Research on overcurrent suppression strategy of true bipolar MMC-HVDC single pole blocking bridge arm

摘要

Due to the characteristics of Vf control in the islanding flexible dc power grid, when the single-pole latching fault occurs at the sending end of the dc power grid, the converter station connected to the new energy island system cannot control the ac voltage and the incoming new energy power at the same time. A healthy pole converter is forced to transfer the active power of the faulty pole converter, which results in the over-current blocking of the healthy pole converter. In this paper, by describing the dynamic process of the bridge arm current when the single-pole locking fault occurs, the mechanism of the over-current is studied, and a new type of additional control is proposed to suppress the magnitude of the over-current of the bridge arm by controlling the dc voltage. Finally, PSCAD/EMTDC simulation results demonstrate the effectiveness of the theoretical analysis and control strategy.