Research on voltage balance control of Modular Multilevel Converter for low frequency operation

This paper analyses the reason of module capacitor voltage fluctuation when the Modular Multilevel Convertor (MMC) provide low frequency output voltage to motor. In order to restrain the voltage fluctuation, appropriate values of the arm inductor and the cell capacitor must be chosen. Furthermore, the common voltage is added in output AC phase voltage and the corresponding inner current in the arms is controlled to balance the energy fluctuation of module capacitor due to low frequency AC current.