Control Approach for the Multi-Terminal HVDC System for the Accurate Power Sharing

This paper presents a new control strategy for voltage source converter based Multi-Terminal High Voltage Direct Current (MTDC) systems. The proposed control approach ensures accurate power sharing between the droop-controlled converter stations. By communicating the power-sharing index between neighboring converters, the proposed approach achieves exact droop control operation independent of the DC system topology and line parameters. The pilot voltage droop based controller, which is an alternative communication-based approach for achieving precise power sharing, was used as a base case for comparison. Modal analysis is carried out to reveal the sensitivity of the system's eigen-values to the changes in control parameters (e.g., power droop gain, proportional integral gains of the proposed controller) and the latencies in the communication. It is demonstrated that the proposed strategy remains in the stable operation even when excessive latencies are encountered in the communication. Nonlinear simulations are conducted in the MATLAB/Simulink environment in four-and five-terminal MTDC grids, validating the capability of the proposed controller to achieve the desirable performance under various operational conditions.