Research on Circulating Current Suppression Strategy of Modular Multilevel Converter

Modular multilevel converter MNIC has been extensively studied in recent years because of its unique adaptability to meet high-voltage and large-capacity scenarios. However, the fluctuation of the capacitor voltage of the MNIC sub-module causes circulating currents between the three-phase units, which affects the working characteristics of the converter, increases system losses, and causes excessive economic costs. After comparing various circulating current suppression methods, an improved traditional PI control circulating current suppression strategy is proposed. The fuzzy PI control strategy controls the voltage and the inner loop quasi-proportional control strategy controls the current to achieve the circulating current suppression effect.