Comparative Analysis on Small-Signal Stability of Multi-Infeed VSC HVDC System With Different Reactive Power Control Strategies

Voltage Source Converter based High Voltage Direct Current (VSC HVDC) technology is used more and more in modern power systems. Consequently, in the ac network, an increasing number of converters are appearing in mutual electrical proximity, thus forming Multi-Infeed (MI)-HVDC systems. For VSC technology, several aspects of MI-HVDC system operation are less well understood compared to Line Commutated Converter (LCC) HVDC systems. This paper studies an MI system which consists of two VSC HVDC schemes based on Modular Multilevel Converters (MMC) interconnected with an ac line and connected to an external grid. The aim of the study is to identify the small-signal stability properties of such a system, thereby focusing on the impact of different outer control loops for reactive power and ac voltage regulation.