Research On High Frequency And High Voltage Gain Modified SEPIC Converter Based On GaN Devices

In recent years,with the advent of wide bandgap semiconductors GaN and SiC,power converters are gradually advancing toward higher frequency and miniaturization.And the system power density has been greatly improved.However,the increase of the switching frequency will increase the influence of the parasitic parameters on the operating state of the system,and the increase of the switching loss will reduce the overall working efficiency.Therefore,this topic applies GaN-FETs and proposes a modified SEPIC converter suitable for high frequency and high voltage gain applications.Because the switch tube works in the soft switch state,it can effectively reduce the switching loss,improve the working efficiency of the system.The use of planar magnetic components effectively increases power density as well.Compared with the traditional SEPIC converter,the proposed topology adds a voltage doubler unit formed by constituting a diode and a capacitor and a step-up transformer,improves the voltage gain.And the switching capacitor resonates with the primary inductance of the transformer to achieve the working state of quasi-resonance,while reducing the voltage stress across the switch tube.A parameter optimization design method is proposed to ensure soft switching within a wide range of input voltage and output load variations.Aiming at the problem that the traditional hard drive circuit has high loss under high frequency conditions,this paper also applies a high frequency resonant gate drive circuit for GaN-FETs.This driver utilizes the parasitic parameters in the circuit and improves the on-off rate of chip driver.And by designing the switch sequence of the N-channel and P-channel MOSFETs,which can effectively reduce the gate drive circuit losses and optimize the switching rate of the driver circuit.In the high-frequency converter,the design of magnetic components is the focus of research.The planarization can reduce the height of the converter,and the winding has the advantages of strong reproducibility and better heat dissipation performance.But the planarization needs to consider parasitic,leakage inductance and magnetic loss and other issues.This paper comprehensively considers the influence of parasitic capacitance and leakage inductance,and adopts the cross-structure design transformer model.In order to further reduce the volume of the converter,a magnetic integration scheme is proposed.The inductor and the transformer are integrated into the same core,which is beneficial to reduce the cost and improve the system power density.In order to obtain better dynamic response,this paper uses the generalized state space averaging method for resonant converter to model,and obtains the corresponding small-signal model.The open-loop Bode plot is used to design the compensation network to optimize the dynamics of the system.In addition,for the operating characteristics of the proposed converter,a hybrid control strategy of PWM and PFM is proposed to ensure the soft switching characteristics of the system while achieving constant current output.An experimental prototype with a rated output of 36 W was designed and built in this topic.The output current was 0.3A,the operating frequency was 1MHz,and the working efficiency of the system reached 91.2% at full load.The experimental results were consistent with the theoretical analysis,and the correctness of the theoretical analysis was verified.