Voltage and Power Balance Control of Cascaded Power Electronic Transformer With Minimum Power Backflow

To solve the problem of voltage imbalance at DC side of rectifier stage of the cascaded power electronic transformer, unbalanced transmission power of each DAB module at the isolation stage and power backflow of each DAB module. the paper, on the basis of analyzing the cause of power backflow, deduced the duty ratio at the minimum power backflow in the case of double phase shift in detail, In addition, a voltage-sharing and average power control strategy based on minimum power backflow was put forward. Of which the voltage equalization control was adopted for the rectifier stage, and average power control based on minimum power backflow was utilized for the isolation stage. The average power control took the power transmitted by each DAB module as the feedback quantity to adjust the phase shifting ratio between the front and rear bridges of the DAB module and the internal phase shifting ratio of the front bridge. Even if the parameters of each DAB module are not balanced, such control strategy, be able to not only guarantee the power balance, but effectively reduce the power backflow and improve the efficiency of the converter. Finally, the effectiveness of the control strategy was verified through simulation.