Study of HVDC controls through efficient dynamic digital simulation of converters

The authors describe a converter model for 6/12 pulse operation and present its application to the study of the performance of converter controls. The simulation is simplified by considering a time-varying equivalent circuit on the DC side, which is derived on the basis of graph theory. Elimination of the need to store connection matrices and a fast and efficient way of generating the converter equations are further innovations introduced here. For the simulation of the HVDC (high-voltage direct-current) system the approach used is to model each component separately and in a modular fashion. These models are interconnected using appropriate interface variables. The control of converters based on digital techniques is considered along with voltage-dependent current order limit (VDCOL). Results for a two-terminal HVDC system under normal operation and abnormal conditions are presented to illustrate the capability of the simulation method