Design And Torque Harmonic Analysis Of Low Torque Ripple Permanent Magnet Synchronous Motor

Torque ripple has always been one of the important properties of permanent magnet synchronous motors.Due to the problem of torque ripple,the application of permanent magnet synchronous motors in some special fields is restricted.To reduce torque ripple,it is necessary to understand the source of torque ripple,analyze the composition of it’s torque harmonics,which requires an accurate mathematical model of the permanent magnet synchronous motor.However,the existing mathematical models of permanent magnet motors cannot accurately calculate the respective torques of permanent magnet motors.Therefore,this paper proposes an improved mathematical model,which uses the method of frozen permeability to make the model accurately calculate the permanent magnet torque and reluctance torque of the motor,and accurately separate the torque harmonics and the model is universial.The work content of the article is as follows:Firstly,based on the classic mathematical model of permanent magnet motors,according to the laws of physics,considering the cross mutual inductance of the dq axis and the flux linkage generated by the permanent magnets on the q axis when the permanent magnet is loaded,the improved mathematical model of the permanent magnet synchronous motor is derived.Then the calculation formula of the average torque and each torque harmonic is given,and the composition of the torque harmonic structure and it’s influencing factors are analyzed.Secondly,according to the design requirements,the stator and rotor of the permanent magnet synchronous motor are designed using the main dimensional formulas,and two motor rotor design schemes are given,namely the "一" type rotor and the "V" type rotor.Using the FEA software J-mag to model it,and using the method of frozen permeability to calculate the back-EMF constant,the self-inductance and mutual inductance of each harmonic in the dq coordinate system are calculated.At the same time,the improved mathematical model is used to analyze the torque harmonics of the two type,verify the correctness of the mathematical model calculations by finite element simulation.Finally,the "一" rotor scheme is determined,and the parameterization method is used to optimize the rotor structure to reduce the torque ripple of the rated load to less than 5%.Using the mathematical model to analyze how the torque harmonics change for each optimized parameter.The design scheme of permanent magnet synchronous motor is determined.Finally,the FEA software J-mag is used to establish the motor model,and the transient field is used to simulate and analyze the motor to obtain the no-load operation result of the motor.The fourier transform is used to obtain the main harmonics of no-load back EMF and the cogging torque.Then the different load states of the motor are analyzed,and the mathematical model is used to analyze how the torque harmonics change with the change of the load.The simulation results are compared with the calculation results of the mathematical model,and the correctness of the mathematical model of the permanent magnet synchronous motor is verified again.