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
$G_{o}$
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
$\Delta$
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
$G_{o}$

$\leq$
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.