Research On Applications Of SiC Power Devices In The AC Servo Drive

With the continuous development of the society and the increasing automation of industrial,civil,and military applications,the demand for AC servo drive systems controlled by permanent magnet synchronous motors is increasing.Some fields,such as electric vehicles,robots,medical devices,numerical control equipment,etc.,are increasingly making demands on the performance of AC servo systems,and at the same time,the power density,volume,efficiency,and environmental temperature tolerance of AC servo systems are gradually increasing.Make specific requirements.In view of this,this article studies the application technology of new SiC MOSFET power devices in AC servo drives,analyzes the superior performance of SiC MOSFETs compared to Si IGBTs,and studies the application of SiC MOSFETs to improve the power density and servo of AC servo drives.The feasibility of performance provides theoretical basis and practical guidance for the engineering design of AC servo drives.Firstly,the structural characteristics and dynamic and static characteristics of SiC MOSFET are analyzed.The switching process of SiC MOSFET is further analyzed.The influence of parasitic capacitance on the switching process is discussed.Three steadystate operating states of SiC MOSFET are given.MOSFET power devices have lower on-resistance,lower threshold voltage,and faster switching speed than Si IGBT power devices.The switching and conduction process of each bridge arm power device in the main circuit of the AC servo driver are analyzed.Based on this,the loss components of the inverter circuit are analyzed,the simplified calculation method of the power device loss is given,and the inverse is derived.The formula for calculating the total loss of the circuit.The method for calculating the reverse conducting loss of SiC MOSFET is proposed,and the difference between Si IGBT and the calculation is pointed out;the simulation model of conduction loss and switching loss is established,and the simplified calculation formula of loss calculation is realized through the simulation model.Based on the simulation model,a comparative analysis was made of the losses of the SiC MOSFET and Si IGBT inverter circuits.It was concluded that the conduction losses and switching losses of the SiC MOSFET inverter circuit are lower than those of the IGBT inverter circuit,in which the SiC MOSFET inverter circuit The advantage of switching loss is more obvious,which reflects the efficiency advantages and switching frequency advantages of SiC MOSFET devices in the application of AC servo drive main loop,and provides a theoretical basis for the design of heat dissipation structure of SiC MOSFET AC driver.The mathematical model of the AC permanent magnet synchronous motor and its vector control system oriented to the rotor field orientation are analyzed.The system’s hardware and software design is further completed based on the vector control system.In the hardware design of the system,the drive of the SiC MOSFET is analyzed and studied.The method of determining the resistance of the series-connected driving source of the driving circuit is proposed.Through this method,the external resistance of the driving circuit can be quickly calculated.The selection of the driving circuit power supply and the calculation method of the driving current are also given.Further design of the SiC MOSFET engineering drive circuit.The overall architecture design of AC servo embedded software was carried out,and the software implementation of the current loop and speed loop PI regulator was focused on;the use of SiC MOSFET in the main loop can increase the operating frequency and increase the requirements for hardware computation processing capability.The program optimization method simulates and analyzes the effect of shortening the dead-time setting time on improving system performance.Based on CREE’s CAS300M12BM2 SiC MOSFET power module and Mitsubishi’s PM300RLA120 IGBT power module,the main circuit of the AC servo driver is built separately,and the mature TMS320F28335 DSP control board is used as the main control unit to assemble the AC servo driver to achieve mature AC permanent magnet synchronization.The motor is the motor under test and an experimental platform is set up.Based on the experimental platform,the losses of the two main loops are compared and analyzed to verify the correctness of the calculations in this paper.The output speed and output current of the SiC MOSFET driver are tested,which shows that the SiC MOSFET power module is used as the master of the drive.The loop helps improve the AC servo output performance.