Research Of PMSM Speed Control System Based On Sliding Mode Variable Structure

Permanent magnet synchronous motor(PMSM)has the advantages of simple structure,small volume,light weight,low loss.It has the characteristics of accurate positioning,fast response and wide speed range,which makes it widely used in robot and precision CNC machine tools,aerospace and other fields.However,PMSM in the mathematical model is a strong coupling,non-linear,multi-variable complex system,which in the working environment also need to solve the internal parameters perturbation,external disturbance and a series of uncertain factors.In this paper,the permanent magnet synchronous motor speed control system is taken as the object of study.The nonlinear control strategy based on sliding mode variable structure control theory and the method of position sensorless are researched.Firstly,aiming at the mathematical model of PMSM,the sliding mode variable structure is chosen as the control method from many nonlinear control theories,and it is applied to PMSM design the controller.According to the different speed range of the PMSM,should be reasonably selected without position sensor technology.The coordinate system and coordinate transformation of PMSM are analyzed concretely,the mathematical model of rotating coordinate system is established,vector control technology is introduced,and vector control method is adopted as its control strategy.The realization steps of SVPWM are described in detail from three aspects: judgment of sector,duty cycle analysis and switch switching.The simulation model of PMSM speed control system is determined.Secondly,on the basis of constant velocity law and exponential law of convergence,a new approximation law is proposed,which verifies the stability and accessibility of the approximation law and is consistent with the tradition al exponential law in dynamic response and chatter,the results show the validity of the law.The PMSM speed controller based on the new approximation law is established.The simulation results verify the superiority of the new approximation law by comparing with the traditional PI speed controller.Finally,the traditional sliding mode observer is established,and the back EMF information is included in the switching function.The stability condition of the sliding mode observer is deduced.Two kinds of r otor speed extraction methods are given.For the low-pass filter,the phase angle compensation of the rotor position is made,and a simulation model based on sensorless vector control system is established.Aiming at the problem that the accuracy of the tr aditional sliding mode observer is not enough,an improved second-order non-singular terminal sliding mode observer method is proposed.The simulation model of the control system based on the new sliding mode observer is constructed.The experimental resul ts show that the new sliding mode observer has a great improvement in estimating the rotor speed and rotor position accuracy.