Cooperative Control Strategy for Power Balance of VSC-MTDC System

In multi terminal flexible direct current transmission systems, the droop control strategy is a widely used means, which can automatically adjust multiple converter stations to balance the power imbalance within the system. However, this strategy is often accompanied by the problem of significant DC voltage offset during power adjustment. On the basis of traditional droop control, this study introduces a feedforward compensation mechanism to adjust unbalanced power, and adopts the technique of moving droop curve to effectively improve the active power compensation capability of VSC-MTDC system in dynamic process, thereby optimizing the response performance of DC voltage. Furthermore, by integrating a DC voltage controller into the droop control strategy and optimizing the increment of the power reference value, precise adjustment of the DC voltage has been achieved. The feasibility and effectiveness of the proposed control strategy were verified by simulating the five terminal VSC-MTDC system using PSCAD/EMTDC software.