Single-End Line Protection of Hybrid HVDC System Based on Boundary Characteristic Frequency Band Energy Ratio

Hybrid high-voltage direct current (HVdc) transmission systems face significant challenges due to long transmission distances and complex corridor environments, which lead to increased fault rates. Furthermore, the adoption of fault self-clearing control strategies in HVdc systems reduces the available time for fault information acquisition and processing. To address these issues, this article proposes a single-ended protection method based on the energy ratio of the boundary characteristic frequency band (CFB). The frequency characteristics of line-commuted converter (LCC), dc transmission line, and modular multilevel converter are first analyzed. Subsequently, the CFB energy ratio of the transient voltage is employed for both fault identification and faulty pole selection. Extensive simulation results demonstrate that the proposed method can identify faults and determine faulty poles within 1 ms. Compared to existing protection schemes, the proposed method exhibits superior performance in tolerating high fault impedance (500$\boldsymbol{\Omega}$) and demonstrates strong robustness against noise interference (10 dB).