4th China International Youth Conference on Electrical Engineering (CIYCEE 2023)

Fractional Frequency Transmission System (FFTS) has gained significant attention in the offshore wind power industry by utilizing the Modular Multilevel Matrix Converter (M3C) as a power converter. However, the direct coupling of inputs and outputs operating at different frequencies within the M3C-FFTS presents substantial challenges for system modeling and control. Hence, this paper presents a novel M3C hybrid modeling method to effectively decouple the power frequency side from the fractional frequency side. The power of each sub-converter bridge arm is represented using αβο, enabling us to derive and calculate detailed mathematical expressions for each power term. This approach establishes a solid theoretical foundation for achieving M3C capacitor voltage balance control. Building upon the hybrid modeling, we propose a novel control strategy for the M3C-FFTS system, aimed at ensuring balanced input and output conditions. The efficacy of the proposed modeling method and control strategy is verified through simulation using MATLAB/Simulink. 

Fractional frequency power transmission,modular multilevel matrix converter (M3C),Differential-mode- common-mode decoupling,Capacitor voltage balance control