Loss Analysis And Efficiency Optimization Of Phase-Shifted Full-Bridge Converter

Phase-shifted full bridge converter is widely used in high power applications due to its low voltage stress and high output power. Besides the above advantages, strong point of phase-shifted full bridge converter also include low loss, high efficiency, low electromagnetic interference, etc. However phase-shifted full bridge converter cannot achieve ZVS under light-load condition, lead to phase-shifted full bridge converter low efficiency under light-load condition, converter most of the time work in light-load mode. Nowadays improve light-load efficiency more concentrated on changing the circuit topology, it is necessary to study change control method for improving light-load efficiency.Firstly, this thesis presents a summarization for hard and soft switching technology, introduce the advantages of soft switching technology. Analyze operation principal of phase-shifted full bridge converter, shortcomings of the current circuit topology for improving light-load efficiency. Then loss model of the converter is established, the loss model of the converter mainly contains of the power MOSFET, the transformer, the inductance and the output diode. Analyze loss of converter based on the loss model. Then based on the proposed loss model, a method is proposed by changing the switching frequency under very light-load condition and optimize dead time under light-load condition to improve the efficiency. After that software and hardware of converter is designed in detail. Experiments are used to verify the loss model and the proposed control method.Experiments are used to verify loss model and the the proposed control method. Experimental results show that when the input voltage is 200-310V, output current is 7-17A, the efficiency can be up to 91.3% under light-load condition,very light-load efficiency can be up to 90.5%. Full-load efficiency can be up to 94.3%. The designed scheme can be widely used in phase-shifted full bridge converter.