Application of MMC with Embedded Energy Storage for Overvoltage Suppression and Fault Ride-through Improvement in Series LCC-MMC Hybrid HVDC System

The series line-commutated converter (LCC) and modular multilevel (MMC) hybrid high-voltage direct current (HVDC) system provides a more economical flexible alternative for ultra-HVDC (UHVDC) transmission, which is the so-called Baihetan-Jiangsu HVDC (BJ-HVDC) project of China. In one LCC two MMCs ( $1+2$ ) operation mode, sub-module (SM) capacitors suffer most rigorous overvoltage induced by three-phase-to-ground fault at grid-side MMC valve-side single-phase-to-ground in internal MMC. order to suppress such huge overvoltage, this paper demonstrates novel employing MMC-based embedded battery energy storage (MMC-BESS). Firstly, inducements SM are analyzed. Then, coordinated with MMC-BESS, new ride-through (FRT) strategies proposed improve FRT capability. Finally, several simulation scenarios carried out on PSCAD/EMTDC. suppression verified against auxiliary device used BJ-HVDC monopolar system. Further, validated southern Jiangsu power grid China based planning data summer 2025. Simulation results show that MMC-BESS could effectively