Characteristic Analysis And Efficiency Optimization Study Of GaN-based Bidirectional DC-DC Converters

The application of oil-fired vehicles has greatly improved the quality of human life,but oil-fired vehicles consume a large amount of non-renewable energy,resulting in environmental pollution and noise pollution.In response,electric cars have emerged.Electric vehicles have the advantages of energy efficient use,energy saving and environmental protection,and can effectively alleviate the energy crisis.As a key part of energy conversion in electric vehicles,bidirectional dc-dc converter is of great significance to its characteristic analysis and efficiency optimization.The third generation of wide bandgap semiconductor gallium nitride(GaN)high electron mobility transistor(HEMT)has many excellent properties,and its application in bidirectional dc-dc converter system has great advantages.The focus of this thesis is to study how to select appropriate switching devices and control mode,so that the bidirectional dc-dc converter system to get higher transmission efficiency.Firstly,Cascode GaN HEMT was selected as the switching device of bidirectional dc-dc converter system,and its static and dynamic characteristics were analyzed,and compared with Si MOSFET.The results showed that Cascode GaN HEMT had better static characteristics and lower power loss.Secondly,the single phase shift(SPS)control and triple phase shift(TPS)control of bidirectional dc-dc converter system are studied,including its working principle,power characteristics,soft switch analysis,small signal modeling analysis,etc.,and the power characteristics and current stress model are given in detail.Aiming at the problem of current stress in the system,an optimal control strategy of current stress based on TPS control principle is proposed to reduce the current stress and improve the transmission efficiency of the system under the condition of soft switch.Thirdly,under the condition of device parasitic parameters,a fine loss model of bidirectional dc-dc converter system based on Cascode GaN HEMT is proposed.The influence of parasitic parameters in Cascode GaN HEMT on the system loss was studied,and the dynamic working process of the system was analyzed.The experimental results show that there is only about 0.71% difference between the loss model and the real loss value.Finally,the simulation model was established based on Matlab and LTspice simulation software,design and build the capacity of 0.9 k W bi-directional DC-DC converter experiment platform,and the Cascode GaN HEMT in this paper is selected to design the driving system,using the optimization control strategy,current stress can make the system stable running,and the experimental results show that the maximum transmission efficiency of the system can reach 96.2%.