To meet ambitious climate goals, power systems are experiencing significant transition towards clean, low- carbon technologies. This transformation is characterized by a growing share of inverter-based resources, which are now present across all parts of the system including generation, transmission and load. Wind and solar power plants are widely deployed on the generation side, as well as HVDC interconnectors and STATCOMs at the transmission level. On the load side, electrolysers and large-scale data canters are expected to grow significantly in the coming years. In addition, Battery Electric Storage Systems (BESS) are being deployed as bidirectional units that can act as both generation and load.

All of these technologies interface with the grid through power electronic converters, which behaviour is mostly driven by control algorithms. This control-driven behaviour adds significant complexity to the overall system dynamics. As a result, the increasing complexity of the grid combined with practical experience gained from system operation and completed projects, highlights the need for continuous refinement of grid connection requirements with respect to system needs and functions, system studies and models.

This paper addresses these challenges by focusing on frequency-dependant impedance behaviour and corresponding analysis across the frequency range of interest starting from 0 Hz up to 2500 Hz. While updates to other system needs and functions as well as study requirements are also being made in response to the evolving grid environment, this paper concentrates specifically on defining HVDC Sub-Synchronous Oscillation (SSO) damping capability and damping performance above 100 Hz, along with the corresponding system studies required to demonstrate compliance with these requirements