Simulation of AC System Impedance in HVDC System Studies

In some studies of HVDC system design, ac system impedance is represented by its inductance at power frequency. However, for several studies better simulation of the impedance- frequency characteristic (from power frequency to a few kilohertz) of the ac system is important. This paper presents a simple approach to calculating an approximate equivalent network consisting of parallel LCR branches and having an impedance-frequency characteristic similar to that given for the ac system. For given typical ac system impedance diagrams (usually obtained from ac system models and simulators), simulation of an ac system by corresponding equivalent networks during studies of certain HVDC problems would provide a more accurate means of designing HVDC systems.