Using integrated gate commutated thyristor (IGCT) to construct an active neutral point clamped (ANPC) three-level converter is an effective way to meet the needs of medium-voltage and high-power converter systems. The inner tube fundamental frequency modulation can reduce the commutation path length of the IGCT valve string

thereby reducing commutation loop spurs and reducing the turn-off voltage stress of the power device. This article first reveals the mechanism of the internal tube overvoltage caused by the existing inner tube fundamental frequency modulation strategy applied to the IGCT-based ANPC topology

and further analyzes the limitations of the existing inner tube overvoltage suppression method based on RCD snubber circuits. Finally

an optimized inner tube fundamental frequency modulation strategy commutation method with inner tube overvoltage suppression function is proposed to completely avoid the inner tube overvoltage problem. The experiment verifies the correctness of the theoretical analysis and the feasibility of the proposed method.