A Control Strategy of VSC-MTDC Transmission System Based on Voltage Margin

This paper presents a control strategy of multi-terminal HVDC transmission system (MTDC) using voltage source converters (VSCs) based on voltage margin, a four-terminal VSC-MTDC system with two transmitting ends and two receiving ends is established and the framework and operation principles of the proposed system are described. The control strategy proposed in this paper adopts constant AC voltage and constant frequency control for the sending-end converter stations. The voltage step difference is formed by setting different voltage reference values for the receiving end converter stations. The relationship between the maximum limit of the d-axis current in the controller and the active power absorbed by the converter station is obtained by deduction. Simulation results by PSCAD/EMTDC under normal and abnormal operation conditions verifies the correctness of the control strategy and the simulation shows that the control method has good steady-state characteristics and dynamic performance.