An Optimised Independent Arm Modulation Strategy Driven by Energy Balance Mechanism for Circulating Current Suppression in Arm‐Multiplexing Modular Multilevel Converters

ABSTRACT The arm‐multiplexing modular multilevel converter (AM‐MMC) is a promising lightweight, high‐power‐density topology owing to its ease of implementation and fault resilience. Nonetheless, conventional modulation strategies require significant circulating currents for energy balance. Accordingly, a time‐domain analytical model is established to systematically elucidate the general energy balance mechanism. The analysis shows that proper regulation of the middle arm voltage allows the AM‐MMC to achieve energy balance with negligible circulating current. Then an optimised independent arm modulation (OIAM) strategy is proposed, involving the systematic design of DC, second‐ and fourth‐harmonic components in the middle arm voltage, allowing the AM‐MMC to operate near the energy balance boundary without circulating current in steady state. Moreover, due to its high energy accumulation efficiency, the fourth‐harmonic circulating current is incorporated using a PR controller to stabilise energy deviation while maintaining dynamic performance with minimal overhead. These features are particularly beneficial when AM‐MMCs employ wide‐bandgap (WBG) devices, whose fast‐switching transients with high dv/dt and di/dt make the converter more sensitive to circulating‐current stress. Finally, an 85 MVA/±35 kV simulation model and a 3.2 kVA/ ± 150 V prototype are developed to validate the proposed OIAM strategy and demonstrate its advantages over conventional modulation strategies.