Transmission Line Fault Location in MMC-HVDC Grids Based on Dynamic State Estimation and Gradient Descent

This paper proposes a new fault location method for transmission lines in MMC-HVDC grids based on dynamic state estimation (DSE) and gradient descent. The method only requires a short data window of 5 ms after the occurrence of the fault and therefore is applicable for MMC-HVDC grids with high-speed tripping techniques. The method first builds a high-fidelity linear dynamic model of the DC transmission line, which accurately describes physical laws of the transmission line during the fault. Afterwards, the consistency between the measurements and the linear dynamic model is evaluated through the DSE algorithm. Finally, the actual fault location which corresponds to the best consistency is determined via the gradient descent algorithm. Compared to the existing DSE based fault location methods which solve highly nonlinear DSE problems, the proposed method only needs to solve a series of linear DSE problems, which overcomes the issues such as large numerical error and high computational burden especially for transmission lines in MMC-HVDC grids. Numerical experiments validates the effectiveness of the proposed method, with different fault types, resistances and locations. In addition, the method only requires a relatively low sampling rate of 20k samples per second.