基于故障电压行波传播项指数系数的柔性直流输电线路单端行波保护原理

Voltage source converter-based high voltage DC (VSC-HVDC) grids have raised high-speed operation and high reliability requirements for relay protection. Firstly, the symbolic expressions of the line-mode fault component voltage traveling wave in case of the internal and external faults were derived, which consist of the traveling wave propagation term and the DC line boundary term. It is theoretically demonstrated that (i) the index for the traveling wave propagation term in case of internal faults is greater than that for the external faults, and (ii) the index is independent of fault impedance. Secondly, the Levenberg-Marquardt (LM) algorithm was introduced to extract the index and an index-based non-unit protection method as well as the protection scheme was proposed. The proposed method is theoretically robust and independent of fault impedance and fault type. Finally, in the simulation, the fitting results have indicated that the symbolic expressions are correct and the extracted indices are effective to characterize the location of the faults. Numerous fault cases of different fault distances, fault impedances, and fault types have demonstrated that the proposed protection scheme has high sensitivity, high operation speed, and high reliability. The proposed protection scheme does not require high sampling frequency.