Circulating Current Suppression Strategy Based on Virtual Impedance and Repetitive Controller for Modular Multilevel Converter Upper and Lower Bridge Arm Capacitance Parameter Asymmetry Conditions

In recent years, modular multilevel converters (MMCs) have been increasingly used in the field of electric vehicle charging and discharging due to their unique performance advantages. However, cascade structure MMCs raises problem circulating current. Due chemical processes, aging effects, etc., capacitance parameters upper lower bridge arms will be asymmetric, which introduce odd harmonics into current, increasing system losses threatening reliability. To address this phenomenon, paper proposes a current suppression strategy with additional virtual impedance (VI) based on repetitive controller (RC). The corresponding simulation models were built for comparative study different strategies. results show that VI-RC can significantly reduce even under asymmetric conditions, total harmonic distortion (THD) arm is only 0.98%, verifies effectiveness proposed strategy.