基于PWM+PFM的LLC谐振变换器软启动研究

Research on Soft-start of LLC Resonant Converter Based on PWM and PFM

启动过程中电流冲击大是LLC谐振变换器研究中不容忽视的问题之一,为优化LLC谐振变换器的启动过程,提出一种基于PWM+PFM的LLC谐振变换器软启动策略。根据数学计算切换2种传统脉宽调制方法,得到一种新的变占空比控制方法,并将其与传统降频控制方法同时应用在LLC谐振变换器的启动阶段。搭建了一台200 W的LLC谐振变换器验证所提方案的可行性,同时与多种传统软启动控制策略进行对比分析。实验结果表明,相对于传统的软启动控制策略,所提控制策略能进一步减小电路中的电流冲击,具有更加安全可靠的启动效果。

The current shock in an LLC resonant converter during its start-up procedure is not negligible.For optimizing this procedure,a soft-start strategy for the LLC resonant converter based on PWM and PFM is proposed.A novel method of variable duty cycle control is obtained by switching two traditional PWM methods according to mathematical calculations.In addition,this control method is combined with the traditional frequency modulation control and then applied at the start-up stage of the LLC resonant converter simultaneously.A 200 W LLC resonant converter was built to verify the feasibility of the proposed scheme.Meanwhile,a comparative analysis was made with a variety of traditional soft-start control strategies.Experimental results show that compared with the traditional sof-start control strategy,the proposed control strategy can further reduce the current shock in the circuit,exhibiting a more secure and reliable start-up effect.