The Modular Multilevel Matrix Converter (M3C) is a high-power high-voltage direct AC/AC power converter topology which is suitable for low frequency power transmission and distribution systems, such as offshore wind power integration, long-distance FFTS and subsea electric system. But it has obvious non-linear characteristics, complex system structure, high model order and complex control task. Based on the analysis of vector control, this paper proposes a high-order sliding mode control (SMC) strategy combining linear sliding mode with non-singular terminal sliding mode to control a high-order nonlinear system. According to the simulation results of the output waveform quality and power characteristics, the M3C has a better performance under SMC than PI control. The control strategy proposed in this paper can quickly and simply control high-order nonlinear strongly coupled systems, which provides ideas for the stability control of power systems.

Modular multilevel matrix converter,fractional frequency offshore wind power system,sliding mode control,nonlinear control