A modified nearest-level modulation method for modular multilevel converter with fewer submodules

The modular multilevel converter (MMC) is considered to be the state of the art in medium- and high-voltage application. The nearest level modulation (NLM) method is one of the most popular modulations, however, when applied to MMC with small number of sub-modular (SM), the output waveforms contain large harmonic components. This paper proposes a modified NLM method. By changing the traditional rounding function to suppress harmonics of the output voltage without obviously changing capacitor voltages and switching frequency of power devices. Besides, the proposed modified method still keep the advantages of traditional NLM method, such as simple implementation. Finally, simulation results based on MATLAB/Simulation verify the effectiveness of the proposed modified NLM method.