Research On Wide Voltage Range Resonant Bidirection DC/DC Converter

Resonant bidirectional DC/DC converters are widely used in many fields,such as aerospace power supply,vehicle power supply,DC distribution microgrid system,etc.,due to their advantages of electrical isolation,bidirectional power transmission,wide voltage range output,soft switching characteristics,low electromagnetic interference and high transmission efficiency.The wide voltage range output of the resonant bi-directional converter is very important for these applications.However,the common three-element LLC resonant converter has the disadvantage of no boost in the reverse direction.At present,four-element resonant converters are based on LLC.By adding one auxiliary element,the disadvantage of no boost in the reverse direction can be solved.On the basis of investigating and analyzing all kinds of existing resonant converters,a new fourelement resonant converter is proposed,which is formed by adding an auxiliary inductance to T-11 LLC.The wide voltage range output and soft switching characteristics of the proposed converter are also studied.By listing the fundamental equivalent circuit diagram of the proposed resonant converter,the voltage gain formula under the forward and reverse conditions is obtained,and the voltage gain characteristic curve is drawn.The influence of different variables on the voltage gain is analyzed.It is theoretically verified that both the forward and reverse of the proposed converter have wide voltage range output characteristics.In addition,from the gain curve,there is only one gain peak in the voltage gain.Compared with the double peak in the four-element CLLC resonant converter,the proposed converter has simple parameters design and simple PFM control.The operation characteristics of the converter at different forward and reverse frequencies are analyzed,and the influence of switching frequency on the realization of soft switching characteristics is obtained.The proposed converter has good soft switching characteristics.The forward and reverse small signal model of the proposed converter is analyzed,and the corresponding open-loop transfer function is deduced through theoretical derivation,and the loop compensation design is carried out.By comparing the bode disgram before and after compensation,the compensation effect is obvious.Using the voltage gain characteristics and combining the forward and reverse output voltage range effectively,the reasonable parameters of the proposed converter are designed and verified by Saber simulation software.The simulation results are consistent with the theoretical analysis,which verifies the correctness of the theory.Combined with parameter design and theoretical analysis,the design of the experimental prototype is guided,and the experimental platform is built.The experiment is controlled by PFM.The experimental results show that the proposed converter,whether forward or reverse,can achieve wide voltage range output and soft switching characteristics by adjusting switching frequency.The output voltage is stable under closed-loop conditions,and the compensation design is reasonable.