Study On An Improved ZVZCS Full Bridge Soft-Switching Converter

With the advancement in technology and the electricity industry, switching supply has been widely used in electricity,aerospace industry, communication etc. And it has been a very active hot technology. Nowadays, high performance, high efficiency and light weight are the most important performance figures of all kinds of converters. But the conventional converter operates in hard switching, low switching frequency and low efficiency. These reasons severely constrain the switching supply to miniaturization, modular direction. So the soft-switching Pulse-Width-Modulation (PWM) technology is proposed. And it makes converter to operate in high efficiency and high frequency as possible. Especially, the phase-shift control full-bridge PWM converter attracts more attention.At present, the ZCS condition can be obtained by introducing an auxiliary circuit into the primary or secondary side. However, these converters introduce other questions too. The auxiliary circuit which consists of loss component or active switch costs the overall efficiency. Converter with tapped inductor or transformer makes the converter somewhat complex and the core loss is inevitable. Converter with snubber circuit seems a good choice and brings a duty cycle boost effect; however, it increases the voltage stress of the secondary rectifier diodes.Considering these, this dissertation provides the analysis and comparison of these converters. Based on the analysis of principles of ZVS and ZVZCS converter, a new topology with two diodes and a capacitor in the auxiliary circuit is proposed to overcome these questions. The operation principle and equivalent circuit structures in different modes are analyzed. The ZVS range of leading-leg and ZCS range of lagging-leg and the operation modes of secondary rectifier are analyzed and compared with other converters. The results show that the converter achieves soft switching easier than conventional converters with fewer components in the auxiliary circuit and without increasing the secondary voltage stress.The operating principle and soft switching achievement condition of converter are analyzed in detail. The topology and parameters of main circuit are given. Based on state-space averaging combined with phase-shifted control mode and characteristics of soft-switching resonant circuit, the small-signal model of improved converter is established. The analysis results and design consideration are verified by a simulation circuit.