高效率LLC谐振变换器的定频混合控制策略

Fixed-frequency hybrid control strategy of high-efficiency LLC resonant converter

LLC谐振变换器为实现输出电压在宽范围内变化,普遍采用变频控制策略。然而变频控制策略存在谐振参数设计困难、变压器体积较大和电磁兼容等问题。为克服变频控制策略中存在的问题,提出定频变母线电压和移相混合控制策略。通过增大副边开关管零电流关断范围,提高变换器的工作效率和功率密度。分析所提控制策略的工作过程和软开关实现条件,并提出谐振网络参数设计方法。

LLC resonant converter generally uses variable frequency control strategy in order to achieve a wide range of output voltage variation. However,the variable frequency control strategy has difficulties in designing resonant parameters,large transformer volume and electromagnetic compatibility. To overcome these problems in the frequency conversion control strategy,a hybrid control strategy of fixed-frequency bus voltage variation and phase shifting is proposed. By increasing the zero current turn-off range of the secondary-side switching transistor,the operating efficiency and power density of the converter are improved. The working process of the proposed control strategy and the soft-switching implementation conditions are analyzed,and the design method of resonant network parameters is proposed.