Research On Torque Ripple Minimization Of PMSM Considering Non-sinusoidal Magnetic Field

Permanent magnet synchronous motor(PMSM)is widely used in various high-precision and high-power control systems,because it has small size,high efficiency,high power factor,high torque output ratio,wide speed range and other advantages.In these cases,it is usually necessary to keep the PMSM’s output torque smooth to ensure that the drive control system has good control performance.In order to let the motor be able to output perfectly smooth electromagnetic torque,it is necessary to keep the motor having completely sinusoidal back EMF and current.However,the distribution of the permanent magnet magnetic field in the air gap and the spatial distribution of the stator windings will affect the EMF in real life.Due to the imperfection of the motor structure design,it cannot reach the ideal state.The rotor magnetic field of motor often has many spatial harmonics,which will lead to the non-sinusoidal magnetic field and affect the torque output.In addition,sensors and sampling accuracy can also cause different degrees of torque ripple.In order to suppress the torque ripple of PMSM,the electromagnetic torque of PMSM is analyzed,and on this basis,some torque ripple suppression strategies are studied.Aiming at the problem of torque ripple in non-sinusoidal PMSM in magnetic field,the electromagnetic torque of motor considering harmonic flux was deduced at first,and the influencing factors of electromagnetic torque ripple were analyzed quantitatively.The electromagnetic torque includes fundamental component and harmonic component,among which harmonic component also includes the secondary high frequency component composed of flux and current harmonics.Then,the torque ripple suppression method based on harmonic current injection method was developed.An optimal harmonic current calculation method based on genetic algorithm(GA)is proposed.By establishing a multi-objective function including two optimization problems of minimum torque peak-to-peak value and minimum loss,the optimal harmonic current is obtained by using GA.The shortcomings of this method are analyzed,and an improvement is made for ignoring the phase angle of harmonic flux.A new objective function is established by using sequence to represent the torque,and the simulation results are given in the paper.An optimal harmonic current calculation method based on Lagrange algorithm is proposed.The expression of harmonic torque amplitude is derived from the formula,and the analytical expression of optimal harmonic current is derived by using Lagrange.An improved method considering the phase angle of harmonic flux is proposed,and the simulation results are given.A harmonic current injection system based on rotating PI control is studied to inject the optimal harmonic current into the motor.When the optimal harmonic current is injected into the motor,the fundamental component can be effectively controlled and the amplification of other sub-harmonics can be preventedThe torque control model of PMSM based on rotating PI control is established on MATLAB/Simulink,and the effectiveness of the two methods is analyzed by simulation.Experimental verification of above torque ripple minimization methods are carried out on an experimental platform based on RT-LAB,and the effectiveness of proposed methods are verified by comparing with the simulation results.