Research On Low-speed And Ripple-Torque Minimization Performance Of Permanent Magnet Synchronous Motor Servo System

As a measurement platform for common mechanical components such as gear, cutlery etc., Computer Numerical Control (CNC) Gear Measurement Centers have strict requirements on the low-speed and ripple-torque performances of the electric servo systems installed in their rotation axis. Permanent magnet synchronous motor (PMSM) has the advantages of Compact size, high performance, low cost and the speed control performance which is close to that of one DC motor. Especially in the recent years , PMSM is applied in CNC Gear Measurement Center to replace the DC motor in the rotation axis servo system. This study is mainly focused on the servo system of Permanent magnet synchronous motor and targeted to achieve low torque ripple and steady low-speed performances.This paper deals with PMSM design optimization firstly. Based on a study of generating mechanism of cogging torque, the impact of the combination of pole numbers and slot numbers on cogging torque is analyzed and the cogging torque is reduced through rational choice of the combination of pole numbers and slot numbers. The permanent magnet pole shape of the PMSM is optimized. A design method of unequal-thickness magnet is put forward for parallel magnetization. This method enables the no-load back EMF to show sinusoidal waveform. The torque ripple caused by the sub-harmonic of air-gap magnetic field is also reduced.The vector control theory and current control strategy for PMSM are discussed on the basis of the mathematical model of PMSM. The principle of space vector pulse width modulation (SVPWM) is analyzed and its realization method is proposed. Also the problems appeared in the operation of the low-speed high-torque PMSM are analyzed. The speed loop controller based on the boundary layer sliding mode is designed for the PMSM vector control system from the perspective of sliding mode control theory. Compared to the conventional sliding mode controller, the new design overcomes the high frequency chattering near the sliding mode face and improves steady state accuracy. Basing on analysis of the influence of dead-time effect on torque fluctuations, the current distortion caused by dead time effect is reduced through reasonably predicting the sectors where the stator current vector lies and compensating average error voltage. Using the Matlab software, the simulation model for PMSM vector control system is established. In addition, the comparative study of the PI controller and sliding mode controller are carried out. The dead time effect compensation method is also studied.Finally, the hardware and software for all-digitalized PMSM control system are designed, Using TMS320F2812 as the core DSP. Detailed explanations are provided for the structure and function of all the parts of the hardware and software in the control system. Low-speed, high-torque permanent magnetic synchronous servo motor system experimental platform is established and experiment is made. Results of the experiment show that the theory and the analysis of simulation are correct. What's more, both the results of the experiment and the simulation suggest that the system has good dynamic and static characteristics and high accuracy, which can meet the requirements of the servo control of Gear Measurement Centers.