AC to Variable DC(Buck and Boost) Modular Multilevel Converter Using Half Bridge and Full Bridge Cells

This paper presents a control strategy of modular multilevel converter which produces variable DC output from a three phase AC source. With this proposed strategy the output DC voltage of the converter can be bidirectional (i.e. both positive and negative) and can be varied to a value higher than the peak input voltage (boost), or to a value lower than the peak input voltage (buck). A simple synchronous reference frame control using level shifted PWM is used. Capacitors are balanced using sorting algorithm. The proposed strategy is implemented in simulation using MATLAB. A potential application of the converter is the development of small DC power supplies producing variable DC voltage from zero to a high value. Also it can be used in DC drives.