Analysis and Modeling of Zero-Voltage-Switching Condition for LCC Resonant Converter in Above-Resonance Operation Mode

The LCC resonant converter in the above-resonance operation mode is gaining popularity in high-voltage generator applications due to its favorable characteristics, including zero-voltage switching (ZVS), step-up capability, and the absorption of parasitics. Nevertheless, with the increase of the voltage gain Go of the resonant tank, the ZVS condition is undermined for the LCC resonant converter. This study aims to characterize the ZVS condition of the LCC resonant converter in the above-resonance operation mode. For this purpose, a two-step-based ZVS analysis is carried out, incorporating the partial steady-state analysis and the dead-time analysis. The outcome of this analysis is the derivation of a set of three necessary conditions that define a sufficient ZVS condition model of the LCC resonant converter in the above-resonance operation mode. According to the analytical dead-time analysis, a discriminator. representing the ZVS performance of the LCC resonant converter is demonstrated, and the ZVS condition can only be achieved when Delta > 0. Moreover, the analysis of the sign of Delta reveals that the LCC resonant converter exhibits a weaker ZVS condition when G(o) > 1 than when G(o) <= 1. On the basis of the proposed ZVS condition model, a design method is proposed to illustrate the influence of the ZVS condition on the output of the step-up LCC resonant converter. Finally, experimental results obtained from a prototype of a 1053-V 222-W output LCC resonant converter are included to validate the accuracy of the theoretical analysis.