Suppression of the Capacitor Voltage ripple in Modular Multilevel Converter for Variable-Speed Drive Applications

Abstract

The modular multilevel converters (MMC) utilization has brought about a transformative impact on high voltage direct current (HVDC) transmission relying on voltage-sourced converters (VSC). However, their application in medium-voltage (MV) variable-speed motor drives has not achieved broad acceptance due to the substantial voltage fluctuation in the capacitor, especially at lower frequencies. The present study introduces a hybrid MMC (HMMC) aimed at markedly limiting capacitor voltage fluctuations, particularly during low motor speeds. Vector control was used to achieve the required motor speed.  The proposed HMMC validity was confirmed through the MATLAB/ SIMULINK environment. The results were compared with conventional MMC from the standpoint of the capacitor voltage fluctuation at low frequencies.