双向全桥L-LLC谐振变换器软启动控制策略研究

Research on soft-start control strategy of bidirectional full-bridge L-LLC resonant converter

全桥L-LLC谐振变换器在启动时存在谐振电流冲击大的现象,通常采用降频方式限制电流尖峰,从特定的高频逐渐降低到谐振频率,而由于谐振变换器的复杂动态特性,很难确定关键参数。因此,基于状态平面分析,提出了适用于全桥L-LLC谐振变换器的软启动策略。通过设计限流带确定最佳启动频率以及合理的降频策略,分三阶段将谐振电流限制在限流带内完成软启动。为了验证所提出的软启动策略的可行性,通过MATLAB/Simulink仿真验证,仿真结果表明,所提出的软启动策略不仅有效降低谐振电流过冲,还明显提高了启动速度,并能够保持原边侧开关管的零电压开通(zero voltage switching,ZVS)以及副边侧整流二极管的零电流关断(zero current switching,ZCS)特性。

The full-bridge L-LLC resonant converter has a large resonant current shock during startup.Usually,the frequency reduction method is used to limit the current peak,and the current is gradually reduced from a specific high frequency to the resonant frequency.Due to the complex dynamic characteristics of the resonant converter,it is difficult to identify key parameters.In this paper,a softstart strategy for full-bridge L-LLC resonant converters is proposed based on state-plane analysis.The optimal starting frequency and a reasonable frequency reduction strategy are determined by designing the current-limiting band,and the resonant current is limited within the current-limiting band in three stages to complete the soft-start.MATLAB/Simulink simulation is conducted to verify the feasibility of the proposed soft-start strategy.The experimental results show that the proposed soft-start strategy not only effectively reduces the resonant current overshoot,but also significantly improves the startup speed,which can realize the primary side switch tube zero voltage switching(ZVS)and zero current switching(ZCS)of the secondary side rectifier diodes.