Research on the Power Control of MMC-PET System Based on VSG and PBC

Power Electronic Transformer (PET) is a new type of power electronic device with flexible topology access, which has a wide range of application prospects in AC and DC microgrids. For the control of the MMC-PET system, which is cascaded by a modular multilevel converter (MMC) and dual active bridge (DAB), the traditional PI control method lacks damping inertia, has poor dynamic performance, and is unable to modulate the frequency actively. This paper proposes a current and voltage control technique based on virtual synchronous generators (VSG) theory and passivity-based control (PBC) theory. Firstly, the basic topology and working principle of MMC-PET are introduced, and the mathematical models of MMC and DAB are analyzed. Secondly, the passivity of MMC is investigated, and the passive controller is combined with the VSG control with primary FM to optimize the MMC-PET control so that the MMC-PET system has the function of primary FM with better robustness. Finally, the MMC-PET system model is constructed in Matlab/Simulink. The simulation experiments of the above VSG and PBC control methods are carried out under the working conditions of frequency fluctuation and load change in the power grid. The results show the feasibility and effectiveness of the proposed MMC-PET system model and control method.