The High-Efficiency Isolated AC–DC Converter Using the Three-Phase Interleaved LLC Resonant Converter Employing the Y-Connected Rectifier

The power conversion efficiency of an isolated ac-dc converter is a dominant factor in the overall efficiency of dc distribution systems. To improve the power conversion efficiency of the dc distribution system, a three-phase interleaved full-bridge LLC resonant converter employing a Y-connected rectifier is proposed as the isolated ac-dc high-frequency-link power-conversion system. The proposed Y-connected rectifier has the capability of boosting the output voltage without increasing the transformer's turn ratio. Especially, the frequency of the rectifier's output ripple is six times higher than the switching frequency, thereby reducing the output capacitor and the secondary transformer's RMS current. However, the tolerance of the converter's resonant components in each primary stage causes the unbalance problem of output ripple current. It cannot be solved using conventional control techniques since the structure of the three-phase interleaving has the limitations of individual control capability for each converter. To solve the current unbalance problem, a current balancing method is proposed for the output rectifying current. The performance of the proposed converter and the current balancing method has been verified through experiments using a 10 kW (300 V/33.3 A) prototype converter.