Light-Load Optimization Strategy for <i>CLLC</i> Resonant Converters Based on Asymmetric Variable Duty-Cycle Modulation Control

The CLLC resonant converter is a bidirectional isolated dc/dc converter with excellent soft-switching characteristics. However, the CLLC resonant converter exhibits poor voltage regulation and low operating efficiency under light-load conditions. Therefore, to optimize the light-load voltage regulation performance and enhance the operating efficiency of the CLLC resonant converter under light-load conditions, this article proposes an asymmetric variable duty-cycle modulation (AVDM) control method. AVDM control regulates the output voltage under light-load conditions by varying the duty cycle of the asymmetric square waves in the primary and secondary circuits. Additionally, this article adopts a multifrequency modeling strategy based on a feedforward neural network (FNN) to indirectly analyze the time-domain characteristics of the CLLC resonant converter when using AVDM control. Based on the converter’s time-domain characteristics, the optimal operating points that ensure zero-voltage-switching (ZVS) operation in the CLLC resonant converter under various light-load conditions can be determined. Furthermore, a closed-loop control system utilizing AVDM control can be designed based on the optimal operating points. Finally, the feasibility of the proposed AVDM control is verified by a 2-kW rated power CLLC resonant converter experimental prototype.