An Improved Grouping Transformer's Secondary Windings Current-Sharing Method for Multiphase LLC Converter

Current balancing performance of the existing grouping transformer's secondary windings (GTSW) method is determined by leakage inductance mismatches. Nevertheless, the transformer's leakage inductance parasitic parameters in practice are difficult to accurately design, especially in high-frequency occasions, causing a large current-sharing error between phases. To solve this problem, this article proposes an improved GTSW current-sharing method. By ingeniously changing the connection mode of transformer's secondary windings, the influence of secondary leakage inductance mismatch on current sharing performance is eliminated, and the current sharing performance of secondary side is significantly improved. The first harmonic approximation analysis method is used to establish the current sharing error model of the primary side and secondary side of the system. Furthermore, the current sharing performance of the existing GTSW method and the proposed method is quantitatively compared. Then, the effectiveness of the proposed method is verified by simulation and the two-phase 480 W experiment results. Finally, some great performances of the proposed method are discussed, such as advantages in high-frequency applications, no effect of parasitic capacitance on the current sharing performance, the potential scalability in the case of other dc–dc topology and high current scenarios, and modular expansion capabilities.