Analysis and control of the modular multilevel matrix converter under unbalanced grid conditions

The modular multilevel matrix converter (M³C) is a promising candidate for direct ac-to-ac conversion systems, particularly for low-frequency ac transmission. This paper is focused on the control of the M³C under unbalanced grid conditions. First, the current control structure of the M³C is improved, which not only enables independent control of common mode and circulating currents with a reduced number of controllers, but also enables a pure dc control system. Then, the arm imbalanced power caused by negative-sequence voltage and current is calculated, based on which a feedforward compensation strategy through circulating current is proposed. Performance and effectiveness of the proposed control and modulation strategies are verified by simulation studies conducted in the MATLAB/Simulink software environment.