Analysis of Ripple/Harmonic Coupling Characteristics of M ³ C Under Grid‐Side Asymmetric Faults

ABSTRACT The secure operation of the fractional frequency transmission system faces significant challenges during grid‐side asymmetric faults. This vulnerability stems from two critical technical barriers: the frequency disparity between interconnected grids obscures post‐fault interaction mechanisms, complicating system response analysis and the inherent complexity of modular multi‐ level matrix converter introduces substantial analytical difficulties in fault characteristic identification. This paper proposes a 2D phasor analytical framework that systematically decouples the interactive relationships within M 3 C. Through an iterative analytical approach, the investigation reveals the dynamic cross‐coupling mechanisms between ripples and harmonics under asymmetric faults, particularly addressing the nonlinear interactions between bridge‐arm current and submodule capacitor voltage. The proposed method realises the modelling of multi‐component under‐grid‐side asymmetric faults, precisely delineates the internal coupling modes and further reveals the fault transmission mechanism in the form of a generalised model introduced by fault participation factors. The effectiveness of the proposed method and the accuracy of the analysis are validated through case studies involving three fault scenarios in MATLAB/Simulink.