带耦合电容型桥式ZVS直流-直流变换器

A Zero Voltage Switching Bridge-Type DC-DC Converter with a Coupling-Capacitance

提出一种零电压开通(ZVS)的直流-直流变换器。在一种桥式开关管结构的基础上,通过在串接的两个变压器一次绕组两端并联一个耦合电容Cb,为电路的正常工作构造两个一次绕组共同导通的条件,使得两个绕组能够实现均流。变流器采用移相控制技术,不含输出侧滤波电感,而是利用变压器漏感传递能量,使得四个开关管都能获得宽负载范围的ZVS。二次侧采用开关电容倍压技术,提高了输出电压增益。详细分析了变换器各阶段工作原理、电压增益特性、ZVS实现条件以及Cb的设计。制作了一台开关频率50k Hz、负载600W、42V输入/250V输出的实验样机,该样机在轻载下就能达到92%以上的效率,实验波形验证了理论分析的正确性。

A zero-voltage-switching （ZVS） DC-DC converter is proposed. Based on a bridge-type constructer, a coupling capacitance Cb is added in parallel with two series-connecting primary windings Thus the synchronous operation of the two primary windings and current-sharing can be realized. The phase-shifting PWM method is adopted in this converter, and four power switches can achieve ZVS in a wide load range. This converter neglects the output filter inductor, and only utilizes the leakage inductance of the transformer to transfer energy. The switching-capacitor voltage-double technique is adopted at the secondary side, to improve the voltage gain. The operation theory in each stage is analyzed in detail. Some key characteristics, including voltage gain, ZVS condition and Cb selection, are also explained. One prototype is tested, with 50kHz switching frequency, 600W rated load, 42V input voltage and 250V output voltage. The efficiency can reach to 92.5% under 70W, and the test waveforms verify the theory analysis.