The Research On High Frequency LLC Converter Based On Gan Devices

In the fields of telecommunications,automotive,aerospace,data processing,etc.,miniaturized modular power supplies are widely used.Increasing the switching frequency of the circuit can reduce the volume of passive components and increase the power density of the system.However,high frequency will bring about an increase of switching loss,and the influence of parasitic parameters becomes obvious.In order to deal with these problems,the topology of the circuit,the selection of the switching devices and the design of the magnetic component structure can be optimized accordingly.Firstly,according to the requirements of high efficiency and high-power density,the wide bandgap semiconductor material GaN device,which has a series of advantages such as small parasitic parameters and fast switching speed,is selected.The structure of the half-bridge LLC resonant converter is selected,and the working principle of LLC is analyzed.The system parameters are designed according to the requirements.And considering the influence of the leakage inductance of the secondary side of the transformer,the modified circuit model considering the leakage inductance of the secondary side of the transformer is constructed by the First Harmonic approximation(FHA)approach,and the parameter design process of the system is optimized according to the modified circuit model in order to ensure the soft switching characteristics of the LLC resonant converter.In order to reduce the total volume and increase the power density of the system,the structure of the planar transformer is adopted in this paper.Compared with the traditional wound-type transformer,the planar transformer has plenty of advantages such as smaller size,higher repeatability,and better heat dissipation characteristics.In order to reduce the current and thermal stress of the secondary rectifier,this paper adopts a matrix transformer structure and uses magnetic integration technology to further reduce the volume of the magnetic component.At the same time,using the idea of systematic modeling method,the equivalent model of the planar transformer is established,and the parameters of the planar transformer are designed.At the same time,based on the simulation software,the 3D equivalent model of the planar transformer is constructed,the transformer design result is verified,and the winding structure of the transformer is optimized.In order to achieve better output voltage adjustment,this paper uses the state plane trajectory analysis method to model the LLC circuit.According to the state plane trajectory analysis theory,the circuit startup process is optimized to both reduce the current and thermal stress during the startup process and ensure a quick start of the system.At the same time,according to the state plane trajectory analysis,the dynamic response process of the system is designed and optimized to improve the dynamic characteristics of the system.Finally,in order to verify the accuracy of the theoretical analysis,the experimental prototype with the rated output power of 300 W and the switching frequency of 1MHz is built according to the requirements of the project.The rated input voltage was 48 V,the output voltage was 12 V,and the system efficiency reached 95.6% at rated load condition.The experimental results are consistent with the theoretical analysis and simulation results.