Analysis of the influence of transmission lines on the hundreds of kilohertz harmonics of MMC-HVDC transmission systems

High voltage direct current (HVDC) transmission based on modular multilevel converter (MMC) is the foundation of voltage-sourced converter (VSC-HVDC) transmission, offering superior control and high efficiency, yet it faces persistent harmonic issues. Sustained ultra-high-frequency harmonics (100kHz to several MHz) can cause localized overheating, insulation breakdown, and reduced equipment lifespan, ultimately compromising system reliability. To ensure more stable operation of power systems, this paper establishes an electromagnetic transient simulation model of the MMC-HVDC system. Based on this model, the time-domain waveforms of high-frequency ground harmonic currents at wall bushings and transformer bushings under different transmission line conditions (length, type, and voltage level) are investigated, and their frequency-domain characteristics are analyzed through Fourier transform. Through theoretical derivation and simulation verification, th e influence of transmission lines on high-frequency harmonics in the hundreds-of-kilohertz band is summarized. The research results provide theoretical support and practical guidance for engineering design.