INTRODUCTION

        The full-bridge converter is widely used in medium-to-high power dc–dc conversions because it can achieve soft-switching without adding any auxiliary switches. The soft-switching techniques for PWM full bridge converter can be classified into two kinds: one is zero-voltage-switching (ZVS) and the other is zero-voltage and zero-current-switching (ZVZCS). The   leakage inductance of the transformer and the intrinsic capacitors of the switches are used to achieve ZVS for the switches. The ZVS characteristics are load dependent and will be lost at light load. In ZVZCS PWM full-bridge converters, one leg achieves ZVS, and the other leg achieves ZCS. However, there is serious voltage oscillation across the rectifier diodes caused by the reverse   recovery no matter ZVS or ZVZCS is realized for the switches. In order to overcome this problem resonant inductance and two clamping diodes into the primary side of transformer. The solution eliminates the voltage ringing and overshoot, thus the voltage stress of the rectifier diodes is reduced and introducing losses or an additional controlled power device. The difference between the two locations of the resonant inductance and the transformer was analyzed and an optimal position was presented. Rue net al analyzed the issue in detail and also observed the effects of the blocking capacitor in different positions, and a best scheme was determined. No matter what the positions of the transformer and the resonant inductance are, the resonant inductance is clamped and its current keeps constant when the clamping diodes conduct. The output filter inductance must had enough current ripple so that the clamping diodes turn off naturally, otherwise the clamping diodes will be forced to be turned off, resulting in serious reverse recovery.  

 In this paper, an auxiliary transformer winding is introduced to the ZVS PWM full-bridge converter to be in series with the resonant inductance. The introduced winding not only makes the clamping diode current decay rapidly and reduces the primary side conduction losses, but also can makes the current ripple of the output filter be smaller; hence the output filter capacitor can be reduced. The winding plays the role of forcing the clamping diode current to decay to zero, so it is called reset winding. The operation principle of the proposed converter gives the comparisons between the full-bridge converters with/without reset winding. The experimental results are presented in Section IV to verify the validity of the proposed converter. In recent years, the soft-switching PWM full bridge converters have attracted more anmoreattentions and there are various topologies and modulation strategies were proposed. Phase-shifted zero-voltage-switching (ZVS) PWM full bridge converter realizes ZVS for both leading leg and lagging leg with the use of leakage inductance of the main transformer and the output capacitors of the power switches. Phase-shifted zero-voltage and zero-current-switching(ZVZCS) PWM full bridge converter realizes the ZVS for leading leg and Z lagging leg and  proposed two kinds of PWM full bridge converters which realize ZVS for one leg and ZCS for the other leg It is meaningful to reveal the relationship among these topologies and modulation strategies.

       Quite complex, they are very small and so is the additional cost. Two major techniques are generally employed to achieve soft switching:

·         Zero-Current-Switching (ZCS)

·         Zero-Voltage-Switching (ZVS).

        In this thesis A Novel Zero-Voltage-Switching PWM Full Bridge Converter with a reset winding and  auxiliary LC circuit  is implemented in this converter the  transformer divided in to two parts one is called reset winding anther one is called primary winding  the capacitors are connected  parallel to the  all IGBT switches zero voltage achieved due to the thanks to the  capacitor before  using reset winding  the resonant inductor is blocked so clamping diode  are hard turned off  output filter  inductor is  relatively larger due to effect  reverse recovery current appear power losses  are more efficiency of the converter decreased so that problems  avoided  by using of reset   winding  .   This paper improves the full-bridge converter by introducing a reset winding in series with the resonant inductance to make the clamping diode current decay rapidly when it conducts. The reset winding not only reduces the Conduction losses, but also makes the clamping diodes naturally turn-off and avoids the reverse recovery, improved efficiency of the proposed converter compared with the conventional techniques with using of reset winding1.2 Block Diagram and Its Description

                This Is shown below. It is two stages DC-DC converter one is inversion and the other is rectification. The basic block diagram of A Novel Zero-Voltage-Switching PWM Full Bridge Converter