Research On Torque Ripple Mechanism And Suppression Algorithm Of Permanent Magnet Synchronous Machine

Permanent magnet synchronous machines(PMSM),which are universally employed as the essential electromechanical energy conversion elements in new energy vehicle,new energy generator,industrial AC position servo system,electrical airplane and ship,have the advantages of high efficiency,high energy density,wide speed range and simple maintaiment.However,torque ripples due to harmonic flux,inverter nonlinearity and cogging torque not only influence the smoothness of output torque but also produce mechanical vibration and acoustic noises,thus reduce the performance of the whole system.This paper aims to carry out researches on the mechanism of torque ripples,harmonic current detection and regulation,and torque ripple suppression strategy.This paper firstly gives a mathematical model of PMSM in which time and spatial harmonics are considered,then analyzes the relationship between torque ripples,harmonic current,and harmonic flux.By using coordinate transformation,the relationship is greatly simplified in harmonic rotating coordinates.The theory analysis provides a torque ripple suppression idea which is based on harmonic current injection.In terms of regulating the harmonic current to track the harmonic current commends,harmonic current injection is supposed to conclude two section,harmonic current detection and harmonic current regulation.Based on the production mechanism of harmonic current,this paper proposes two different harmonic current detection methods(second order general integral filter and harmonic coordinate transformation).In addition,conventional harmonic current regulators have the disadvantages of delay,overshoot,and oscillation because of the low pass filter.For the purpose of avoiding those disadvantages,the paper develops the harmonic current regulator by cancelling the low pass filter to reduce the delay and promote the response speed of harmonic current controllers.A torque ripple estimator based on mechanical model is established by extracting speed fluctuations to improve the parameter robustness.Setting torque ripple minimization and injected harmonic current minimization as primary and secondary objective functions of gradient descent optimization(GDO)respectively,the GDO will automatically locate the optimal harmonic current commends,which are essential to harmonic current regulators mentioned above.The proposed algorithm,which not only eliminates the torque ripples but also guarantees the minimal injected harmonic current,does not contain complicated computation and is simple to implemented in actual system.Furthermore,the parameters of machine are not required in GDO,that makes the algorithm more practical and applicable in other kinds of machine system.Eventually,the simulation and experiments results have verified the effectiveness of the strategies.Besides,the torque ripple suppression strategy has been applied to a elevator-employed axial flux permanent magnet(AFPM)traction machine system,and the test results verify the value of the strategy in industrial application.