Operation of MMC-Based VSC-HVDC System Under Geomagnetic Disturbance

This paper presents a novel analysis of the performance of an MMC-based HVDC system in the presence of a solar storm. The detailed models of an MMC and SMs are used to acquire the accurate behavior of the MMC during the GIC. The analysis demonstrates that the current harmonics arising from the DC shift in the transformer flux are distributed between the MMC and grid. A model for the distribution of the current harmonics is introduced. It is revealed that the distribution of the 2
^nd
harmonic of the current is affected not only by the MMC impedance but also by the output current and voltage of the converter as well. Also, due to the unity power factor strategy in the control system of the MMC, the converter does not respond to the increase in reactive power consumption by the transformer. Consequently, a control scheme is proposed to minimize the contribution of the grid in the reactive power augment. This control scheme provides the saturated transformer with the reactive power injected by MMC. The system is implemented in EMTP-RV, and the proficiency of the proposed control scheme is verified through simulation.