Simulation study of harmonic characteristics of modular multilevel converter in medium voltage DC power system on ship

Abstract

[Objectives] For a Medium Voltage Direct Current(MVDC) power system on a ship, the application of the Modular Multilevel Converter(MMC)is a hot research topic. Whether the output voltage waveform of the MMC is a sine wave will directly determine the working performance of the MVDC power grid and load,so it is particularly important to improve the harmonic performance of the MMC.[Methods] First,based on the MVDC power system of a ship,the interactions between the harmonic characteristics, voltage level and number of bridge arm Sub-Modules(SMs)of the MMC inverter are studied. Next,the harmonic variation tendency of the MMC under the influence of the sampling period,carrier wave frequency,modulation ratio and arm inductance are studied in detail.[Results] It is found that a higher voltage grade MMC needs to be equipped with a larger number of SMs. When the number of SMs is given, the sampling period and modulation ratio play major roles in the harmonic improvement of the MMC.[Conclusions] The results of this paper can provide valuable references for selecting the parameter design of medium pressure MMC inverters.

Keywords

• Modular Multilevel Converter(MMC)
• Medium Voltage Direct Current(MVDC) power system
• harmonic characteristics
• medium voltage grade