Application of virtual synchronization control strategy in MMC based VSC-HVDC system

In this paper the virtual synchronization control strategy is applied to MMC based VSC-HVDC system to improve the performances of stable state and dynamic state. The small signal model of the virtual synchronization controller is built to show the performance when the system is subjected to small interferes. Then the characteristics of the system in different operation state are analyzed. As the virtual synchronization control can be self-synchronized automatically with the grid without requiring any dedicated physical synchronization control units, the MMC based VSC-HVDC system can track the grid frequency accurately after connected to the grid. When the grid fails or needs offline maintenance, it can continue to operate in islanded mode. The validity and effectiveness of the proposed control strategy is verified by extensive simulations in PSCAD/EMTDC.