Harmonic Analysis and Suppression Strategy Research of M3C Converter Based on Fractional Frequency Transmission System

The modular multilevel matrix converter (M3C) is an essential device in fractional frequency transmission system(FFTS), characterized by the absence of an intermediate DC link and a complex harmonic problem. In order to enhance the operational stability of the M3C, reduce equipment damage rates, and mitigate economic losses, this paper focuses on the topology of M3C and its fundamental operational relationships under both symmetric and asymmetric operating conditions. Specifically, the study investigates the voltage ripple across capacitors and the current harmonics in bridge arms. Furthermore, the harmonics are categorized based on phase sequences, and corresponding suppression strategies are proposed to address the diverse harmonic phase sequences.