High error-tolerable unit protection for VSC-MTDC independent of data synchronization

Abstract

Unit protection is a promising technique to enable full coverage for DC lines in the VSC-based Multiterminal DC (VSC-MTDC) grid. However, this type of protection element usually performs as a back-up one, mainly due to its limited speed and error-tolerance capability. To solve this problem, a novel type of unit protection is proposed in this paper. Based on the profile of initial surge arrival, this paper uses the Hausdorff Distance (HD) to measure the similarity between the initial backward/forward surges in a short time-window, which distinguishes internal faults from external ones, eliminating the need for data synchronization. To enhance high error-tolerance capability, an adaptive median filtering-based approach is proposed to reduce the impact of abnormal voltage spikes and white noise, while maintaining the similarity profile of the initial backward/forward surges for the calculation of HD. Simulation results demonstrate that the proposed protection method is capable of identifying internal faults before the blocking of the Half-bridge MMC converter, and the resistive coverage is 300 Ohm in most cases. Under the external fault condition, the proposed protection can be secure enough even in the challenging scenario of white noises and abnormal spikes considered.