Coordinated control of power loss and capacitor voltage ripple reduction for AC voltage boosted FBSM MMC with second harmonic circulating current injection

Reducing the converter loss,sub-module voltage ripple and handling DC short-circuit faults in high-voltage direct current systems are crucial for the economical and reliable operation of modular multilevel converters(MMCs).This study proposes a coordinated control method of power loss reduction and capacitor voltage balancing for AC voltage boosted full-bridge sub-module(FBSM)-MMC by controlling the second harmonic component in the circulating current.The relationship between converter loss and second harmonic circulating current(SHCC)is firstly derived for AC voltage boosted FBSM-MMC.From the analysis,it can be seen that the converter loss and ripple can be optimised by injecting the SHCC into the arm current when compared with SHCC elimination.Simulation results of an AC voltage boosted FBSM-MMC with typical parameters using PSCAD/EMTDC confirm the feasibility and validity of the proposed loss and ripple reduction method.