Inter-arm self-balancing characteristics of modular multilevel matrix converter

• M3C frequency-domain model. • Interarm self-balancing in M3C: characteristic and influencing factors. • A novel control strategy based on interarm self-balancing characteristic. Modular Multilevel Matrix Converter (M3C) is the key frequency converter of flexible low-frequency ac transmission system, but the inter-arm balancing strategy is usually complicated due to its degree of freedom of difference-mode terms of submodule capacitor voltage. To solve this issue, the input, output and circulating current model and internal energy dynamics model of M3C are firstly established based on the two-dimensional sequence analysis method. Then, the M3C arm power equation is derived considering the difference-mode terms of submodule capacitor voltage to reveal the inter-arm self-balancing phenomenon, and its influencing factors are analyzed. Accordingly, a novel control scheme for high-voltage, high-capacity scenarios is designed. The outer loop eliminates the eight inter‑arm voltage balancing controllers required in conventional control scheme. Finally, the inter-arm self-balancing of M3C is verified in MATLAB/Simulink. The result shows that the proportional gain inner-cycle current control is the major influence factor of inter-arm self-balancing, and the self-balancing performance declines with the proportional gain increasing for typical control bandwidth.