Mode analysis and optimum design of bidirectional CLLC resonant converter for high-frequency isolation of DC distribution systems

This paper points out the low accuracy of the traditional fundamental harmonic approximation (FHA) in predicting the gain characteristics and resonant behaviors of the full-bridge isolated bidirectional CLLC resonant converter, which results in great impediments in optimally designing the resonant tank parameters. Given these drawbacks of FHA for CLLC converter, this paper proposes a novel operation mode analysis for CLLC resonant converter. Compared with traditional FHA, the operation mode analysis not only explains the appearance of various operation modes, but also provides the accurate description of the gain characteristics and resonant behaviors. Based on the operation mode analysis and the typical application in dc distribution systems for CLLC resonant converter, the influence of multiple factors for CLLC resonant converter is clarified and an optimal design methodology is developed further. Applying this design method, the converter can minimize the conduction loss while the required gain of a fixed switching frequency range is maintained. At last, the experiment results verify the correctness of the operation mode analysis and the excellent performance of CLLC resonant converter constructed by the proposed design methodology.