Research On Electromagnetic Vibration And Noise Of Permanent Magnet Vernier Motor For Electric Vehicle In-wheel Drive Application

To cope with the multiple challenges brought about by economic development,energy crisis and environmental pollution,electric vehicles have attracted extensive attention and been vigorous development as an effective solution.Meanwhile,the direct-drive in-wheel motor drive system has become an important development direction of the future electric vehicle drive system due to its unique advantages,such as high transmission efficiency,simple and compact structure,and small size.As the main power system of the inwheel drive electric vehicle,the in-wheel motor needs to have the characteristics of high efficiency,high power density,high torque density and low torque pulsation etc.Meanwhile,due to the particularity of its working environment,the research on key technical issues such as vibration and noise mechanism analysis and suppression of in-wheel motors is crucial to the development of in-wheel-drive electric vehicles.The permanent magnet Vernier motor(PMVM)based on the principle of modulation has the advantages of highpower density,high-torque density,and low-torque ripple,which make it be one of the important candidates for in-wheel drive motors.However,due to the particularity of its working principle and stator/rotor topology,the generation of electromagnetic excitation in PMVMs is more complicated,which makes the vibration and noise generation mechanism of PMVMs different from that of conventional permanent magnet synchronous motors(PMSMs).At this stage,the theoretical research on the vibration and noise mechanism analysis of the PMVM and the design of the PMVM with low vibration and noise is relatively scarce,and it urgently needs to be supplemented and improved.In summary,the PMVMs for electric vehicle in-wheel motor are taken as the research object in this dissertation.The electromagnetic vibration and noise mechanism and optimization of PMVM for in-wheel motor are studied in detail.The main research work can be summarized as follows:(1)The working principle of magnetic field modulation,the slot/pole combination and the motor topology of the external rotor PMVM are different from the conventional PMSMs,which makes the electromagnetic force harmonics more complex and the analysis more difficult.Combined with the magnetic field modulation principle and Maxwell stress tensor method,the harmonic characteristics of the electromagnetic force acting on the external rotor is theoretically analyzed and quantitatively verified by the finite element method.The research reveals the generation mechanism of electromagnetic force harmonics of external rotor PMVMs,and proposes a method for determining the space order of the lowest non-zero order electromagnetic force harmonic and specific electromagnetic force harmonic suitable for the PMVM,and expounds the modulation mechanism of the electromagnetic force of the PMVMs caused by the design factors such as special slot/ pole combination and stator/ rotor topologies.In addition,the influence of consequnet-pole rotor and split-tooth stator with unequal tooth/ slot widths on the cogging torque of PMVMs is revealed,and the design method conducive to reducing the cogging torque is put forward.The research lays a foundation for the study of the electromagnetic vibration and noise mechanism,and the optimal design of low vibration and noise for the PMVMs.(2)The unbalanced magnetic force(UMF)of the motor is essentially the specific manifestation of the electromagnetic force harmonic of order 1,which has a special effect and contribution to the vibration and noise of the motor system.The working principle,slot/ pole combination and motor topologies of external rotor PMVMs are different from those of conventional PMSMs,which lead to the unclear mechanism of UMF.The generation mechanism and suppression measures of UMF are systematically studied from the perspectives of slot /pole combination,stator/rotor topologies and winding structure design,combined with the principle of magnetic field modulation and finite element method.The research reveals the influence law of slot/ pole combination of PMVM on UMF,and summarizes the existence criterion of UMF.The key factors causing the increase of UMF caused by the structure of consequent-pole rotor are explained.The UMF suppression measures are proposed from the aspects of the slot/ pole combination,stator/ rotor topologies and winding design,etc.,which can effectively suppress the UMF and maintain the high torque output capacity of PMVM.In addition,the expressions of electromagnetic force acting on the external rotor with different air-gap eccentricities are derived,and it is revealed that static and dynamic air-gap eccentricities have opposite modulation effects on electromagnetic force harmonics in the stator/rotor coordinate system.(3)Aiming at the generation mechanism of the electromagnetic vibration and noise of the external-rotor PMVM,a systematic study is carried out from the structural modal characteristics and the electromagnetic vibration and noise characteristics of the external-rotor system and the internal-stator system respectively.The variation laws of the mode shapes of the external-rotor system and the internal-stator system are analyzed and summarized,the concrete diagram of the tangential bending mode shapes of the internal-stator teeth is introduced,and the modes of each order of the stator teeth are defined.It is clarified that the vibration noise of the external-rotor PMVMs comes from the radial vibration of the external-rotor caused by the radial electromagnetic force and the tangential bending vibration of the internal-stator teeth caused by the tangential electromagnetic force,in which the contribution of the tangential bending vibration of the stator teeth to the noise can not be ignored.The influence mechanism of consequent-pole rotor modulation and stator structure on the stator/ rotor vibration and noise characteristics of PMVMs is clarified.In addition,the unbalanced magnetic tension has a significant effect on the vibration deformation of the in-wheel motor.The research provides an important theoretical basis for the vibration and noise analysis and optimization of PMVM for in-wheel drive application.(4)The direct-drive in-wheel motors have more stringent requirements on torque,vibration and noise,loss,as well as volume and cost,etc.Aiming at the problems of long winding ends,large winding loss and large unbalanced magnetic pulling force in the existing external-rotor PMVM,facing the design and application requirements of in-wheel motor,a dual three-phase fractional slot external rotor consequent-pole permanent magnet vernier motor with high output torque,short winding end and small UMF is designed by integrating the research on the mechanism of electromagnetic force and UMF of PMVMs.On this basis,the response surface method and particle swarm optimization algorithm are used to optimize the torque,vibration and noise performance of the motor,and the output torque and vibration and noise are improved at the same time.The research provides a valuable reference for the design and optimization of PMVM for highperformance in-wheel drive application.(5)Experimental study on the prototype of external-rotor consequent-pole PMVM.Considering the change of structural material properties and the non-ideal contact between rotor and casing,the equivalent finite element structural model of external rotor system is established,and the accuracy of the model is verified by modal experimental results.According to the calculation and test results of motor noise,it is verified that the externa-rotor system is the main source of noise,and the noise generated by the internalstator can not be ignored.Combined with the vibration deformation of the external rotor at the peak noise,the modulation effect of the consequent-pole rotor on the electromagnetic vibration noise is verified.In addition,through the noise experimental tests,the effects of loads,speeds and inverter current harmonics on the vibration and noise characteristics are further studied.Aiming at the working principle of magnetic field modulation and motor topologies of PMVMs,the electromagnetic force harmonics generation mechanism,the generation mechanism and suppression of UMF,and the structural vibration characteristics of the stator and rotor system of PMVMs are systematically studied in this dissertation.In addition,combined with the above research,the multi-objective optimization design of the external-rotor consequent-pole PMVM with high torque and low-vibration & noise performance for electric vehicle application is realized.The research work of this dissertation not only complements and perfects the existing research on vibration & noise of permanent magnet motors,but also has important reference value for the high-torque and low-vibration & noise design of PMVMs for electric vehicle applications.