Study of Control Scheme for VSC-HVDC Interconnection Engineering Based on Cascaded Three-Level Converter

With the continuous growth of electricity load on islands, the original AC submarine transmission cable is faced with the problems of relatively weak grid structure and insufficient transmission capacity. In order to improve the power supply reliability of island system, based on the technical and economic advantages of the C-NPC (cascaded neutral point clamped three-level converter), its topology is applied to the VSC-HVDC interconnection engineering for islands for the first time. The potential instability problems of C-NPC under different control strategies are analyzed. An additional control strategy for the DC voltage sharing and AC current sharing among C-NPC modules is proposed. The effectiveness of the additional control method is verified by PSCAD simulation. Taking an engineering as the object, the typical system operation simulation is carried out, which verifies good operation characteristics of the island system.