Shift Phase Full-bridge Soft-switching Dc / Dc Converter

The paper focuses on a 24VDC/300VDC, Phase-Shifted Full-Bridge soft switched DC/DC converter with UC3875 as its kernel controller. High power density as well as high efficiency has always been the goal to pursue in the field of modem electric power converters. To achieve the goal, a converter is designed based on the selection of the main circuit topology and the control method through theoretic analyzing and simulation.Full-Bridge converter is selected as the main circuit topology in this paper. Due to many of its advantages, it has been the mainstream topology adopted in large capacity, high performance power converters. The increase of the power density must be based on quickening the switching frequency, therefore, soft switching is desired. The paper adopts Phase-Shifted Full-Bridge zero-voltage-switched (PS FB ZVS) technology instead of traditional hard switching technology to decrease the switching wastage. Itgets good results.There are two disadvantages in the traditional FB PS ZVS DC/DC converter: one is the loss of duty cycle of output voltage of secondary winding is high, the other is it is hard to realize ZVS for the lagging arm in light load condition. The realization of ZVS is at the cost of giving up a moiety of duty cycle, it can reduce but there is no idea to avoid it. The loss of duty cycle is serious in low voltage, high current input condition. It decreases the efficiency of the converter and makes it have no significance to realize ZVS. According to these problems, a saturable inductance and auxiliary resonant circuit is introduced in the paper. The loss of duty cycle is greatly reduced due to the adoption of saturable inductance and auxiliary resonant circuit and the lagging arm can realize ZVS in light load condition due to the adoption of auxiliary resonant circuit. The adoption of saturable inductance and auxiliary resonant circuit resolves the conflict between realizing ZVS in a wide range of load and serious loss of duty cycle in low voltage, high current input condition. It realizes ZVS while reduces the loss of duty cycle nearly to zero and makes the FB PS ZVS technology can be commendably used in this type of DC/DC converters.To achieve a good performance both statically and dynamically, closed loop control method has to be applied. The paper takes advantage of a double closed-loop control method based on average-current mode and improves the static and dynamic performance of the converter.Based on the analyzing of the theory, the parameters of main circuit, control circuit and closed-loop part are designed through simulation. Some performances of the converter are also analyzed in the simulation.Finally, experimental results of the converter are presented and discussed in the paper.