Research Of High Power Density Maglev Chopper Based On Silicon Carbide Devices

As the core drive device of maglev train suspension control system,suspension chopper reliably and efficiently work always influences the safety and efficiency of the whole vehicle.In order to optimize the performance of Changsha maglev train chopper,this paper mainly focuses on switching oscillation problem caused by SiC(Silicon Carbide)MOSFET(Metal-Oxide-Semiconductor Field Effect Transistor)instead of traditional IGBT(Insulated Gate Bipolar Transistor)chopper.Other issues,such as active gate driver design and switching loss during operation,are also considered.Finally,a test platform of suspension chopper is designed to investigate switching performance of silicon carbide devices.The main research contents of this paper are described as follows:1.Analysis of silicon carbide MOSFET switching process.On the basis of analyzing basic structure and static characteristics of silicon carbide MOSFET,the MOSFET switching process is analyzed.In particular,the oscillation phenomena in the switching process are modeled and analyzed.After getting the switching oscillation mechanism,various factors that cause the oscillation are confirmed.Especially,operation status in the non-ideal state is considered,and switching operation trajectory is drawn to fit actual situation.2.Analysis and simulation of driving circuit of silicon carbide MOSFET.Many factors are put forward,which need to be considered in the design of MOSFET driving circuit of silicon carbide MOSFET.Then the influence of switching waveform by the traditional method of changing gate resistor through the hard switching circuit simulation are analyzed,and active gate drive control method is designed.Two suppression effects by different switching oscillation strategies are compared.One is the gate resistance transformation.The other is active gate drive control.3.Study on the application of silicon carbide suspension chopper.Based on the analysis of basic structure of the maglev chopper,the chopper internal loss types are summarized.Then issues about silicon carbide MOSFET instead of IGBT are highlighted,and the switching losses of SiC MOSFET and IGBT simulation are calculated.Simulation results prove that the use of the silicon carbide MOSFET can reduce power consumption of the whole suspension chopper,so as to optimize the suspension chopper and achieve high power density operation.Finally,some other problems should be considered in the chopper during the process of application.4.Analysis and experimental results of suspension chopper test platform.The switching performance of SiC MOSFET is obtained in the double pulse test circuit.Method of test platform switching waveforms is analyzed.According to the requirements of high speed measurement circuit,hardware and sensors of test platform are designed and selected.The final measurements of switching waveforms of IGBT and SiC MOSFET are depicted and made a detailed analysis and comparison.