HVDC models used in stability studies

The author discusses the new generation of detailed models for HVDC systems that were recently introduced in power system stability programs. These models represent the high-speed dynamics of the converter controllers as well as the L/R dynamics of the DC transmission. Older DC models based on pseudo-steady-state relationships are still in general use. The author addresses the following questions concerning the two types of models: (1) To what extent is simulation accuracy impacted by using the older HVDC model? (2) Is the difference in precision significant compared to other uncertainties which are inherent in stability calculations? He also considers a third type of HVDC model, which relieves some of the assumptions associated with the pseudo-steady-state models. The third type of model does not represent high-frequency effects but can represent the temporary dynamic condition when neither the rectifier nor the inverter are at control angle limits. It is concluded that this model is more accurate than the pseudo-steady-state model during the recovery period and is just as easy on the computer budget