Assessment of AC network modeling impact on small-signal stability of AC systems with VSC HVDC converters

The increasing number of flexible ac transmission systems (FACTS) and high voltage direct current (HVDC) systems is changing perspectives on small-signal stability in ac grids, as traditional steady-state modeling does not allow representing higher-frequency interactions between synchronous generators, ac grid and power electronic-based devices. Since dynamically modeling all grid components typically result in an overly complex system model with a very high order, hybrid network models have been put forward as a compromise to increase the scope of the study, whilst keeping the overall system model order manageable. They do so by combining grid dynamics in the vicinity of the power electronic devices with steady-state assumptions for the rest of the network. This paper examines the impact of converter and grid parameters on the outcome of the stability analysis through comparative examples of a double multi-infeed (MI) HVDC system and a single and double HVDC infeed in the IEEE 39 bus system and by using either steady-state or dynamic line models. Doi ng so, it determines the most relevant parameters to the boundary selection between a dynamic and a static ac grid model in hybrid network models.