Single-ended protection method based on spectrum of natural frequency for lines in MMC-HVDC grids

This paper proposes an improved single-ended protection method for Modular Multilevel Converter-based High Voltage Direct Current (MMC-HVDC) lines based on natural frequency spectrum of current measurements. Unlike traditional protection schemes relying on derivatives of traveling waves, boundary voltage characteristics or transient energies, the proposed method derives the mathematical expression and the natural frequencies of measured currents in detail. By comparing these theoretical peaks with the actual measured peak frequencies which are obtained via the MUSIC algorithm, internal faults can be distinguished from external ones. The method requires only single-ended current measurements, and avoids ultra-high sampling rates. Simulation results prove that the proposed method is valid under different fault locations and resistances.