A novel directional pilot protection independent of line parameters and boundary elements for MMC-HVDC grid

In MMC-HVDC grid, the pilot protection is generally used as the backup protection for dc line. And in some dc grids, it can be considered as the primary protection, such as in the system using MMCs with fault-handling capability. However, most of the existing dc line pilot protections are highly dependent on accurate line pa-rameters or line boundary elements (e.g., dc reactor), whose implementation complexity problem and engi-neering universality problem still need to be researched. In this paper, a novel directional pilot protection for MMC-HVDC grid, based on the ratio of high-frequency and low-frequency measured impedances, is proposed. Compared with the existing methods, the proposed protection does not need to obtain line parameters previ-ously, thus significantly reducing the engineering implementation complexity. In addition, the proposed method is independent of line boundary elements, thus being suitable for the dc grid with no boundary reactors (or very small). Finally, the off-line simulation test based on PSCAD and real-time simulation test based on RTDS are developed to prove the feasibility and superiority of the proposed method.