Research On Sensorless Control System Of Permanent Magnet Synchronous Motor Based On Sliding Mode Observer

Permanent magnet synchronous motor has the advantages of high power density,good speed control performance,and is widely used in transportation,industrial manufacturing and other fields.In the process of vector control of permanent magnet synchronous motor,position sensor is needed to obtain accurate rotor position information,but the installation of position sensor will increase system cost and reduce system reliability.Therefore,this dissertation studies the sensorless control strategy of permanent magnet synchronous motor.Firstly,the closed-loop control system of permanent magnet synchronous motor was studied.On the basis of analyzing the structure and working principle of the motor,the mathematical model of permanent magnet synchronous motor was established,and the control quantity was decoupled by projecting the mathematical model into the rotating coordinate system through coordinate transformation.By studying the working principle of vector control and space vector pulse width modulation,the double closed-loop vector control system of permanent magnet synchronous motor was established,which established the foundation for the research of sensorless control strategy.Secondly,the position estimation algorithm of sliding mode observer was studied.In order to solve the chattering problem caused by switching function in traditional position estimation algorithm of sliding mode observer,a new function reaching law was proposed,which can effectively suppress high frequency chattering and improved the estimation accuracy of back potential.In order to solve the problem of error amplification and phase lag in traditional sliding mode observer position extraction method,the arctangent function used to extract position information was improved to phase locked loop,which solved the problem of phase lag and reduced the estimation error.Then,the sensorless starting control and switching strategy of permanent magnet synchronous motor were studied.Aiming at the static stage before starting the motor,the method of initial position prepositioning was studied.The starting strategy of constant current frequency ratio control was studied for the motor running at low speed.Aiming at the transition stage from low speed to medium speed,the state switching process based on power Angle selfbalancing characteristics was studied,and the feasibility of sensorless motor startup and state switching strategy was verified in the simulation platform.Finally,the experimental platform of permanent magnet synchronous motor was built to verify the research content of this dissertation.Combined with the rated parameters of the experimental motor,the hardware experimental platform of the motor control system was designed,and the software algorithm program was written according to the working flow of the system.The experimental results showed that the improved sliding mode observer position estimation algorithm can effectively suppress the high-frequency chattering in the traditional algorithm and reduced the estimation error.It was also verified that the compound control strategy adopted in this dissertation,which switched from constant current frequency ratio to sliding mode observer control,can realize the operation of the motor without position sensor in a wide speed range.