Research On Torque Control Of PMSM With Nonideal Back EMF

Permanent Magnet Synchronous Motors(PMSM)are widely used in many high-performance drive control applications due to its high efficiency,high torque-inertia ratio,and wide speed range.High-performance drive control requires high smoothness of output torque.However,due to the nonideal characteristics of motor structure design,the rotor magnetic field of PMSM usually contains a large number of spatial harmonics,resulting in non-ideal characteristics of its back EMF.In turn,the output torque has a large ripples,which limits the application of the PMSM in high-precision drive control situation.Direct Torque Control(DTC)is a high-performance motor control method following Field Oriented Control(FOC).It eliminates the method of decoupling in vector control,directly controls the flux linkage and torque of the motor,which is simple.and has high Dynamic performance.However,the traditional DTC has the disadvantage of large torque ripple due to the problem of the switching frequency is not constant,which greatly limits its application and development.Direct Torque Control based on Space Vector Modulation(SVM-DTC)can effectively reduce the ripple in the output torque,but the torque ripple due to the non-ideal characteristics of the motor still exists.Therefore,it is of great engineering significance to study the torque control strategy and reduce torque the torque ripple under the DTC system of PMSM.In this paper,the structure and characteristics of PMSM are briefly introduced,and the reason why the back EMF of PMSM is non-ideal is clarified.The mathematical model of the ideal back EMF and the non-ideal back EMF PMSM in different coordinate systems is given.The simulation model of the non-ideal back EMF pPMSM is established by means of MATLAB/Simulink.Aiming at the problem of Stator Flux Linkage Observation in Permanent Magnet Synchronous Motor Direct Torque Control system,this paper improves the traditional pure integral stator flux linkage observer,the performance of first-order LPF,LPF with amplitude and phase compensation,and the LPF+HPF Stator Flux Linkage Observer are discussed in details.It is concluded that the LPF+HPF Stator Flux Linkage Observer can completely eliminate the influence of DC offset and integral initial value and improve the accuracy of flux linkage observation.The influence of the dead time effect of the inverter on the accuracy of the stator flux linkage observation is analyzed.A Stator Flux Linkege Observer considered the dead time effect is proposed.The basic principle and implementation of conventional DTC and SVM-DTC of PMSM are analyzed.With MATLAB/Simulink,the simulation experiments of two control methods are carried out,and the conclusion that SVM-DTC can effectively reduce the torque ripple is obtained.Aiming at the current harmonics and torque ripple caused by the non-ideal sinusoidal distribution of the rotor flux in the air gap,based on the SVM-DTC system,a harmonic flux extraction strategy and harmonic voltage injection strategy are proposed.The current harmonic suppression strategy further reduces the torque ripple caused by the non-ideal characteristics of the PMSM,and the effectiveness of the harmonic injection is verified by simulation.Finally,based on theoretical analysis and simulation experiments,a PMSM control experimental platform is built based on RT-LAB.The PMSM stator flux linkage observation and DTC and SVMDTC experiments were carried out,which laid the foundation for future research.