Simplified Time-Domain High-Order Model for MMC-HVDC Converter Stations During Line Faults Considering Line Boundary Elements

Accurate modeling of MMC-HVDC converter stations during faults is essential for designing protection and fault location techniques of MMC-HVDC transmission lines. The existing widely adopted RLC equivalent model fails to consider the effect of line boundary elements such as boundary inductors and capacitors. To improve the modeling accuracy, this paper proposes a fourth order and a sixth order circuit model to represent the discharging process during faults. The model considers not only the MMC but also the boundary inductors and capacitors. With the physical laws during faults, the equivalent dynamic model for different fault types are established using differential equations. To validate the accuracy of the model, the instantaneous voltages at source terminals are measured, and the instantaneous currents are calculated to be compared to the measured instantaneous currents. Numerical experiments in PSCAD/EMTDC show that the proposed equivalent source models can well match the physical laws of the MMC-HVDC stations during the discharging process caused by the fault. The results also demonstrate that the accuracy of the proposed models is higher than the accuracy of the existing model.