Proposed a New Voltage Rebalancing Method for Pole-to-Ground Fault in Bipolar Two-Level VSC-HVDC

Two-level converter and modular multilevel converter (MMC) are the most commonly used converters in voltage-source converter-based high-voltage direct current (VSC-HVdc) system. Pole-to-ground fault is the most probable temporary dc fault in a bipolar VSC-HVdc system, which causes a voltage drop across the faulty pole and an overvoltage on the healthy pole. In order to restart the system after fault clearance, it must first eliminate the unbalanced voltage on the poles. The speed of voltage rebalancing is so important issue for fast restarting. In this article, a new voltage rebalancing method comprised of a simple auxiliary circuit is proposed in the bipolar two-level VSC-HVdc. The proposed scheme not only has fast restarting speed but also minimize power losses during restoration. Moreover, its control system is simple. The principles of the proposed scheme, design considerations, and control method of that are investigated. Finally, the proposed scheme is verified by the simulation and experimental results in a bipolar two-level VSC-HVdc.