Design And Research Of Vehicle Auxiliary Inverter Based On SiC MOSFET Applied In Locomotives

With the continuous development and improvement of China’s rail transit construction,high-speed trains are gradually moving towards intelligent,lightweight,and high-security。Vehicle auxiliary inverter is one of the most important devices in high-speed trains,and the lightweight and economy of high-speed trains also require miniaturization and high power density of auxiliary inverters.At present,the auxiliary inverter based on silicon device has reached the development bottleneck,and it is difficult to break through in terms of efficiency and power density.Therefore,research on auxiliary inverter based on third-generation semiconductor device is needed to further improve the performance and reliability of the device to meet the development of high-speed trains.SiC MOSFET has the advantages of high breakdown voltage,fast switching speed,high operating junction temperature,etc.SiC MOSFET is used as the power device of the auxiliary inverter,which can improve the switching frequency of the inverter,and also reduce the system loss,volume and weight.Therefore,this paper takes the auxiliary inverter based on SiC MOSFET as the research object,and studies the switch mechanism of SiC MOSFET,the control algorithm of inverters and the design of low-power experimental prototype.The main work is summarized as follows:Firstly,because is sensitive to parasitic parameters and will produce voltage and current spikes in the switching process,the switch transient process of SiC MOSFET is modeling mathematically,and the mathematical expressions of drain-source voltage and drain current of SiC MOSFET in the switching transient process are deduced.The influence of driving circuit parameters such as driving resistance,driving voltage and gate-source capacitance on voltage overshoot,current overshoot and switching loss is analyzed.Using PSpice software,a double pulse test circuit is built,and the SiC MOSFET power module of BSM300D12P2E001 model of Rohm Company is selected.Based on the PSpice model of the module,the simulation analysis is carried out.By changing the driving circuit parameters one by one,the characteristic of voltage and current of SiC MOSFET are observed to verify the accuracy of the theoretical analysis.Secondly,the mathematical model of three-phase three-wire auxiliary inverters is deduced,and the analysis shows that when the output of the inverter is connected with unbalanced load,the output voltage will be unbalanced,and when the inverter is connected with non-linear load,the output voltage of the inverter will contain low-order harmonics.The dual closed-loop voltage and current PI control algorithm and the deadbeat control algorithm of auxiliary inverters is studied and verified by simulation.The simulation results show that,when the output of the inverter is connected with unbalanced load,the output voltage will be unbalanced,and when the inverter is connected with non-linear load,the output voltage of the inverter will contain low-order harmonics by using the double closed-loop PI control algorithm.However,the deadbeat control algorithm can ensure that the output voltage of the inverter is not affected by the load type,and the harmonic component is significantly smaller than that of the double closed-loop PI control algorithm.Thirdly,an experimental prototype of auxiliary inverter based on SiC MOSFET is designed and built.The prototype consists of eight parts: main power circuit,LC filter circuit,driving circuit of SiC MOSFET,voltage and current detection circuit,signal conditioning circuit,DSP controller and auxiliary power supply.The design process of voltage and current sampling circuit and signal conditioning is explained in detail,the design method of LC filter circuit is given,the driving characteristics of SiC MOSFET are analyzed,and the driving circuit is designed.Finally,on the experimental prototype of low power auxiliary inverters designed,the control program of auxiliary inverters based on TI’s TMS30F28335 controller is compiled.The performance of the voltage and current double closed-loop PI control algorithm and the deadbeat control algorithm are verified experimentally.The experimental results are consistent with the theoretical analysis.