This project between KU Leuven and the French transmission system operator Rte analyzed Voltage Source Converter (VSC)-based High Voltage Direct Current (HVDC) links in a bipolar configuration with Grid-Forming (GFM) Modular Multilevel Converters (MMCs). The studies evaluated the impact of GFM-MMCs on AC system dynamics and investigated the small-signal stability of the system to identify interactions between GFM-MMCs and AC systems.
Start date: 1 August 2020
End date: 31 July 2024
Voltage Source Converter (VSC) based High Voltage Direct Current (HVDC) connections are becoming a popular solution for grid expansion project. The increasing power ratings of VSC HVDC interconnectors make the bipolar configuration an interesting alternative to be considered over its symmetrical monopolar counterpart. At the same moment, Grid-Forming (GFM) converter control strategies are being proposed as a possible solution to power system stability concerns raised by the increased share of inverter-based resources. When it comes to bipolar VSC HVDC links, including GFM control principles to the picture raises several unanswered research questions.
The main objectives of project were:
- To analyze the grid-forming capabilities of a bipolar MMC-based VSC HVDC link for different system control configurations
- To evaluate the impact of the GFM-MMCs impact on the AC system dynamics
- To investigate the small-signal stability of bipolar HVDC connections with GFM converters and identify interactions between converters and AC systems depending on the location of these GFM converters with a particular focus on the sub-synchronous modes that significantly influence system dynamics
- To identify the presence of potentially unwanted interactions among GFM converters and eventually design a control strategy for their mitigation
