Modeling and Analysis of Modular Multi-level Converter-Based HVDC Systems to Investigate Geomagnetic Disturbance Effects.

The MMC-based HVDC systems provide excellent performance. As geomagnetic disturbances (GMD) can be catastrophic events for the power system including MMCs, this research is dedicated to investigating the GMD impacts on the MMC systems. A practical system is selected to provide the most realistic and reliable results. An analytical model is provided to determine the share of the MMC in the harmonics resulting from transformer saturation. Also, a mitigating control block is designed and proposed to eliminate major harmonics in the grid current in the case of GMD. It improves the power quality in the grid, and it reduces the risk of blackout in the system. A control approach is proposed for the reactive power compensation during GMD. It supports grid voltage stability. Simulation results are provided to validate the effectiveness of the proposed methods, which improve the grid power quality and reduce the risk of voltage collapse.