Separated Resonant Networks Based PSFB Converter For High-power Conversion

Recently,there is a growing interest in plug-in hybrid electric vehicles(PHEV)and electric vehicle(EV)because of the development of electric vehicle technology and the growing shortage of fossil fuels.Electric vehicle technology has high energy conversion efficiency,cleanness,safety,and low unit driving cost.However,due to limitations of battery technology,its cruising range is lower than that of conventional fuel vehicles,so high-power fast charging Technology is especially important.Due to the wide voltage regulation range and fixed switching frequency of the traditional phase-shifted full-bridge converter,it becomes the main topology of the DC/DC converter in the high-power fast charging technology.However,traditional phase-shifted full-bridge converters still have certain drawbacks,such as narrower soft switching range,larger conduction loss,and the duty cycle loss of transformer secondary side,which limits the application in high-power charging technology.Firstly,combing the characteristics of single assistant resonant circuit phase-shifted full-bridge converter and double-inductor rectifier,a novel phase-shifted full-bridge converter based on separated assistant resonant network has been proposed in this paper.The proposed converter is based on a traditional phase-shifted full-bridge converter with two sets of resonant networks,each consisting of a capacitor and two diodes.Combining with the characteristics of proposed topology,the Input-Series Output-Paralle(ISOP)connection method is used to improve the voltage safety margin of the switch on inverter bridge.Then,combing with theoretical derivation and simulation analysis,the working principle of the topology is introduced in detail.On this basis,the parameters of the separated resonant network are optimized.The proposed topology has achieved a wide range of the leading leg zero-voltage switching(ZVS)and lagging leg zero-current switching(ZCS).The voltage of transformer secondary side is clamped by the capacitors in assistant networks,which makes the duty cycle loss for proposed topology is nearly zero.The capacitors in assistant networks resonate with series leakage inductor in the positive switching half period and negative switching half period respectively.Hence,part of the energy at the freewheeling stage of the traditional PSFB converter is transmitted to the outside through the way of charging and discharging of the resonant capacitors,which effectively reduces the circulating loss of the transformer primary side.Moreover,the frequency stress of the diode in the assistant network is reduced to half comparing to the conventional assistant circuit and the peak value of the current stress is also reduced by 14.9%,which is suitable for the application in the high-power conversion.Finally,to verify the correctness of the operating principle and the theoretical analysis,a 20 kW,switching frequency 20 kHZ,input voltage 760 V,output voltage 250-600 V prototype of proposed topology has been designed.The superiority of proposed topology in high-power conversion is verified by the analysis of steady-state experimental waveforms of different working states,experimental waveform of soft-switching under different loads,and efficiency measurement under a wide load range.