改进型零电压转换PWM软开关功率变换器的实现机理分析

为改进传统谐振缓冲功率变换器(RSI)应用于高精度场合纹波较大的问题,提出一种改进型零电压转换(ZVT)脉宽调制(PWM)软开关功率变换器。通过LC环节减小输出电流纹波,并采用负载分段实现软开关的方式。轻载下利用交变的滤波电感电流实现主开关器件的零电压开通,重载下通过合理的导通谐振回路实现软开关,同时辅助开关器件实现零电流开关。该拓扑可采用PWM控制,具有效率高、纹波噪声小和开关频率固定的优点。通过分析电路的实现机理,对各工作时区进行解析计算,并给出实现软开关的条件。最后通过实验,在200kHz的开关频率下,验证了电路的有效性。相比于硬开关,效率得到了很大的提升,而相比于RSI在效率上虽有降低,但输出噪声却大幅减小。

The Analysis of a Novel Zero-Voltage-Transition PWM Soft-Switching Power Converter

In order to solve the problems of large current ripple of resonant snubber inverter in high-precision application, a novel zero-voltage-transition (ZVT) PWM soft-switching power converter was proposed. A LC branch is added to reduce the current ripple. In light load condition, the filter inductor current changing polarity is used to achieve zero-voltage switching of the main switches;while in heavy load condition, the properly conducted resonant branch can contribute zero-voltage switching of the main switches. Meanwhile, the auxiliary switches can work in zero-current switching. This topology has the advantages of high efficiency, low switching current ripple and fixed switching frequency. In this paper, detailed circuit operation is described and the main parameters in each period are calculated. The soft-switching condition is analyzed. A hardware prototype has been designed and tested to verify the validity of this proposed topology with relatively high switching frequency 200kHz. Compared with hard-switching power converter in the same condition, the efficiency is improved a lot. However, the efficiency is a little lower than that of RSI, but the output current noise is far lower than that of RSI.