Research Of The Full Bridge PWM Soft Switching Power

A great many of conventional full phase shift converters are according zero voltage switch technique to achieve soft switching. This converter is very simple to control, with less switching wastage, it will enhance switching frequency in a large scale, and thus, it will carry out converter miniaturization. Because of primary side have switching electric current procession, it will have a large of electric conduction wastage and it will difficult to achieve zero voltage switches under the circumstance of light load. In recent years, in order to solve disadvantage of zero voltage converter, zero-voltage-zero-current converter has been design. In this converter, its leading-leg switches can achieve zero voltage switching, at the same time, its lagging-leg switches can achieve zero current switching. In this situation, question of difficult achieving soft switching on light load has been solved. Conventional zero-voltage-zero-current switch technique contains using blocking capacitor and saturation inductance, passive clamp technique, active clamp technique and energy buffer network and so on to achieve zero-voltage-zero-current soft switch. They can solve the conventional full bridge converter’s disadvantages well, but they always have many shortcomings.In this paper, a novel soft switching converter has been design in connection with above questions. An auxiliary circuit which is composed of an inductance and a capacity is added on the leading-leg switches to enhance leakage inductance current. Thus, the leading-leg of converter can achieve zero voltage switching well in light load circumstances. Lagging-leg switching resonance circuit can achieve zero current switching well through clamp technique. Concerning resonant inductance voltage will high while resonance, it will induce a large output ripple coefficient of voltage and voltage unstable, in order to solve this question, a clamp diode is added between clamp capacitor and output filter capacitor in this paper, it limits charging voltage of resonant inductance and avoid high output ripple coefficient of voltage because of oversized charging voltage of both ends of resonant inductance. According to robust design, DC-DC converter can achieve zero-voltage-zero-current switch at a wide range of change of load, at the same time, in order to enhance power factor of output and to reduce total harmonic distortion and power network pollution produced from commutation of switching power uncontrollable element, a active power factor correction(APFC) circuit is added on the input of switching power. This APFC is optional designed according to add a midpoint tap on boost voltage inductance and pulse compensation technique. Compared with conventional boost APFC circuit, it reduced impact current of the diode reverse recovery and output voltage ripple. It enhanced input power factory above 0.99 and reduced power network pollution which come from the harmonic.At the end of this paper, the output of APFC circuit is the input of DC-DC converter, according to simulation and analysis, achieved a good output voltage characteristic at last.