Grid-connected/off-grid Switching Control Strategy of MMC-PET AC/DC Hybrid Microgrid Based on Disturbance Observer

A grid-connected/off-grid switching control strategy based on disturbance observer (DO) is proposed to address the transient overcurrent and overvoltage during switching process of grid-connected mode and off-grid mode of AC/DC hybrid microgrids based on modular multilevel converters (MMC) and power electronic transformers (PET), which affect transmission quality and increase equipment losses. In this strategy, a DO observer is used to track the sudden change in current caused by grid-connected/off-grid switching, the difference between the actual current and the theoretical current is used as the equivalent interference quantity, and it is then input into the current inner loop controller for compensation, thereby achieving suppression of the sudden current change. Finally, an MMC-PET AC/DC hybrid microgrid system is built on Matlab/Simulink software, and the effectiveness and feasibility of the switching control strategy proposed in this paper are verified by simulating and comparing the scenarios in the presence and absence of a DO observer during two switching of grid-connected mode and off-grid mode.