Research On Improvement Strategy Of Direct Torque Control For Permanent Magnet Synchronous Motor

In recent years,strategic emerging industries have been developing rapidly,and the development of efficient motor control system is an indispensable key link.The permanent magnet synchronous motor(PMSM)is a key component in the control systems of electric vehicles,robots and other devices due to its easy maintenance,compact structure and high energy conversion efficiency.The traditional direct torque control(DTC)adopts the proportional integral(PI)speed regulation strategy.The system is susceptible to external disturbances,system parameter changes,friction and other non-repetitive disturbances in the operation process,and it is difficult to meet the requirements of the motor control performance in the field.Therefore,it is very important to design effective control methods.This thesis takes PMSM as the research object,takes direct torque control as the basic control strategy,adopts sliding mode control and sensorless control methods.The main research content of this thesis includes the following three parts:(1)Aiming at the problem of torque pulsation in PMSM direct torque control system,a mathematical model of PMSM is established.Using space vector pulse width modulation technology,sliding mode control is introduced and a sliding mode controller is designed to replace PI controller.The simulation results show that the improved control system can effectively weaken the torque ripple.(2)In order to further weaken the torque ripple and reduce the influence of the total disturbance on the control performance,a new sliding mode control method based on tracking differentiator and RBF neural network is proposed.Firstly,the state variable is added to the traditional exponential reaching law to obtain a new hybrid reaching law.Theoretical analysis can make the system converge to the equilibrium point faster and weaken chattering phenomenon.Based on this,a sliding mode speed controller is designed.Then,a tracking differentiator is designed to estimate the given speed signal and its differential signal to realize the new sliding mode control.Finally,the RBF neural network is used to approximate the uncertain disturbance of the system.The simulation results show that the proposed control method has good robustness and tracking ability under sudden change of speed and load.(3)In order to solve the problems of complex system,high cost and poor effect under extreme working conditions caused by mechanical sensors in traditional control systems,the model reference adaptive method is used to estimate the speed;Then,in order to further improve the estimation performance,a new parameter adaptive law is proposed by introducing the three-stage fal function in active disturbance rejection control theory.The simulation results show that the model reference adaptive method can effectively estimate the rotational speed.After introducing fal function,the system has better estimation effect.Through the study of the above control strategies,this thesis can provide reliable support for the stable operation of PMSM direct torque control system.