Circulating Currents Suppression Strategies for Modular Multilevel Converter

This work presents a comparative study of two control strategies proposed to minimize the circulating currents in modular multilevel converters. Different control strategies and algorithms can be used to regulate and equalize the DC voltages of the submodules of modular converters. However, despite of the accurate voltage regulation, circulating currents arise between the positive and negative arms of the converter's branches, as well as between the phases of the converter, due to small imbalances on the terminal and submodules voltages. Thus, a mathematical modeling of the circulating current is presented and the performance of two strategies, one based on dq synchronous reference frame controller and the other based on a resonant controller, are investigated. Simulations results are presented to validate the theoretical analyses and to evaluate the effectiveness of both controllers to minimize the circulating currents of the modular converters.