| With the rapid development of power electronic technology,switching power supply is developing to high frequency and miniaturization.Therefore,it’s necessary to improve the work frequency of the power elements.But this will cause the problem of switching loss increasing,so the soft switching technology is put forward.Soft switching technology can improve the operation environment of power switches,reduce the switching loss,improve the conversion efficiency,increase the switching frequency and reduce the volume of converter.Meanwhile,it can reduce the electromagnetic interference(EMI)and switching noise.Half bridge three-level DC/DC converter has the advantage that the voltage stress of the switches is only half of the dc input voltage,which is especially suitable for high voltage applications by combining with the soft switching technology.Therefore,half bridge three-level DC/DC converter and its soft switching technology have been widely studied.Based on the systemic research,this paper introduces the classification,development condition and soft switching technology of half bridge three-level DC/DC converter.Then this paper analyzes the working principle of several typical three-level converters including conventional zero-voltage switching(ZVS)HB TL converter and zero-voltage and zero-current switching(ZVZCS)HB TL converter using tapped inductor.Conventional ZVS HB TL converter can realize ZVS for all switches by utilizing the leakage inductance of the transformer and parallel capacitance.But the converter has difficult to realize ZVS for lagging switches under light load,and it has problems of large circulating loss and duty ratio loss.ZVZCS HB TL converter using tapped inductor can realize ZVS for leading switches.Moreover,it can realize zero-current switching(ZCS)for lagging switches and decrease the circulating loss.But the converter has a problem that the leakage inductance of the tapped inductor will aggravates voltage parasitic ringing at the rectifier diodes.To solve these problems,this paper presents a ZVZCS HB TL DC/DC converter with a simple passive auxiliary resonant circuit based on the ZVZCS HB TL converter using tapped inductor.By employing the secondary auxiliary circuit,parallel capacitors and transformer leakage inductor,the proposed converter can realize soft switching for all switches.Besides,it can reduce circulating loss and increase the conversion efficiency.The structure of the auxiliary circuit is simple and the holding capacitor in the auxiliary circuit can eliminate the voltage parasitic ringing at the rectifier diodes caused by the leakage inductance of the coupled inductor.The circulating current of auxiliary circuit can be self-adjusted according to the load condition.The proposed ZVZCS HB TL converter in this paper can realize ZVS for leading switches over light load to heavy load,and ZCS for lagging switches over full load.Firstly,this paper analyzes the working principle of the converter in detail.Besides,the effects of coupled inductor turn ratio m and holding capacitance Ch on soft switching implementation conditions and the characteristics of the converter are discussed.Then,the parameter design principles are given.Finally a 2.7 kW-50 kHz simulation circuit is built on Cadence.The effectiveness of the proposed converter is verified by the simulation results. |
PDF Full Text Request