Impact of inverter station on torsional dynamics of parallel HVDC-AC power system

The authors investigate the impact of an inverter station on the torsional dynamics of a turbine-generator set which is located at the rectifier side of a parallel HVDC-AC power system. The stiffness of an AC bus is described in terms of its effective short-circuit ratio (ESCR). The studies show that depending on the stiffness of the inverter AC bus and electrical coupling between the inverter and rectifier AC buses, the inverter closed loop control can have a noticeable contribution to the instability of torsional dynamics. This adverse torsional impact is observed in the study results even when the inverter AC bus is fairly strong (ESCR larger than 5.0)