ZVS Analysis and Control Strategy for Back-Stage of Single-Phase AC-DC-DC Converter With Low-Frequency DC-Link Voltage Ripple

As a module of power electronic transformer (PET), single-phase isolated ac-dc-dc converter is popular in high-power applications. However, there is inherent instantaneous power difference between ac input and dc output, which leads to a significant low-frequency voltage ripple on the dc-link capacitor. It will affect the performance of dual active bridge (DAB), such as the range of zero voltage switch (ZVS) and output voltage ripple. So, the relationship between ZVS range of DAB converter and the input voltage is deduced. According to this relationship, leakage inductance of transformer is designed to realize full power range soft switching of the back-stage DAB. To suppress output voltage ripple, a feedback linearization control strategy is proposed. Finally, the rationality of the designed transformer leakage inductor and effectiveness of the proposed control strategy are verified by simulation. The simulation results show that the dc-link voltage ripple does not significantly increase the peak and RMS current of transformer, and the designed leakage inductor can realize ZVS in full power range of when the dc-link capacitor contains ripple. Moreover, the proposed control strategy can suppress the dc-link ripple transferring to the output.