Research On Wide-range Soft-switching Full-bridge DC-DC Converter

The phase-shift full-bridge converter is a common topology for DC-DC power conversion in medium and high-power applications.In recent years,it has been widely used with the rapid development of hybrid vehicles,renewable energy,telecommunications and other fields.The traditional phase-shift full-bridge DC-DC converter utilizes the primary leakage inductance of the transformer and the parasitic capacitance of the switch to achieve soft switching within a certain range and reduce switching losses.However,because the energy stored in the leakage inductance of the transformer primary side is small,the soft-switching range of the conventional phase-shift full-bridge converter is narrow,and the zero-voltage switching(ZVS)condition of the lagging leg is difficult to achieve.Although increasing the transformer leakage inductance can expand the range of soft switching,it will increase the loss of the secondary duty cycle and the voltage oscillation of the rectifier diodes.To solve the above problems,a phase-shift full-bridge DCDC converter with a new LCL passive auxiliary circuit is presented,which has the following characteristics: 1)the auxiliary circuit can provide inductive compensation current before the lagging-leg switches are turned on,thus expanding the ZVS soft-switching range of the converter;2)because the converter no longer relies on the energy stored in the leakage inductance to achieve soft-switching,the transformer leakage inductance can be designed as small as possible to avoid negative effects;3)special current waveforms in the new auxiliary circuit make it have a smaller circulation current;4)compensating peak current provided by the auxiliary circuit can be adaptively adjusted within a narrow frequency range as needed,therefore,it can further reduce the circulating loss caused by the introduction of the auxiliary circuit and make the whole efficiency of new converter higher.The main work of this paper is as follows:1.Detailed model analysis of the new converter is performed,and the corresponding steady-state mathematical model is established;the expression of compensating current on auxiliary circuit is given,the mathematical expressions of primary side current and DC voltage gain of transformer on main power circuit are given and the influence of leakage inductance on main power circuit is analyzed through the establishment of mathematical model;the ZVS soft-switching conditions of lagging-leg and leading-leg switches are given.2.Detailed comparative study is performed on the new converter and the reference converter(a phase-shift full-bridge converter with a single inductance auxiliary circuit),including the characteristics of compensating current provided by the auxiliary circuit,the RMS current in auxiliary circuit,loss distribution of converter,and stress of switches.3.According to the established mathematical model,a detailed example design process of the new converter is given.The influence of frequency variation on the converter is analyzed,and the relationship model between the switching frequency and the phase shift angle in the adaptive mode is established.4.Based on the designed parameters,an experimental prototype was made.Comparative experiments were performed on the new converter and the reference converter,and the experimental studies were performed in the fixed frequency mode and the adaptive frequency mode,respectively.The experimental results verify the correctness of the mathematical model,the effectiveness of the design method,and the rationality of auxiliary circuit design.