Energy storage requirements of full-bridge modular multilevel converter with zero sequence voltage injection

Hybrid transmission systems associated with line commutated converters (LLC) and voltage source converters (VSC) have gradually become a particular solution for high voltage direct current (HVDC) transmission. The full-bridge submodule (FBSM) based modular multilevel converter (FB-MMC) has gained significant attention for its dc voltage reversal and fault ride through capabilities. However, large capacitance is essential for high power transmission of FB-MMC, increasing cost and size rapidly. This paper analyzes the FBSM voltage fundamental frequency and second-order harmonic fluctuations of the FB-MMC with zero sequence voltage injection. The design principles of the FBSM capacitance are also presented compared with the one without zero sequence voltage injection under equivalent voltage ripple conditions. Finally, comparative simulation results on a FB-MMC system verify the correctness of the analyses.