A Nine-Level Asymmetrical Full-Bridge Submodule-Based Modular Multilevel Converter for HVDC Systems With Reduced Submodule Count and Improved Efficiency

The article introduces an upgraded version of the Nine-Level (9-L) Asymmetrical full bridge Submodule (A-SM) based Modular Multilevel Converter (MMC) for High Voltage Direct Current (HVDC) transmission. This enhanced design decreases the quantity of MMC SMs by a quarter in comparison to the conventional MMC, while still upholding high output power quality. The Nine-level A-SM-based MMC provides the advantages of modularity, dependability, and exceptional harmonic performance, all the while streamlining the system, reducing expenses, and minimizing size. The improved hybrid modulation scheme and Voltage Balancing (VB) algorithm were devised and successfully validated through simulation. Thorough HVDC simulation assessments display the 9-L A-SM-based MMC's ability to manage real power and its resilience to DC faults. A small-scale hardware implementation of a 9-L A-SM-based MMC with four A-SMs per leg is showcased to confirm its operational concept. In contrast to the symmetrical full-bridge SM-based MMC, the 9-L A-SM-based MMC exhibits enhanced efficiency, decreased semiconductor devices, reduced voltage sensors, and a notably smaller arm inductor size.