Analysis And Design Of DC-DC Converter Based On GaN Device

Power devices based on Si semiconductor materials have been difficult to improve in performance.Based on wide bandgap semiconductor materials,the performance of devices can be effectively improved.Research on new wide bandgap semiconductor devices has become a hot topic.Based on the new wide-bandgap semiconductor GaN device,it has the advantages of traditional Si semiconductor devices in high frequency,low loss,high temperature,large-scale integration,etc.,in the fields of DC/DC converters,inverters,motor drives,etc.Has received extensive attention and application.As the switching rate of GaN devices increases,the parasitic parameters in the circuit path have an increasingly obvious influence on the switching process of GaN devices.Excessive parasitic parameters can inhibit the switching performance of GaN devices and cannot show their excellent performance and advantages.In order to study the influence of parasitic parameters on the switching characteristics,the switching process of GaN devices was firstly analyzed.The double-pulse test circuit was built in LTspice.The influence of parasitic parameters on the switching characteristics of GaN devices was analyzed by simulation.The law of the influence of different parasitic parameters guides the layout of the GaN-based device in the hardware circuit PCB design.Then,based on the dead time setting problem of GaN HEMT in DC-DC converter is studied in this paper.Due to the large voltage drop of the GaN HEMT during the reverse conduction process,the reverse conduction loss caused by the dead time during the high frequency switching process significantly affects the efficiency of the converter.In order to optimize the dead time of the converter,the synchronous Buck converter is taken as an example to analyze the switching process of GaN HEMT in dead time.According to the analysis of the dead time of different load current conditions,a kind of optimized dead time setting method is proposed.At the same time,the continuous time model of the non-ideal converter is established.The discrete time model is obtained by discretizing the continuous time model by the impulse response invariant method,and the differences between different models are compared and analyzed.At the same time,the digital control loop under high frequency switch is designed further.The realization method of high resolution DPWM is introduced.By analyzing the characteristics of different DPWM modulation methods,a control strategy of hybrid modulation method is proposed,according to the operation state of the system.The state switching modulation mode can not only improve the accuracy of the system output voltage,but also improve the dynamic characteristics of the system.The digital compensator is designed by means of bilinear transformation method,and the specific design flow is given.Finally,the hardware circuit design process is discussed in detail,and a 480 W synchronous Buck converter based on GaN device GS66508 T is successfully developed.The switching frequency is 500 kHz,which verifies the rationality of circuit design and control strategy.the efficiency of the converter is increased by 1.3% adopting optimized dead time,and the highest efficiency is up to 94.8%.The proposed control strategy can improve the dynamic performance of the system,and the load transient response speed is faster,which verifies the rationality and effectiveness of the control strategy.