Research On High Frequency Vehicle DC-DC Converter Based On Gan Device

Electric vehicles have become the focus of attention in the new era due to their high reliability,good safety,low cost-effectiveness,and environmental friendliness.As a key component of electric vehicles,the power supply is a bridge connecting the high-voltage system and the low-voltage system in the vehicle.Because the space in the car is very small,high frequency and small volume become its research difficulties.The use of new gallium nitride devices can realize the power supply working at ultra-high frequency,which is conducive to improving power supply performance.A vehicle power supply was designed with power density and high efficiency as the goal,and it was researched and optimized from the aspects of circuit topology,transformer design and control method.In this paper,the GaN device is studied first.The gallium nitride device has the characteristics of high electron mobility,small reverse recovery charge,and strong electric field breakdown capability.It is suitable for high frequency,high temperature,and high pressure applications.The characteristics and structure of GaN devices and ordinary silicon devices are compared to show the superior performance of GaN devices.Analyze the parasitic parameters of gallium nitride devices,propose measures to avoid the influence of parasitic effects,and design and optimize the drive circuit on this basis.The switch performance test of the GaN device was carried out,and the on and off states were observed through the experimental results.The input voltage of the vehicle power supply fluctuates greatly and the range is wide.After comprehensive consideration,the BOOST + LLC two-stage circuit is used as the power supply topology.The BOOST circuit stabilizes the bus voltage at 400 V,which is convenient for the adjustment and control of the LLC circuit in the subsequent stage.The LLC circuit can improve the overall efficiency of the power supply due to its soft switching characteristics.Analyze the working principle of the circuit,use the fundamental wave analysis method and time domain analysis to study the LLC circuit,get the gain characteristic curve,analyze the change trend,and use this as the basis to design and optimize the circuit parameters and derive the dead time,Use the software for simulation,and further adjust the parameters slightly according to the simulation results.In order to achieve the requirements of high power density and small size,this paper chooses a planar matrix transformer to replace the traditional vertical transformer.The structure of the matrix transformer is optimized,a matrix form in which the primary and secondary transformers are connected in parallel is proposed to reduce the conduction loss,and the two transformers are integrated on an E-shaped core using the principle of magnetic flux cancellation.In order to accurately design the leakage inductance of the transformer,a leakage inductance model was established,the expression of the leakage inductance value was derived,and simulation verification was performed with simulation software.The transformer winding structure is also optimized,and the magnetic integration technology is used to integrate the secondary synchronous rectifier switch tube and the capacitor into the secondary winding,which greatly reduces the termination loss.Using Ansys software simulation,observe the current density and magnetic field intensity cloud map,the current achieves average shunt.Finally,the overall design of the vehicle power supply is carried out.The synchronous rectification scheme of LLC converter is researched,and an adaptive dead time control method is proposed,which has good transient performance and a significant improvement in efficiency.The PFM + PWM mixed control method is selected.When PFM is used for heavier loads,PWM is used for lighter loads,which can make the converter operate stably within the full load.Finally,make an experimental board for experimental testing,observe and analyze the experimental waveform,and achieve the goals of high power density and high efficiency.