A Single-End Protection Scheme for Hybrid MMC HVDC Grids Considering the Impacts of the Active Fault Current-Limiting Control
Saizhao Yang, Wang Xiang, Meng Zhou, Wenping Zuo, Jinyu Wen
Abstract
In the hybrid modular multilevel converter (MMC) based high voltage direct current (HVDC) systems, the fault current can be actively suppressed by the converter itself, which endows a smaller requirement for current-limiting reactors (CLR) and a larger time margin for fault detection algorithms, comparing with the half-bridge MMC. But the robustness to fault resistance and noise disturbance of existing boundary protection schemes will be deteriorated with small CLRs. Moreover, the fast response of the fault current-limiting control will change the output DC voltage of hybrid MMC, which affects the fault characteristics and may cause mal-operation of existing protection algorithms. Thus, a single-end protection scheme considering the impacts of the active current-limiting control is proposed for the hybrid MMC based DC grids. The traveling-wave characteristics under different fault stages are analyzed to evaluate the impacts of the fault current-limiting control. In addition, a coordination protection strategy versus different fault conditions is adopted to improve reliability. Various cases in PSCAD/EMTDC are simulated to verify that the proposed method is robust to fault resistance, fault distance, power reversal, AC faults, and immune to noise.