Research On Inverter Circuit Design And Modulation Strategy Of Servo System Based On Silicon Carbide Devices

AC servo drive system has the advantages of wide speed range,rapid response speed,and high control precision.It is currently being widely used in equipment manufacturing and industrial automation,mass transit,spaceflight industry and other areas.Applying wide-bandgap power devices such as SiC MOSFET to servo drive system can reduce losses and improve system efficiency,and high switching speeds increase switching frequency,reduce the volume of passive components,and improve motor dynamic response performance.However,applying SiC MOSFET to the servo system also brings new challenges.This thesis focuses on the hardware design optimization and efficiency improvement of the high power density servo drive based on SiC MOSFET.In view of high voltage and current rate of change caused by the high switching speed of SiC MOSFET,the gate crosstalk and voltage oscillation problems caused by the influence of parasitic parameters are analyzed.By analyzing the switching process of SiC MOSFET,the causes of gate crosstalk and voltage oscillation problems are determined.The parasitic parameter analysis model is established,and the influence of each parasitic parameter is studied in depth,and a clear optimization direction is proposed for hardware design optimization.Aiming at the problem of increased switching loss caused by the increase of switching frequency,this paper studies the discontinuous modulation strategy.First,based on the three-phase inverter circuit,the conduction loss and switching loss expressions of SVPWM and DPWM are derived,and the function of driver loss with power factor angle under different modulation strategies is quantitatively obtained,and the harmonics under different modulation strategies are analyzed.Through analysis,the relationship between harmonic distortion and modulation ratio under different modulation strategies is obtained,and the common mode voltage and conducted EMI of SVPWM and DPWM are compared.At the same time,the DPWM modulation strategy is improved for the working condition of the permanent magnet synchronous motor,the loss threshold is determined according to the heat dissipation capacity of the driver,and the switching of different modulation strategies is realized according to the load current,which realizes the balance of efficiency and harmonics.Finally,the hardware of the servo driver based on SiC MOSFET is designed and optimized,and a high power density servo driver based on SiC MOSFET is built.This thesis focuses on optimizing the PCB layout of the inverter circuit,and uses ANSYS Q3 D software to extract the parasitic inductance of the laminated bus bar structure,so as to draw attention to the PCB wiring,and finally realize the stable operation of the driver at 200 V / 50 A.At the same time,the actual test of the efficiency of different modulation strategies proves that the efficiency of the DPWM modulation strategy described in this thesis is significantly improved compared with the SVPWM.