The Research Of Phase-shift Full-bridge Zero-voltage-switching Converter

After decades of development, phase-shifted full-bridge soft-switching converters are widely used in the high power DC applications and have been more and more mature, so that it has became mainstream. Studying phase-shifted full-bridge converter which has high power density and high reliability has important theoretical and practical significance.The key technique of high efficiency PSFB converter includes the oscillation parasitic of rectifier diodes and the soft switching technique. This thesis focuses on the research about the phase-shift full bridge zero-voltage-switching (PSFB-ZVS) converter. The main content of the thesis includes the principle of PSFB converter, soft-switching technique and oscillation parasitic of rectifier diodes. Among them, eliminating the oscillation parasitic of rectifier diodes and achieving the lagging arm soft-switching technique are the focus of the research.In order to overcome the problems of voltage spikes caused by the rectifier diodes duing to the reverse recovery, there are many ways to elimination the rectifier parasitic oscillation used in the PSFB converter, such as RC snubber circuit, adopting two clamping diodes in the first side of transformer to clamp voltage technique, and etc. But the technique of RC snubber circuit will cause much energy loss, and couldn't eliminate the first peak voltage of rectifier diodes. In addition, the latest research shows that the clamping diodes is turned off with serious reverse recovery when the converter operates in discontinuous current mode (DCM). So if the PSFB converter operates with small load, the clamping diodes will break and reduce the reliability of the systems. So a novel ZVS converter topology is proposed which is based on the clamping diodes technique. In this new design, we adopt the voltage clamp circuit. The second side of transformer replaces the first side. The availability of spikes-suppressor is validated by simulation and experimentalOn the other hand, when the lagging arm of the PSFB-ZVS converter achieves ZVS, the rectified diodes turn on at the same time. This makes the transformer become short circuit and makes the filter inductance can not be together with resonant induntance, which makes the junction capacitance are lack of energy at the time of charging and discharging energy. As a result, it is difficult for the lagging arm of the PSFB-ZVS converter to complete ZVS. This thesis analyses explicitly the reasons of the difficulty for the lagging arm to achieve ZVS, and a converter whose lagging arm paralleled are in parallel assistant network is proposed. This design can make the lagging arm achieve ZVS at universal load, and the correctness of the design is validated by the simulation and experimental.