Analysis of integration of multi-terminal HVDC network to weak grids

In this study, the integration of multi-terminal high voltage direct current (HVDC) systems to weak power grids is analysed under different grid strengths and control methods. In this study, a modular multi-level converter based MTDC network is considered. The analysis showed the importance of voltage control of DC network. The voltage control of DC network needs to be performed from the converter station connected to the strongest AC network. Furthermore, the analysis shows that either droop or proportional-integral control can be used for controlling the DC voltage of the MTDC network connected to one or more weak grids. However, the droop control of DC voltage provides faster response compared to PI with larger steady state error. Finally, the analysis showed that the modular multi-level converter (MMC)-based MTDC is capable of ride-through unbalanced AC side faults even if the faults occur in a weak grid.