A Coordinated Control Strategy for VSC MTDC System

In order to balance the system dynamic response speed and the ability to precisely control the active power of converter, and to ensure a certain rigidity of DC voltage control, the control strategy that the constant power characteristics in characteristic curve of DC voltage margin control is converted into characteristic of slope control is proposed, which is also taken as the control characteristic of assistant station. The constant DC voltage control is used in master station, and the combination of constant DC current control and DC voltage droop control is applied in other stations. The corresponding structure and parameters of the controller are designed according to the control characteristic of converter station. In the end, a five terminal VSC MTDC model is developed in PSCAD/EMTDC, and simulations are carried out under different operating conditions. The results show that the coordinated control strategy can meet the requirements when the system operates under different conditions.