Cao Yijia

A new modular multilevel type solid statetransformer with internal model control method

To overcome the limitation of the existing topologies and control strategies of Solid State Transformers, a Modular Multilevel Converter type solid state transformer (MMC-SST) topologies and its corresponding internal model control (IMC) method is introduced in this paper. Firstly, the structure and operation characteristics of MMC-SST were analyzed, and accordingly its mathematical model of input and output-stage in synchronous rotating d-q frame was established. Secondly, a new kind of duel-loop control structure was developed by combining the IMC current inner loop and PI voltage outer loop, according to the characteristics of IMC. Lastly, a simulation model of MMC-SST was established based on Matlab/Simulink, the grid side voltage amplitude mutation, load capacity transient and grid side power factor change in various conditions are simulated. Results show that the MMC-SST based on internal model control can run under different power factor, as well as the fast transient response of voltage and current , strong ability to resist load disturbance characteristics, and can improve the robustness of the system.