Impedance Modeling of Modular Multilevel Matrix Converter with Decoupled Control Strategy Based on Harmonic State-Space Method

Low-frequency transmission system (LFTS) has become a highly competitive technical solution for the long-distance transmission of wind power electricity. Because power transmission systems that adopt multilevel converters have generally been plagued by stability issues, it is necessary to research the dynamic characteristics of modular multilevel matrix converter(M³C). The paper proposes an impedance model of M³C, which adopts the decoupled control strategy, and the frequency-domain impedance characteristic of M³C is characterized applying harmonic state-space (HSS) method. Firstly, the configurations of the main circuit and control system of M³C are analyzed, and the equations describing characteristics of M³C are organized. Secondly, the relationship between voltage and current at the converter ports is derived, and the impedance model is established. The modelling process is based on the HSS method and can describe the excitation and response characteristics of different small-signal harmonics within the frequency-domain. Finally, The simulation verification based on Matlab/Simulink has been carried out, which verified the correctness of the impedance model proposed, and the impedance characteristics of the M³C are presented. The modelling method has the advantages of being precise and easy to be widely applied.