Impact of Grid Strength on HVDC Connection Requirements

AC Grid Codes are well documented and constantly being updated by industry and electricity system operators. However, the deployment of power electronics-based technology into conventional ac power systems brings significant challenges for system operators. As high-voltage direct-current (HVDC) technologies keep developing, the existence of hybrid ac and dc systems may be standard in future power grids. Although HVDC brings flexibility to the system, the control strategies have become more complex. In addition, stability issues brought by a reduced system inertia resulting from the gradual replacement of synchronous machines with HVDC-connected generation are becoming very important-particularly when connected to weak ac grids. Therefore, the compliance of conventional Grid Codes should be settled urgently to tackle operational challenges. In this paper, Grid Code requirements on HVDC schemes connected to weak grids are presented. Reactive power and fault ride-through requirements specified by the European Network Code and the Great Britain Grid Code on HVDC are analyzed in detail. The impact of grid strength on the operational requirements of HVDC systems connected to weak grids and compliance testing are performed through simulation studies conducted on a test system.