Advanced modelling of the harmonic impedances of AC-DC converters

A fast numerical-linearisation technique is used with the harmonic-domain algorithm to calculate the harmonic impedances of AC-DC converters. The accuracy of the new method is illustrated by comparison with existing simplified models. The method is then used to determine the effect of local and remote converter plant on the harmonic impedances throughout the power system. It is shown that it is essential to represent the converter impedance accurately at frequencies below 500 Hz, a region where these impedances have considerable effect on the damping of parallel resonances.