中文摘要：

高压直流（HVDC）输电换流器两侧的谐波阻抗对确定地磁感应电流（GIc）引发的谐波有重要意义。对比了有外部激发和无外部激发2种情况下HVDC换流变的直流偏磁机理，并根据三端口网络模型计算、等效出的谐波阻抗，研究了在GIC作用下换流变偏磁后的谐波水平。PSCAD／EMTDC仿真表明，GIC激发的谐波取决于系统的谐波阻抗。当直流输电系统对某次谐波存在谐振点或呈现高阻抗时。可导致系统谐波明显放大，严重时会引起直流输电工程闭锁。

英文摘要：

The harmonic impedance on two sides of converters in HVDC transmission system is important in determinating the harmonics due to GIC （geomagnetic induced currents）.This paper compares two kinds of mechanism about the HVDC converter transformer magnetic DC bias with external excitation or not, and studies the harmonic level produced by the converter transformer due to GIC according to the calculated and equivalent harmonic impedance by three-port network model. PSCAD/EMTDC simulation results prove that harmonic level induced by GIC depends on the harmonic impedance, and harmonics could be obviously amplified and even block the HVDC transmission project, if there are resonance points or the system presents high impedance to certain harmonic.