Single-ended protection method of MMC-HVDC transmission line based on random matrix theory

The physical electrical boundary at both ends of the MMC-HVDC transmission line is composed of smoothing reactors and has a high-frequency blocking effect. This behavior causes the time-domain characteristics of the initial part of the polar line current waveform to be significantly different under the internal and external MMCHVDC line faults, and can lead to two different fault modes. However, the operation of the DC line traveling wave protection with du/dt as the core can be easily affected in the presence of high resistance (HR). Furthermore, it is difficult to set the criterion setting value. To solve the aforementioned problems, this paper proposes a line single-ended protection method based on the random matrix theory (RMT). First, the difference between the internal and external line current fault modes is analyzed. Second, the physical characteristics of the two modal differences in the RMT are analyzed. Third, the single Ring Law is used to achieve visualization, and mutation energy is used as the starting criterion. The fixed values of the spectral radius and Euclidean distance of the spectral radius are utilized as the identification criteria for the internal and external line faults. Furthermore, the set value of the spectral radius is used as the fault selection criterion. Last, a 77-level bipolar MMC-HVDC system grounded through the grounding electrode lead is built in RTDS to verify the adaptability of the proposed method to HR and noise. The results show that the method can quickly and reliably detect DC line faults and fault poles under different fault locations and different transition resistances, and the RMT protection can be further improved with the increasing number of fault samples.