Research On ZVS Full-bridge DC-DC Converter With Auxiliary Circuit

The phase-shifted full-bridge converter can realize soft switching within a certain range by using the leakage inductance of the transformer.It has the advantages of simple circuit topology and control method,and is widely used in various fields.However,conventional phase-shifted full-bridge converters are difficult to realize soft switching at light loads.Although increasing the leakage inductance of transformer can expand the range of soft switching,it will increase the secondary side duty cycle loss of the transformer and diode voltage oscillation.Aiming at the problems of conventional phase-shifted full-bridge converter,this paper presents a novel phase-shifted full-bridge DC-DC converter with a passive auxiliary circuit.The new converter uses the magnetizing inductance of the transformer,and adds a simple LC series circuit on the secondary side of the transformer.This converter can achieve soft switching in a wide load range from light load to full load and wide input voltage range.The soft switching realization of the new converter no longer depends on the energy in the leakage inductance of the transformer,so the leakage inductance of the transformer can be designed as small as enough to avoid negative effects.The main works of this paper are as follows:Firstly,the operation principles of phase-shifted full-bridge converter using the magnetizing inductance of the transformer to achieve ZVS and phase-shifted full-bridge converter with a novel passive auxiliary circuit are compared and analyzed.Furthermore,through analysis of the operating state of two converters,the mathematical models are established.Based on the established mathematical models,the steady-state gains and the ZVS conditions of two converters are given.Secondly,the frequency-sensitive characteristics of the compensation current of the two converters are compared and analyzed.It is proved that the compensation current of the converter with LC series auxiliary circuit is more sensitive to frequency variation in the same phase shift angle range.At the same time,the RMS values of the compensation currents in the two converters are compared,and it is theoretically proved that the converter with LC series auxiliary circuit has smaller circulating losses under the condition that the same peak compensation current is provided.Finally,according to the established mathematical model,the design process of the main circuit and auxiliary circuit parameters of the converter is given,and the fixed frequency mode and the adaptive frequency mode of the converter are analyzed and designed respectively.Based on the designed parameters,an experimental prototype is made.The experimental results verify the correctness of the mathematical model and the effectiveness of the design method.A comparative experiment is carried out on the phase-shifted fullbridge converter using magnetizing inductance to achieve ZVS and the phase-shifted fullbridge converter with a novel passive auxiliary branch.The results show that the proposed phase-shifted full-bridge converter with LC auxiliary circuit can achieve soft switching from light load to full load and wide input voltage range,with higher efficiency.Experimental results show that the novel converter has higher efficiency in the adaptive frequency mode than the fixed frequency mode.