HVDC CONVERTER TRANSFORMER CORE SATURATION INSTABILITY - A FREQUENCY-DOMAIN ANALYSIS

The interaction between an HVDC converter and the saturation character istic of a converter transformer can lead to a type of harmonic instab ility widely known as converter transformer core saturation instabilit y. The paper presents a linearised direct frequency domain analysis of the mechanism behind this instability. Using linearised converter tra nsfer functions and transformer saturation characteristics on AC and D C system equivalents, the system equations are solved to describe the phenomenon. A measure of the level of stability, saturation stability factor, is derived and utilised to predict the system dynamics. The an alysis is verified by dynamic simulation of several systems.