Capacitance Minimization and Constraint of CHB Power Electronic Transformer Based on Switching Synchronization Hybrid Phase-Shift Modulation Method of High Frequency Link

For the power electronic transformer based on cascaded H bridges with single inductor quad active bridge (SIQAB), this article proposes a submodule (SM) capacitance minimization scheme based on switching synchronization hybrid phase-shift modulation (SSHPSM) of high frequency link. Under SSHPSM, the primary side of SIQAB-stage operates in switched-capacitor mode to realize the automatic elimination of the second-order-frequency voltage ripple of SM capacitor without complex control, which helps to reduce the capacitance of SM and improve the power density of the system. The principle of low-frequency ripple transfer and cancellation is analyzed from the perspective of electric and magnetic coupling, and it shows that the scheme is still applicable under the influence of the nonideal factors. The power losses distribution and efficiency of dc–dc-stage and the capacitance constraints of SM are carried out. Furthermore, the operation feasibility of the proposed scheme in the case of the typical critical conditions are evaluated, including the low-frequency operation for motor drive and the fault ride-through ability of three-phase voltage asymmetry for grid-tied conditions. Finally, the proposed scheme is verified by simulation and experiment.