Electromagnetic transient simulation of the multi-terminal HVDC system on Power Systems Computer Aided Design / Electromagnetic Transients including DC (PSCAD/EMTDC) is conducted to provide fault TW signals, which are analysed in MATLAB. A corresponding equivalent test model developed in a real-time digital simulator is also provided for conducting a supplementary study to verify and further research this fault location method.