Analysis of Coupling Effects on Overhead VSC-HVDC Transmission Lines From AC Lines With Shared Right of Way

The coupling of fundamental frequency voltages and currents on voltage-source converter (VSC)-HVDC overhead transmission lines from neighboring ac lines is analyzed. The complementary modulation components at dc and second harmonic frequencies on the ac side of the converter resulting from the fundamental frequency coupling are analyzed. A mathematical model is developed for the VSC converter that accurately represents modulation effects to and from its ac and dc sides. This model is shown to be significantly different from that of a conventional line-commutated converter. This model is validated by using electromagnetic transients simulation. The model is then combined with an accurate frequency-domain model of the transmission lines and the converter ac-side equipment, and used to conduct parametric analysis of the coupling effects. As the induced 0-Hz (dc) modulation component on the ac side is of serious concern, parametric plots are presented showing its variation with factors, such as ac/dc separation distance, paralleled length, transposition and VSC operating point.