Review of Current-Sharing Schemes for Multiphase LLC Resonant Converter

This article presents a review of current-sharing schemes for multiphase LLC resonant converters. Because only the input-parallel output-parallel (IPOP) structure does not have the characteristic of automatic current sharing, this article focuses on the current-sharing schemes for the IPOP structure. Based on the fundamental harmonic analysis model, the current imbalance for IPOP converters caused by the tolerances of different resonant elements has been analyzed. Furthermore, a qualitative technique based on the gain curves is proposed to evaluate current-sharing performance. Then, the existing current-sharing schemes are categorized into passive and active methods based on whether they are sampling the output current. This article comprehensively compares these methods on additional circuits, control complexity, current-sharing performance, and ripple cancelation effect for multiphase IPOP LLC resonant converters. After that, the inner mechanisms of current-sharing schemes are revealed and the existing current-sharing schemes are classified into four catalogs according to the controlled variables for voltage gain regulation. Then, an intuitive method to depict the current-sharing process with voltage gain curves regulation is presented and six typic cases have been illustrated. Finally, the work in this article has summarized and future research trends for multiphase LLC converter are also discussed.