A Current Reallocation Strategy to Attenuate the Peak Arm Current of the Modular Multilevel Matrix Converter

The modular multilevel matrix converter (M³C) is a promising candidate for direct ac-to-ac conversion systems. This paper proposes a novel arm current reallocation strategy for the M³C to attenuate the peak arm current. The principle of the proposed strategy is to dynamically adjust the distribution of the positive-sequence current components among the three star-figure subconverters according to their respective instantaneous zero-sequence current components. First, a square-value-based strategy is proposed and its performance in attenuating the peak arm current at different current conversion ratios is evaluated. Then, the impacts of the proposed strategy on the root-mean-square value of the arm current and submodule capacitor voltages ripple are analyzed. Based on the analysis, an algorithm for determination of the reallocation coefficient, and embedment of the proposed strategy in the existing control methods is developed. Based on the proposed strategy and depending on the current conversion ratio of the M³C, up to 14.6%-21.6% of the peak arm current can be attenuated. Performance and effectiveness of the proposed current reallocation strategy are verified by simulation studies conducted in the MATLAB/Simulink software environment.