宽电压应用定频LLC谐振变换器的PWM控制策略

APWM control strategy of fixed frequency LLC resonant converter for wide voltage applications

传统频率控制的LLC谐振变换器存在频率调节范围宽、转换效率低等问题,不适用于宽电压范围的应用场合。为了解决这些问题,提出一种全桥LLC谐振变换器的PWM控制策略,通过调节开关管的占空比实现增益调节。谐振变换器2个下桥臂的开关采用固定的频率控制,开关频率等于谐振频率,而2个上桥臂的开关采用PWM控制来调节输出电压。在PWM控制策略下,明显缩小了谐振变换器的频率调节范围。此外,原边侧开关管和副边侧整流二极管分别实现零电压导通(ZVS)和零电流关断(ZCS),有效地降低了变换器的开关损耗。最后,搭建功率为1.5 kW、输入电压为400 V、输出电压为250~500 V的仿真系统和实验原型,验证PWM控制策略的有效性。

The conventional frequency-controlled LLC resonant converter suffers from wide frequency regulation range and low conversion efficiency,so that it is unsuitable for wide voltage range applications with a wide voltage range.In order to solve these problems,a PWM control strategy of the full-bridge LLC resonant converter is proposed in this paper,which realizes the gain adjustment by adjusting the duty cycle of the switch The switches of two lower arms of the resonant converter are controlled by a fixed frequency,and the switching frequency is equal to the resonant frequency,while the switches of the two upper arms are controlled by PWM to adjust the output voltage.With the method,the frequency variation range of the resonant converter is significantly narrowed.In addition,the switches of primary circuit and the rectifier diodes of secondary circuit could achieve zero voltage switching(ZVS)and zero current switching(ZCS),respectively,which effectively reduces the switching losses of the converter.Finally,the 1.5 kW simulation and experimental prototype with 400 V input voltage,250~500 V output voltage are established to verify the effectiveness of the proposed PWM control strategy.