移相控制的LLC变换器轻载增益研究

传统的LLC谐振变换器为适应负载宽范围变化常采用变频控制策略,但存在调频范围过宽、限制感性元件设计、造成了额外的损耗等问题.因此采用变频移相控制方法以缩小调频范围,能够较好地实现原边开关管零电压开关ZVS(zero-voltage switching)及副边整流二极管零电流开关ZCS(zero-current swit...

Research on Light-load Gain of Phase-shift Controlled LLC Converter

To adapt to the wide range of load variation, the conventional LLC resonant converter adopts a frequency conversion control strategy. However, the range of frequency modulation is too wide, which limits the design of inductive components, and further causes problems such as additional loss. Therefore, the frequency conversion combined with phase shift(FC-PS) control is usually adopted to reduce the frequency modulation range, and it can better realize zero-voltage switching(ZVS) of a switching tube on the primary side and zero-current switching(ZCS) of a rectifier diode on the secondary side. But the difficulty in achieving ZVS within dead time T_d increases additionally due to the lagging and leading arms under light load. In this paper, through the analysis of the working waveforms of the circuit, the idea of optimal processing the circuit''s working waveforms by the traditional analysis method is inherited, and the time-domain analysis method is combined. Under the premise of satisfying the realization of ZVS, the effect of dead-time on the gain of output voltage is studied. By idealizing the circuit''s working waveforms and considering the charging/discharging process with the participation of parasitic capacitance of switch, the function of gain G over parameters such as phase shift duty ratio D, dead time T_d, and switching frequency f_s is established with the combination of the critical realization condition for ZVS in dead time. Finally, the optimal phase-shift duty ratio and dead time are derived with both the consideration of dead time and the satisfaction of requirement for a given gain. The effectiveness of the proposed method was verified by designing a simulated prototype and an experimental prototype with rated input of 200 V, rated output of 160 V, and output rated load of 5%.