A Method of Balancing Control for Capacitor Voltage of Modular Multilevel Converter

Abstract

This paper introduces the operation principle of modular multilevel converter and balancing control method of capacitor voltage. Considering the condition under external disturbance which may lead to outputting unbalanced voltage and waveform distortion when using traditional single-phase bridge average voltage control, three-phase bridge average voltage control is proposed combined with carrier phase-shifting modulation. Proportion integral adjustment is adopted for sub-module capacitor voltage so that the modular capacitor voltage fluctuation can be maintained in a stable range. Simulation shows the feasibility of capacitor voltage balancing control.

Keywords

• modular multilevel converter(MMC)
• high voltage direct current(HVDC)
• carrier phase-shifting modulation
• voltage balancing control
• circulating current