Research On The High Frequency Isolated Converter With The Ga N Devices For Wide Voltage Range Applications

As an indispensable part of power electronic equipment,switching mode power supply is being improved and optimized with the rapid development of science and technology.High efficiency,reliability,low loss and high power density are always the constant pursuit of switching mode power supply.Power semiconductor devices are widely used in power electronics and power converters,such as DC/DC converter,rectifier,inverter,etc.The performance of power semiconductor devices directly affects the power conversion efficiency and quality of the converter.Therefore,the requirements for power semiconductor devices are also increasing.Light,thin,small and low energy consumption have become the inevitable trend of its development.Gallium Nitride(Ga N),as a third-generation semiconductor material,has the advantages of greater bandgap width,higher breakdown electric field intensity and higher electron saturation drift speed compared with the Silicon(Si)material.Therefore,gallium nitride material has a broad prospect in high temperature,high frequency,high voltage applications.E-mode Ga N Transistor(Gallium Nitride High Electron Mobility Transistor,Ga N HEMT)as a new type of power semiconductor devices,due to the unique material and structure,the switching speed can reach more than ten times of the silicon MOSFET,while greatly reducing the switching loss and conduction loss.The increase in switching frequency can effectively reduce the volume of energy storage components and magnetic components,which is beneficial to improve the power density of the power supply.Therefore,the gallium nitride transistor is suitable for applications requiring higher power density.At this stage,because the highest voltage level of Ga N devices is about 600 V,it is still necessary to select a multi-level voltage structure converter to reduce the switching stress of the device.It should be pointed out that when the voltage variation range is too wide,a topology with a wide range of voltage regulation capabilities must also be selected during the design processIn Chapter 1,the research status of Ga N devices and wide-range converter topologies is elaborated.In Chapter 2,the characteristics and problems of Ga N devices are analyzed.When the converter of Ga N HEMT as a power switch is under high frequency control,the influence of parasitic parameters in the device and the circuit on the switching characteristics is amplified.This paper takes Buck converter as an example to explain this kind of problem and analyze its reasons.At the same time,based on the resonant circuit constructed by the parasitic capacitance of the device and the inductance of the circuit,a soft switching control strategy in discontinous conducion mode is proposed.In Chapter 3,based on the traditional two-stage structure of three-level Buck cascade half-bridge LLC,the operating principle and switching mode are analyzed,and the voltage-sharing control strategy of input capacitors is designed.In addition,the two-stage cascade structure without intermediate capacitance is also discussed and analyzed,and a comparison between the two schemes is given.In Chapter 4,based on the two-stage cascade structure,a isolated converter with the Ga N devices for wide voltage range applications is designed,an experimental prototype is built,and the correctness of the theoretical analysis is verified by the experimental results.