Research On Sensorless Direct Torque Control Of Permanent Magnetic Synchronous Motor

Permanent magnet synchronous motor has the advantages of simple structure,small loss,high efficiency and reliable operation,which has been widely used in civil,aerospace and military fields.Direct torque control(DTC)is another high-performance control technology after vector control.It takes the flux torque as the direct controlled quantity,which has the characteristics of fast response and strong robustness.However,the problems of torque ripple and switch frequency instability in DTC limit the application of DTC.In addition,in order to obtain the information of rotor,it is usually necessary to install mechanical sensors,which will increase the cost and complexity of the system and reduce the reliability of the system.Therefore,the following research is carried out for the direct torque control technology and sensorless algorithm in the paper.Firstly,the control strategy of PMSM and the development status of sensorless are described,and the basic structure and classification of motor are introduced.The mathematical models in different coordinate systems are established,and the control idea of DTC and the control principle of each module are analyzed.The simulation results show that the traditional DTC system has fast response and strong robustness,but there are problems of torque ripple and inverter switch instability.Secondly,aiming at the problems of traditional DTC,an improved algorithm based on second order sliding mode control is proposed.The algorithm replaces hysteresis controller and the traditional switch table with SVPWM technology,and the second order sliding mode controller is used instead of PI controller to suppress the deviation between the flux loop and the torque loop.The simulation results show that the improved DTC can effectively reduce the flux and torque ripple.Finally,the identification theory of MRAS is introduced and applied to the improved DTC system.The traditional MRAS speed identification algorithm is solved by Popov theory.In addition,in order to reduce the influence of stator resistance on the adjustable model and stator flux estimation.An improved MRAS strategy is proposed,which is designed to identify the resistance and speed simultaneously.The identified resistance value is updated to the adjustable model module of MRAS and the stator flux estimation module in real time.The simulation results show that the improved MRAS can effectively reduce the influence of resistance on the adjustable model and stator flux,improve thespeed identification accuracy and the dynamic and static performance of the system.