Research On Low-speed Performance Of Permanent Magnet Synchronous Motor Servo System

With the continuous development of permanent magnet synchronous motor servo control technology,permanent magnet synchronous motor servo system has been widely used in aerospace,CNC machine tools,robotics,industrial automation and many other areas.However,the current middle and high-end server system products in the market are mainly made in Europe,America and Japan,therefore,to study independent high-performance permanent magnet synchronous motor servo system is of great significance.Several key technologies on the aspects of influencing low-speed performance of permanent magnet synchronous motor servo system are studied in this research subject.Firstly,the paper introduces the background and development trends of AC servo system,points out several factors that affect low-speed performance of permanent magnet synchronous motor.The mathematical model of permanent magnet synchronous motor is analyzed under vector control.Permanent magnet synchronous motor vector control method and space vector pulse width modulation technology is also introduced.Secondly,as the dead zone effect brings adverse effects to permanent magnet synchronous motor vector control system,a method of voltage compensation which determines the current polarity according to the rotor position is put forward.This method is a software approach to compensate voltage,so it does not increase the cost of hardware system and has the advantage of easy to achieve.The dead-time compensation control strategy is simulated in Matlab/Simulink,the simulation results show that the voltage compensation strategy proposed in the paper can improve the current sinusoidal degree of permanent magnet synchronous motor,reduce motor's torque ripple,and improve the system operation performance at low speed.Thirdly,for optical encoder has non-detection zone due to the limitation of resolution at too low speed,and the speed lag will become increasingly apparent by using the traditional indirect speed measuring method,the real-time speed identification method by designing state observer which use the extended Kalman filter is proposed.Considering the abrupt change of load torque will affect the system speed,the designed observer can also identify load torque.Then the identified load torque is taken as feed-forward compensation of torque current controller,in order to reduce the impact of speed caused by the abrupt change of load torque.The simulation results show that the extended Kalman filter instantaneous speed observer can accurately identify the speed of motor at low speed in real time.Finally,the hardware and software of AC permanent magnet synchronous motor servo system are designed in the paper.A set of 17.3kW AC permanent magnet synchronous motor servo system is independently researched.Relevant experiments are conducted on this platform,and the experimental results indicate that the system has good dynamic and static performance,wide speed range and good low-speed performance.