Research On The Strategy Of Restraining Torque Ripple By Direct Torque Control Of Permanent Magnet Synchronous Motor

Permanent magnet synchronous motor(PMSM)has been widely used in industry because of its small size,wide speed range,large output torque,high power density,fast response speed and high reliability.Direct torque control(DTC)is used to control the motor.Its idea is novel,and the control system designed has the advantages of quick response,strong robustness,simple structure and so on.Therefore,it has attracted the attention of a large number of experts and scholars.However,the control method has the defects of large flux observation error and torque ripple.Therefore,it is of great practical significance to carry out some research on it.According to the characteristics of PMSM’s structure,this paper studies the problems of flux error and torque ripple in the process of direct torque control of PMSM.Firstly,the development status of PMSM and its special structure are introduced.After comparing different motor control strategies,a direct torque control system with relatively excellent indexes of each phase is introduced.Based on its principle,the simulation model of PMSM direct torque control system is built by Matlab / Simulink software.According to the simulation results,the simulation results are verified Besides the validity of the model,the defect of the direct torque control system,that is,the cause of excessive torque ripple,is analyzed and discussed.Secondly,in view of the six sector division of flux space in pmsm-dtc control system,which will lead to large torque ripple and asymmetric flux increment at the sector boundary,the traditional six sector is divided into twelve sectors to optimize the control system.For the deviation between the observed value of torque and flux and the actual value caused by the change of the resistance value of the stator in the low speed state of the motor,a resistance estimator is designed to use the current to observe the change of the resistance of the stator in real time,so as to reduce the flux and torque error in the operation of the system and achieve the purpose of restraining the torque ripple.Finally,the traditional DTC hysteresis comparator is used as the starting point,and the direct torque control combined with space vector modulation is proposed for the function of the hysteresis comparator in the control system and its two sides.On this basis,the torque angle increment of variable limiting control and the improvement of integrator compensation in flux calculation are carried out for the control system.The simulation results show that this method can significantly reduce the flux and torque ripple in traditional direct torque control,and make the inverter work at a constant switching frequency.