An Overview on the Primary Control of VSC-MTDC Systems

Offshore wind farms are one of the most significant renewable resources in providing the power demand of the onshore AC grids. The development of power electronics devices recently has caused the optimal use of wind power in the context of VSC-MTDC systems. The proper operation of the VSC-MTDC systems strictly depends on the DC-link voltage control and optimal power-sharing during normal and post-contingency conditions. Accordingly, in this paper, the hierarchical control structure of the VSC-MTDC systems, modeling of voltage source converter (VSC) based on its control system implementation, and limitations of VSCs are investigated. Furthermore, a detailed review of the various types of the inner-current control loop implementation (PI linear control, sliding-mode control, and model predictive control), coordination strategies of the primary control layer (master-slave, voltage margin, and droop-based methods), and control modes of VSCs are proposed.