An Enhanced DC Voltage Droop-Control for the VSC--HVDC Grid

This paper introduces an enhanced droop-based dc-voltage control method, including dead-band, for applications to the high-voltage direct-current (HVDC) grid that utilizes the voltage-sourced converter (VSC) technology. The proposed droop-control structure also autonomously imposes energy balance between the HVDC grid and its host ac system. The droop-control method (1) divides the VSC stations into four groups, (2) activates the droop-control of each group based on a prespecified voltage margin, and (3) introduces an improved power-voltage characteristic for desirable VSC station dynamic performance. Feasibility and performance of the proposed control method are evaluated based on time-domain simulation studies in the PSCAD platform, using the IEEE-39-Bus system that imbeds a five-terminal VSC-HVDC grid. Each VSC station is a monopolar modular multilevel converter (MMC). The study results show that the proposed droop-control method enables the HVDC-AC system to reach a new steady state after transient events.