Modeling, control, and protection of modular multilevel converter-based multi-terminal HVDC systems: A review

Multi-terminal direct current (MTDC) grids provide the possibility of meshed interconnections between regional power systems and various renewable energy resources to boost supply reliability and economy. The modular multilevel converter (MMC) has become the basic building block for MTDC and DC grids due to its salient features, i.e., modularity and scalability. Therefore, the MMC-based MTDC systems should be pervasively embedded into the present power system to improve system performance. However, several technical challenges hamper their practical applications and deployment, including modeling, control, and protection of the MMC-MTDC grids. This paper presents a comprehensive investigation and reference in modeling, control, and protection of the MMC-MTDC grids. A general overview of state-of-the-art modeling techniques of the MMC along with their performance in simulation analysis for MTDC applications is provided. A review of control strategies of the MMC-MTDC grids which provide AC system support is presented. State-of-the art protection techniques of the MMCMTDC systems are also investigated. Finally, the associated research challenges and trends are highlighted.