Research On The Comprehensive Control Scheme Of Modular Multilevel Matrix Converter-based Power Electronic Transformer

As one of the most important equipment in the power system, power transformer is used in various electric fields widely, while the defects such as large volume, heavy weight of the traditional transformer always exist. Today, with the wind, solar and other kinds of distributed energy access, and the widely use of power electronics device, power quality of power system is reduced greatly, however, the user demand on power quality is getting higher and higher. Traditional power transformer has not satisfied the requirements of modern power system.Power Electronic Transformer (PET) as a new type of transformer, combined with the characteristics of the power electronic converter and transformer, can control the primary side and secondary side flexibly, have a lot of new features and potential to solve new problems in modern power system. Restricted by the voltage and power of existing switching devices, the study of PET most focus in the field of medium and small power. With the study of medium/high-voltage high-power power electronic converter, makes people begin to pay attention to study application of PET in high pressure and high power occasion. The existing structure of medium/high pressure high-power PET is cascade in high voltage stage, and parallel in low voltage stage. This kind of structure needs series many HF/MF transformers, and lots of power electronic devices. Although realized the application of PET in high voltage and large capacity field, but compared with the traditional transformer, its Improvement on volume and weight is not enough.Low voltage power devices are used in medium or high voltage applications via a new cascade H bridge modular multilevel matrix converter (M3C/MMMC) with the merits:low harmonic content and dU/dt, don’t need a large number of clamp diode and flying capacitor, and easy to modular. In this paper, M3C is the high voltage input side of M3C-based PET, which can combine the merits of M3C. M3C can realize direct AC/AC transformation, don’t need the intermediate dc link, and the topology need only one MF/HF transformer, rather than to series many transformers. This topology save the cost of PET, and has greater advantages on volume and weight.In this paper, the main research object is M3C-based PET. Analyses the basic topological structure and the basic principle, in detail, and present the related topology; establish the mathematical model of PET circuit; design the control strategy of the PET:input stage adopts hierarchical capacitance voltage outer loop control and arm current inner loop control, and output stage adopts phase shift closed-loop control; design circuit parameters of PET and its modulation strategy; study the control strategy of MMC-based PET, at last. Simulation results show the effectiveness of the proposed control strategy and the rationality of the circuit parameters design.