Research On Torque Ripple Suppression In Direct Torque Control Of Three-phase Permanent Magnet Synchronous Motor

With the increasing demand for the environment,many industries have changed from fossil fuel-driven machine to electric-driven machine,so the use of motor is increasing year by year,and the growth rate of permanent magnet synchronous motor(PMSM)is the fastest.At present,the main control methods of permanent magnet synchronous motor are Field Oriented Control(FOC)and Direct Torque Control(DTC).DTC is widely used because of its simple structure and fast response.However,the obvious shortcoming of DTC is not negligible.If the torque ripple is larger,it will lead to serious consequences.Torque ripple suppression has been studied for more than ten years.Previous researchers have proposed a variety of improvement methods,and the effect of improvement is uneven.On the basis of predecessors,this paper improves the control structure of traditional P.MSMDTC.The structure difference between permanent magnet synchronous motor and three-phase asynchronous motor is that the rotor of permanent magnet synchronous motor is embedded with permanent magnet,while the asynchronous motor is winding or good conductor.Permanent magnet synchronous motor(PMSM)can be divided into three categories according to the different embedding modes of permanent magnets,and two categories according to whether the inductances of the two axes are equal or not.In this paper,the mathematical model of permanent magnet synchronous motor is given,including voltage equation,flux equation,torque equation and so on.The coordinate conversion formula is also given.In this paper,the principle of direct torque control of permanent magnet synchronous motor is described.After that,the causes of the torque ripple of direct torque control of permanent magnet synchronous motor are analyzed in detail.The main reasons include four points,and other common reasons.According to the characteristics of the cause of torque ripple in direct torque control,two kinds of improvement methods are proposed.The first kind of improvement is simple and local.The control accuracy is improved by adding zero voltage vector,weak magnetic module and interval subdivision,and the control accuracy is improved when the load changes abruptly.It is simple and practical to improve the control accuracy.In the second part,the hysteresis comparator is removed directly and the voltage predictive control is used,but its essence is direct torque control.Firstly,the space voltage pulse width modulation technology is used to improve the system,and then the sliding mode control combined with the space pulse width modulation technology is used to improve the system.These methods are all aimed at some reasons of the torque ripple.The improvement theory is also analyzed in this paper.The simulation experiment is carried out on MATLAB/simulink,and the comparative experiment is adopted.After designing the experimental method and parameters,the simulation is carried out.The simulation outputs stator current diagram,motor speed diagram,electromagnetic torque diagram and stator flux linkage diagram.By comparing with each other,the results show that the improvement effect of adding zero vector,using weak magnetic module and interval subdivision is not obvious on the whole,but the restraint effect is obvious when the load changes.The improved direct torque control using space pulse width modulation technology and sliding mode control has better effect.But the effect is not good in high speed and heavy load area.Although the method of torque ripple used in this paper works well,it is based on the simulation results.In practice,the problem of physical devices must be considered.Secondly,the improvement can only be obvious in a small range or in some specific cases.The scope of application needs to be improved.Future improvements to PMSMDTC will mainly use intelligent control and better hardware.