Research on modeling and control strategy of modular multilevel matrix converter based on double dq coordinate transformation

Modular multilevel matrix converter (M3C) is a new topology of ac/ac power converter, which has very broad application prospects in asynchronous interconnection of high-voltage and high-power systems. Therefore, it's significant to study mathematical modeling and control strategy of M3C. By implementing αβ0 coordinate transformation in 3 subconverters respectively, it could be found that during symmetry operation the non-zero sequence component of each subconverter was only related to the components of input-side system and the zero sequence component was only related to the output-side components. Based on this conclusion, the paper first implemented dq coordinate transformation not only in the non-zero sequence components but also in the zero sequence components and thereby deduces the mathematical model of M3C under dq axis. The model decoupled two kinds of frequency components and converts them into DC components. The control strategy of the deduced M3C mathematical model was also proposed in this paper. Under this control strategy, all components were of clear physical concept and all controlled variables were dc components during steady state. Therefore, it was easier to ensure the non-error regulation of the control system compared to previous literatures which control M3C under αβ0 axis. The simulation results of M3C in Matlab environment verify the correctness of the mathematical model and superiority of the control strategy.