**5. Conclusions**

In this paper, a topology derivation methodology under USPWM is proposed to determine all possible full-bridge topologies for small leakage current. A unified circuit model based on USPWM is provided. Secondly, a mathematic method called the "MN principle" is then proposed to determine all possible topologies. Four rules and a derivation procedure are also provided. Thirteen simplified topologies are derived using this method. All existing topologies have been covered, and four new topologies have been found. These topologies can be classified into two topology families: the first includes topologies in which extra diodes are used for current flowing, while the body-diode functions as the extra diode to flow freewheeling current in the second family topologies. Finally, the proposed method is extended to the topologies under DFUSPWM, and three corresponding topologies have been derived, and two new topologies found.

**Author Contributions:** Conceptualization, X.Y., X.W.; funding acquisition, X.W.; investigation, X.Y.; software, X.Z.; validation, X.Z., X.W.; writing—original draft, X.Y.; writing—review and editing, H.W. and Y.-F.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** Research on Topology, Passive Current Sharing Mechanism and Control for Multiphase Resonant Converter with Coupled Resonant Tank: 51977069; Research on High-power and High-efficiency Electro-acoustic Transduction Mechanism and Control Method: 51837005.

**Conflicts of Interest:** The authors declare no conflicts of interest.
