Single-Ended Protection of VSC-HVdc Outgoing Line Based on Backward Traveling Wave Time-Domain Weighted Optimization

This article considers the problems of high difficulty in fault analysis of direct current (dc) line in a voltage source converter (VSC)–high-voltage direct current (HVdc) outgoing system from wind farms and the poor adaptability of traditional protection principle. To solve these problems, this article proposes single-ended protection of the VSC-HVdc outgoing line based on the time-domain weighted optimization (TDWO) of a fault backward traveling wave (BTW). The analysis of the propagation process of the internal fault (IF) and external fault (EF) voltage BTW and the attenuation characteristics of the dc line and boundary shows that the voltage BTW measured by the protection element decreases significantly under IF. When an EF occurs, the variation range of the voltage measured by the protection element is small, and the higher the frequency is, themore significant the difference between them is. The fault data are optimized by using the time-domain weighted coefficient, and the fault distinction between the IF and EF is expanded. In addition, the fault identification criterion is constructed according to the time-domain weighted coefficient. The proposed protection method is verified by experiments using a renewable energy grid-connected system constructed on a real-time digital simulation (RTDS) platform. The experimental results show that the proposed protection method can identify faults rapidly with a small amount of calculation and realize the full-line action with high speed, reliability, and sensitivity. The maximum achievable sampling rate for safeguarding equipment is up to 50 kHz; the proposed method, with a sampling rate of 20 kHz, has an application value in practical engineering.