A new modular multilevel type solid state transformer with internal model control method

Abstract

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.