Harmonic Characteristics and Influence Factors of Output Voltage in Modular Multilevel Converters

This paper focuses on the harmonic characteristics and influence factors of the AC output voltage in a MMC converter, which plays an important role in the design and operation of practical MMC-HVDC projects. Firstly, the specific expression of the AC output voltage is derived. Secondly, a test model based on PSCAD/EMTDC is set up to verify the derived analytical expressions. Lastly, the harmonic characteristics and influence factors of the output voltage is discussed. This paper reaches a conclusion that the number of sub-modules, the voltage modulation ratio, the operation conditions and the control frequency are four key factors that influence the harmonic characteristics of the AC output voltage.