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

• Main Authors: Muchao Xiang, Jiabing Hu, Yufeng Qiu
• Format: Article
• Language: English
• Published: Wiley 2018-12-01
• Series: High Voltage
• Subjects: HVDC power convertors; power capacitors; voltage control; power grids; electric current control; capacitor voltage ripple reduction; FBSM MMC; converter loss; sub-module voltage ripple; high-voltage direct current systems; modular multilevel converters; coordinated control method; power loss reduction; full-bridge sub-module-MMC; arm current; second harmonic circulating current injection; DC short-circuit; AC voltage boosted full-bridge sub-module; SHCC elimination
• Online Access: https://digital-library.theiet.org/content/journals/10.1049/hve.2018.5050

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.