Research Of LLC Converter Based On GaN Devices

As an important power electronic equipment of modern society,switching power supply is widely used in various field.High efficiency,miniaturization,high reliability,interference immunity have become the mainstream of nowadays development.The improvement of circuit topological structure and the advance of switching devices are the two main ways for the progress of switching power supply.The third generation broadband band-gap semiconductor technology revolution is now in the ascendant.And the GaN transistors are attracting more and more attention from practitioners because of their performance and gradually mature manufacturing processes.Its advantages are switching loss and conduction loss can substantially reduce to fit the high frequency application occasion.With the increase in frequency,the energy storage element and the magnetic components to shrink the size of the converter.Parasitic capacitance and stray inductance are one order of magnitude smaller than the traditional Si devices which can help to improve the EMC characteristics.In order to match the characteristic of GaN power devices and highlights their performance advantages,the inner structure and conduction mechanism were analyzed.After several driving topologies compared,choose out the totem column driving circuit as the driving form.And aiming at the problem of shooting through and error switching,driving circuit structures was optimized by theoretical calculation.An optimal dead-time was given.The above measure can ensure the normal operation of the converter in high frequency.Based on previous analysis on GaN HEMT's characteristics,a LLC resonant converter used for the TEM(Aero Time-domain Electromagnetic)exploration was designed.By simplifying the model through Fundamental Wave Analysis(FWA)method,the overall design process was given.According to the requirement of electrical properties,values of resonant components was calculated.And EMI simulation of the PCB layout was executed to indicate the distribution situation of current,electric field,magnetic field which helped to improve the EMC characteristics of the converter.At last an test porotype was built to verify the correctness of design.The experiment results showed the ZVS and ZCS performances achieved and dead-time control can optimize the efficiency.The output voltage ripple is within acceptable limits.At the end of the thesis a summary of the work was made and some suggestions for future work were put forward.