Dynamic Propagation Mechanism in Multi- Terminal AC/DC Hybrid Power Systems

This paper investigates the propagation of dynamic transients through High Voltage Direct Current (HVDC) connections based on Voltage Source Converters (VSC-HVDC). The analysis explores the conditions for the occurrence of strong dynamic interactions in hybrid AC/DC systems under different control strategies. The results reveal that the parameters of the droop control in the DC system significantly affect the propagation of strong dynamic interactions between the Virtual Synchronous Generator (VSG) control subsystem and the remaining subsystems. Under DC voltage droop control, the transmission between VSCs involved in DC voltage control becomes bidirectional, and instability from the local AC system will propagate throughout the entire AC/DC power system. Finally, using a 5-terminal hybrid AC/DC power system from CIGRE as an example, the paper provides a comparative analysis of the open-loop mode coupling induced by different DC control strategies and their propagation characteristics, thereby validating the correctness of the analysis and conclusions.