High-Precision Time-Domain Analysis Method Based on the Superposition Principle for CLLC Converter in Above-Resonant-Frequency Mode

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The CLLC converter is widely used in applications requiring highly efficient bidirectional power flows. However, multiple resonant components make its modeling and analysis quite challenging, hence, hard to reach a higher operating efficiency. In this article, the method based on the superposition principle is proposed to provide a more accurate analysis for CLLC converters in the above-resonant-frequency-mode (ARFM) and simplified time-domain analysis is employed for below-resonant-frequency mode. First, the principle of the novel method is analyzed within the introduction of the operating modes for CLLC converter. Then, the time-domain expressions regarding the voltage-gain, resonant currents, and resonant voltages are derived by using the proposed method in ARFM. Afterward, the soft-switching conditions are then redefined in a more accurate way. More detailed synchronous-rectification (SR) timings are derived, which is followed by the optimal hardware parameter design. The proposed concept is finally verified through a 1.5-kW resonant CLLC prototype. The experiment has confirmed that the voltage gain and peak values are consistent with the theoretical calculations. And the operating efficiency is improved by 1.8% with the accurate soft-switching and SR compared with the uncontrolled rectification as confirmed by experimental results. Furthermore, the proposed method surpasses the time-domain analysis method to implement SR considering the parasitic capacitance of switches.

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