一种高效率软开关充电机的研究

Research on a high-efficient and soft-switching charger

针对充电机输出电压范围宽、不能在全输出范围内实现高效率的特点,提出了一种软开关充电机。前级采用无桥PFC电路,实现了功率因数校正及中间母线电压的快速控制;后级采用高效率的全桥LLC谐振电路,实现了开关管的零电压开通(ZVS)和整流二极管的零电流关断(ZCS)。在固定中间母线电压时,LLC谐振电路在输出高压或低压时工作在远离谐振频率点而存在效率偏低的缺点,提出了据输出电压来动态调节中间母线电压的控制策略,减小了频率变化范围,提高低压和高压输出时的效率。最后通过一台AC 120 V输入,母线电压DC 200~240 V,输出DC 130~200 V的充电机样机。实验测得充电机额定运行下的效率为91.8%;通过动态调整母线电压测得在130 V输出时整机效率从87.4%提高到90.1%,200 V输出则从89.3%提高到91.0%。

In view of the wide range changing of output voltage and difficulty to realize high-efficient in any output voltage, a soft-switch charger is proposed. The former-stage circuit of charger adopts bridgeless power factor correction, which can achieve sinusoidal wave of input current and fast control of bus voltage. The latter power section utilizes high-efficient full bridge LLC resonant circuit, realizing zero voltage turn-on of switches and zero current turn-off of rectifier diode. When bus voltage is fixed, the operating frequency will deviate series resonance frequency greatly at the minimum and maximum output voltage, resulting in low efficient. A control strategy of changing bus voltage with the output voltage is proposed, reducing the range of frequency changes and improving efficient at both ends of the output voltage. Finally a prototype is designed, which is AC 120 V input, bus voltage ranges from DC 200 V to 240 V, output voltage ranges from DC 130 V to 200 V. Experimental charger efficient is 91.8% at the rated state; by using the new strategy efficient can be raised from 87.4% to 90.1% at 130 V output, from 89.3% to 90.1% at 200 V output, respectively.