Analysis And Suppression Of Electromagnetic-origin Vibration And Noise Of Stator-permanent- Magnet Brushless Machines For Electric Vehicle Applications

Stator-permanent-magnet(Stator-PM)brushless machine is a strong candidate for electric vehicle traction application because of its high reliability.Electric vehicle traction motors are required to have low noise and vibration.Although the vibration and acoustic noise of traditional electric machines has been discussed widely and profoundly,the vibration and noise behavior of statorpermanent-magnet brushless machines is rarely studied.In this thesis,the vibration and noise of Stator-PM brushless machines is researched focusing on three aspects,which are electromagnetic force calculation,modal calculation and noise estimation.The main content of this thesis can be summarized as follows:(1)Two FSPM(flux-switching permanent magnet)machines and two FRPM(flux-reversal permanent magnet)machines with different slot-pole combinations and the same external dimensions as the IPMSM(interior permanent magnet synchronous machine)of Prius 2010 hybrid vehicle are designed and their torque capabilities are optimized.The electromagnetic force of these motors are calculated by FEM model and 2D-Fourier transformed to show their harmonic components.It is found that the lowest spatial order of the harmonic components is decided by the number of repetition cycles of the electromagnetic field in the airgap.The equation that decides the spatial orders and the temporal orders of the electromagnetic forces of a Stator-PM brushless machine is proposed by summarizing the simulation results.(2)Modal test of an FRPM prototype machine with 6 slots in the stator and 8 teeth on the rotor is carried out to measure its natural frequencies.The same machine is then simulated using FEM models,in which the windings are treated in three different ways,to get the estimation of its natural frequencies.The simulation results of the full-winding model and the end-winding-neglected model show good agreement with the test results(error<5%).However,the natural frequencies of the nowinding model are 10% lower than that of the test results.Afterwards,the modals of Prius2010 IPMSM and other four previously designed machines(two FSPM machines and two FRPM machines)are simulated with full-winding model.By analysing the simulation results,it is found that the natural frequencies of pure circumferential modals are mostly influenced by the thickness of the stator yoke and the shell,but the natural frequencies of mixed circumferential and axial modals are affected by both the radial and axial dimensions.(3)The noise of the prototype FRPM machine at no load is measured in a semi-anechoic room and then simulated with FEM.The average deviation of simulated resonance frequencies from the test results is about 10%.FEM is then used on the Prius2010 IPMSM,the previously designed two FSPM machines and two FRPM machines to find out their noise and vibration performance.It is found that a harmonic component of electromagnetic force tends to trigger the resonance of modals with the same spatial order and adjacent temporal frequency.But when there is no such modals,the harmonic component of force can also trigger the resonance of modals with spatial orders multiples of the force,or sometimes,even modals with irrelevant spatial order but close temporal frequency.The 18/15 FSPM machine is then simulated at no load with an injection of a 5kHz additional harmonic current to find out the influence of high-frequency current harmonics on its noise behavior.It is found that the spatial and temporal orders of the electromagnetic force harmonics still follows the original equation with the current harmonic injection.Moreover,the influence of the harmonic current on the vibration and noise behavior of the FSPM machine is rather small.(4)Two methods for noise and vibration reduction are provided for Stator-PM brushless machines.One of them is to increase the repetition cycles of electromagnetic field in the airgap so that the lowest spatial order of the electromagnetic force harmonics can be increased.The other is to make the stator yoke or the shell thicker so that the natural frequencies of low order modals can be increased.The 18/15 FSPM machine is then simulated with its shell thickness increased from 18 mm to 48 mm.The results confirmed that a thicker shell can increase the natural frequencies of an electric machine,thus reducing its vibration and noise.