Modeling on Transient Characteristic and Suppression Control of DC Fault in MMC-HVDC System

This paper focuses on analyzing the transient characteristic of DC transmission line fault in the modular multilevel converter based high voltage direct current (MMC-HVDC) system. Equivalent circuit models of DC transmission line pole-to-ground fault, pole-to-pole fault and line breaking fault are established respectively in this paper. The mechanism of DC faults is analyzed and mathematical expressions of fault voltage and fault current are derived. The transient processes of these faults are analyzed based on the equivalent circuit models. The suppression control for DC fault based on virtual impedance is studied to reduce the over current level. Simulation results with a 2-terminal MMC-HVDC model on the RT-LAB platform verify the modeling and analysis on transient characteristic and the effect of suppression control of DC transmission line fault. (paper)