Research on AC/DC Harmonic Transfer Characteristics of Hybrid HVDC System

For the hybrid HVDC(High Voltage Direct Current) transmission system composed of LCC (Line-commuted Converter) and VSC(Voltage Source Converter), it was found that when the asymmetric fault or inrush current occured in the LCC rectifier station, the current and voltage of VSC inverter station would perceive large harmonic components in AC and DC side, and the high-frequency harmonic protection configured in VSC converter station had the risk of maloperation. In order to analyze the mechanism, the sequence component dynamic phasor mathematical models of LCC and VSC are established respectively, and then the harmonic transfer characteristics of the hybrid HVDC system composed of LCC rectifier and VSC inverter are studied. Based on the electromagnetic transient model of hybrid HVDC system, the simulation verifies the above AC/DC harmonic transfer characteristics, reveals the reasons for the maloperation of VSC converter station high-frequency harmonic protection. The protection can be optimized by adding the braking locking criterion or filtering the 2-7th components in the harmonic calculation.