Design And Characteristic Research Of Phase Shifted Full Bridge Converter Based On Composite Bridge Rectifier

Since its birth in the last century,power electronics technology has been maintaining the momentum of rapid development,its area of application has been continuously expanding,and nowadays power electronics technology has been taking up an increasing role in social production and life.Among them,the DC conversion circuit,which converts between two different DC voltages(or currents),is an important part of power electronics technology.In accordance with the conversion mode,DC conversion circuits can be divided into two categories:direct conversion circuits and indirect conversion circuits,including six basic circuits and a number of derivative circuits based on the basic circuits,which are adopted in a lot of power electronics equipments.As power electronics are updated and integrated,the switching frequency is raised,but the losses are also increased,and soft-switching technology is applied to DC conversion circuits to improve this defect.Of all the soft-switching DC conversion circuits,the PSFB(phase shifted full bridge)converter is popular in medium and high power applications owing to its fixed switching frequency,simple control,low stress on switches,and high power density,and is chosen as the main research object of this paper.The application of PSFB converter is wide,and different applications have different specific requirements for PSFB converter.Optimizing and improving the converter topology reasonably to provide excellent performance in specific applications,is essential for the popularization of PSFB converter.In this paper,we intend to investigate the improved design of PSFB converter topology for different applications by addressing several inherent defects of traditional PSFB converter,such as the limited soft-switching range of lagging-leg switches,duty-cycle loss on the secondary side of the transformer,and circulating loss during zero state.First,for the applications with high input voltage and high output current,an input series output hybrid full bridge converter with composite bridge rectifier structure is proposed.Through the auxiliary capacitor and specific modulation scheme,the circulating loss during the zero state is eliminated,the duty cycle loss on the secondary side of the transformer is reduced,and the soft switching range of the lagging-leg switches is widened.The input series structure reduces the voltage stress of the primaryside semiconductor devices,while the composite bridge rectifier structure combined with the modulation scheme improves the rectifier voltage waveform and effectively suppresses the output current ripple.In addition,a closed-loop feedback control scheme is designed to implement the input voltage balance control and output voltage control functions via the analysis of the dynamic characteristics of the proposed converter.Second,for the applications with large input voltage variations,an improved PSFB converter with composite bridge structure on both primary and secondary sides is proposed,where two full bridge units are combined together by multiplexing a leg.The power equalization of the two full bridge units is achieved by a symmetrical modulation scheme,which reduces the semiconductor components stress and transformer VA rating.With the utilization of auxiliary capacitor and the secondary side auxiliary switches,all switches have a wide soft-switching range in a large input voltage variation range,ensuring the high efficiency of the proposed converter in a wide input voltage range.Finally,based on the theoretical analysis of the two proposed converters,sets of experimental parameters have been designed and the experimental prototypes have been built respectively to verify the effectiveness of the two proposed improved PSFB soft-switching converters for different applications.