Research On Three-Level Dual-Buck Inverter Based On GaN Device

Inverters are important electric energy conversion devices,and their output power quality and inverter efficiency are of great significance to the stable operation of the system and energy saving.The three-level dual-buck inverter circuit has the advantages of no bridge arm straight-through and independent continuity circuit,which has become one of the hot spots of inverter research.GaN power devices have excellent performance such as high switching speed and low conduction loss,which can significantly improve the performance and efficiency of inverters.This paper addresses a class of simplified clamped three-level dual Buck inverters,the improved modulation strategy that can improve its output voltage quality is investigated and the efficiency problem of GaN-based inverters is analyzed.For the simplified clamped three-level dual-buck inverter circuit topology,the circuit structure and operating modes are first analyzed to study the effects of midpoint voltage offset and switching sequence on the output voltage quality and efficiency of the circuit,and to determine the optimal switching sequence under SPWM carrier cascade modulation.Next,the advantages and disadvantages of the full-cycle and halfcycle operation of the dual-buck full-bridge inverter circuit are analyzed to lay the foundation for further research on the output voltage over-zero distortion problem.For the output voltage over-zero distortion problem of three-level dual-buck inverter circuit,an analysis method based on equivalent circuit is firstly proposed to transform the output voltage over-zero distortion problem into a second-order system,and two modulation strategies are further proposed to suppress the voltage over-zero distortion.The first is a hybrid modulation strategy,which uses full-cycle control in the region before and after the output voltage crosses zero,and half-cycle control in the other time domains.This strategy can effectively suppress the output voltage over-zero distortion,but it will increase the system loss.The second is the duty cycle compensation modulation strategy,which derives the relationship between output voltage and duty cycle,and compensates the duty cycle by this relationship when the output voltage distortion occurs.This modulation strategy does not change the operation mode and does not generate additional losses,which has a better suppression effect on the over-zero distortion.For the efficiency of GaN devices based on inverter circuits,firstly,the structure and characteristics of GaN devices are introduced,the switching process of GaN devices is analyzed,and the calculation formula of switching loss of GaN devices is deduced.Secondly,the losses of each part and the overall efficiency of the three-level dual Buck inverter system based on GaN devices are analyzed.Finally,a three-level dual Buck inverter based on GaN devices is built,and the output voltage over-zero distortion suppression experiments are conducted on this device and the system efficiency is tested to verify the correctness of the theoretical analysis.