Motion Equation Modeling of LCC-HVDC Station for Analyzing DC and AC Network Interactions

Line Commutated Converter based High Voltage Direct Current (LCC-HVDC) Transmissions are widely applied in delivering large-capacity electricity in China. Multiple large-capacity LCC-HVDC transmissions make the dynamic coupling among AC and DC networks become stronger. Existing literature have reported some stability problems caused by dynamic interactions among AC and DC power grids, but the mechanism behind have not been totally understood and revealed. To analyze the dynamic interactions among AC and DC power grids, this paper presents a small-signal model to understand the external characteristic of LCC-HVDC stations based on motion equation concept. Comparison of time-domain simulation response with detailed switching model shows that the proposed model can hold the main behaviors of concern. Dynamic interactions among AC and DC power grids are studied based on the proposed model in a two-terminal LCC-HVDC system. Analytical results demonstrate that there exists power dynamics in receiving AC grid when sending AC grid subjects to a disturbance, and effects of converter stations' controller parameters on the power dynamics are well explained by physical relationship among state variables of the proposed model.