Positive and Negative Sequence Circulating Current Control Strategy based on M3C Frequency Domain Characteristics

The modular multilevel matrix converter (M3C) transmission system demonstrates significant engineering application potential due to its ability to enhance line transmission capacity and improve the utilization of renewable energy through frequency division transmission technology. The harmonic characteristics during M3C steady-state operation differ from those of other converters, such as the modular multilevel converter (MMC). Moreover, the circulating current (CC) in M3C can impact the power quality and stability of the system. However, research on the frequency characteristics of M3C CC and its control strategy remains limited. To address this, this paper first determines the harmonic frequency distribution of M3C steady-state operation by leveraging the time-domain model of bridge arm electrical parameters. Secondly, it derives equivalent circuit models for power frequency, low frequency, and CC, providing a foundation for subsequent decoupled control design. Furthermore, based on the harmonic frequency domain characteristics, a positive and negative sequence PR-based CC control strategy is proposed, effectively suppressing CC harmonics in the bridge arm current during steady-state operation. Finally, the harmonic frequency characteristics and the proposed CC control method are verified by Matlab/Simulink time-domain simulations.