Search

This paper develops a new control strategy for voltage source converter (VSC) based multi-terminal high voltage dc (MT-HVDC) grids for enhancing the mutual frequency support between MT-HVDC interconnected asynchronous ac systems. The existing droop control structure of VSCs is augmented with an additional feedback voltage-based loop that generates a voltage shifting term to be added to the original dc voltage reference. The addition of this integrator-based controller nullifies the difference between voltage errors seen at adjacent converter stations. This action helps to overcome inaccuracies in the mutual frequency support caused by the uneven voltages across a dc system. The proposed strategy uses only local variables for the continuous-time control; thus, it does not rely on a high-bandwidth communication network, and its performance is not affected by the change of ac systems’ parameters. Modal analysis is carried out to investigate the stability of the proposed controller. Finally, comprehensive simulation studies are used to verify the proposed strategy’s performance and compare it with recently reported alternative controllers. [ABSTRACT FROM AUTHOR]

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 eigenvalues 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. [ABSTRACT FROM AUTHOR]