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

  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.