Research On Control Technology Of Direct Drive Servo System Using Permanent Magnet Synchronous Motor Under Low Speed Rang For Aerospace Application

Servo system is widely used in many fields such as national economy and national defense construction,but the traditional servo system with deceleration mechanism can hardly meet the requirements of higher performance,accuracy and reliability because of complex transmission structure,and its application is limited.Direct drive servo system has natural advantages in these areas,and has been developed rapidly in recent years.Especially in aerospace and other special application fields,direct drive servo system is very popular because of many harsh restrictions such as reliability,performance,space and so on.In this paper,the low-speed operation control technology of direct-drive permanent magnet synchronous motor servo system is studied under the background of aerospace application.Firstly,the general situation,development trend and research status of servo system are described,and the background and research ideas of this topic are introduced.Then,the mathematical model and vector control principle of permanent magnet synchronous motor are analyzed,and the commonly used three-loop control structure and design ideas of servo motor are introduced,which lays a foundation for subsequent research.In order to overcome the problems of limited computing power of space-level digital signal processor(DSP)and insufficient peripheral resources for multi-motor control,this paper takes advantage of field programmable gate array(FPGA),adopts the control architecture of "DSP+FPGA",and optimizes the current loop of permanent magnet servo motor in the FPGA,so as to ensure the high control performance of current loop and alleviate the pressure of operation and resources of DSP.In this paper,the overall structure and scheme of current loop design are firstly analyzed,and the key functional modules are designed in detail.Then,the working sequence of current loop is studied,the current loop bandwidth is expanded by using bilateral asymmetric pulse width modulation,and the performance of current loop is further improved.In addition,in order to meet the needs of multi-motor control,a pipeline control structure which can effectively save the resource cost of the FPGA is introduced.Due to space constraints,the research object of this paper uses and enlarges the cogging torque of the motor to cancel the electromagnetic brake.This special application will undoubtedly increase the torque ripple of the permanent magnet servo motor in low speed direct drive operation and further increase the difficulty of speed control.Aiming at this problem,this paper first analyses the effect of large cogging torque on speed performance of target motor,and points out the limitations of existing direct cogging torque suppression methods in the application of this paper;furthermore,this paper puts forward the concept of virtual cogging torque,and analyses the principle and rule of virtual cogging torque to reset the locating point of motor,so as to obtain the idea and method of large cogging torque suppression for text target motor.On this basis,combined with the current loop,a speed control algorithm for low-speed operation based on virtual cogging torque is proposed,and the concrete design steps and implementation scheme are given..Aiming at the background of aerospace application,this paper designs the software and hardware of multi-motor servo driver,and develops a complete experimental platform.Based on this experimental platform,a series of experiments have been carried out.The experimental results show that the current loop based on FPGA has good dynamic and static performance,and the proposed speed control algorithm based on virtual cogging torque can effectively suppress cogging torque,greatly improve the low-speed operation performance of the motor,thus proving the correctness and effectiveness of the control scheme in this paper.