Research On LLC Resonant Converter Based On GaN Device

In recent years,with the rapid development of aerospace,communication equipment and other fields,miniaturized and high-efficiency power modules have been widely used and the development of power modules will tend to be high-frequency,high-efficiency and high-power density.The power density of the power supply can be increased by increasing the switching frequency,but it will cause the switching losses of the system to increase.In order to reduce the switching loss,the LLC resonant converter topology that can achieve soft switching is selected in this paper,but with the further increase of the switching frequency,the switching loss is still relatively large.To this end,a new semiconductor device gallium nitride(GaN)is combined with an LLC resonant converter,utilizing the advantages of gallium nitride,such as small size,fast turn-on speed and low on-state resistance,to reduce switching losses while increasing the frequency.In addition,the careful and effective design of the high-frequency transformer can greatly reduce the volume,reduce losses and improve the overall efficiency of the power supply.In this paper,the conduction mechanism,key parameters and driving characteristics of GaN devices are introduced in detail.The working modes of the LLC resonant converter in different operating frequency ranges are analyzed,and the process of zero-voltage switching(ZVS)for primary switch tube and zero-current switching(ZCS)for secondary rectifier tube is introduced emphatically.The equivalent circuit model is established based on First-Harmonic Approximation(FHA)and the normalized gain function is obtained.By drawing its corresponding curve,the influence of different parameters on the normalized gain is analyzed,and the main parameters of the resonant tank are optimized.In addition,the selection of PCB planar transformer can further improve the efficiency and power density of the power supply.In order to improve the steady-state and dynamic performance of the system,this paper adopts the extended description function method to establish a small-signal model and obtain the open-loop transfer function.The open-loop transfer function is modified to take into account the delay caused by digital control and the gain introduced by an ideal sampling switch.According to the corrected transfer function and Bode diagram,a double closed-loop control loop with a 4P2Z compensator in the inner loop and a PI compensator in the outer loop is designed to improve the dynamic characteristics of the system,and a simulation model is built for verification.In order to more intuitively express the effectiveness of the compensation design in this topic,this paper builds a test prototype test platform according to the design parameters and sets the closed-loop control of the double PI compensator as the control group.The dynamic responses of the two designs are compared when the input voltage and load change,and the experimental results are consistent with the simulation results.The results show that the dynamic response speed designed in this paper is faster,the output voltage ripple is smaller,the steady-state and dynamic performance of the system is better,and ZVS can be achieved in the full working range.In addition,the efficiency curves under different output powers show that the conversion efficiency of the system is up to 95.22%,which further verifies the rationality and correctness of the design in this paper.